The magnetostriction of nikel and gadolinium

Abstract

Nickel. An optical grid method has been used to check the anomaly in the λl00, T curve (Comer and Hunt 1955) in a nickel crystal. The results appeared to confirm the anomaly but as the method could not be calibrated independently there was considerable doubt about their accuracy. A solenoid capable of giving fields of 10,500 oersteds has been constructed, and magnetostriction measurements carried out using the capacitance bridge method of Corner and Hunt, on the [100] specimen in the temperature range 20 K to 630 K, and on the [111] specimen in the temperature range 78 K to 630 K, The results show that the λl00,T anomaly does not exist. Reasons are given for the error in the optical, grid method, and the results obtained by the capacitance bridge method are discussed in relation to those of Corner and Hunt, and to the theoretical equation of Vonsovsky (194-0). Extrapolation of the X,T curves to 0 K gives λlll = -28 x 10(^-6), λ100 = -57 x 10(^-6). Gadolinium. A zone melting apparatus has been constructed for the purpose of segregating the impurities in a piece of polycrystalline gadolinium in order to grow a single crystal. The grain size has been increased but no single crystal has been produced. Magnetostriction and intensity of magnetization measurements have been made on an ellipsoid of polycrystalline gadolinium in the temperature range 78 K to 350 K. The results show that gadolinium has a large volume effect, and the volume magnetostriction is proportional to the square of the paramagnetic magnetization above the Curie point. The saturation magnetization shows an anomaly at 150 K, and becomes zero at 233 K. The contribution of the volume magnetostriction to the thermal expansion of gadolinium is shown to be too small to account for the thermal expansion anomaly except in the immediate neighbourhood of the Curie point.