Spin reorientation and in-plane magnetoresistance of lightly doped La_{2-x}Sr_{x}CuO_{4} in magnetic fields up to 55 T

TL;DR

This study investigates the in-plane magnetoresistance of lightly doped La_{2-x}Sr_{x}CuO_{4} in high magnetic fields, revealing a field-induced weak-ferromagnetic transition and isotropic negative MR linked to spin reorientation.

Contribution

It provides new insights into the spin reorientation and magnetoresistance behavior in lightly doped LSCO, challenging previous reports of spin-flop transitions and highlighting the role of weak-ferromagnetic moments.

Findings

Large negative MR appears in magnetically ordered states.

No spin-flop transition observed in the Néel state.

Negative MR saturates around 40 T and is isotropic within the ab plane.

Abstract

The magnetoresistance (MR) in the in-plane resistivity is measured in magnetic fields up to 55 T in lightly doped La_{2-x}Sr_{x}CuO_{4} in the N\'eel state (x = 0.01) and in the spin-glass state (x = 0.03) using high-quality untwinned single crystals. In both cases, a large negative MR is observed to appear when the magnetic order is established. For x = 0.01, it is found that the MR is indicative of a one-step transition into a high-field weak-ferromagnetic state at around 20 T when the magnetic field is applied from the spin easy axis (b axis), which means that there is no spin-flop transition in the N\'eel state of this material; this is contrary to a previous report, but is natural in light of the peculiar in-plane magnetic susceptibility anisotropy recently found in this system. In the spin-glass state, we observe that the large (up to \sim20%) negative MR saturates at around 40 T, and this MR is found to be essentially isotropic when the magnetic field is rotated within the ab plane. Our data show that the large negative MR is inherent to LSCO in a magnetically ordered state, in which the weak-ferromagnetic (WF) moment becomes well-defined; we discuss that the observed MR is essentially due to the reorientation of the WF moments towards the magnetic field direction both in the N\'eel state and in the spin-glass state.