Magnetic Phases of a Highly Frustrated Magnet, ${\mathrm{ZnCr}}_2{\mathrm{O}}_4$, up to an Ultrahigh Magnetic Field of 600 T

The Faraday rotation and magneto-optical absorption spectral measurements were conducted to reveal the full-magnetization process and map out a magnetic phase diagram of a typical geometrical frustrated magnet, ${\mathrm{ZnCr}}_2{\mathrm{O}}_4$, by using the electro-magnetic flux compression method in ultrahigh magnetic fields up to 600 T. A fully polarized ferromagnetic phase is observed in which the absorption spectra associated with an exciton-magnon-phonon transition disappears. Furthermore, prior to the fully polarized ferromagnetic phase above 410 T, we found a novel magnetic phase above 350 T at 4.6 K followed by a canted $3:1$ phase.

Figure 1

(a) Magnetization obtained by the Faraday rotation method in magnetic fields of up to 600 T generated by the EMFC method at 4.6 K and up to 190 T by the STC method at 9 K as described in Ref. 5. (b) Absorption intensity change at a wavelength of 635 nm at 4.6 K as a function of the magnetic field. The broken lines at 120, 350, and 410 T indicate anomalies observed in the absorption intensity.

Figure 2

(a) Magnetization processes obtained from the Faraday rotation by the EMFC method measured at several temperatures. (b) Absorption intensity change in the wavelength of 635 nm at several temperatures as a function of magnetic field.

Figure 3

(a) Magneto-optical spectra obtained by streak spectroscopy at 12 K and in several magnetic fields. (b) Absorption intensity changes in several wavelengths at 12 K as a function of magnetic field derived from Fig. 3a. The dotted arrow is the point of a wavelength (635 nm) used for the Faraday rotation.

Figure 4

Magnetic phase diagram constructed from data in Fig. 2a and Ref. 5. Cross symbols indicate transition points observed by the Faraday rotation method. Broken lines show anomalies appeared in the magneto-optical absorption.