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Four-fold Anisotropic Magnetoresistance in Antiferromagnetic Epitaxial Thin Films of MnPt$_{x}$Pd$_{1-x}$
Authors:
Shivesh Yadav,
Shikhar Kumar Gupta,
Mohit Verma,
Debjoty Paul,
Abira Rashid,
Bhagyashree Chalke,
Rudheer Bapat,
Nilesh Kulkarni,
Abhay Gautam,
Arti Kashyap,
Shouvik Chatterjee
Abstract:
Antiferromagnets are emerging as promising alternatives to ferromagnets in spintronics applications. A key feature of antiferromagnets is their anisotropic magnetoresistance (AMR), which has the potential to serve as a sensitive marker for the antiferromagnetic order parameter. However, the underlying origins of this behavior remains poorly understood, particularly, in thin film geometries. In thi…
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Antiferromagnets are emerging as promising alternatives to ferromagnets in spintronics applications. A key feature of antiferromagnets is their anisotropic magnetoresistance (AMR), which has the potential to serve as a sensitive marker for the antiferromagnetic order parameter. However, the underlying origins of this behavior remains poorly understood, particularly, in thin film geometries. In this study, we report the observation of AMR in epitaxial thin films of the collinear L1$_{0}$ antiferromagnet MnPt$_{x}$Pd$_{1-x}$. In the thicker films, AMR is dominated by a non-crystalline two-fold component, which emerges from domain reconfiguration and spin canting under applied magnetic field. As the film thickness is reduced, however, a crystalline four-fold component emerges, accompanied by the appearance of uncompensated magnetic moment, which strongly modifies the magnetotransport properties in the thinner films. We demonstrate that interfacial interactions lead to a large density of states (DOS) at the Fermi level. This enhanced DOS, combined with disorder in the thinner films, stabilizes the uncompensated moment and results in a four-fold modulation of the DOS as the Neel vector rotates, explaining the observed AMR behavior.
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Submitted 8 June, 2025; v1 submitted 5 December, 2024;
originally announced December 2024.
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Spin-Polarisation measurement using NbN-Insulator-Ferromagnet Tunnel Junction with oxidized barrier
Authors:
Pritam Das,
John Jesudasan,
Rudheer Bapat,
Pratap Raychaudhuri
Abstract:
We report a two-step process for the fabrication of superconductor-insulator-normal metal tunnel junctions using NbN as the superconducting electrode and its surface oxide as the insulating tunnel barrier, and investigate its efficacy in measuring spin-polarisation of ferromagnets using the Meservey-Tedrow technique. We observe that for NbN film thickness below 10 nm, under the application of para…
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We report a two-step process for the fabrication of superconductor-insulator-normal metal tunnel junctions using NbN as the superconducting electrode and its surface oxide as the insulating tunnel barrier, and investigate its efficacy in measuring spin-polarisation of ferromagnets using the Meservey-Tedrow technique. We observe that for NbN film thickness below 10 nm, under the application of parallel magnetic field, the superconducting density of states show clear "Zeeman" splitting into spin-up and spin-down sub-bands. Tunnelling measurements on devices where ferromagnetic Co is used as the normal electrode shows that these devices can be used to reliably measure spin polarisation of a ferromagnet at temperatures up to 1.6 K. The simplicity of our fabrication process, and the ability to perform spin-polarisation measurements at 4He temperatures makes NbN a very attractive candidate for spin polarisation measurements.
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Submitted 4 September, 2022;
originally announced September 2022.
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Superconductivity in amorphous RexZr (x ~ 6) thin films
Authors:
Surajit Dutta,
Vivas Bagwe,
Gorakhnath Chaurasiya,
A. Thamizhavel,
Rudheer Bapat,
Pratap Raychaudhuri,
Sangita Bose
Abstract:
We report the growth, characterization and superconducting properties of a new amorphous superconductor, RexZr ( x ~ 6 ), in thin film form. Films were grown by pulsed laser deposition with the substrate kept at room temperature. Films with thickness larger than 40 nm showed a superconducting transition temperature (Tc) of 5.9 K. Superconducting properties were measured for films with varying thic…
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We report the growth, characterization and superconducting properties of a new amorphous superconductor, RexZr ( x ~ 6 ), in thin film form. Films were grown by pulsed laser deposition with the substrate kept at room temperature. Films with thickness larger than 40 nm showed a superconducting transition temperature (Tc) of 5.9 K. Superconducting properties were measured for films with varying thickness from 120 to 3 nm. The normal state resistance scales linearly with inverse of thickness. The transition temperature, critical field, coherence length, penetration depth and superconducting energy gap changes marginally with decreasing film thickness down to 8 nm. Scanning tunneling spectroscopy and penetration depth measurements provide evidence for a single gap strong coupling s-wave superconductor. Magneto-transport properties indicate a rich magnetic field-temperature phase diagram with the possibility of vortex liquid phases existing over a large fraction of the mixed state.
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Submitted 22 December, 2020;
originally announced December 2020.
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Magnetocrystalline anisotropy in the Kondo lattice compound CeAgAs$_2$
Authors:
Rajib Mondal,
Rudheer Bapat,
S. K. Dhar,
A. Thamizhavel
Abstract:
We report on the single crystal growth and anisotropic physical properties of CeAgAs$_2$. The compound crystallizes as on ordered variant of the HfCuSi$_2$-type crystal structure and adopts the orthorhombic space group $Pmca$~(\#57) with two symmetry inequivalent cerium atomic positions in the unit cell. The orthorhombic crystal structure of our single crystal was confirmed from the powder x-ray d…
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We report on the single crystal growth and anisotropic physical properties of CeAgAs$_2$. The compound crystallizes as on ordered variant of the HfCuSi$_2$-type crystal structure and adopts the orthorhombic space group $Pmca$~(\#57) with two symmetry inequivalent cerium atomic positions in the unit cell. The orthorhombic crystal structure of our single crystal was confirmed from the powder x-ray diffraction and from electron diffraction patterns obtained from the transmission electron microscope. The anisotropic physical properties have been investigated on a good quality single crystal by measuring the magnetic susceptibility, isothermal magnetization, electrical transport and heat capacity. The magnetic susceptibility and magnetization measurements revealed that this compound orders antiferromagnetically with two closely spaced magnetic transitions at $T_{\rm N1} = 6$~K and $T_{\rm N2} = 4.9$~K. Magnetization studies have revealed a large magnetocrystalline anisotropy due to the crystalline electric field (CEF) with an easy axis of magnetization along the [010] direction. The magnetic susceptibility measured along the [001] direction exhibited a broad hump in the temperature range 50 to 250~K, while typical Curie-Weiss behaviour was observed along the other two orthogonal directions. The electrical resistivity and the heat capacity measurements revealed that CeAgAs$_2$ is a Kondo lattice system with a magnetic ground state.
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Submitted 19 July, 2018;
originally announced July 2018.
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Rheology of hydrating cement paste: crossover between two aging processes
Authors:
Atul Varshney,
Smita Gohil,
B. A. Chalke,
R. D. Bapat,
S. Mazumder,
S. Bhattacharya,
Shankar Ghosh
Abstract:
The roles of applied strain and temperature on the hydration dynamics of cement paste are uncovered in the present study. We find that the system hardens over time through two different aging processes. The first process dominates the initial period of hydration and is characterized by the shear stress $σ$ varying sub-linearly with the strain-rate $\dotγ$; during this process the system is in a re…
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The roles of applied strain and temperature on the hydration dynamics of cement paste are uncovered in the present study. We find that the system hardens over time through two different aging processes. The first process dominates the initial period of hydration and is characterized by the shear stress $σ$ varying sub-linearly with the strain-rate $\dotγ$; during this process the system is in a relatively low-density state and the inter-particle interactions are dominated by hydrodynamic lubrication. At a later stage of hydration the system evolves to a high-density state where the interactions become frictional, and $σ$ varies super-linearly with $\dotγ$; this is identified as the second process. An instability, indicated by a drop in $σ$, that is non-monotonic with $\dotγ$ and can be tuned by temperature, separates the two processes. Both from rheology and microscopy studies we establish that the observed instability is related to fracture mechanics of space-filling structure.
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Submitted 1 March, 2017;
originally announced March 2017.
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Comparison of GaN nanowires grown on c-, r- and m-plane sapphire substrates
Authors:
Carina B. Maliakkal,
A. Azizur Rahman,
Nirupam Hatui,
Bhagyashree A. Chalke,
Rudheer D. Bapat,
Arnab Bhattacharya
Abstract:
Gallium nitride nanowires were grown on c-plane, r-plane and m-plane sapphire substrates in a showerhead metalorganic chemical vapor deposition system using nickel catalyst with trimethylgallium and ammonia as precursors. We studied the influence of carrier gas, growth temperature, reactor pressure, reactant flow rates and substrate orientation in order to obtain thin nanowires. The nanowires grew…
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Gallium nitride nanowires were grown on c-plane, r-plane and m-plane sapphire substrates in a showerhead metalorganic chemical vapor deposition system using nickel catalyst with trimethylgallium and ammonia as precursors. We studied the influence of carrier gas, growth temperature, reactor pressure, reactant flow rates and substrate orientation in order to obtain thin nanowires. The nanowires grew along the <10-11> and <10-10> axes depending on the substrate orientation. These nanowires were further characterized using x-ray diffraction, electron microscopy, photoluminescence and Raman spectroscopy.
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Submitted 4 January, 2016; v1 submitted 4 September, 2015;
originally announced September 2015.
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Light matter interaction in WS$_{2}$ nanotube-graphene hybrid devices
Authors:
John P. Mathew,
Gobinath Jegannathan,
Sameer Grover,
Pratiksha D. Dongare,
Rudheer D. Bapat,
Bhagyashree A. Chalke,
S. C. Purandare,
Mandar M. Deshmukh
Abstract:
We study the light matter interaction in WS$_{2}$ nanotube-graphene hybrid devices. Using scanning photocurrent microscopy we find that by engineering graphene electrodes for WS$_{2}$ nanotubes we can improve the collection of photogenerated carriers. We observe inhomogeneous spatial photocurrent response with an external quantum efficiency of $\sim 1\%$ at 0 V bias. We show that defects play an i…
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We study the light matter interaction in WS$_{2}$ nanotube-graphene hybrid devices. Using scanning photocurrent microscopy we find that by engineering graphene electrodes for WS$_{2}$ nanotubes we can improve the collection of photogenerated carriers. We observe inhomogeneous spatial photocurrent response with an external quantum efficiency of $\sim 1\%$ at 0 V bias. We show that defects play an important role and can be utilized to enhance and tune photocarrier generation.
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Submitted 4 December, 2014;
originally announced December 2014.
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Magnetic behavior of nanocrystalline ErCo2
Authors:
Sitikantha D Das,
Niharika Mohapatra,
Kartik K Iyer,
R. D. Bapat,
E. V. Sampathkumaran
Abstract:
We have investigated the magnetic behavior of the nanocrystalline form of a well-known Laves phase compound, ErCo2 - the bulk form of which has been known to undergo an interesting first-order ferrimagnetic ordering near 32 K - synthesized by high-energy ball-milling. It is found that, in these nanocrystallites, Co exhibits ferromagnetic order at room temperature as inferred from the magnetizati…
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We have investigated the magnetic behavior of the nanocrystalline form of a well-known Laves phase compound, ErCo2 - the bulk form of which has been known to undergo an interesting first-order ferrimagnetic ordering near 32 K - synthesized by high-energy ball-milling. It is found that, in these nanocrystallites, Co exhibits ferromagnetic order at room temperature as inferred from the magnetization data. However, the magnetic transition temperature for Er sublattice remains essentially unaffected as though the (Er)4f-Co(3d) coupling is weak on Er magnetism. The net magnetic moment as measured at high fields, sat at 120 kOe, is significantly reduced with respect to that for the bulk in the ferrimagnetically ordered state and possible reasons are outlined. We have also compared the magnetocaloric behavior for the bulk and the nano particles.
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Submitted 26 June, 2009;
originally announced June 2009.