Magnetotransport evidence for irreversible spin reorientation in the collinear antiferromagnetic state of underdoped Nd2-xCexCuO4

The antiferromagnetic ground state of electron-doped 214-cuprates is relatively robust, extending, with increasing doping, up to at least the superconducting region of the phase diagram. However, whether the long-range antiferromagnetism persists inside the superconducting doping range still remains a controversial issue. Here we make use of the strong spin-charge coupling for probing changes in the spin system of underdoped $\mathrm{Nd}_{2-x}\mathrm{Ce}_x\mathrm{CuO}_4$ crystals via magnetotransport measurements. We present a detailed study of the out-of-plane magnetoresistance in nonsuperconducting, $0.05\,\leq x\,< 0.12$, as well as in superconducting, $0.12\,\leq x\,\leq 0.13$, samples as a function of the strength and orientation of the magnetic field applied parallel to the $\mathrm{CuO}_2$ layers. In addition to the kink at the field-induced transition between the noncollinear and collinear AF configurations, a sharp irreversible feature has been 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.