Forced Magnetostriction of Nickel, Cobalt, and Iron at 4.2°K

Abstract

The longitudinal magnetostriction in single-crystal samples of nickel and cobalt and a polycrystal of iron was measured at 4.2°K in applied magnetic fields H up to 37 kOe. The forced magnetostriction in nickel was found to change sign for different crystal orientations. This probably explains the apparently contradictory results of previous attempts to measure the forced magnetostriction, either indirectly by the change of magnetization with hydrostatic pressure, or directly by measurements of the volume magnetostriction. A single crystal of cobalt magnetized along its easy c axis has a forced magnetostriction linear in H above 17 kOe, corresponding to ∂ε3/∂H = +2.4×10−10 Oe−1, where ε3 is the strain along the c axis. The magnetostriction in a single crystal of cobalt having its axis at an angle of 72° to the c axis is still not linear at H = 37 kOe, but appears to be approaching the same value of ∂ε/∂H. If ∂ε/∂H and the saturation magnetization σ0 of cobalt are assumed to be isotropic, this value of ∂ε/∂H and the elastic constants yield a value, ∂lnσ0/∂p = −3.4±0.4×10−4 kbar−1. for the pressure derivative of σ0, which is to be compared with the value −2.18×10−4 kbar−1 obtained by Kouvel and Hartelius by direct pressure measurements at room temperature. The forced magnetostriction of the polycrystalline iron sample is linear in H above H = 20 kOe, corresponding to ∂ε/∂H = 1.43±0.03×10−10 Oe−1. This value agrees with other measurements made at room temperature and at liquid-helium temperature, within their experimental accuracy.