科研之友
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摘要
A local electronic theory of transition-metal magnetism at finite temperatures is presented, which takes into account longitudinal and transverse spin fluctuations on the same footing. The magnetic properties are determined in the framework of a rotational-invariant d-band model Hamiltonian by applying a four-field Hubbard-Stratonovich functional-integral method in the static approximation. The role of transverse spin excitations on the temperature-dependent magnetic properties is investigated by performing alloy averages in the single-site virtual crystal approximation. Bulk Fe is considered as the representative example for the applications. Results are given for the average magnetization M, for the spin-excitation energies, and for the transverse and longitudinal contributions to the local magnetic moments mu(l) at atom l. The importance of noncollinear spin excitations is quantified by comparison with the corresponding collinear calculations. An important reduction of about 33% of the calculated Curie temperature T-C is obtained, which now amounts to 1250 K and is thus relatively close to the experimental value. The longitudinal (transverse) components of mu(l) are found to decrease (increase) as a function of temperature until the full rotational symmetry is reached at T-C. This reflects the increasing importance of the transverse spin fluctuations. The origin of the temperature dependence of M and mu(l) is analyzed in terms of the local spin-fluctuation energies.
- 出版日期2015-5-15
