Magnetic field dependent cycloidal rotation in pristine and Ge-doped CoCr2O4

We report a soft x-ray resonant magnetic scattering study of the spin configuration in multiferroic thin films ${\mathrm{Co}}_{0.975}{\mathrm{Ge}}_{0.025}{\mathrm{Cr}}_{2}{\mathrm{O}}_{4}$ (Ge-CCO) and ${\mathrm{CoCr}}_{2}{\mathrm{O}}_{4}$ (CCO) under low high fields from 0.2 to 6.5 T. A characterization Ge-CCO at field was performed, results were compared with those pure CCO. The ferrimagnetic phase transition temperature ${T}_{C}\ensuremath{\approx}95\phantom{\rule{0.28em}{0ex}}\mathrm{K}$ ${T}_{S}\ensuremath{\approx}27\phantom{\rule{0.28em}{0ex}}\mathrm{K}$ are comparable observed In Ge-CCO, ordering wave vector ($qq0$) below ${T}_{S}$ is slightly larger that CCO, unlike diffraction intensity consists two contributions show dissimilar polarization dependence. coercive temperatures than one reported for both compounds, an unexpected reversal spiral helicity, therefore electric polarization, on simply cooling. addition, we find change helicity as function momentum transfer peak indicative presence multiple spirals.