Angle-resolved magnetoresistance in the strongly anisotropic quantum magnet TmB4

Abstract

Precise angle-resolved magnetoresistance (ARMR) measurements in various magnetic fields enabled us to create illustrative distributions of $\mathrm{\ensuremath{\Delta}}\ensuremath{\rho}/\ensuremath{\rho}(\ensuremath{\varphi},\phantom{\rule{0.16em}{0ex}}H)$ in $\mathrm{Tm}{\mathrm{B}}_{4}$, where $\ensuremath{\varphi}$ is the angle between the sample $c$ axis and applied magnetic field $H$. These distributions reveal the charge transport anisotropy in this strongly Ising anisotropic quantum antiferromagnet with a geometrically frustrated Shastry-Sutherland lattice exhibiting fractional magnetization plateaus. While in the paramagnetic region $\mathrm{\ensuremath{\Delta}}\ensuremath{\rho}/\ensuremath{\rho}(\ensuremath{\varphi},\phantom{\rule{0.16em}{0ex}}H)$ reaches its maxima for $H\phantom{\rule{0.16em}{0ex}}\ensuremath{\perp}\phantom{\rule{0.16em}{0ex}}c$, below the N\'eel temperature ${T}_{N}=11.7$ K the situation is different. Here the main MR features appear for $H\ensuremath{\parallel}c$, i.e., along the easy axis of magnetic anisotropy, and correspond to magnetic phases and phase transitions between them. It is interesting that all the above features (maxima) related with the scattering of conduction electrons on spin magnetic structure are related with fractional magnetization plateaus. With increasing $\ensuremath{\varphi}$ MR anomalies shift to higher fields. Above the field of magnetic saturation, moreover, significant MR maxima have been observed at certain angles which correspond to specific directions in the crystal lattice, pointing to field directions in which the scattering of conduction electrons on the magnetic structure is the highest. Thus, ARMR appears to be a sensitive experimental tool reflecting the angular dependence of the interplay between charge carriers and magnetic structure as a function of temperature and applied magnetic field.