arXiv subjects

Subham Majumdar

Publications and source records attributed to Subham Majumdar.

At least 19 recordsLinked to original sources

arXiv2026

Semi-Dirac States and Quantum Linear Magnetoresistance in Helimagnetic Pnictide MnP

Large linear positive magnetoresistance (LPMR) in topological and magnetic materials remains a subject of intense debate, particularly in noncollinear spin systems where spin-dependent scattering complicates charge transport. Manganese phosphide (MnP), a helimagnetic binary pnictide with multiple field-induced magnetic transitions, provides a useful platform to investigate the interplay between complex magnetism and electronic topology. Here, we present a comprehensive experimental and theoretical investigation of phase-dependent magnetotransport in high-quality MnP single crystals. Hall measurements reveal an anomalous Hall effect dominated by skew scattering at high temperatures and a finite topological Hall effect in the noncollinear fan (FAN) and low-temperature screw (SCR) phases. At low temperatures, we observe a large, non-saturating LPMR reaching nearly 800 percent at 4 K and 15 T, with a pronounced linear field dependence in the field-polarized ferromagnetic (FM2) state. First-principles calculations reveal a strongly anisotropic semi-Dirac-like band at the Y point that progressively approaches the Fermi level from the SCR to FAN and FM2 states. Our analysis indicates that the resulting small Fermi pocket can access the extreme quantum-limit regime at experimentally accessible fields, providing a microscopic framework for the observed LPMR within Abrikosov's quantum magnetoresistance theory.

cond-mat.str-el↗

arXiv2025

Intriguing Magnetocaloric Effect in Multiferroic Ba3RRu2O9 (R=Ho, Gd, Tb, Nd) with Strong 4d-4f Correlations

Here we demonstrate the magnetocaloric effect (MCE) of a 4d-4f correlated system, namely Ba3RRu2O9 (R= Ho, Gd, Tb, Nd). The compound Ba3HoRu2O9 antiferromagnetically orders at 50 K where both the Ho and Ru-moments order, followed by another phase transition ~ 10 K. Whereas, the compound Ba3GdRu2O9 and Ba3TbRu2O9 orders at 14.5 and 10.5 K respectively, where the ordering of both R and Ru moments are speculated. Our results reveal robust MCE around low-T magnetic phase transition for all the heavy rare-earth members (Ho, Gd, Tb) in this family. The heavy rare-earth members exhibit an intriguing MCE behavior switching from conventional to non-conventional MCE. Interestingly, the light R-member, Ba3NdRu2O9, orders ferromagnetically below 24 K where Nd-moments order, followed by Ru-ordering below 18 K, exhibits a positive MCE below and above FM-ordering. The compelling MCE are attributed to temperature dependent complex spin-reorientations for different R-members and anisotropy.

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arXiv2025

Interplay of Orbital Degeneracy and Vacancies in Stabilizing Collinear Magnetic Order in Cr$_{1+\delta}$Te$_2$

Cr$_{1+\delta}$Te$_2$, a two-dimensional van der Waals ferromagnet, displays a contested magnetic structure, poised between collinear and non-collinear spin configurations. In this work, we investigate the magnetic structure of Cr$_{1.33}$Te$_2$ at the microscopic level by combining single-crystal neutron diffraction, X-ray absorption spectroscopy, and first-principles calculations. Neutron diffraction measurements reveal a distinct collinear spin alignment, whereas spectroscopic analyses reveal inherent structural vacancies at both Cr and Te sites. These vacancies lead to local symmetry breaking that elevates the orbital degeneracy of the Cr 3$d$ states, as demonstrated by our first-principles analysis. The resulting modification of magnetocrystalline anisotropy emerges as the key mechanism stabilising the collinear magnetic ground state over the non-collinear one in the presence of vacancies. Our findings uncover a vacancy-driven route to control spin anisotropy and magnetic ordering in layered ferromagnets, offering new insights into the design of tunable 2D magnetic materials.

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arXiv2025

Atypical Ferrimagnetism in Ni$_4$Nb$_2$O$_9$

Ferrimagnetism typically emerges from chemically distinct magnetic ions or the same element at two inequivalent crystallographic sites, rendering unequal moments. In contrast, Ni4Nb2O9 has been recently discovered to show a different mechanism, where identical Ni2 ions with the same ligand coordination develop unequal magnetic moments purely due to differences in local environments. Here, we investigate the microscopic origin of this emergent mechanism through a synergy of powder neutron diffraction, inelastic neutron scattering, and first principle based calculations. We demonstrate that the NiA and NiB sublattices, while sharing the same nominal valence, differ in their magnetic dimensionality NiA forms quasi one dimensional chains with enhanced p d hybridization and a reduced magnetic moment, whereas NiB retains a nearly two-dimensional geometry and a full S 1 moment. Our results underscore the pivotal role of spin dimensionality and local structural distortions in stabilizing ferrimagnetism in systems with electronically equivalent magnetic ions.

cond-mat.mtrl-sci↗

arXiv2025

Weak Itinerant Ferromagnetism (WIFM) in MAX phase compound Cr$_{1.9}$Fe$_{0.1}$GeC

Magnetic MAX phase compounds are important materials for studying the two-dimensional magnetism because of their layered crystallographic structure. The hexagonal MAX phase compound Cr$_2$GeC is a Pauli paramagnet, and here we report the induction of an ordered magnetic state by doping Fe at the Cr site. Induced magnetism for small doping concentrations (indicated as 5% and 2.5%) is found to have a weak itinerant ferromagnetic character. The Rhodes-Wolhfarth ratio is found to be 13.29, while the coefficient of electronic heat capacity ($\Gamma$) is 27 mJ-mol$^{-1}$K$^{-2}$ for Cr$_{1.9}$Fe$_{0.1}$GeC. Our x-ray magnetic circular dichorism measurement confirms that the magnetic moment arises from the Fe atom only, and Cr has negligible contribution towards the ordered moment. Our critical analysis indicates that the magnetic phase transition in Cr$_{1.9}$Fe$_{0.1}$GeC follows mean field theory.

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arXiv2025

Magnetic Metastability driven Anomalous Hall Effect in Fe$_{x}$TaS$_2$

We report here the observation of robust thermoremanent magnetization (TRM) in Fe-intercalated TaS$_2$ single crystal Fe$_{x}$TaS$_2$, which develops upon cooling under a moderate magnetic field of 500 Oe or higher. The thermoremanence is found to exist in a zero magnetic field up to a temperature as high as 160 K, which is well above the ferromagnetic Curie point ($T_C =$ 90 K) of the sample. The TRM in this compound can be traced back to the strong Ising character and the quasi-two-dimensional nature of the spins. The analysis of the magnetization data indicates the presence of short-range magnetic correlation in the form of a Griffiths singularity above $T_C$ to a temperature as high as 2$T_C$. The TRM is further manifested in the form of a large anomalous Hall effect (AHE) in zero magnetic field. In contrast to TRM, which exists well above $T_C$, the thermoremanent Hall effect vanishes as soon as the sample is heated above $T_C$. This may be an indication that a long-range ordered phase is essential for the emergence of AHE.

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arXiv2024

Magnetic field induced arrested state and observation of spontaneous anomalous Hall effect in TbMn$_6$Sn$_6$

The quasi two-dimensional kagome ferrimagnet TbMn$_6$Sn$_6$ is investigated for thermo-remanent magnetization and Hall effects. On cooling under a moderate magnetic field, the sample attains a magnetization value close to the saturation magnetization. Upon heating in a very small magnetic field, the sample continues to maintain the large value of magnetization, which eventually diminishes distinctly at around 200 K manifesting an ultrasharp jump. A similar feature is also observed in the Hall resistivity, which holds its saturation value when heated back in zero field after being field-cooled. The ultrasharp jump in magnetization is also get reflected in our Hall data. The observed data is exotic and can be rooted to the large anisotropy and the strong exchange interaction.

cond-mat.mtrl-sci↗

arXiv2024

Suppression of Intrinsic Hall Effect through Competing Berry Curvature in Cr$_{1+\delta}$Te$_2$

We conducted a comprehensive analysis of the magnetic and electronic transport properties of the layered chalcogenide Cr$_{1+\delta}$Te$_2$ in its single crystalline form. This material exhibits a ferromagnetic transition at a critical temperature of $T_C = 191$ K, characterized by significant thermal hysteresis in the magnetization data below this temperature. Measurements of isothermal magnetization, magnetocaloric effect, and magnetoresistance indicate that the system exhibits strong magnetocrystalline anisotropy, with the $c$-axis serving as the easy axis of magnetization. The Cr$_{1+\delta}$Te$_2$ compound shows pronounced anomalous Hall effect (AHE); however, existing experimental and theoretical data do not provide a clear understanding of the nature and origin of this phenomenon. Our experimental findings suggest that the skew scattering mechanism primarily accounts for the observed AHE. In contrast, our theoretical study reveals the presence of gapped nodal points accompanied by non-zero Berry Curvature, which are expected to contribute towards intrinsic AHE. A detailed analysis of the electronic band structure, obtained through density functional theory calculations, reveals that the Berry Curvature at different nodal points exhibit both positive and negative signs. These opposing contributions largely cancel each other out, thereby significantly diminishing the intrinsic contribution to the AHE.

cond-mat.mtrl-sci↗

arXiv2024

Does carrier localization affect the anomalous Hall effect?

The effect of carrier localization due to electron-electron interaction in anomalous Hall effect is elusive and there are contradictory results in the literature. To address the issue, we report here the detailed transport study including the Hall measurements on $β$-Mn type cubic compound Co$_7$Zn$_7$Mn$_6$ with chiral crystal structure, which lacks global mirror symmetry. The alloy orders magnetically below $T_c$ = 204 K, and reported to show spin glass state at low temperature. The longitudinal resistivity ($ρ_{xx}$) shows a pronounced upturn below $T_{min}$ = 75 K, which is found to be associated with carrier localization due to quantum interference effect. The upturn in $ρ_{xx}$ shows a $T^{1/2}$ dependence and it is practically insensitive to the externally applied magnetic field, which indicate that electron-electron interaction is primarily responsible for the low-$T$ upturn. The studied sample shows considerable value of anomalous Hall effect below $T_c$. We found that the localization effect is present in the ordinary Hall coefficient ($R_0$), but we failed to observe any signature of localization in the anomalous Hall resistivity or conductivity. The absence of localization effect in the anomalous Hall effect in Co$_7$Zn$_7$Mn$_6$ may be due to large carrier density, and it warrants further theoretical investigations, particularly with systems having broken mirror symmetry.

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arXiv2022

Two-band conduction as a pathway to non-linear Hall effect and unsaturated negative magnetoresistance in the martensitic compound GdPd2Bi

The present work aims to address the electronic and magnetic properties of the intermetallic compound GdPd$_2$Bi through a comprehensive study of the structural, magnetic, electrical and thermal transport on a polycrystalline sample, followed by theoretical calculations. Our findings indicate that the magnetic ground state is antiferromagnetic in nature. Magnetotransport data present prominent hysteresis loop hinting a structural transition with further support from specific heat and thermopower measurements, but no such signature is observed in the magnetization study. Temperature dependent powder x-ray diffraction measurements confirm martensitic transition from the high-temperature (HT) cubic Heusler $L2_1$ structure to the low-temperature (LT) orthorhombic $Pmma$ structure similar to many previously reported shape memory alloys. The HT to LT phase transition is characterized by a sharp increase in resistivity associated with prominent thermal hysteresis. Further, we observe robust Bain distortion between cubic and orthorhombic lattice parameters related by $a_{orth} = \sqrt{2}a_{cub}$, $b_{orth} = a_{cub}$ and $c_{orth} = a_{cub}/\sqrt{2}$, that occurs by contraction along $c$-axis and elongation along $a$-axis respectively. The sample shows an unusual `non-saturating' $H^2$-dependent negative magnetoresistance for magnetic field as high as 150 kOe. In addition, non-linear field dependence of Hall resistivity is observed below about 30 K, which coincides with the sign change of the Seebeck coefficient. The electronic structure calculations confirm robust metallic states both in the LT and HT phases. It indicates complex nature of the Fermi surface along with the existence of both electron and hole charge carriers. The anomalous transport behaviors can be related to the presence of both electron and hole pockets.

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arXiv2022

Self organized criticality of magnetic avalanches in disordered ferrimagnetic material

We observe multiple step-like jumps in a Dy-Fe-Ga-based ferrimagnetic alloy in its magnetic hysteresis curve at 2 K. The observed jumps have a stochastic character with respect to their magnitude and the critical field of occurrence, and the jumps do not show any temporal effect. The jump size distribution follows a power law variation indicating the scale invariance nature of the jumps. We have invoked a simple two-dimensional random bond Ising-type spin system to model the dynamics. Our computational work can qualitatively reproduce the jumps and their scale invariant character. It also elucidates that the flipping of antiferromagnetically coupled Dy and Fe clusters is responsible for the observed discrete avalanche-like features in the hysteresis loop. These characteristics indicate that the present phenomenon can be well described within the realm of self-organized criticality

cond-mat.str-el↗

arXiv2022

Evidence of exchange-striction and charge disproportionation in the magneto-electric material Ni3TeO6

The chiral magneto-electric compound Ni3TeO6 is investigated through temperature-dependent synchrotron-based powder x-ray diffraction and x-ray absorption spectroscopy between 15 to 300 K. Our work provides direct evidence for the exchange-striction in the material around the concomitant onset point of collinear antiferromagnetic and magneto-electric phases. The x-ray absorption near edge spectra and x-ray photoelectron spectra show that the sample consists of both Ni2+ and Ni3+ ions in the lattice. The ionic state of Ni is found to be quite robust, and it is largely independent of the preparation route. Additionally, the minority Te4+ state is found to coexist with the majority Te6+ state, which may arise from the charge disproportionation between Ni and Te ions (Ni2+ + Te6+ --> Ni3+ + Te4+). The observed mixed valency of Ni is also confirmed by the total paramagnetic moment per Ni atom in the system. This mixed valency in the metal ions and the exchange-striction may be attributed to the observed magneto-electric effect in the system.

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arXiv2022

Observation of Griffiths-like phase in the quaternary Heusler compound NiFeTiSn

The quaternary Heusler compound NiFeTiSn can be considered to be derived from the exotic pseudogap-compound Fe2TiSn by the replacement of one Fe atom by Ni. In contrast to Fe2TiSn, which shows a disorder-induced ferromagnetic phase, the ground state of NiFeTiSn is antiferromagnetic with the signature of spin canting. Interestingly, NiFeTiSn shows a Griffiths-like phase characterized by isolated ferromagnetic clusters before attaining the antiferromagnetic state. The Griffiths-like phase is possibly associated with the antisite disorder between Fe and Ti sites as evident from our powder X-ray diffraction study. The compound also shows rather an unusual temperature dependence of resistivity, which can be accounted for by the prevailing structural disorder in the system. NiFeTiSn turned out to be a rare example where a Griffiths-like phase is observed in a semiconducting 3d transition metal-based intermetallic compound with an antiferromagnetic ground state.

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arXiv2022

The interplay between structural, magnetic and electronic states in the pyrochlore iridate Eu2Ir2O7

We address the concomitant metal-insulator transition (MIT) and antiferromagnetic ordering in the novel pyrochlore iridate Eu2Ir2O7 by combining x-ray absorption spectroscopy, x-ray and neutron diffractions and density functional theory (DFT) based calculations. The temperature dependent powder x-ray diffraction clearly rules out any change in the lattice symmetry below the MIT, nevertheless a clear anomaly in the Ir-O-Ir bond angle and Ir-O bond length is evident at the onset of MIT. From the x-ray absorption near edge structure (XANES) spectroscopic study of Ir-L3 and L2 edges, the effective spin-orbit coupling is found to be intermediate, at least quite far from the strong atomic spin-orbit coupling limit. Powder neutron diffraction measurement is in line with an all-in-all-out magnetic structure of the Ir-tetrahedra in this compound, which is quite common among rare-earth pyrochlore iridates. The sharp change in the Ir-O-Ir bond angle around the MIT possibly arises from the exchange striction mechanism, which favors an enhanced electron correlation via weakening of Ir-Ir orbital overlap and an insulating phase below TMI . The theoretical calculations indicate an insulating state for shorter bond angle validating the experimental observation. Our DFT calculations show a possibility of intriguing topological phase below a critical value of the Ir-O distance, which is shorter than the experimentally observed bond length. Therefore, a topological state may be realized in bulk Eu2Ir2O7 sample if the Ir-O bond length can be reduced by the application of sufficient external pressure.

cond-mat.str-el↗

arXiv2021

Non-Fermi liquid behavior in a mixed valent metallic pyrochlore iridate Pb$_2$Ir$_2$O$_{7-δ}$

Non-Fermi liquid behavior in some fermionic systems have attracted significant interest in last few decades. Certain pyrochlore iridates with stronger spin-orbit coupling strength have recently been added to the list. Here, we provide evidence of such a non-Fermi liquid ground state in another mixed valent metallic pyrochlore iridate Pb$_2$Ir$_2$O$_{7-δ}$, through the combined investigation of electronic, magnetic and thermodynamic properties as a function of temperature ($T$) and applied magnetic field ($H$). Resistivity measurement showed a linear temperature dependence down to 15~K below which it shows $ρ\sim T^{3/2}$ dependence while magnetic susceptibility diverges as $χ$(T) $\sim$ $T^{-α}$ ($α< 1$) below 10~K. While a strong negative $Θ_{CW}$ has been observed from Curie-Weiss fitting, absence of any long range order down to 80~mK only indicates presence of strong inherent geometric frustration in the system. Heat capacity data showed $C_p$ $\sim$ $T\ln(T_0/T)$ + $βT^3$ dependence below 15~K down to 1.8~K. More importantly spin-orbit coupling strength by x-ray absorption spectroscopy was found to be weaker in Pb$_2$Ir$_2$O$_{7-δ}$ compared to other pyrochlore iridates. In absence of any large moment rare earth magnetic ion, Pb$_2$Ir$_2$O$_{7-δ}$ presents a rare example of an irirdate system showing non-Fermi liquid behaviour due to disordered distribution of Ir$^{4+}$ and Ir$^{5+}$ having markedly different strengths of spin-orbit coupling which might offer a prescription for achieving new non-Fermi liquid systems.

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arXiv2021

Competing magnetic interactions and magnetocaloric effect in Ho$_5$Sn$_3$

The rare-earth intermetallic compound Ho$_5$Sn$_3$ demonstrates fascinating magnetic properties which include temperature-driven multiple magnetic transitions and field driven metamagnetism. We address the magnetic character of this exciting compound through a combined experimental and theoretical studies. Ho$_5$Sn$_3$ orders antiferromagnetically below $~28$ K, and shows further spin reorientation transitions at 15 K and 12 K. We observe a sizable amount of low-temperature magnetocaloric effect in Ho$_5$Sn$_3$ with a maximum value of entropy change $ΔS$ = -9.5 JKg$^{-1}$K$^{-1}$ for an applied field of $H$ = 50 kOe at around 30 K. The field hysteresis is almost zero above 15 K where magneto-caloric effect is important. Interestingly, $ΔS$ is found to change its sign from positive to negative as the temperature is increased above about 8 K, which can be linked to the multiple spin reorientation transitions. The signature of the metamagnetism is visible in the $ΔS$ versus $H$ plot. The magnetic ground-state, obtained from the density functional theory based calculation, is susceptible to the effective Coulomb interaction ($U_{\rm eff}$) between electrons. Depending upon the value of $U_{\rm eff}$, the ground-state can be ferromagnetic or antiferromagnetic. The compound shows large relaxation (14\% change in magnetization in 60 min) in the field cooled state with a logarithmic time variation, which may be connected to the competing magnetic ground-states observed in our theoretical calculations. The competing magnetic ground-states is also evident from the small value of the paramagnetic Curie-Weiss temperature.

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arXiv2019

Octahedral tilting and emergence of ferrimagnetism in cobalt-ruthenium based double perovskites

Rare earth based cobalt-ruthenium double perovskites A$_2$CoRuO$_6$ (A = La, Pr, Nd and Sm) were synthesized and investigated for their structural and magnetic properties. All the compounds crystallize in the monoclinic $P2_1/n$ structure with the indication of antisite disorder between Co and Ru sites. While, La compound is already reported to have an antiferromagnetic state below 27 K, the Pr, Nd and Sm systems are found to be ferrimagnetic below $T_c$ = 46, 55 and 78 K respectively. Field dependent magnetization data indicate prominent hysteresis loop below $T_c$ in the samples containing magnetic rare-earth ions, however magnetization does not saturate even at the highest applied fields. Our structural analysis indicates strong distortion in the Co-O-Ru bond angle, as La$^{3+}$ is replaced by smaller rare-earth ions such as Pr$^{3+}$, Nd$^{3+}$ and Sm$^{3+}$. The observed ferrimagnetism is possibly associated with the enhanced antiferromagnetic superexchange interaction in the Co-O-Ru pathway due to bond bending. The Pr, Nd and Sm samples also show small magnetocaloric effect with Nd sample showing highest value of magnitude $\sim$ 3 Jkg$^{-1}$K$^{-1}$ at 50 kOe. The change in entropy below 20 K is found to be positive in the Sm sample as compared to the negative value in the Nd counterpart.

cond-mat.mtrl-sci↗

arXiv2014

Barocaloric and Magnetocaloric Effects in Fe49Rh51

We report on calorimetry under applied hydrostatic pressure and magnetic field at the antiferromagnetic (AFM)-ferromagnetic (FM) transition of Fe$_{49}$Rh$_{51}$. Results demonstrate the existence of a giant barocaloric effect in this alloy, a new functional property that adds to the magnetocaloric and elastocaloric effects previously reported for this alloy. All caloric effects originate from the AFM/FM transition which encompasses changes in volume, magnetization and entropy. The strong sensitivity of the transition temperatures to both hydrostatic pressure and magnetic field confers to this alloy outstanding values for the barocaloric and magnetocaloric strengths ($|ΔS|$/$Δp$ $\sim$ 12 J kg$^{-1}$ K $^{-1}$ kbar$^{-1}$ and $|ΔS|$/$μ_0ΔH$ $\sim$ 12 J kg$^{-1}$ K$^{-1}$ T$^{-1}$). Both barocaloric and magnetocaloric effects have been found to be reproducible upon pressure and magnetic field cycling. Such a good reproducibility and the large caloric strengths make Fe-Rh alloys particularly appealing for solid-state cooling technologies at weak external stimuli.

cond-mat.mtrl-sci↗