Magnetic superfluid state in the frustrated spinel oxide CdCr2O4revealed by ultrahigh magnetic fields

Abstract

We investigated the magnetic-field-induced phases of a typical three-dimensional frustrated magnet, CdCr${}_{2}$O${}_{4}$, in magnetic fields of up to 120 T using both the electromagnetic induction method and magneto-optical spectroscopy of the $d$-$d$ transitions and the exciton-magnon-phonon transitions. Anomalies were observed in the magneto-optical absorption intensity as well as the differential magnetization prior to a fully polarized magnetic phase, revealing a magnetic phase associated with changes in both the crystal and magnetic structures accompanied by the first-order phase transition. A magnetic superfluid state, such as an umbrella-like magnetic structure or a spin-nematic state, is proposed as a candidate for this phase, which is found universally in the series of chromium spinel oxides, $A$Cr${}_{2}$O${}_{4}$ ($A$ $=$ Zn, Cd, Hg).