Showing 1–29 of 29 results for author: Wang, K Y

$C_{3}$-Symmetry-induced Antisymmetric Planar Hall effect and Magnetoresistance in Single-Crystalline Ferromagnets

Authors: W. J. Qin, B. Yang, Y. Z. Tian, B. W. Zheng, K. Y. Wang, B. Y. Huang, Y. B. Yang, W. Q. Zou, D. Wu, P. Wang

Abstract: The planar Hall effect (PHE) is typically symmetric under magnetic field reversal, as required by the Onsager reciprocity relations. Recent advances have identified the antisymmetric PHE (under magnetic field reversal) as an intriguing extension in magnetic systems. While new mechanisms have been proposed, the role of conventional anisotropic magnetoresistance (AMR) in this phenomenon remains uncl… ▽ More The planar Hall effect (PHE) is typically symmetric under magnetic field reversal, as required by the Onsager reciprocity relations. Recent advances have identified the antisymmetric PHE (under magnetic field reversal) as an intriguing extension in magnetic systems. While new mechanisms have been proposed, the role of conventional anisotropic magnetoresistance (AMR) in this phenomenon remains unclear. Here, we report the experimental discovery of an antisymmetric (with respect to both magnetic field and magnetization) PHE and magnetoresistance in single-crystal $Co_{30}Pt_{70}$ (111) thin films with $C_{3}$ rotational symmetry and perpendicular magnetic anisotropy (PMA). We demonstrate that both antisymmetric effects arise naturally from the intrinsic fourth-rank AMR tensor inherent to C3-symmetric planes, assisted by PMA. Our findings link conventional AMR to antisymmetric galvanomagnetic responses, offering new insights into symmetry-governed transport in crystalline ferromagnets. △ Less

Submitted 26 November, 2025; v1 submitted 4 November, 2025; originally announced November 2025.

The identification of the dominant donors in low temperature grown InPBi materials

Authors: G. N. Wei, D. Xing, Q. Feng, W. G. Luo, Y. Y. Li, K. Wang, L. Y. Zhang, W. W. Pan, S. M. Wang, S. Y. Yang, K. Y. Wang

Abstract: Combined with magnetotransport measurements and first-principles calculations, we systematically investigated the effects of Bi incorporation on the electrical properties of the undoped InP1-xBix epilayers with 0<x<2.41%. The Hall-bar measurements reveal a dominant n-type conductivity of the InPBi samples. The electron concentrations are found to decrease firstly as x increases up to x=1.83%, and… ▽ More Combined with magnetotransport measurements and first-principles calculations, we systematically investigated the effects of Bi incorporation on the electrical properties of the undoped InP1-xBix epilayers with 0<x<2.41%. The Hall-bar measurements reveal a dominant n-type conductivity of the InPBi samples. The electron concentrations are found to decrease firstly as x increases up to x=1.83%, and then increase again with further increasing Bi composition, whiles the electron mobility shows an inverse variation to the electron concentration. First-principle calculations suggest that both the phosphorus antisites and vacancy defects are the dominant donors responsible for the high electron concentration. And their defect concentrations show different behaviors as Bi composition x increases, resulting in a nonlinear relationship between electron concentration and Bi composition in InPBi alloys. △ Less

Submitted 29 March, 2016; originally announced March 2016.

Comments: 17 pages, 4 figures, 1 table

Bismuth-content dependent of the polarized Raman spectra of the InPBi alloys

Authors: G. N. Wei, T. Q. Hai, Q. Feng, D. Xing, W. G. Luo, K. Wang, L. Y. Zhang, S. M. Wang, K. Y. Wang

Abstract: We have systematically investigated the optical properties of the InP1-xBix ternary alloys with 0<x<2.46%, using high resolution polarized Raman scattering measurement. Both InP-like and InBi-like optical vibration modes (LO) were identified in all the samples, suggesting most of the Bi-atoms are incorporated into the lattice sites to substitute P-atoms. And the intensity of the InBi-like Raman mo… ▽ More We have systematically investigated the optical properties of the InP1-xBix ternary alloys with 0<x<2.46%, using high resolution polarized Raman scattering measurement. Both InP-like and InBi-like optical vibration modes (LO) were identified in all the samples, suggesting most of the Bi-atoms are incorporated into the lattice sites to substitute P-atoms. And the intensity of the InBi-like Raman modes increase exponentially as Bi-content increasing. Linearly red-shift of the InP-like longitudinal optical vibration modes was observed to be 1.1 cm-1 of percent Bi, while that of the InP-like optical vibration overtones (2LO) were nearly doubled. In addition, through comparing the difference between the Z(X,X)Z and Z(X,Y)Z Raman spectra, Longitudinal Optical Plasmon Coupled (LOPC) modes are identified in all the samples, and their intensities are found to be proportional to the electron concentrations. △ Less

Submitted 14 December, 2015; originally announced December 2015.

Longitudinal Spin Seebeck Effect in Silver Strip on CoFe Film

Authors: Y. Sheng, M. Y. Yang, Y. Cao, K. M. Cai, G. N. Wei, G. H. Yu, B. Zhang, X. Q. Ma, K. Y. Wang

Abstract: We report the experimental observation of the spin Seebeck effect (SSE) in Ag/CoFe noble metal/magnetic metal bilayers with a longitudinal structure. Thermal voltages jointly generated by the anomalous Nernst effect (ANE) and the SSE were detected across the Ag/CoFe/Cu strip with a perpendicular thermal gradient. To effectively separate the SSE and the ANE part of the thermal voltages, we compared… ▽ More We report the experimental observation of the spin Seebeck effect (SSE) in Ag/CoFe noble metal/magnetic metal bilayers with a longitudinal structure. Thermal voltages jointly generated by the anomalous Nernst effect (ANE) and the SSE were detected across the Ag/CoFe/Cu strip with a perpendicular thermal gradient. To effectively separate the SSE and the ANE part of the thermal voltages, we compared the experimental results between the Ag/CoFe/Cu strip and Cu/CoFe/Cu strip, where two samples processed with the heating power instead of the temperature difference through the thin CoFe film. The respective contributions of the ANE and SSE to thermal voltage were determined, and they have the ratio of 4:1. The spin current injected through CoFe/Ag interface is calculated to be 1.76 mA/W. △ Less

Submitted 28 October, 2015; originally announced October 2015.

Magnetic Coupling in Ferromagnetic Semiconductor GaMnAs/AlGaMnAs Bilayer Devices

Authors: Y. F. Cao, Yanyong Li, Yuanyuan Li, G. N. Wei, Y. Ji, K. Y. Wang

Abstract: We carefully investigated the ferromagnetic coupling in the as-grown and annealed ferromagnetic semiconductor GaMnAs/AlGaMnAs bilayer devices. We observed that the magnetic interaction between the two layers strongly affects the magnetoresistance of the GaMnAs layer with applying out of plane magnetic field. After low temperature annealing, the magnetic easy axis of the AlGaMnAs layer switches fro… ▽ More We carefully investigated the ferromagnetic coupling in the as-grown and annealed ferromagnetic semiconductor GaMnAs/AlGaMnAs bilayer devices. We observed that the magnetic interaction between the two layers strongly affects the magnetoresistance of the GaMnAs layer with applying out of plane magnetic field. After low temperature annealing, the magnetic easy axis of the AlGaMnAs layer switches from out of plane into in-plane and the interlayer coupling efficiency is reduced from up to 0.6 to less than 0.4. However, the magnetic coupling penetration depth for the annealed device is twice that of the as-grown bilayer device. △ Less

Submitted 23 January, 2015; originally announced January 2015.

Comments: 10 pages, 4 figures

Journal ref: Science China 57(2014)1471

Transport and Capacitance properties of Charge Density Wave in few layer 2H-TaS2 Devices

Authors: Y. F. Cao, K. M. Cai, L. J. Li, W. J. Lu, Y. P. Sun, K. Y. Wang

Abstract: We carefully investigated the transport and capacitance properties of few layer charge density wave (CDW) 2H-TaS2 devices. The CDW transition temperature and the threshold voltage vary from device to device, which is attributed to the interlayer interaction and inhomogeneous local defects of these micro-devices based on few layer 2H-TaS2 flakes. Semiconductivity rather than metallic property of 2H… ▽ More We carefully investigated the transport and capacitance properties of few layer charge density wave (CDW) 2H-TaS2 devices. The CDW transition temperature and the threshold voltage vary from device to device, which is attributed to the interlayer interaction and inhomogeneous local defects of these micro-devices based on few layer 2H-TaS2 flakes. Semiconductivity rather than metallic property of 2H-TaS2 devices was observed in our experiment at low temperature. The temperature dependence of the relative threshold voltage can be scaled to (1- T / Tr )^0.5+delta with delta=0.08 for the different measured devices with presence of the CDWs. The conductance-voltage and capacity-voltage measurements were performed simultaneously. At very low ac active voltage, we found that the hysteresis loops of these two measurements exactly match each other. Our results point out that the capacity-voltage measurements can also be used to define the threshold depinning voltage of the CDW, which give us a new method to investigate the CDWs. △ Less

Submitted 9 July, 2014; originally announced July 2014.

Comments: 4 pages, 4 figures

Journal ref: CHIN. PHYS. LETT. Vol. 31, No. 7 (2014) 077203

Piezo-Voltage Manipulation of the Magnetization and Magnetic Reversal in Thin Fe Film

Authors: Y. Y. Li, W. G. Luo, L. J. Zhu, J. H. Zhao, K. Y. Wang

Abstract: We carefully investigated the in-plane magnetic reversal and corresponding magnetic domain structures in Fe/GaAs/piezo-transducer heterostructure using longitudinal magneto-optical Kerr microscopy. The coexistence of the <100> cubic magnetic anisotropy and uniaxial magnetic anisotropy was observed in our Fe thin film grown on GaAs. The induced deformation along [110] orientation can effectively ma… ▽ More We carefully investigated the in-plane magnetic reversal and corresponding magnetic domain structures in Fe/GaAs/piezo-transducer heterostructure using longitudinal magneto-optical Kerr microscopy. The coexistence of the <100> cubic magnetic anisotropy and uniaxial magnetic anisotropy was observed in our Fe thin film grown on GaAs. The induced deformation along [110] orientation can effectively manipulate the magnetic reversal with magnetic field applied along magnetic uniaxial hard [110] axes. The control of two-jump magnetization switching to one-jump magnetization switching during the magnetic reversal was achieved by piezo-voltages with magnetic field applied in [100] direction. The additional uniaxial anisotropy induced by piezo-voltages at -75 /75V are -1.400/1400 J/m3 . △ Less

Submitted 10 March, 2014; originally announced March 2014.

Comments: 15 pages, 5 figures

Anisotropic Current-Controlled Magnetization Reversal in the Ferromagnetic Semiconductor (Ga,Mn)As

Authors: Yuanyuan Li, Y. F. Cao, G. N. Wei, Yanyong Li, Y. Ji, K. Y. Wang, K. W. Edmonds, R. P. Campion, A. W. Rushforth, C. T. Foxon, B. L. Gallagher

Abstract: Electrical current manipulation of magnetization switching through spin-orbital coupling in ferromagnetic semiconductor (Ga,Mn)As Hall bar devices has been investigated. The efficiency of the current-controlled magnetization switching is found to be sensitive to the orientation of the current with respect to the crystalline axes. The dependence of the spin-orbit effective magnetic field on the dir… ▽ More Electrical current manipulation of magnetization switching through spin-orbital coupling in ferromagnetic semiconductor (Ga,Mn)As Hall bar devices has been investigated. The efficiency of the current-controlled magnetization switching is found to be sensitive to the orientation of the current with respect to the crystalline axes. The dependence of the spin-orbit effective magnetic field on the direction and magnitude of the current is determined from the shifts in the magnetization switching angle. We find that the strain induced effective magnetic field is about three times as large as the Rashba induced magnetic field in our GaMnAs devices. △ Less

Submitted 8 March, 2013; originally announced March 2013.

Comments: 11 pages,3 figures, submitted to Appl. Phys. Lett

Journal ref: Applied Physics Letters 103, 022401 (2013)

Spin and Orbital Splitting in Ferromagnetic Contacted Single Wall Carbon Nanotube Devices

Authors: K. Y. Wang, A. M. Blackburn, H. F. Wang, J. Wunderlich, D. A. Williams

Abstract: We observed the coulomb blockade phenomena in ferromagnetic contacting single wall semiconducting carbon nanotube devices. No obvious Coulomb peaks shift was observed with existing only the Zeeman splitting at 4K. Combining with other effects, the ferromagnetic leads prevent the orbital spin states splitting with magnetic field up to 2 Tesla at 4K. With increasing magnetic field further, both posi… ▽ More We observed the coulomb blockade phenomena in ferromagnetic contacting single wall semiconducting carbon nanotube devices. No obvious Coulomb peaks shift was observed with existing only the Zeeman splitting at 4K. Combining with other effects, the ferromagnetic leads prevent the orbital spin states splitting with magnetic field up to 2 Tesla at 4K. With increasing magnetic field further, both positive or negative coulomb peaks shift slopes are observed associating with clockwise and anticlockwise orbital state splitting. The strongly suppressed/enhanced of the conductance has been observed associating with the magnetic field induced orbital states splitting/converging. △ Less

Submitted 6 March, 2013; originally announced March 2013.

Journal ref: APPLIED PHYSICS LETTERS 102, 093508 (2013)

Current-driven domain wall motion across a wide temperature range in a (Ga,Mn)(As,P) device

Authors: K. Y. Wang, K. W. Edmonds, A. C. Irvine, G. Tatara, E. De Ranieri, J. Wunderlich, K. Olejnik, A. W. Rushforth, R. P. Campion, D. A. Williams, C. T. Foxon, B. L. Gallagher

Abstract: Current-driven magnetic domain wall motion is demonstrated in the quaternary ferromagnetic semiconductor (Ga,Mn)(As,P) at temperatures well below the ferromagnetic transition temperature, with critical currents of the order 10^5Acm^-2. This is enabled by a much weaker domain wall pinning compared to (Ga,Mn)As layers grown on a strain-relaxed buffer layer. The critical current is shown to be compar… ▽ More Current-driven magnetic domain wall motion is demonstrated in the quaternary ferromagnetic semiconductor (Ga,Mn)(As,P) at temperatures well below the ferromagnetic transition temperature, with critical currents of the order 10^5Acm^-2. This is enabled by a much weaker domain wall pinning compared to (Ga,Mn)As layers grown on a strain-relaxed buffer layer. The critical current is shown to be comparable with theoretical predictions. The wide temperature range over which domain wall motion can be achieved indicates that this is a promising system for developing an improved understanding of spin-transfer torque in systems with strong spin-orbit interaction. △ Less

Submitted 30 December, 2010; v1 submitted 6 May, 2010; originally announced May 2010.

Comments: 12 pages, 3 figures

Journal ref: APPLIED PHYSICS LETTERS 97, 262102 (2010)

Domain Wall Resistance in Perpendicular (Ga,Mn)As: dependence on pinning

Authors: K. Y. Wang, K. W. Edmonds, A. C. Irvine, J. Wunderlich, K. Olejnik, A. W. Rushforth, R. P. Campion, D. A. Williams, C. T. Foxon, B. L. Gallagher

Abstract: We have investigated the domain wall resistance for two types of domain walls in a (Ga,Mn)As Hall bar with perpendicular magnetization. A sizeable positive intrinsic DWR is inferred for domain walls that are pinned at an etching step, which is quite consistent with earlier observations. However, much lower intrinsic domain wall resistance is obtained when domain walls are formed by pinning lines i… ▽ More We have investigated the domain wall resistance for two types of domain walls in a (Ga,Mn)As Hall bar with perpendicular magnetization. A sizeable positive intrinsic DWR is inferred for domain walls that are pinned at an etching step, which is quite consistent with earlier observations. However, much lower intrinsic domain wall resistance is obtained when domain walls are formed by pinning lines in unetched material. This indicates that the spin transport across a domain wall is strongly influenced by the nature of the pinning. △ Less

Submitted 29 December, 2010; v1 submitted 15 January, 2010; originally announced January 2010.

Comments: 9 pages, 3 figures

Journal ref: J. Magn. Magn. Mater 322,3481(2010)

Magneto-optical and micromagnetic simulation study the current driven domain wall motion in ferromagnetic (Ga,Mn)As

Authors: K. Y. Wang, A. C. Irvine, R. P. Campion, C. T. Foxon, J. Wunderlich, D. A. Williams, B. L. Gallagher

Abstract: We have studied current-driven domain wall motion in modified Ga_0.95Mn_0.05As Hall bar structures with perpendicular anisotropy by using spatially resolved Polar Magneto-Optical Kerr Effect Microscopy and micromagnetic simulation. Regardless of the initial magnetic configuration, the domain wall propagates in the opposite direction to the current with critical current of 1~2x10^5A/cm^2. Conside… ▽ More We have studied current-driven domain wall motion in modified Ga_0.95Mn_0.05As Hall bar structures with perpendicular anisotropy by using spatially resolved Polar Magneto-Optical Kerr Effect Microscopy and micromagnetic simulation. Regardless of the initial magnetic configuration, the domain wall propagates in the opposite direction to the current with critical current of 1~2x10^5A/cm^2. Considering the spin transfer torque term as well as various effective magnetic field terms, the micromagnetic simulation results are consistent with the experimental results. Our simulated and experimental results suggest that the spin-torque rather than Oersted field is the reason for current driven domain wall motion in this material. △ Less

Submitted 28 May, 2008; originally announced May 2008.

Comments: 10 pages, 3 figures, to be published in J. Magn. Magn. Mater

Magnetic reversal under external field and current-driven domain wall motion in (Ga,Mn)As: influence of extrinsic pinning

Authors: K Y Wang, A C Irvine, J Wunderlich, K W Edmonds, A W Rushforth, R P Campion, C T Foxon, D A Williams, B L Gallagher

Abstract: We investigate the anisotropy of magnetic reversal and current-driven domain wall motion in annealed Ga_0.95Mn_0.05As thin films and Hall bar devices with perpendicular magnetic anisotropy. Hall bars with current direction along the [110] and [1-10] crystallographic axes are studied. The [110] device shows larger coercive field than the [1-10] device. Strong anisotropy is observed during magneti… ▽ More We investigate the anisotropy of magnetic reversal and current-driven domain wall motion in annealed Ga_0.95Mn_0.05As thin films and Hall bar devices with perpendicular magnetic anisotropy. Hall bars with current direction along the [110] and [1-10] crystallographic axes are studied. The [110] device shows larger coercive field than the [1-10] device. Strong anisotropy is observed during magnetic reversal between [110] and [1-10] directions. A power law dependence is found for both devices between the critical current (JC) and the magnetization (M), with J_C is proportional to M^2.6. The domain wall motion is strongly influenced by the presence of local pinning centres. △ Less

Submitted 26 May, 2008; originally announced May 2008.

Comments: 12 pages, 12 figures, submitted to New Journal of Physics

Domain imaging and domain wall propagation in (Ga,Mn)As thin films with tensile strain

Authors: K. Y. Wang, A. W. Rushforth, V. A. Grant, R. P. Campion, K. W. Edmonds, C. R. Staddon, C. T. Foxon, B. L. Gallagher, J. Wunderlich, D. A. Williams

Abstract: We have performed spatially resolved Polar Magneto-Optical Kerr Effect Microscopy measurements on as-grown and annealed Ga0.95Mn0.05As thin films with tensile strain. We find that the films exhibit very strong perpendicular magnetic anisotropy which is increased upon annealing. During magnetic reversal, the domain walls propagate along the direction of surface ripples for the as-grown sample at… ▽ More We have performed spatially resolved Polar Magneto-Optical Kerr Effect Microscopy measurements on as-grown and annealed Ga0.95Mn0.05As thin films with tensile strain. We find that the films exhibit very strong perpendicular magnetic anisotropy which is increased upon annealing. During magnetic reversal, the domain walls propagate along the direction of surface ripples for the as-grown sample at low temperatures and along the [110] direction for the annealed sample. This indicates that the magnetic domain pattern during reversal is determined by a combination of magnetocrystalline anisotropy and a distribution of pinning sites along the surface ripples that can be altered by annealing. These mechanisms could lead to an effective method of controlling domain wall propagation. △ Less

Submitted 3 May, 2007; originally announced May 2007.

Comments: 8 pages, 3 figures. to appear in Journal of Applied Physics

Control of Coercivities in (Ga,Mn)As Thin Films by Small Concentrations of MnAs Nanoclusters

Authors: K. Y. Wang, M. Sawicki, K. W. Edmonds, R. P. Campion, A. W. Rushforth, A. A. Freeman, C. T. Foxon, B. L. Gallagher, T. Dietl

Abstract: We demonstrate that low concentrations of a secondary magnetic phase in (Ga,Mn)As thin films can enhance the coercivity by factors up to ~100 without significantly degrading the Curie temperature or saturation magnetisation. Magnetic measurements indicate that the secondary phase consists of MnAs nanoclusters, of average size ~7nm. This approach to controlling the coercivity while maintaining hi… ▽ More We demonstrate that low concentrations of a secondary magnetic phase in (Ga,Mn)As thin films can enhance the coercivity by factors up to ~100 without significantly degrading the Curie temperature or saturation magnetisation. Magnetic measurements indicate that the secondary phase consists of MnAs nanoclusters, of average size ~7nm. This approach to controlling the coercivity while maintaining high Curie temperature, may be important for realizing ferromagnetic semiconductor based devices. △ Less

Submitted 15 December, 2005; originally announced December 2005.

Comments: 8 pages,4 figures. accepted for publication in Appl. Phys. Lett

Journal ref: Applied Physics Letters 88, 022510 (2006)

Low-temperature magnetization of (Ga,Mn)As semiconductors

Authors: T. Jungwirth, J. Masek, K. Y. Wang, K. W. Edmonds, M. Sawicki, M. Polini, Jairo Sinova, A. H. MacDonald, R. P. Campion, L. X. Zhao, N. R. S. Farley, T. K. Johal, G. van der Laan, C. T. Foxon, B. L. Gallagher

Abstract: We report on a comprehensive study of the ferromagnetic moment per Mn atom in (Ga,Mn)As ferromagnetic semiconductors. Theoretical discussion is based on microscopic calculations and on an effective model of Mn local moments antiferromagnetically coupled to valence band hole spins. The validity of the effective model over the range of doping studied is assessed by comparing with microscopic tight… ▽ More We report on a comprehensive study of the ferromagnetic moment per Mn atom in (Ga,Mn)As ferromagnetic semiconductors. Theoretical discussion is based on microscopic calculations and on an effective model of Mn local moments antiferromagnetically coupled to valence band hole spins. The validity of the effective model over the range of doping studied is assessed by comparing with microscopic tight-binding/coherent-potential approximation calculations. Using the virtual crystal k.p model for hole states, we evaluate the zero-temperature mean-field contributions to the magnetization from the hole kinetic and exchange energies, and magnetization suppression due to quantum uctuations of Mn moment orientations around their mean-field ground state values. Experimental low-temperature ferromagnetic moments per Mn are obtained by superconducting quantum interference device and x-ray magnetic circular dichroism measurements in a series of (Ga,Mn)As semiconductors with nominal Mn doping ranging from ~2% to 8%. Hall measurements in as-grown and annealed samples are used to estimate the number of uncompensated substitutional Mn moments. Based on our comparison between experiment and theory we conclude that all these Mn moments in high quality (Ga,Mn)As materials have nearly parallel ground state alignment. △ Less

Submitted 10 August, 2005; originally announced August 2005.

Comments: 11 pages, 11 figures, submitted to Phys. Rev. B

GaMnAs grown on (311) GaAs substrates: modified Mn incorporation and new magnetic anisotropies

Authors: K. Y. Wang, K. W. Edmonds, L. X. Zhao, M. Sawicki, R. P. Campion, B. L. Gallagher, C. T. Foxon

Abstract: We report the results of a detailed study of the structural, magnetic and magnetotransport properties of as-grown and annealed Ga0.91Mn0.09As thin films grown on (311)A and (311)B GaAs substrates. The high Curie temperature and hole density of the (311)B material are comparable to those of GaMnAs grown on (001) GaAs under the same growth conditions, while they are much lower for the (311)A mater… ▽ More We report the results of a detailed study of the structural, magnetic and magnetotransport properties of as-grown and annealed Ga0.91Mn0.09As thin films grown on (311)A and (311)B GaAs substrates. The high Curie temperature and hole density of the (311)B material are comparable to those of GaMnAs grown on (001) GaAs under the same growth conditions, while they are much lower for the (311)A material. We find evidence that Mn incorporation is more efficient for (311)B than for (001) and significantly less efficient for (311)A which is consistent with the bonding on these surfaces. This indicates that growth on (311)B may be a route to increased Curie temperatures in GaMnAs. A biaxial magnetic anisotropy is observed for the (311) material with easy axes along the [010] and [001] out-of-plane directions. An additional uniaxial in-plane anisotropy is also observed with the easy axis along for the (311)A material, and along for the (311)B material. This new observation may be of importance for the resolution of the outstanding problem of the origin of uniaxial anisotropy in (001) GaMnAs. △ Less

Submitted 30 July, 2005; originally announced August 2005.

Comments: 16 pages, 6 figures and 1 table. accepted by Phys. Rev. B

Journal ref: Phys. Rev. B 72, 115207 (2005)

Anisotropic Magnetoresistance and Magnetic Anisotropy in High-quality (Ga,Mn)As Films

Authors: K. Y. Wang, K. W. Edmonds, R. P. Campion, L. X. Zhao, C. T. Foxon, B. L. Gallagher

Abstract: We have performed a systematic investigation of magnetotransport of a series of as-grown and annealed Ga1-xMnxAs samples with 0.011 <= x <= 0.09. We find that the anisotropic magnetoresistance (AMR) generally decreases with increasing magnetic anisotropy, with increasing Mn concentration and on low temperature annealing. We show that the uniaxial magnetic anisotropy can be clearly observed from… ▽ More We have performed a systematic investigation of magnetotransport of a series of as-grown and annealed Ga1-xMnxAs samples with 0.011 <= x <= 0.09. We find that the anisotropic magnetoresistance (AMR) generally decreases with increasing magnetic anisotropy, with increasing Mn concentration and on low temperature annealing. We show that the uniaxial magnetic anisotropy can be clearly observed from AMR for the samples with x >= 0.02. This becomes the dominant anisotropy at elevated temperatures, and is shown to rotate by 90o on annealing. We find that the in-plane longitudinal resistivity depends not only on the relative angle between magnetization and current direction, but also on the relative angle between magnetization and the main crystalline axes. The latter term becomes much smaller after low temperature annealing. The planar Hall effect is in good agreement with the measured AMR indicating the sample is approximately in a single domain state throughout most of the magnetisation reversal, with a two-step magnetisation jump ascribed to domain wall nucleation and propagation. △ Less

Submitted 10 June, 2005; originally announced June 2005.

Comments: 27 pages, 8 figures, accepted by Phys. Rev. B

Journal ref: Phys. Rev. B 72, 085201 (2005)

Prospects of high temperature ferromagnetism in (Ga,Mn)As semiconductors

Authors: T. Jungwirth, K. Y. Wang, J. Masek, K. W. Edmonds, Jurgen Konig, Jairo Sinova, M. Polini, N. A. Goncharuk, A. H. MacDonald, M. Sawicki, R. P. Campion, L. X. Zhao, C. T. Foxon, B. L. Gallagher

Abstract: We report on a comprehensive combined experimental and theoretical study of Curie temperature trends in (Ga,Mn)As ferromagnetic semiconductors. Broad agreement between theoretical expectations and measured data allows us to conclude that T_c in high-quality metallic samples increases linearly with the number of uncompensated local moments on Mn_Ga acceptors, with no sign of saturation. Room temp… ▽ More We report on a comprehensive combined experimental and theoretical study of Curie temperature trends in (Ga,Mn)As ferromagnetic semiconductors. Broad agreement between theoretical expectations and measured data allows us to conclude that T_c in high-quality metallic samples increases linearly with the number of uncompensated local moments on Mn_Ga acceptors, with no sign of saturation. Room temperature ferromagnetism is expected for a 10% concentration of these local moments. Our magnetotransport and magnetization data are consistnent with the picture in which Mn impurities incorporated during growth at interstitial Mn_I positions act as double-donors and compensate neighboring Mn_Ga local moments because of strong near-neighbor Mn_Ga-Mn_I antiferromagnetic coupling. These defects can be efficiently removed by post-growth annealing. Our analysis suggests that there is no fundamental obstacle to substitutional Mn_Ga doping in high-quality materials beyond our current maximum level of 6.2%, although this achievement will require further advances in growth condition control. Modest charge compensation does not limit the maximum Curie temperature possible in ferromagnetic semiconductors based on (Ga,Mn)As. △ Less

Submitted 9 May, 2005; originally announced May 2005.

Comments: 13 pages, 12 figures, submitted to Phys. Rev. B

Journal ref: Phys. Rev. B 72, 165204 (2005)

Intrinsic and Extrinsic Contributions to the Lattice Parameter of GaMnAs

Authors: L. X. Zhao, C. R. Staddon, K. Y. Wang, K. W. Edmonds, R. P. Campion, B. L. Gallagher, C. T. Foxon

Abstract: We report on measurements of the crystal structure and hole density in a series of as-grown and annealed GaMnAs samples. The measured hole densities are used to obtain the fraction of incorporated Mn atoms occupying interstitial and substitutional sites. This allows us to make a direct comparison of the measured lattice parameters with recent density functional theory (DFT) predictions. We find… ▽ More We report on measurements of the crystal structure and hole density in a series of as-grown and annealed GaMnAs samples. The measured hole densities are used to obtain the fraction of incorporated Mn atoms occupying interstitial and substitutional sites. This allows us to make a direct comparison of the measured lattice parameters with recent density functional theory (DFT) predictions. We find that the decrease in lattice constant observed on annealing is smaller than that predicted due to the out diffusion of interstitial Mn during annealing. The measured lattice parameters after annealing are still significantly larger than that of GaAs even in samples with very low compensation. This indicates that the intrinsic lattice parameter of GaMnAs is significantly larger than that of GaAs, in contradiction to the DFT prediction. △ Less

Submitted 13 January, 2005; originally announced January 2005.

Comments: To appear in Appl. Phys. Lett.,13 pages,3 figures and 1 table

Magnetism in (Ga,Mn)As Thin Films With TC Up To 173K

Authors: K. Y. Wang, R. P. Campion, K. W. Edmonds, M. Sawicki, T. Dietl, C. T. Foxon, B. L. Gallagher

Abstract: We have investigated the magnetic properties of (Ga,Mn)As thin films with Mn concentration between 1 and 9%. Ferromagnetic transition temperatures TC of up to 173K are observed. The results are compared to the predictions of the Zener mean-field theory. We find no evidence of a fundamental limit to TC. We have investigated the magnetic properties of (Ga,Mn)As thin films with Mn concentration between 1 and 9%. Ferromagnetic transition temperatures TC of up to 173K are observed. The results are compared to the predictions of the Zener mean-field theory. We find no evidence of a fundamental limit to TC. △ Less

Submitted 18 November, 2004; originally announced November 2004.

Comments: presented at ICPS-27; 2 pages

Search For Hole Mediated Ferromagnetism In Cubic (Ga,Mn)N

Authors: M. Sawicki, T. Dietl, C. T. Foxon, S. V. Novikov, R. P. Campion, K. W. Edmonds, K. Y. Wang, A. D. Giddings, B. L. Gallagher

Abstract: Results of magnetisation measurements on p-type zincblende-(Ga,Mn)N are reported. In addition to a small high temperature ferromagnetic signal, we detect ferromagnetic correlation among the remaining Mn ions, which we assign to the onset of hole-mediated ferromagnetism in (Ga,Mn)N. Results of magnetisation measurements on p-type zincblende-(Ga,Mn)N are reported. In addition to a small high temperature ferromagnetic signal, we detect ferromagnetic correlation among the remaining Mn ions, which we assign to the onset of hole-mediated ferromagnetism in (Ga,Mn)N. △ Less

Submitted 21 October, 2004; originally announced October 2004.

Comments: 2 pages, 1 figure, proc. ICPS 27, Flagstaff '04

Journal ref: Proc. 27th Int. Conf. on Phys. of Semicon., Flagstaff, Az, July 2004, eds. J. Menendez and Ch. Van de Walle, (New York 2005) p. 1371.

Large tunneling anisotropic magnetoresistance in (Ga,Mn)As nanoconstrictions

Authors: A. D. Giddings, M. N. Khalid, J. Wunderlich, S. Yasin, R. P. Campion, K. W. Edmonds, J. Sinova, T. Jungwirth, K. Ito, K. Y. Wang, D. Williams, B. L. Gallagher, C. T. Foxon

Abstract: We report a large tunneling anisotropic magnetoresistance (TAMR) in a thin (Ga,Mn)As epilayer with lateral nanoconstrictions. The observation establishes the generic nature of this effect, which originates from the spin-orbit coupling in a ferromagnet and is not specific to a particular tunnel device design. The lateral geometry allows us to link directly normal anisotropic magnetoresistance (AM… ▽ More We report a large tunneling anisotropic magnetoresistance (TAMR) in a thin (Ga,Mn)As epilayer with lateral nanoconstrictions. The observation establishes the generic nature of this effect, which originates from the spin-orbit coupling in a ferromagnet and is not specific to a particular tunnel device design. The lateral geometry allows us to link directly normal anisotropic magnetoresistance (AMR) and TAMR. This indicates that TAMR may be observable in other materials showing a comparable AMR at room temperature, such as transition metal alloys. △ Less

Submitted 8 September, 2004; originally announced September 2004.

Comments: 4 pages, 4 figures

Journal ref: Phys. Rev. Lett. 94, 127202 (2005).

P-type conductivity in cubic GaMnN layers grown by molecular beam epitaxy

Authors: S. V. Novikov, K. W. Edmonds, A. D. Giddings, K. Y. Wang, C. R. Staddon, R. P. Campion, B. L. Gallagher, C. T. Foxon

Abstract: Cubic (zinc-blende) Ga1-xMnxN layers were grown by plasma-assisted molecular beam epitaxy on GaAs (001) substrates. Some of the structures also contained cubic AlN buffer layers. Auger Electron Spectroscopy and Secondary Ion Mass Spectroscopy studies clearly confirmed the incorporation of Mn into cubic GaN, the Mn being uniformly distributed through the layer. X-ray diffraction studies demonstra… ▽ More Cubic (zinc-blende) Ga1-xMnxN layers were grown by plasma-assisted molecular beam epitaxy on GaAs (001) substrates. Some of the structures also contained cubic AlN buffer layers. Auger Electron Spectroscopy and Secondary Ion Mass Spectroscopy studies clearly confirmed the incorporation of Mn into cubic GaN, the Mn being uniformly distributed through the layer. X-ray diffraction studies demonstrated that the Mn-doped GaN films are cubic and do not show phase separation up to a Mn concentrations of x<0.1. P-type conductivity for the cubic Ga1-xMnxN layers was observed for a wide range of the Mn doping levels. The measured hole concentration at room temperature depends non-linearly on the Mn incorporation and varies from 3x10^16 to 5x10^18 cm-3. △ Less

Submitted 21 November, 2003; originally announced November 2003.

Comments: 7 pages, 3 figures

Journal ref: Semiconductor Science and Technology 19, L13-16 (2004)

Mn Interstitial Diffusion in (Ga,Mn)As

Authors: K. W. Edmonds, P. Boguslawski, K. Y. Wang, R. P. Campion, N. R. S. Farley, B. L. Gallagher, C. T. Foxon, M. Sawicki, T. Dietl, M. B. Nardelli, J. Bernholc

Abstract: We present a combined theoretical and experimental study of the ferromagnetic semiconductor (Ga,Mn)As which explains the remarkably large changes observed on low temperature annealing. Careful control of the annealing conditions allows us to obtain samples with ferromagnetic transition temperatures up to 159 K. Ab initio calculations, and resistivity measurements during annealing, show that the… ▽ More We present a combined theoretical and experimental study of the ferromagnetic semiconductor (Ga,Mn)As which explains the remarkably large changes observed on low temperature annealing. Careful control of the annealing conditions allows us to obtain samples with ferromagnetic transition temperatures up to 159 K. Ab initio calculations, and resistivity measurements during annealing, show that the observed changes are due to out-diffusion of Mn interstitials towards the surface, governed by an energy barrier of about 0.7-0.8 eV. The Mn interstitial is a double donor resulting in compensation of charge carriers and suppression of ferromagnetism. Electric fields induced by high concentrations of substitutional Mn acceptors have a significant effect on the diffusion. △ Less

Submitted 7 July, 2003; originally announced July 2003.

Comments: 5 pages, 4 figures, submitted to Physical Review Letters

Journal ref: Physical Review Letters 92, 037201 (2004)

DC-transport properties of ferromagnetic (Ga,Mn)As semiconductors

Authors: T. Jungwirth, Jairo Sinova, K. Y. Wang, K. W. Edmonds, R. P. Campion, B. L. Gallagher, C. T. Foxon, Qian Niu, A. H. MacDonald

Abstract: We study the dc transport properties of (Ga,Mn)As diluted magnetic semiconductors with Mn concentration varying from 1.5% to 8%. Both diagonal and Hall components of the conductivity tensor are strongly sensitive to the magnetic state of these semiconductors. Transport data obtained at low temperatures are discussed theoretically within a model of band-hole quasiparticles with a finite spectral… ▽ More We study the dc transport properties of (Ga,Mn)As diluted magnetic semiconductors with Mn concentration varying from 1.5% to 8%. Both diagonal and Hall components of the conductivity tensor are strongly sensitive to the magnetic state of these semiconductors. Transport data obtained at low temperatures are discussed theoretically within a model of band-hole quasiparticles with a finite spectral width due to elastic scattering from Mn and compensating defects. The theoretical results are in good agreement with measured anomalous Hall effect and anisotropic longitudinal magnetoresistance data. This quantitative understanding of dc magneto-transport effects in (Ga,Mn)As is unparalleled in itinerant ferromagnetic systems. △ Less

Submitted 3 February, 2003; originally announced February 2003.

Comments: 3 pages, 3 figures

Journal ref: Appl. Phys. Lett. 83, 320 (2003)

Anisotropic Magnetoresistance in GaMnAs films

Authors: K. Y. Wang, K. W. Edmonds, R. P. Campion, L. X. Zhao, A. C. Neumann, C. T. Foxon, B. L. Gallagher, P. C. Main

Abstract: The magnetoresistance in a series of Ga1-xMnxAs samples with 0.2 =< x =< 0.8 have been measured for three mutually orthogonal orientations of the external magnetic field. The anisotropy magnetoresistance decreases with increasing of the Mn content, which means that the magnetic disorder or defects scattering increases with increasing of Mn content. And also the magneto-crystalline anisotropy inc… ▽ More The magnetoresistance in a series of Ga1-xMnxAs samples with 0.2 =< x =< 0.8 have been measured for three mutually orthogonal orientations of the external magnetic field. The anisotropy magnetoresistance decreases with increasing of the Mn content, which means that the magnetic disorder or defects scattering increases with increasing of Mn content. And also the magneto-crystalline anisotropy increases with increasing of Mn concentration. △ Less

Submitted 29 November, 2002; originally announced November 2002.

Comments: Presented at ICPS-26, July 2002

High Curie temperature GaMnAs obtained by resistance-monitored annealing

Authors: K. W. Edmonds, K. Y. Wang, R. P. Campion, A. C. Neumann, N. R. S. Farley, B. L. Gallagher, C. T. Foxon

Abstract: We show that by annealing Ga1-xMnxAs thin films at temperatures significantly lower than in previous studies, and monitoring the resistivity during growth, an unprecedented high Curie temperature Tc and conductivity can be obtained. Tc is unambiguously determined to be 118 K for Mn concentration x=0.05, 140 K for x=0.06, and 120 K for x=0.08. We also identify a clear correlation between Tc and t… ▽ More We show that by annealing Ga1-xMnxAs thin films at temperatures significantly lower than in previous studies, and monitoring the resistivity during growth, an unprecedented high Curie temperature Tc and conductivity can be obtained. Tc is unambiguously determined to be 118 K for Mn concentration x=0.05, 140 K for x=0.06, and 120 K for x=0.08. We also identify a clear correlation between Tc and the room temperature conductivity. The results indicate that Curie temperatures significantly in excess of the current values are achievable with improvements in growth and post-growth annealing conditions. △ Less

Submitted 24 September, 2002; originally announced September 2002.

Comments: 4 pages, submitted to Applied Physics Letters

The Hall effect and hole densities in high Tc GaMnAs thin films

Authors: K. W. Edmonds, K. Y. Wang, R. P. Campion, A. C. Neumann, C. T. Foxon, B. L. Gallagher, P. C. Main

Abstract: By studying the Hall effect in a series of low resistivity Ga1-xMnxAs samples, accurate values for the hole density p, Mn concentration x, and Curie temperature Tc are obtained over the range 0.015=<x=<0.08. The hole density corresponds to 90% of the Mn concentration at low x, and has a maximum value of 1.0x10-27 m-3 when Tc=125K for x=0.06. This data allows the first meaningful comparison of me… ▽ More By studying the Hall effect in a series of low resistivity Ga1-xMnxAs samples, accurate values for the hole density p, Mn concentration x, and Curie temperature Tc are obtained over the range 0.015=<x=<0.08. The hole density corresponds to 90% of the Mn concentration at low x, and has a maximum value of 1.0x10-27 m-3 when Tc=125K for x=0.06. This data allows the first meaningful comparison of mean field predicted Curie temperatures with experiment over a wide range of x. The theory is in qualitative agreement with experiment, but overestimates Tc at large x and underestimates TC at low x. △ Less

Submitted 23 August, 2002; v1 submitted 24 May, 2002; originally announced May 2002.

Comments: Submitted to Appl. Phys. Lett., 8 pages, 4 figs