Magnetic Anisotropy Measurement of MnO Single Crystal

Abstract

The magnetic anisotropy of MnO single crystal, grown by the Verneuil method, was measured using a torque balance. The results of the torque measurements at liquid air temperature could be summarized within experimental errors by a formula
T=C₁H²sin (2θ+ε₁)+C₂H⁴sin (4θ+ε₂)+C₃H⁶,
where H is the applied field intensity, θ the angle of rotation of H relative to the crystal, and ε’s and C’s are constants which depend in a certain way on the kind of crystallographic axis of suspension. In the case where [111] is the direction of suspension, C₂=0. The C₃H⁶ term changed its sigh when the rotation was made in the revere sense; thus it represents a rotational hysteresis term. Alternative theoretical interpretations of the new 4θ-term are presented: it arises either from a possible small anisotropy energy within the easy plane of magnetization, or from reversible movements of the walls which separate different antiferromagnetic domains. Discussion to favor the latter is given.