arXiv subjects

Ramesh C Budhani

Publications and source records attributed to Ramesh C Budhani.

3 recordsLinked to original sources

arXiv2026

Magneto Transport and Spin Reorientation in Pt Co78Ho22 Heterostructures Near the Sublattice Compensation Temperature

Metallic amorphous ferrimagnets of 3d transition metals (TM) and rare earths (RE) with 4f electrons exhibit rich magneto transport behavior due to the interplay between the 3d and 4f magnetic sublattices and their interaction with mobile charges. Tuning the TM and RE concentrations in the alloy can effectively modulate the compensation temperature, where the moments of the two sublattices point in opposite direction leading to a net zero magnetization. Despite extensive magnetotransport studies in Gd and Tb based 3d 4f systems, Ho based alloys remain comparatively underexplored, even though Ho possesses the largest orbital angular momentum (OAM) among the lanthanides. This unquenched OAM can strongly impact magnetic anisotropy and magnetotransport in ferrimagnetic heterostructures. Here, we have investigated the anomalous Hall resistivity , dc magnetization, and spin Hall magnetoresistance (SHMR) of Co78Ho22.Al film and a Pt.Co78Ho22.Al heterostructure deposited using multitarget magnetron sputtering. The Hall resistivity of both systems shows a distinct sign reversal and prominent wing-shaped hysteresis loops in the vicinity of the compensation temperature (Tcomp), which is accompanied by the minimum saturation magnetization near Tcomp. Furthermore, the SHMR in Pt.Co78Ho22.Al film is enhanced due to the Pt layer. These HM interface-induced prominent features of magneto-transport are addressed in the light of the existing theories of spin flop transitions, spin orbit torque, and microscopic phase separation, which may lead to the formation of 3d and 4f magnetic clusters in the film.

cond-mat.mtrl-sci↗

arXiv2025

Intrinsic Berry phase contribution to Hall conductivity in CoS$_2$

In Weyl semi-metals, the conduction and valence bands intersect at distinct points on the Brillouin zone (Weyl points), which act as monopoles of Berry curvature in momentum space. This nontrivial band topology, identified from electronic structure calculations, gives rise to various exotic magneto-transport properties. Hybrid functional calculations that incorporate a portion of exact exchange, magneto-transport measurements, and temperature-dependent resistivity confirm nontrivial band topology and half-metallicity in CoS$_2$ of magnetic ordering temperature $T_{\rm C} \approx 120~\mathrm{K}$. However, electronic structure calculations also show that application of small strain transforms this half metallic character to the metallic. Interestingly, the magnetoresistance (MR) of the CoS$_2$ films is characterized by a reentrant weak localization above a critical field at $T \leq 60\,\mathrm{K}$ and a negative to positive transition in MR as the $T$ goes from $ T_{\rm C}$. Experimental observation of anomalous Hall resistivity and $ab~initio$ computed band structure, Berry curvature, and Hall conductivity ($σ_{xy}$) demonstrate that the $σ_{xy}$ in CoS$_2$ is primarily driven by the intrinsic Karplus-Luttinger contribution, often linked to Berry phase physics.

cond-mat.mtrl-sci↗

arXiv2025

Anomalous and Planar Hall Effects in Cobalt-Holmium Thin Films Near Magnetic Sublattice Compensation

Metallic amorphous ferrimagnets derived from alloying 3d transition metals with 4f electron rare earths host fascinating effects of compensation between the 3d and 4f magnetic sublattices. Here, a detailed study of anisotropic magnetoresistance (AMR), planar Hall effect (PHE) and anomalous Hall effect (AHE) are reported on a series of CoHo thin films over a wide field temperature phase space. Close to magnetic compensation temperature, the AHE loops show a double sign reversal and signatures of spin flop transition at higher fields. The AMR and PHE also display strong deviations from the classical angular dependence seen in soft ferromagnets like permalloy as the angle between in-plane current and magnetic field is scanned from 0 to 360 degrees. It is argued that the non zero orbital angular momentum of Ho ions in the lattice and stabilization of bubble domains below magnetic saturation may be responsible for such features. Direct imaging of magnetic textures with X ray photoelectron microscopy shows formation of stripe domain patterns in the regime of sublattice compensation. Such stripes are likely to transform into magnetic bubbles before full saturation is reached in a large magnetic field.

cond-mat.mes-hall↗