Faraday rotation of spinel oxide under ultrahigh magnetic field

We studied the magnetic properties of ZnCr2O4 under an ultra-high magnetic field by using the Faraday rotation method. We used a single turn coil system to generate a pulsed high field up to 180 T and used a He-Ne laser as a light source. We chose a 45 degree angle between the polarizer and the analyzer and measured a transient Faraday rotation signal by using a photo-diode and a transient recorder. The sample temperature was kept below Neel temperature during the experiment. We observed a discernible discontinuity in a Faraday rotation signal at 120 T. This discontinuity is considered to represent the first-order phase transition which is observed also in CdCr2O4which has the same geometrical structure as ZnCr2O4.