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Antiferromagnetic to Ferrimagnetic Phase Transition and Possible Phase Coexistence in Polar Magnets (Fe$_{1-x}$Mn$_x$)$_2$Mo$_3$O$_8$
Authors:
Yuting Chang,
Lei Gao,
Yunlong Xie,
Bin You,
Yong Liu,
Rui Xiong,
Junfeng Wang,
Chengliang Lu,
JunMing Liu
Abstract:
In the present work, magnetic properties of single crystal (Fe$_{1-x}$Mn$_x$)$_2$Mo$_3$O$_8$ ($0<x<1$) have been studied by performing extensive measurements. A detailed magnetic phase diagram is built up, in which antiferromagnetic state dominates for $x<0.25$ and ferrimagnetic phase arises for $x>0.3$. Meanwhile, sizeable electric polarization of spin origin is commonly observed in all samples,…
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In the present work, magnetic properties of single crystal (Fe$_{1-x}$Mn$_x$)$_2$Mo$_3$O$_8$ ($0<x<1$) have been studied by performing extensive measurements. A detailed magnetic phase diagram is built up, in which antiferromagnetic state dominates for $x<0.25$ and ferrimagnetic phase arises for $x>0.3$. Meanwhile, sizeable electric polarization of spin origin is commonly observed in all samples, no matter what the magnetic state is. For the samples hosting a ferrimagnetic state, square-like magnetic hysteresis loops are revealed, while the remnant magnetization and coercive field can be tuned drastically by simply varying the Mn-content or temperature. Possible coexistence of the antiferromagnetic and ferrimagnetic phases is proposed to be responsible for the remarkable modulation of magnetic properties in the samples.
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Submitted 16 September, 2023;
originally announced September 2023.
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Structural origin of the Jeff=1/2 antiferromagnetic phase in Ga-doped Sr2IrO4
Authors:
H. W. Wang,
L. Y. Zhang,
N. Hu,
B. You,
Y. T. Chang,
S. L. Yuan,
C. L. Lu,
J. M. Liu
Abstract:
Sr2IrO4 hosts a novel Jeff =1/2 Mott state and quasi-two-dimensional antiferromagnetic order, providing a unique avenue of exploring emergent states of matter and functions that are extraordinarily sensitive to any structural variations. While the correlation between the physical property and lattice structure in Sr2IrO4 has been a focused issue in the past decade, a common perception assumes that…
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Sr2IrO4 hosts a novel Jeff =1/2 Mott state and quasi-two-dimensional antiferromagnetic order, providing a unique avenue of exploring emergent states of matter and functions that are extraordinarily sensitive to any structural variations. While the correlation between the physical property and lattice structure in Sr2IrO4 has been a focused issue in the past decade, a common perception assumes that the magnetic ordering is essentially determined by the Ir-O-Ir bond angle. Therefore, a delicate modulation of this angle and consequently a major modulation of the magnetic ordering, by chemical doping such as Ga at Ir site, has been extensively investigated and well believed. In this work, however, we present a whole package of structure and magnetism data on a series of single crystal and polycrystalline Sr2Ir1-xGaxO4 samples, revealing the substantial difference in the Néel temperature TN between the two types of samples, and the TN value for the polycrystalline sample x = 0.09 is even 64 K higher than that of the single crystal sample x = 0.09 (deltaTN ~ 64 K at x = 0.09). Our systematic investigations demonstrate the crucial role of the c/a ratio in tuning the interlayer coupling and thereby the Neel point TN, i.e. a higher TN can be achieved as c/a is reduced. The notable differences in structural parameters between the two groups of samples are probably caused by additional strain due to the massive grain boundaries in polycrystalline samples. The present work suggests an additional ingredient of physics that is essential in modulating the emergent properties in Sr2IrO4 and probably other iridates.
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Submitted 16 September, 2023;
originally announced September 2023.
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Strain tuned magnetotransport of Jeff=1/2 antiferromagnetic Sr2IrO4 thin films
Authors:
N. Hu,
Y. K. Weng,
K. Chen,
B. You,
Y. Liu,
Y. T. Chang,
R. Xiong,
S. Dong,
C. L. Lu
Abstract:
In this work, we report observation of strain effect on physical properties of Sr2IrO4 thin films grown on SrTiO3 (001) and LaAlO3 (001) substrates. It is found that the film on LaAlO3 with compressive strain has a lower antiferromagnetic transition temperature (TN~210 K) than the film on SrTiO3 (TN~230 K) with tensile strain, which is probably caused by modified interlayer coupling. Interestingly…
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In this work, we report observation of strain effect on physical properties of Sr2IrO4 thin films grown on SrTiO3 (001) and LaAlO3 (001) substrates. It is found that the film on LaAlO3 with compressive strain has a lower antiferromagnetic transition temperature (TN~210 K) than the film on SrTiO3 (TN~230 K) with tensile strain, which is probably caused by modified interlayer coupling. Interestingly, magnetoresistance due to pseudospin-flip of the film on LaAlO3 is much larger than that of tensile-strained film on SrTiO3, and robust anisotropic magnetoresistance is observed in the former, but H-driven reversal behavior is seen in the latter. By performing first principles calculations, it is revealed that epitaxial strain plays an efficient role in tuning the canting angle of Jeff=1/2 moments and thus net moment at every IrO2 layer, responsible for the difference in magnetoresistance between the films. The reversal of anisotropic magnetoresistance in the thin film on SrTiO3 can be ascribed to stabilization of a metastable stable with smaller bandgap as the Jeff=1/2 moments are aligned along the diagonal of basal plane by H. However, theoretical calculations reveal much higher magnetocrystalline anisotropy energy in the film on LaAlO3. This causes difficulties to drive the Jeff=1/2 moments to reach the diagonal and thereby the metastable state, explaining the distinct anisotropic magnetoresistance between two samples in a qualitative sense. Our findings indicate that strain can be a highly efficient mean to engineer the functionalities of Jeff=1/2 antiferromagnet Sr2IrO4.
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Submitted 16 September, 2023;
originally announced September 2023.
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Colossal linear magnetoelectricity in polar magnet Fe2Mo3O8
Authors:
Yuting Chang,
Yakui Weng,
Yunlong Xie,
Bin You,
Junfeng Wang,
Liang Li,
Jun-Ming Liu,
Shuai Dong,
Chengliang Lu
Abstract:
Linear magnetoelectric effect is an attractive phenomenon in condensed matters and provides indispensable technological functionalities. Here a colossal linear magnetoelectric effect with diagonal component alfa_33 reaching up to ~480 ps/m is reported in a polar magnet Fe2Mo3O8, and this effect can persist in a broad range of magnetic field (~20 T) and is orders of magnitude larger than reported v…
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Linear magnetoelectric effect is an attractive phenomenon in condensed matters and provides indispensable technological functionalities. Here a colossal linear magnetoelectric effect with diagonal component alfa_33 reaching up to ~480 ps/m is reported in a polar magnet Fe2Mo3O8, and this effect can persist in a broad range of magnetic field (~20 T) and is orders of magnitude larger than reported values in literature. Such an exceptional experimental observation can be well reproduced by a theoretical model affirmatively unveiling the vital contributions from the exchange striction, while the sign difference of magnetocrystalline anisotropy can also be reasonably figured out.
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Submitted 16 September, 2023;
originally announced September 2023.
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Antiferromagnetic multi-level memristor using linear magnetoelectricity
Authors:
Y. T. Chang,
J. F. Wang,
W. Wang,
C. B. Liu,
B. You,
M. F. Liu,
S. H. Zheng,
M. Y. Shi,
C. L. Lu,
J. -M. Liu
Abstract:
The explosive growth of artificial intelligence and data-intensive computing has brought crucial challenge to modern information science and technology, i.e. conceptually new devices with superior properties are urgently desired. Memristor is recognized as a very promising circuit element to tackle the barriers, because of its fascinating advantages in imitating neural network of human brain, and…
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The explosive growth of artificial intelligence and data-intensive computing has brought crucial challenge to modern information science and technology, i.e. conceptually new devices with superior properties are urgently desired. Memristor is recognized as a very promising circuit element to tackle the barriers, because of its fascinating advantages in imitating neural network of human brain, and thus realizing in-memory computing. However, there exist two core and fundamental issues: energy efficiency and accuracy, owing to the electric current operation of traditional memristors. In the present work, we demonstrate a new type of memristor, i.e. charge q and magnetic flux φ space memristor, enabled by linear magnetoelectricity of Co4Nb2O9. The memory states show distinctly linear magnetoelectric coefficients with a large ratio of about 10, ensuing exceptional accuracy of related devices. The present q-φ type memristor can be manipulated by magnetic and electric fields without involving electric current, paving the way to develop ultralow-energy-consuming devices. In the meanwhile, it is worth to mention that Co4Nb2O9 hosts an intrinsic compensated antiferromagnetic structure, which suggests interesting possibility of further integrating the unique merits of antiferromagnetic spintronics such as ultrahigh density and ultrafast switching. Linear magnetoelectricity is proposed to essential to the q-φ type memristor, which would be accessible in a broad class of multiferroics and other magnetoelectric materials such as topological insulators. Our findings could therefore advance memristors towards new levels of functionality.
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Submitted 25 October, 2021;
originally announced October 2021.
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Interfacial Partitioning Enhances Microextractionby Multicomponent Nanodroplets
Authors:
Zixiang Wei,
Jae Bem You,
Hongbo Zeng,
Xuehua Zhang
Abstract:
The sensitive and reliable in-droplet chemical analysis benefits from the enhanced partition of an analyte into the droplets. This work, we will show that chemical reactions in surface nanodroplets can shift the partition of analytes from a highly diluted solution to the droplets. Seven types of organic acids with partition coefficients (LgP) ranging from -0.7 to 1.87 are used as model analytes di…
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The sensitive and reliable in-droplet chemical analysis benefits from the enhanced partition of an analyte into the droplets. This work, we will show that chemical reactions in surface nanodroplets can shift the partition of analytes from a highly diluted solution to the droplets. Seven types of organic acids with partition coefficients (LgP) ranging from -0.7 to 1.87 are used as model analytes dissolved in an oil solution that are extracted from the flow into aqueous nanodroplets immobilized on a substrate. The timescale of integrated extraction and reaction in droplets was represented by the decoloration time of the droplets. Our results show that the effective distribution coefficient of the analyte can be decreased by 3 to 11 times of the distribution coefficient of the analyte in the bulk liquids. The principle behind the significantly shifted partition is proposed to be enhanced the transfer of the analyte across the droplet surface. The chemical reaction in the droplets enhances the partition of the analyte from a highly diluted solution. Our results show that the interfacial behavior of the analyte may be advantageous as it may improve extraction and partition. Such enhanced extraction may be leveraged for sensitive chemical detection using reactive droplets.
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Submitted 30 September, 2021;
originally announced October 2021.
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Surface nanodroplet-based nanoextraction from sub-milliliter volumes of dense suspensions
Authors:
Jae Bem You,
Detlef Lohse,
Xuehua Zhang
Abstract:
Cleaner analytic technique for quantifying compounds in dense suspension is needed for wastewater and environment analysis, chemical or bio-conversion process monitoring, biomedical diagnostics, food quality control among others. In this work, we introduce a green, fast, one-step method called nanoextraction for extraction and detection of target analytes from sub-milliliter dense suspensions usin…
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Cleaner analytic technique for quantifying compounds in dense suspension is needed for wastewater and environment analysis, chemical or bio-conversion process monitoring, biomedical diagnostics, food quality control among others. In this work, we introduce a green, fast, one-step method called nanoextraction for extraction and detection of target analytes from sub-milliliter dense suspensions using surface nanodroplets without toxic solvents and pre-removal of the solid contents. With nanoextraction, we achieve a limit of detection (LOD) of 10^(-9) M for a fluorescent model analyte obtained from a particle suspension sample. The LOD lower than that in water without particles 10^(-8) M, potentially due to the interaction of particles and the analyte. The high particle concentration in the suspension sample thus does not reduce the extraction efficiency, although the extraction process was slowed down up to 5 min. As proof of principle, we demonstrate the nanoextraction for quantification of model compounds in wastewater slurry containing 30 wt% sands and oily components (i.e. heavy oils). The nanoextraction and detection technology developed in this work may be used as fast analytic technologies for complex slurry samples in environment industrial waste, or in biomedical diagnostics.
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Submitted 9 May, 2021;
originally announced May 2021.
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Effects of chemical and geometric micro-structures on crystallization of surface droplets during solvent exchange
Authors:
Howon Choi,
Zixiang Wei,
Jae Bem You,
Huaiyu Yang,
Xuehua Zhang
Abstract:
In this work, we investigate crystallization from droplets formed on micro-patterned surfaces. By solvent exchange in a micro-chamber, a ternary solution consisting of a model compound beta-alanine, water, and isopropanol, was displaced by a flow of isopropanol. In the process, oiling-out droplets formed and crystallized. Our results showed that the shape and size of the crystals on micro-patterne…
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In this work, we investigate crystallization from droplets formed on micro-patterned surfaces. By solvent exchange in a micro-chamber, a ternary solution consisting of a model compound beta-alanine, water, and isopropanol, was displaced by a flow of isopropanol. In the process, oiling-out droplets formed and crystallized. Our results showed that the shape and size of the crystals on micro-patterned surfaces could be simply mediated by the flow conditions of solvent exchange. Varying flow rate, concentration, or channel height led to the formation of a thin film with micro-holes, connected network of crystals, or small diamond-shaped crystals. Rough micro-structures on the surface allowed the easy detachment of crystals from the surface. Beyond oiling-out crystallization, we demonstrated that the crystal formation from another solute dissolved in the droplets could be triggered by solvent exchange. The length of crystal fibers after the solvent exchange process was shorter at a faster flow rate. This study may provide further understanding to effectively obtain crystallization from surface droplets through the solvent exchange approach.
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Submitted 14 April, 2021;
originally announced April 2021.
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Enhanced displacement of phase separating liquid mixtures in 2D confined spaces
Authors:
Gilmar F. Arends,
Jae Bem You,
John M. Shaw,
Xuehua Zhang
Abstract:
Displacing liquid in a confined space is important for technological processes, ranging from porous membrane separation to CO$_{2}$ sequestration. The liquid to be displaced usually consists of multiple components with different solubilities in the displacing liquid. Phase separation and chemical composition gradients in the liquids can influence the displacement rate. In this work, we investigate…
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Displacing liquid in a confined space is important for technological processes, ranging from porous membrane separation to CO$_{2}$ sequestration. The liquid to be displaced usually consists of multiple components with different solubilities in the displacing liquid. Phase separation and chemical composition gradients in the liquids can influence the displacement rate. In this work, we investigate the effects of liquid composition on the displacement process of ternary liquid mixtures in a quasi-2D microchannel where liquid-liquid phase separation occurs concurrently. We focused on model ternary mixtures containing 1-octanol, ethanol, and water. These mixtures are displaced with water or with ethanol aqueous solution. The spatial distribution of subphases arising from phase separation and the displacement rates of the solution are impacted by the initial ternary solution composition. The boundary between the solution and displacing liquid changes from a defined interface to a diffusive interface as the initial 1-octanol composition in the solution is reduced. The displacement rate also varies non-linearly with the initial 1-octanol composition. The slowest displacement rate arises in the intermediate 1-octanol concentration, where a stable three-zone configuration forms at the boundary. At very low 1-octanol concentration, the displacement rate is fast, associated with droplet formation and motion driven by the chemical concentration gradients formed during phase separation. The excessive energy provided from phase separation may contribute to the enhanced displacement at intermediate to high 1-octanol concentrations, but not at the low 1-octanol concentration with enhancement from induced flow in confinement. The knowledge gained from this study highlights the importance of manipulating phase separation to enhance mass transport in confinement for a wide range of separation processes.
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Submitted 25 February, 2021;
originally announced February 2021.
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Self-propelling Microdroplets Generated and Sustained by Liquid-liquid Phase Separation in Confined Spaces
Authors:
Xuehua Zhang,
Jae Bem You,
Gilmar F. Arends,
Jiasheng Qian,
Yibo Chen,
Detlef Lohse,
John M. Shaw
Abstract:
Flow transport in confined spaces is ubiquitous in technological processes, ranging from separation and purification of pharmaceutical ingredients by microporous membranes and drug delivery in biomedical treatment to chemical and biomass conversion in catalyst-packed reactors and carbon dioxide sequestration. In this work, we suggest a distinct pathway for enhanced liquid transport in a confined s…
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Flow transport in confined spaces is ubiquitous in technological processes, ranging from separation and purification of pharmaceutical ingredients by microporous membranes and drug delivery in biomedical treatment to chemical and biomass conversion in catalyst-packed reactors and carbon dioxide sequestration. In this work, we suggest a distinct pathway for enhanced liquid transport in a confined space via self-propelling microdroplets. These microdroplets can form spontaneously from localized liquid-liquid phase separation as a ternary mixture is diluted by a diffusing poor solvent. High speed images reveal how the microdroplets grow, break up and propel rapidly along the solid surface, with a maximal velocity up to ~160 um/s, in response to a sharp concentration gradient resulting from phase separation. The microdroplet self-propulsion induces a replenishing flow between the walls of the confined space towards the location of phase separation, which in turn drives the mixture out of equilibrium and leads to a repeating cascade of events. Our findings on the complex and rich phenomena of self-propelling droplets suggest an effective approach to enhanced flow motion of multicomponent liquid mixtures within confined spaces for time effective separation and smart transport processes.
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Submitted 28 December, 2020;
originally announced December 2020.
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Microfluidic device coupled with total internal reflection microscopy for in situ observation of precipitation
Authors:
Jia Meng,
Jae Bem You,
Gilmar F. Arends,
Hao Hao,
Xiaoli Tan,
Xuehua Zhang
Abstract:
In situ observation of precipitation or phase separation induced by solvent addition is important in studying its dynamics. Combined with optical and fluorescence microscopy, microfluidic devices have been leveraged in studying the phase separation in various materials including biominerals, nanoparticles, and inorganic crystals. However, strong scattering from the subphases in the mixture is prob…
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In situ observation of precipitation or phase separation induced by solvent addition is important in studying its dynamics. Combined with optical and fluorescence microscopy, microfluidic devices have been leveraged in studying the phase separation in various materials including biominerals, nanoparticles, and inorganic crystals. However, strong scattering from the subphases in the mixture is problematic for in situ study of phase separation with high temporal and spatial resolution. In this work, we present a quasi-2D microfluidic device combined with total internal reflection microscopy as an approach for in situ observation of phase separation. The quasi-2D microfluidic device comprises of a shallow main channel and a deep side channel. Mixing between a solution in the main channel (solution A) and another solution (solution B) in the side channel is predominantly driven by diffusion due to high fluid resistance from the shallow height of the main channel, which is confirmed using fluorescence microscopy. Moreover, relying on diffusive mixing, we can control the composition of the mixture in the main channel by tuning the composition of solution B. We demonstrate the application of our method for in situ observation of asphaltene precipitation and beta-alanine crystallization.
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Submitted 13 December, 2020;
originally announced December 2020.
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Viscosity-Mediated Growth and Coalescence of Surface Nanodroplets
Authors:
Jia Meng,
Jae Bem You,
Xuehua Zhang
Abstract:
Solvent exchange is a simple method to produce surface nanodroplets on a substrate for a wide range of applications by displacing a solution of good solvent, poor solvent and oil (Solution A) by a poor solvent (Solution B). In this work, we show that the growth and coalescence of nanodroplets on a homogeneous surface is mediated by the viscosity of the solvent. We show that at high flow rates of v…
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Solvent exchange is a simple method to produce surface nanodroplets on a substrate for a wide range of applications by displacing a solution of good solvent, poor solvent and oil (Solution A) by a poor solvent (Solution B). In this work, we show that the growth and coalescence of nanodroplets on a homogeneous surface is mediated by the viscosity of the solvent. We show that at high flow rates of viscous Solution B, the final droplet volume deviates from the scaling law that correlates final droplet volume to the flow rate of non-viscous Solution B, reported in previous work. We attribute this deviation to a two-regime growth in viscous Solution B, where transition from an initial, fast regime to a final slow regime influenced by the flow rate. Moreover, viscous solution B hinders the coalescence of growing droplets, leading to a distinct bimodal distribution of droplet size with stable nanodroplets, in contrast to a continuous size distribution of droplets in non-viscous case. We demonstrate that the group of small droplets produced in high viscosity environment may be applied for enhanced fluorescence detection with higher sensitivity and shorter response time. The finding of this work can potentially be applied for mediating the size distribution of surface nanodroplets on homogeneous surface without templates.
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Submitted 16 May, 2020;
originally announced May 2020.
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Electric field Control of Exchange Bias by Resistive Switching
Authors:
L. J. Wei,
Z. Z. Hu,
Y. J. Wang,
G. X. Du,
Y. Yuan,
J. Wang,
H. Q. Tu,
B. You,
S. M. Zhou,
Y. Hu,
J. Du
Abstract:
We demonstrated an electric field controlled exchange bias (EB) effect accompanied with unipolar resistive switching behavior in the Si/SiO2/Pt/Co/NiO/Pt device. By applying certain voltages, the device displays obvious EB in high-resistance-state while negligible EB in low-resistance-state. Conductive filaments forming and rupture in the NiO layer but near the Co-NiO interface are considered to p…
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We demonstrated an electric field controlled exchange bias (EB) effect accompanied with unipolar resistive switching behavior in the Si/SiO2/Pt/Co/NiO/Pt device. By applying certain voltages, the device displays obvious EB in high-resistance-state while negligible EB in low-resistance-state. Conductive filaments forming and rupture in the NiO layer but near the Co-NiO interface are considered to play dominant roles in determining the combined resistive switching and EB phenomena. This work paves a new way for designing multifunctional and nonvolatile magnetic-electrical random access memory devices.
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Submitted 4 October, 2017;
originally announced October 2017.
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Elementary specific spin and orbital moments of ultrathin CoFeB amorphous films on GaAs(100)
Authors:
Yu Yan,
Cong Lu,
Hongqing Tu,
Xianyang Lu,
Wenqing Liu,
Junlin Wang,
Iain Will,
Balati Kuerbanjiang,
Vlado K. Lazarov,
Jing Wu,
Johnny Wong,
Biao You,
Jun Du,
Rong Zhang,
Yongbing Xu
Abstract:
Nanoscale CoFeB amorphous films have been synthesized on GaAs(100) and studied with X-ray magnetic circular dichroism (XMCD) and transmission electron microscopy (TEM). We have found that the ratios of the orbital to spin magnetic moments of both the Co and Fe in the ultrathin amorphous film have been enhanced by more than 300% compared with those of the bulk crystalline Co and Fe, and in specific…
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Nanoscale CoFeB amorphous films have been synthesized on GaAs(100) and studied with X-ray magnetic circular dichroism (XMCD) and transmission electron microscopy (TEM). We have found that the ratios of the orbital to spin magnetic moments of both the Co and Fe in the ultrathin amorphous film have been enhanced by more than 300% compared with those of the bulk crystalline Co and Fe, and in specifically, a large orbital moment of 0.56*10^-6 B from the Co atoms has been observed and at the same time the spin moment of the Co atoms remains comparable to that of the bulk hcp Co. The results indicate that the large uniaxial magnetic anisotropy (UMA) observed in the ultrathin CoFeB film on GaAs(100) is related to the enhanced spin-orbital coupling of the Co atoms in the CoFeB. This work offers experimental evidences of the correlation between the UMA and the elementary specific spin and orbital moments in the CoFeB amorphous film on the GaAs(100) substrate, which is significant for spintronics applications.
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Submitted 20 May, 2016;
originally announced May 2016.
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Spin and orbital moments of nanoscale Fe3O4 epitaxial thin film on MgO/GaAs(100)
Authors:
W. Q. Liu,
Y. B. Xu,
P. K. J. Wong,
N. J. Maltby,
S. P. Li,
X. F. Wang,
J. Du,
B. You,
J. Wu,
P. Bencok,
R. Zhang
Abstract:
Nanoscale Fe3O4 epitaxial thin film has been synthesized on MgO/GaAs(100) spintronic heterostructure, and studied with X-ray magnetic circular dichroism (XMCD). We have observed a total magnetic moment of (3.32 +- 0.1) uB/f.u., retaining 83% of the bulk value. Unquenched orbital moment of (0.47 +- 0.05) uB/f.u. has been confirmed by carefully applying the sum rule. The results offer direct experim…
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Nanoscale Fe3O4 epitaxial thin film has been synthesized on MgO/GaAs(100) spintronic heterostructure, and studied with X-ray magnetic circular dichroism (XMCD). We have observed a total magnetic moment of (3.32 +- 0.1) uB/f.u., retaining 83% of the bulk value. Unquenched orbital moment of (0.47 +- 0.05) uB/f.u. has been confirmed by carefully applying the sum rule. The results offer direct experimental evidence of the bulk-like total magnetic moment and a large orbital moment in the nanoscale fully epitaxial Fe3O4/MgO/GaAs(100) heterostructure, which is significant for spintronics applications.
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Submitted 26 March, 2015;
originally announced March 2015.
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Electronically Guided Self Assembly within Quantum Corrals
Authors:
R. X. Cao,
B. F. Miao,
Z. F. Zhong,
L. Sun,
B. You,
W. Zhang,
D. Wu,
An Hu,
S. D. Bader,
H. F. Ding
Abstract:
A grand challenge of nanoscience is to master the control of structure and properties in order to go beyond present day functionality. The creation of nanostructures via atom manipulation by means of a scanning probe represents one of the great achievements of the nano era. Here we build on this achievement to self-assemble nanostructures within quantum corrals. The structuring is guided by the qu…
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A grand challenge of nanoscience is to master the control of structure and properties in order to go beyond present day functionality. The creation of nanostructures via atom manipulation by means of a scanning probe represents one of the great achievements of the nano era. Here we build on this achievement to self-assemble nanostructures within quantum corrals. The structuring is guided by the quantum confinement of the electronic density of a silver metallic substrate within the corrals. We experimentally demonstrate different self-organized Gd atomic structures confined within 30-nm circular and triangular Fe quantum corrals. This approach enables the creation of model systems to explore and understand new nanomaterials and device prototypes.
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Submitted 6 September, 2012;
originally announced September 2012.
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Spin Hall Angle Quantification from Spin Pumping and Microwave Photoresistance
Authors:
Z. Feng,
J. Hu,
L. Sun,
B. You,
D. Wu,
J. Du,
W. Zhang,
A. Hu,
Y. Yang,
D. M. Tang,
B. S. Zhang,
H. F. Ding
Abstract:
We present a method to quantify the spin Hall angle (SHA) with spin pumping and microwave photoresistance measurements. With this method, we separate the inverse spin Hall effect (ISHE) from other unwanted effects for permalloy/Pt bilayers using out-of-plane microwave excitation. Through microwave photoresistance measurements, the in- and out-of-plane precessing angles of the magnetization are det…
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We present a method to quantify the spin Hall angle (SHA) with spin pumping and microwave photoresistance measurements. With this method, we separate the inverse spin Hall effect (ISHE) from other unwanted effects for permalloy/Pt bilayers using out-of-plane microwave excitation. Through microwave photoresistance measurements, the in- and out-of-plane precessing angles of the magnetization are determined and enabled for the exact determination of the injected pure spin current. This method is demonstrated with an almost perfect Lorentz line-shape for the obtained ISHE signal and the frequency independent SHA value as predicted by theory. By varying the Pt thickness, the SHA and spin-diffusion length of Pt is quantified as 0.012 (0.001) and 8.3 (0.9) nm, respectively.
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Submitted 28 March, 2012;
originally announced March 2012.
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Angular Dependence of X-ray Absorption Spectrum for Field-aligned Fe-based Superconductors
Authors:
B. C. Chang,
Y. B. You,
T. J. Shiu,
M. F. Tai,
H. C. Ku,
Y. Y. Hsu,
L. Y. Jang,
J. F. Lee,
Z. Wei,
K. Q. Ruan,
X. G. Li
Abstract:
Anisotropic Fe K-edge and As K-edge X-ray absorption near edge spectrum (XANES) measurements on superconducting (T_c = 52 K) (Sm_{0.95}La_{0.05})FeAs(O_{0.85}F_{0.15}) field-aligned microcrystalline powder are presented. The angular dependence of Fe pre-edge peak (dipole transition of Fe-1s electrons to Fe-3d/As-4p hybrid bands) relative to the tetragonal ab-plane of aligned powder indicates lar…
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Anisotropic Fe K-edge and As K-edge X-ray absorption near edge spectrum (XANES) measurements on superconducting (T_c = 52 K) (Sm_{0.95}La_{0.05})FeAs(O_{0.85}F_{0.15}) field-aligned microcrystalline powder are presented. The angular dependence of Fe pre-edge peak (dipole transition of Fe-1s electrons to Fe-3d/As-4p hybrid bands) relative to the tetragonal ab-plane of aligned powder indicates larger density of state (DOS) along the c-axis, and is consistent with the LDA band structure calculation. The anisotropic Fe K-edge spectra exhibit a chemical shift to lower energy compared to FeO which are closely related to the itinerant character of Fe^{2+}-3d^6 orbitals. The anisotropic As K-edge spectra are more or less the mirror images of Fe K-edge due to the symmetrical Fe-As hybridiztion in the FeAs layer. Angular dependence of As main peak (dipole transition of As-1s electrons to higher energy hybrid bands) was observed suggesting character of As-4d e_g orbitals.
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Submitted 22 September, 2009;
originally announced September 2009.