We report a soft x-ray resonant magnetic scattering study of the spin configuration in multiferroic thin films of Co0.975Ge0.025Cr2O4 (Ge-CCO) and CoCr2O4 (CCO), under low- and high-magnetic fields, from 0.2 T up to 6.5 T. A characterization of Ge-CCO at a low magnetic field is performed and the results are compared to those of pure CCO. The ferrimagnetic phase transition temperature TC≈95 K and the multiferroic transition temperature TS≈27 K in Ge-CCO are comparable to those observed in CCO. In Ge-CCO, the ordering wave vector (qq0) observed below TS is slightly larger compared to that of CCO, and, unlike CCO, the diffraction intensity consists of two contributions that show a dissimilar x-ray polarization dependence. In Ge-CCO, the coercive field observed at low temperatures was larger than the one reported for CCO. In both compounds, an unexpected reversal of the spiral helicity and therefore the electric polarization was observed on simply magnetic field cooling. In addition, we find a change in the helicity as a function of momentum transfer in the magnetic diffraction peak of Ge-CCO, indicative of the presence of multiple magnetic spirals.
@article{arxiv.2010.01518,
title = {Magnetic field dependent cycloidal rotation in pristine and Ge doped CoCr$_2$O$_4$},
author = {N Ortiz Hernandez and S Parchenko and J R L Mardegan and M Porer and E Schierle and E Weschke and M Ramakrishnan and M Radovic and J A Heuver and B Noheda and N Daffe and J Dreiser and H. Ueda and U Staub},
journal= {arXiv preprint arXiv:2010.01518},
year = {2021}
}