The Magnetic Anisotropy of Manganous Fluoride between 12 and 295°K

Abstract

The magnetic anisotropy of single crystals of MnF2, a typical antiferromagnetic substance, has been measured over the temperature range 12 to 295°K. At temperatures above 100°K the anisotropy is of the order of 0.1 percent of the susceptibility and the greater susceptibility is in the direction of the c axis of the tetragonal crystal. Below 70°K the anisotropy becomes extraordinarily large and the susceptibility in the direction of the c axis is smaller than that perpendicular to this axis. Within the limit of experimental error, the anisotropy was independent of field strength up to 10,000 gauss. From the present measurements, combined with those of previous investigators on the powder susceptibility, the directional susceptibilities parallel and perpendicular to the c axis have been calculated. As the temperature is lowered from 70 to 14°K, the perpendicular susceptibility increases by about 12 percent and the parallel susceptibility approaches zero at zero temperature. These results are discussed in connection with the theory of antiferromagnetism proposed by Van Vleck.