Magnetotransport evidence of irreversible spin reorientation in the collinear antiferromagnetic state of underdoped Nd_(2-x)Ce_xCuO₄

We make use of the strong spin-charge coupling in the electron-doped cuprate $\mathrm{Nd}_{2-x}\mathrm{Ce}_x\mathrm{CuO}_4$ to probe changes in its spin system via magnetotransport measurements. We present a detailed study of the out-of-plane magnetoresistance in underdoped single crystals of this compound, including the nonsuperconducting, $0.05\,\leq x\,\leq 0.115$, and superconducting, $0.12\,\leq x\,\leq 0.13$, compositions. Special focus is put on the dependence of the magnetoresistance on the field orientation in the plane of the CuO$_2$ layers. In addition to the kink at the field-induced transition between the noncollinear and collinear antiferromagnetic configurations, a sharp irreversible feature is found in the angle-dependent magnetoresistance of all samples in the high-field regime, at field orientations around the Cu--O--Cu direction. The obtained behavior can be explained in terms of field-induced reorientation of Cu$^{2+}$ spins within the collinear antiferromagnetic state. It is, therefore, considered as an unambiguous indication of the long-range magnetic order.