arXiv subjects

Matthias Gutmann

Publications and source records attributed to Matthias Gutmann.

7 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↗

arXiv2026

Anomalous magnetotransport in a non-collinear correlated kagome ferromagnet MgMn6Sn6

Magnetic kagome metals provide a fertile platform for exploring unusual magnetotransport phenomena arising from the intricate interplay between electronic topology, electron correlations, and magnetic order. MgMn6Sn6 is a room-temperature kagome ferromagnet with strong in-plane magnetic anisotropy. Here, we report a combined study of single-crystal neutron diffraction (SCND) and magnetotransport properties of MgMn6Sn6, supported by first-principles calculations. Our SCND measurements reveal a non-collinear arrangement of Mn magnetic moments within the basal plane of the kagome bilayer. The Hall conductivity shows a substantial intrinsic contribution of approximately 0.29 e^2/h per kagome layer, which is nearly isotropic with respect to the field orientation. At low temperatures, the anomalous Hall conductivity develops a pronounced anisotropic extrinsic component, highlighting the directional sensitivity of scattering processes. The significantly large value of the Sommerfeld coefficient, in the absence of f-electrons, underscores enhanced electron correlation. Therefore, the non-collinear kagome ferromagnet MgMn6Sn6 is a promising candidate for studying the effects of electron correlation on magnetotransport properties.

cond-mat.mtrl-sci↗

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.

cond-mat.str-el↗

arXiv2025

Emergent ferromagnetic ladder excitations in heavy fermion superconductor CeSb$_{2}$

Low-dimensional spin fluctuations play a crucial role in unconventional superconductors, with quasi-one-dimensional spin excitations potentially linked with spin-triplet superconductivity. The heavy fermion superconductor CeSb$_2$ exhibits an unusual large inverted S-shaped upper critical field that suggests a possible triplet pairing state within its pressure-induced superconducting dome. Using inelastic neutron scattering, we discover quasi-one-dimensional magnetic excitations in CeSb$_2$ emerging from nearly square Ce layers with minor orthorhombic deformation. We show that the data are well described by a ferromagnetic spin ladder model, where the "rungs" of the ladder straddle Ce bilayers. Moreover, we find that diffuse excitations akin to those in the ordered phase persist well above $T_{\rm N}$, suggesting that quasi-one-dimensional ferromagnetic paramagnons may significantly contribute to the unusual superconductivity that appears under pressure once magnetic order is suppressed.

cond-mat.supr-con↗

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.

cond-mat.str-el↗

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↗

arXiv2022

Investigation of metamagnetism and crystal-field splitting in pseudo-hexagonal CeRh$_3$Si$_2$

CeRh$_3$Si$_2$ has been reported to exhibit metamagnetic transitions below 5~K, a giant crystal field splitting, and anisotropic magnetic properties from single crystal magnetization and heat capacity measurements. Here we report results of neutron and x-ray scattering studies of the magnetic structure and crystal-field excitations to further understand the magnetism of this compound. Inelastic neutron scattering (INS) and resonant inelastic x-ray scattering (RIXS) reveal a $J_z$\,=\,1/2 groundstate for Ce when considering the crystallographic $a$ direction as quantization axis, thus explaining the anisotropy of the static susceptibility. Furthermore, we find a total splitting of 78\,meV for the $J$\,=\,5/2 multiplet. The neutron diffraction study in zero field reveals that on cooling from the paramagnetic state, the system first orders at $T_{\text{N}_1}=4.7$\,K in a longitudinal spin density wave with ordered Ce moments along the $b$-axis (i.e. the [0 1 0] crystal direction) and an incommensurate propagation vector $\textbf{k}=(0,0.43,0$). Below the lower-temperature transition $T_{\text{N}_2}=4.48$\,K, the propagation vector locks to the commensurate value $\textbf{k}=(0,0.5,0)$, with a so-called lock-in transition. Our neutron diffraction study in applied magnetic field $H\parallel b$-axis shows a change in the commensurate propagation vector and development of a ferromagnetic component at $H=3$\,kOe, followed by a series of transitions before the fully field-induced ferromagnetic phase is reached at $H = 7$\,kOe. This explains the nature of the steps previously reported in field-dependent magnetization measurements. A very similar behaviour is also observed for the $H\parallel$ [0 1 1] crystal direction.

cond-mat.str-el↗