Magnetism in transition metals at finite temperatures. II. Application to the thermodynamic excitations in iron: spin waves and TC

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Abstract
For pt.I see ibid., vol.12, no.1, p.177 (1982). A previously described mathematical technique is applied to the excited states of ferromagnetic iron. The calculations considering only the d band are used although a preliminary calculation involving an s band is included. This shows that no qualitative differences appear although values of the local moment m and spin-wave stiffness D are brought into better quantitative agreement with experiment. It is shown that the local environment (largely the nearest neighbours) of perturbed spins dominates the excitation energy, and that this energy is higher if the local order is 'rough' ( Del 2m=0) than if it is 'smooth' ( Del 2m=0). Two easily calculable excitations, the spin spiral and alternating tilt, are shown to be broadly representative of the high-energy excitations. A set of Heisenberg J are calculated and give a reasonable mean field value for TC. Finally, spin-wave dispersion curves are calculated both at low q from the spin spirals, and over a wide range of q from the Heisenberg J. The low-q stiffness was found to be in good agreement with experiment when both s and d bands were used, but was somewhat lower in the calculations with only d bands.

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