A theory of magneto-volume effects of itinerant-electron magnets. I. Spontaneous volume magnetostriction

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Abstract
The magneto-volume effects of ferromagnetic and antiferromagnetic metals are discussed by using the spin-fluctuation theory for finite-temperature magnetism developed by the present author with the use of the functional-integral method. The authors calculate the temperature-dependent magnetic pressure, from which the spontaneous volume magnetostriction is obtained, by taking account of the volume dependences of the electron-electron interaction and of the band structure. The theory is shown to yield an interpolating description covering the weak- and strong-coupling limits and to reduce to the Hartree-Fock theory at T=0K. Numerical calculations are performed for GCC Fe and FCC NiFe alloys. Attention is paid to the Invar alloy, whose anomaly is well accounted for by the present calculation.