Magnetic anisotropy and domain structure in gadolinium

Abstract

The magnetocrystalline anisotropy constants of high quality single crystals of gadolinium have been measured using torque magnetometry. The redetermination of the anisotropy constants was necessary due to the poor agreement between the previous measurements which had been made on uncharacterized material of varying quality. The easy direction of magnetization was determined from the anisotropy constants and it is in good agreement with the direct measurements of Corner and Tanner (1976), made on the same crystal, and the neutron diffraction results of Cable and Wollan (1968). It is suggested that the lack of agreement in the previous determinations of the constants was due to the quality of the crystals used, particularly with respect to their oxygen content. A treatment of the magnetostatic energy of nonmagnetic inclusions in gadolinium and their contribution to the total anisotropy is given which can explain the discrepancies between the results of the various previous investigations of the easy direction and anisotropy. The magnetic domain structure of gadolinium was investigated using the Bitter wet colloid technique and a dry colloid technique suitable for low temperature work (90K to 291K). The formation of domains at the Curie temperature (291K) and also the disappearance of a clear domain structure at about 230K, below which there is an easy cone of magnetization, was observed. No magnetic domains were observed below 230K. Around 230K it was expected that there would not be a clear domain structure due to the low value of the anisotropy but the reasons for the non-appearance of domains below about 150K. where the anisotropy is large again, are not clear as Corner and Saad (19 77a) have observed clear domain patterns on gadolinium at 77K.