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

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.

12 pages, 12 figures