Physics – Condensed Matter – Strongly Correlated Electrons
Scientific paper
2010-04-24
J. Phys. A: Math. Theor. 43 (2010) 195004
Physics
Condensed Matter
Strongly Correlated Electrons
20 pages, 4 figures
Scientific paper
10.1088/1751-8113/43/19/195004
A characteristic feature of the Gaussian approximation in the functional-integral approach to the spin-fluctuation theory is the jump phase transition to the paramagnetic state. We eliminate the jump and obtain a continuous second-order phase transition by taking into account high-order terms in the expansion of the free energy in powers of the fluctuating exchange field. The third-order term of the free energy renormalizes the mean field, and fourth-order term, responsible for the interaction of the fluctuations, renormalizes the spin susceptibility. The extended theory is applied to the calculation of magnetic properties of Fe-Ni Invar.
Grebennikov V. I.
Melnikov Nikolai B.
Reser B. I.
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