High magnetic field evolution of ferroelectricity in CuCrO 2

CuCrO2 offers insights into the different types of spiral magnetic orderings that can form spontaneously due to frustration in triangular-lattice antiferromagnets. We explore the magnetic phase diagram up to 65 T along all the principal axes, and also use electric polarization to probe changes in the spiral order at high magnetic fields. It is known that at zero magnetic field a proper-screw spiral of the Cr S =32 spins forms that in turn induces electric polarization with six possible orientations in the ab plane. Applied magnetic fields in the (hard) ab plane have been shown to induce a transition to cycloidal-spiral magnetic order above 5.3 T in those domains that have spins perpendicular to the applied magnetic field. We show that the cycloidal order remains unchanged all the way up to 65 T, which is one quarter of the extrapolated saturation magnetization. On the other hand, for magnetic fields along the (easy) c axis, we observe a transition in the electric polarization near 45 T, and it is followed by a series of steps and/or oscillations in the electric polarization. The data are consistent with a proper-screw-to-cycloidal transition that is pushed from 5.3 to 45 T by easy-axis anisotropy, and is in turn followed by stretching of the magnetic spiral through commensurate and incommensurate wave vectors. This work also highlights the ability of the magnetically induced electric polarization to probe complex magnetic orders in regimes of phase space that are difficult to reach with neutron diffraction.