Electron spin resonance in the diluted uniaxial antiferromagnet Mg1-xFexCl2

Abstract We report electron spin resonance experiments at millimeter and submillimeter wavelengths performed on single crystal samples of the randomly diluted uniaxial antiferromagnet Mg 1- x Fe x Cl 2 . Four resonance modes are observed in the x = 0.554 sample, three of which are assigned to the antiferromagnetic, in-phase ferromagnetic and out-of-phase ferromagnetic resonances, respectively. From the concentration dependence of the resonance frequency of the in-phase ferromagnetic mode, an accurate value for the single ion anisotropy constant is obtained (|D| = 6.3 cm −1 ).