Pressure Dependence of the Magnetization of Cobalt

Single-crystal and polycrystalline specimens of cobalt were subjected at room temperature to hydrostatic pressures up to about 5 kbars, and the effects on their magnetizations were measured in fields up to 14 kOe. For the single crystal magnetized along its easy axis, complete saturation was achieved at about 3 kOe, and above this field the pressure dependence of the magnetization (per g) remained constant at a saturation value, σs−1 (∂σs/∂p), of −2.18×10−4 kbars−1. This value is shown to be identifiable with the pressure dependence of the atomic moment at 0°K and has the same sign and even roughly the same magnitude as the recent low-temperature pressure results for iron and nickel. For the cobalt polycrystal, the change in magnetization with pressure varied widely (though smoothly) with field before attaining the above saturation value at about 13 kOe. The lack of saturation at lower fields was attributed entirely to magneto-crystalline anisotropy, and a graphical integration method applied to the data gave the result: K−1(∂K/∂p) = −23.2×10−4 kbars−1, where K is the total anisotropy energy (per g) and is linearly related to the anisotropy coefficients, K1 and K2. The similarity in sign and the order of magnitude difference between the K−1(∂K/∂p) and σs−1 (∂σs/∂p) values for cobalt are closely analogous to the situation previously found in iron and an iron-silicon alloy.