Magnetic Field Dependence of the Ground-StategFactor in Cerous Magnesium Nitrate

A reduction with magnetic field of the ground-state $g$ factor in the trigonal plane in single crystals of cerous magnesium nitrate has been measured by EPR at 4.2°K with frequencies between 35 and 125 GHz. A value of $g_{\perp }=1.840\mathrm{}\pm 0.002$ is determined at 35 GHz. Theoretical predictions employing the known temperature-independent component of the magnetic susceptibility and energy of the first excited state are in good agreement with the measurements. In addition, the $g$ factor of the free radical of diluted 2,2-diphenyl-1-picryl-hydrazyl (DPPH) was found to be field-independent (to an accuracy of 0.1%) for fields as high as 45 kG.