Spin-Charge Coupling in lightly doped Nd$_{2-x}$Ce$_{x}$CuO$_4$

TL;DR

This study uses neutron scattering to explore how magnetic fields influence spin structures in Nd$_2$CuO$_4$ and its doped variant, revealing strong spin-charge coupling in electron-doped copper oxides.

Contribution

It provides direct experimental evidence of spin-charge coupling effects in electron-doped cuprates through neutron scattering and magnetoresistance measurements.

Findings

Magnetic field induces spin-flop transitions and c-axis disorder.

Hysteresis observed in antiferromagnetic phase transitions.

Spin-charge coupling significantly affects transport properties.

Abstract

We use neutron scattering to study the influence of a magnetic field on spin structures of Nd$_2$CuO$_4$. On cooling from room temperature, Nd$_2$CuO$_4$ goes through a series of antiferromagnetic (AF) phase transitions with different noncollinear spin structures. While a c-axis aligned magnetic field does not alter the basic zero-field noncollinear spin structures, a field parallel to the CuO$_2$ plane can transform the noncollinear structure to a collinear one ("spin-flop" transition), induce magnetic disorder along the c-axis, and cause hysteresis in the AF phase transitions. By comparing these results directly to the magnetoresistance (MR) measurements of Nd$_{1.975}$Ce$_{0.025}$CuO$_4$, which has essentially the same AF structures as Nd$_2$CuO$_4$, we find that a magnetic-field-induced spin-flop transition, AF phase hysteresis, and spin c-axis disorder all affect the transport properties of the material. Our results thus provide direct evidence for the existence of a strong spin-charge coupling in electron-doped copper oxides.