"Magnetostriction measurements in magnetically ordered crystals using double crystal x ray diffractometry"

Abstract

Magnetostriction measurements have been made on a thin film uniaxial garnet Tb(_2)Lu(_1)Fe(_5)O(_12) a double crystal diffractometer. A value of the magnetostriction constant ʎ (_111)was determined from an analysis of the measurements which employed a least squares technique. The value obtained, ʎ (_111)= (8.12-1.00)xl0(^-6), was in agreement with an expected value obtained by a linear weighting of the pure Rare Earth Iron garnet measurements of another author. Small (<10(^-5)) magnetostriction measurements in materials possessing only 180 magnetic domain walls, where an applied magnetic field is needed, have not previously been reported. The measurement given here made use of the fine resolving power of the double crystal diffractometer, and of a specially constructed electromagnet. A description of these two instruments has also been given. A review of magnetostriction measurements using single crystal X ray diffraction techniques points out the main limitation here of a comparatively low resolving power. Also, without an applied magnetic field, magnetostriction measurements by the X ray diffraction technique can only be made in crystals which have magnetic domain walls other than of the 180 type. Measurements made on different parts of the sample, and even at different parts of the rocking curve, showed considerable variation. This was attributed to local strains in the crystals used. A topographic study of the samples, using the double crystal diffractometer, revealed some of the strains which can be responsible for the local variation in magnetic anisotropy. Such an "in situ" study displays the power of this particular measurement technique over the commonly used electrical resistance strain gauge method. In the latter, various defects in the crystal structure may not be rrcvt-Mied during the course of measurement. Variations in individual magneto striction measurements may be related almost simultaneously to the defects in the crystal structure when the X ray double diffraction technique is used.