Anisotropic magnetoresistance in the itinerant antiferromagnetic EuTiO3

Abstract

We report on measurements of the anisotropic magnetoresistance (AMR) of doped EuTiO 3 . It is shown that the primary contribution to the AMR is the crystalline component, which depends on the relative orientation between the magnetic moments and the crystal axes. With increasing magnetic field, a four-fold crystalline AMR undergoes a change in its alignment with respect to the crystal axes. The results are discussed in the context the coupling between spin canting, electronic structure, and transport. We discuss the potential role of Weyl points in the band structure. At high fields, the AMR transitions to uniaxial symmetry, which is lower than that of the lattice, along with a cross-over from positive to negative magnetoresistance.3 Spin-orbit coupling plays a central role in the anisotropic magnetoresistance (AMR) and anomalous Hall effect (AHE) [1] of itinerant ferromagnets and in materials with topologically non-trivial electronic states. While an elegant theoretical framework exists for the intrinsic AHE and its connection to the Berry curvature of the electronic bands [2-7], AMR remains comparatively less well understood. Recently, both AMR and AHE have also attracted significant attention in antiferromagnetic metals and semiconductors [8,9]. For example, significant AHEs in non-collinear antiferromagnets have been discovered [10][11][12]. Another phenomenon of recent interest is the potential coupling between the orientation of the Néel vector and the topology of the electronic states in antiferromagnets with symmetry-protected Dirac and/or Weyl points in their band structure [13,14]. Both AHE and AMR can serve as signatures of such interactions [13][14][15].Degenerately doped, antiferromagnetic EuTiO 3 is an interesting testbed for these ideas for several reasons. Despite a small net magnetization, it exhibits an intrinsic AHE that changes sign as a function of the carrier density [16][17][18]. This is indicative of the Fermi level being located near a Weyl point or an avoided crossing, which are sources of Berry curvature [5,7]. Recent density functional calculations (DFT) show the presence of Weyl points, which are near the Fermi level for the doping concentration where the sign changes in the AHE are observed, in case of ferromagnetic order [17]. At zero applied fields, the Eu moments order antiferromagnetically (G-type) [19, 20] with a Néel temperature of ~6 K that is relatively insensitive to the amount of doping [17]. A collinear spin arrangement cannot give rise to Weyl points, because time reversal and inversion symmetry are both present. This can also be seen in DFT calculations (see Supplementary Information [21]). Under applied magnetic fields, however, the spins cant and produce a small net magnetization [17]. The Eu spin orientation can

In-plane antiferromagnetic moments in axion topological insulator candidate EuIn$_2$As$_2$

“…5(g). Magnetic field-induced changes in the AMR have also been observed in other topological materials such as ZrTe 5 and EuTiO 3 37,38 . The applied magnetic field controls both the spin canting as well as Zeeman splitting leading to topological phase transitions such as the movement of Weyl points 37,38 .…”

“…Magnetic field-induced changes in the AMR have also been observed in other topological materials such as ZrTe 5 and EuTiO 3 37,38 . The applied magnetic field controls both the spin canting as well as Zeeman splitting leading to topological phase transitions such as the movement of Weyl points 37,38 . For an AF topological insulator, the detailed magnetization of such a system are key to the topological nature and controllable by various ways.…”

Cluster‐Size‐Dependent Linear Magnetoelectric Coupling Effect in Na0.5Bi0.5TiO3/FeCo Composites

“…It is well known that the electronic doping and carrier density can control the magnetism of oxides based on the coupling between spin canting and electronic structure. [ 18,19 ] However, the XRD results show that there is almost no shift of peaks. Thus, the unexpected doping effect can be ignored.…”

Correlating magnetic structure and magnetotransport in semimetal thin films of Eu$_{1-x}$Sm$_x$TiO$_3$

“…Corroborating this, the ab-plane is the magnetic easy plane as probed by both film magnetoresistance and magnetometry. 10,13 Our earlier neutron diffraction measurements established that, at zero field, the G-type AFM order of the parent system persists in metallic samples (n < 9×10 20 cm −3 ) with only a slightly decreasing onset temperature. 12 In this study, we report the evolution of magnetic order under an applied in-plane magnetic field in a series of Eu 1−x Sm x TiO 3 samples with chemical potentials that span across the proposed Weyl nodes in this compound.…”

“…In addition to the Weyl physics, anisotropic magnetoresistance (AMR) measurements of this material system reveal symmetry changes suggestive of field-driven magnetic phase transitions. 13 The origins of these various transitions seen in AMR are however currently unclear, as are the underpinnings of other anomalous transverse magnetotransport in this material. For instance, the field dependence of the AHE resistance is nonlinear, nonmonotonic, and not proportional to magnetization.…”