arXiv subjects

Arabinda Haldar

Publications and source records attributed to Arabinda Haldar.

14 recordsLinked to original sources

arXiv2026

Orbital Hall effect-driven spin-orbit torque enhancement in Ti-based systems via rare-earth interface engineering

Orbital currents in light metals offer large orbital Hall conductivities, yet translating this into practical spin-orbit torque efficiency is hindered by fundamental limitations. In this work, we introduce a Gd interlayer between a Ti orbital source and a Co ferromagnet to enhance the orbital torque efficiency. Ferromagnetic resonance-based spin (orbital) pumping measurements identify an optimal Gd thickness of around 4 nm, where the orbital-to-spin conversion efficiency reaches its maximum. The Ti-thickness dependence of the inverse orbital Hall effect signal confirms a bulk orbital Hall origin in Ti and yields a qualitative orbital diffusion length exceeding 20 nm. Spin-torque ferromagnetic resonance measurements demonstrate a fivefold enhancement of the SOT efficiency in Ti(20 nm)/Co compared to a Gd(4 nm)/Co reference. Interestingly, the trilayer Ti/Gd/Co architecture exhibits a spin (orbital) torque efficiency greater than 1, which is higher than that of the bilayer Ti/Co and Gd/Co structures, irrespective of Ti thickness. These results establish rare-earth interlayer engineering as a viable route to enhanced orbital torque efficiency for next-generation spin-orbitronic devices.

cond-mat.mtrl-sci↗

arXiv2026

Enhanced Spin-to-Charge Conversion in Bi2Se3/NiFe via Interface Engineering with a Ti Spacer Layer

Topological insulators have attracted significant attention in spintronics due to their topological surface states and spin-momentum-locking-driven spin-to-charge conversion. Among these, Bi2Se3 has been extensively investigated because of its large bulk bandgap and single Dirac cone band structure. However, spin-to-charge conversion strongly depends on the quality of the topological insulator/ferromagnet interface. Here, we investigate spin-to-charge conversion in a sputter-deposited heterostructure comprising a topological insulator (Bi2Se3) and a ferromagnetic NiFe thin film separated by a titanium spacer layer. The Bi2Se3 layer is deposited on a silicon substrate for industrial compatibility. Pure spin current is injected into the Bi2Se3 layer through the titanium spacer via spin pumping induced by spin precession during microwave-driven ferromagnetic resonance of the ferromagnetic film. Spin pumping studies are performed by varying the Bi2Se3 thickness. The Gilbert damping parameter exhibits a significant 55% increase at a Bi2Se3 thickness of 4 nm, indicating a pure surface-state contribution. The spin Hall angle, which quantifies the spin-to-charge conversion efficiency, increases by an order of magnitude upon insertion of the titanium spacer layer. This enhancement is attributed to the suppression of interdiffusion between the Bi2Se3 and NiFe layers by titanium, thereby preserving the topological surface states. These findings highlight the important role of titanium spacer layers in spintronic devices based on topological materials.

cond-mat.mtrl-sci↗

arXiv2024

Vanadium Doped Magnetic MoS2 Monolayers of Improved Electrical Conductivity as Spin-Orbit Torque Layer

Two-dimensional (2D) transition metal di-chalcogenide layers with high electrical conductivity and spin-orbit coupling (SOC) can find huge potential in spintronic devices. With limited success of 2D spin Hall material development, we demonstrate vanadium (V) substitutionally doped monolayer MoS2 (VMS) as a potential spin Hall material having tunable electrical conductivity, SOC strength, and room temperature magnetism. Systematic enhancement in the electrical conductivity is observed with the extent of V doping, where it is enhanced from ~0.3 S/m of MoS2 to ~100000 S/m upon doping to the level of 9 atomic%. Ferromagnetic resonance (FMR) based spin-pumping experiments indicate the spin transport across the junction of permalloy (Py) and VMS. Spin-torque FMR measurements demonstrate the suggesting latter's potential as a spin-orbit torque layer in 2D spintronic devices.

physics.app-ph↗

arXiv2021

Effect of seed layer thickness on Ta crystalline phase and spin Hall angle

Heavy metal-ferromagnet bilayer structures have attracted great research interest for charge-to-spin interconversion. In this work, we have investigated the effect of the permalloy seed layer on the Ta polycrystalline phase and its spin Hall angle. Interestingly, for the same deposition rates the crystalline phase of Ta deposited on Py seed layer strongly depends on the thickness of the seed layer. We have observed a phase transition from $α$-Ta to ($α$+$β$)-Ta while increasing the Py seed layer thickness. The observed phase transition is attributed to the strain at interface between Py and Ta layers. Ferromagnetic resonance-based spin pumping studies reveal that the spin-mixing conductance in the to ($α$+$β$)-Ta is relatively higher as compared to the to $α$-Ta. Spin Hall angles of to $α$-Ta and to ($α$+$β$)-Ta are extracted from inverse spin Hall effect (ISHE) measurements. Spin Hall angle of the to ($α$+$β$)-Ta is estimated to be $θ$_SH=-0.15 which is relatively higher than that of to $α$-Ta. Our systematic results connecting the phase of the Ta with seed layer and its effect on the efficiency of spin to charge conversion might resolve ambiguities across various literature and open up new functionalities based on the growth process for the emerging spintronic devices.

cond-mat.mtrl-sci↗

arXiv2010

Magnetic, magnetocaloric and neutron diffraction studies on TbNi5-xMx (M = Co and Fe) compounds

The effect of substitution of Co and Fe for Ni in TbNi5 on the structural, magnetic and magneto-thermal properties has been investigated. Considerable enhancement of Curie temperature is observed with Fe substitution, whereas the increase is nominal in the case of Co. Neutron diffraction measurements reveal the redistribution of moments and site preference of substitutional ions in Ni 2c and 3g sites. In TbNi4Fe, both Ni and Fe as well as Tb are found to carry moment while in the case of TbNi4Co, mainly Tb carries the moment. Magnetocaloric behavior has been investigated from the magnetization and the heat capacity measurements. The magnetic and magnetocaloric properties are found to be strongly correlated in these compounds.

cond-mat.str-el↗

arXiv2010

Observation of re-entrant spin glass behavior in (Ce1-xErx)Fe2 compounds

Clear experimental evidence of re-entrant spin glass state has been revealed in Er doped CeFe2 compounds. The zero field cooled - field cooled bifurcation in dc magnetization, frequency dependence of freezing temperature, relaxation in zero field cooled magnetization and presence of large remanence confirm the spin glass state in these compounds. Frequency dependence is found to follow the critical slowing down mechanism. The random substitution of Er and the change in the valence state of Ce along with an enhancement of the ferromagnetic component in the Fe sublattice seem to be responsible for the spin glass state. Using detailed experimental protocols, we also prove that the low temperature state in these compounds is not a magnetic glass. The absence of exchange bias gives an indication that there is no coexistence of ferromagnetism and spin glass state in these compounds. The RSG state is found to be associated with the randomly magnetized clusters instead of atomic level randomness.

cond-mat.str-el↗

arXiv2010

Magnetic and the magnetocaloric properties of Ce1-xRxFe2 and Ce(Fe1-xMx)2 compounds

We have studied selected rare earth doped and transition metal doped CeFe2 compounds by examining their structural, magnetic and magneto-thermal properties. With substitution of Ce by 5 and 10% Gd and 10% Ho, the Curie temperature can be tuned to the range of 267-318 K. Localization of Ce 4f electronic state with rare earth substitutions is attributed for the enhancement of Curie temperature. On the other hand, with Ga and Al substitution at the Fe site, system undergoes paramagnetic to ferromagnetic transition and then to an antiferromagnetic phase on cooling. The magnetocaloric effect across the transitions has been studied from both magnetization isotherms and heat capacity data. It is shown that by choosing the appropriate dopant and its concentration, the magnetocaloric effect around room temperature can be tuned.

cond-mat.str-el↗

arXiv2010

Magnetostructural transition in Ce(Fe0.975Ga0.025)2 compound

The magnetic and magnetostructural properties of the polycrystalline Ce(Fe0.975Ga0.025)2 have been investigated as a function of temperature and magnetic field. In Ce(Fe0.975Ga0.025)2 the magnetic transition from antiferromagnetic (AFM) to ferromagnetic state (FM) is accompanied by a structural transformation from rhombohedral to cubic structure. Phase coexistence is present during both the temperature and field driven transformations from the AFM to FM phase.

cond-mat.str-el↗

arXiv2010

Magnetization jumps and relaxation effect in doped CeFe2

For the first time, we find that the dynamic antiferromagnetic phase present in CeFe2 gets stabilized with Ga and Si substitutions. We find that phenomena such as strain-induced first order jumps in the magnetization curves, asymmetry between the M-H curves during the increasing and decreasing field cycles, the envelope curve being inside the virgin curve, occur in these compounds. Temperature and time dependences of magnetization show that the compounds possess glassy behavior at low temperatures. Multi-step magnetization behavior, unusual relaxation effect, thermal and magnetic history dependence, which are signatures of the martensitic scenario due to the strong magneto-structural coupling, are found to be present in this system. We also show that one can induce the magnetization steps with the help of appropriate measurement protocol. Detailed magnetization relaxation studies have been carried out to understand the dynamics of magnetic phase transition.

cond-mat.str-el↗

arXiv2010

Metastable magnetization behavior in magnetocaloric R6Co1.67Si3 (R=Tb and Nd) compounds

Magnetic field and time induced steps have been observed in the recently discovered ternary silicide R6Co1.67Si3. Huge relaxation steps are observed across different loops in the low temperature magnetization isotherms. Giant relaxation present in this system indicates the existence of incubation time to get the saturated moment at a certain field. Measurement protocol sensitive magnetization behavior observed in this system may arise from the strong magnetostructural coupling and/or magnetic frustration. Electrical resistivity and magnetoresistance also reflect the magnetic state of the compound. Magnetocaloric effect is found to be large at temperatures close to the magnetic transition temperature.

cond-mat.str-el↗

arXiv2010

Temperature and magnetic field induced structural transformation in Si doped CeFe2: in-field x-ray diffraction study

Using x-ray powder diffraction technique at various temperatures and applied magnetic fields, we have studied the magnetostructural properties of Ce(Fe0.95Si0.05)2. The x-ray diffraction data establish quantitative relationships between bulk magnetization and the evolution of structurally distinct phases with magnetic field and temperature, and confirm the distinct features of first order phase transition like supercooling and superheating, metastability, and phase co-existence of different structural polymorphs. We observe the lattice volume mismatch across the structural phase transition, which appears to be the cause for the step behavior of the magnetization isotherms at low temperatures. The present study shows that the lattice distortion has to be treated explicitly, like spin, along with the effects of lattice-spin coupling to account for the magnetization behavior of this system. This structure template can resolve the issue of kinetics in this material as observed in different time scale measurements and with different experimental protocols.

cond-mat.str-el↗

arXiv2010

Stabilization of antiferromagnetism in CeFe2 alloys: Effects of chemical and hydrostatic pressure

Effects of Al, Mn and Sb dopings in CeFe2 and effect of applied pressure have been investigated. Al doping gives rise to the FM-AFM transition and a reduction in the magnetic moment and TC values, clearly indicating the growth of the AFM component. Mn and Sb dopings only cause a reduction in TC value. It is found that in general external pressure enhances the antiferromagnetism in both the pure and the doped alloys. Enhancement of the Ce 4f- Fe 3d hybridization as a result of dopings and with the external pressure may be the reason for the stabilization of antiferromagnetism in these alloys.

cond-mat.str-el↗

arXiv2008

Anomalous magnetization behavior in Ce(Fe,Si)2

We report the effect of Si doping on the magnetization behavior of CeFe2. It is found that Si stabilizes the dynamic antiferromagnetic state of CeFe2. Multi-step magnetization behavior, unusual relaxation effect, thermal and magnetic history dependence, which are signatures of martensitic scenario, are found to be present in this system. We also show that one can induce the magnetization steps with the help of appropriate measurement protocol. Detailed magnetization relaxation studies have been carried out to understand the dynamics of magnetic phase transition.

cond-mat.str-el↗

arXiv2008

Magnetism in Gallium doped CeFe_2: The martensitic scenario

Ce(Fe_{1-x}Ga_x)_2 compounds with x = 0, 0.01, 0.025 and 0.05 have been investigated to unravel the effect of Ga on the magnetic state of CeFe_2. For the first time, we find that the dynamic antiferromagnetic phase present in CeFe_2 gets stabilized with Ga substitution. The hysteresis loops show that while the compounds with x = 0 and 0.01 show normal behavior, the other two show multiple magnetization steps across the antiferromagnetic-ferromagnetic transition region. The virgin curve is found to lie outside the envelope curve in these two compounds, similar to the observations made in Ru and Re substituted CeFe_2 compounds. Temperature, sweep rate and time dependences of the magnetization show that the compounds with x >=0.025 possess glassy behavior at low temperatures. Various results obtained reveal that these two compounds belong to the martensite family.

cond-mat.str-el↗