Numerical calculation of local magnetic characteristics of Fe, Co and Ni at finite temperatures

Abstract

The transverse and longitudinal local susceptibilities, the dynamic spin correlation function and the local magnetic moment of Fe, Co and Ni are calculated, using the first-principles density of states and the dynamic non-local approximation of the spin-fluctuation theory. A remarkable agreement between theory and experiments on magnetovolume effect and neutron scattering has been found.

Problem of temperature dependence in the dynamic spin-fluctuation theory for strong ferromagnets

“…Since at fixed temperatures the spin fluctuations ζ x and ζ z are of the same order, a modification of the system of the SFT based on the transformation to the mean fluctuation (for the description see the appendix) has been successfully used in the coordinate bisection calculations [4][5][6][7][8][9][10].…”

“…First, we demonstrate that the instability is not an artefact of the calculation method. To this end, we show that the coordinate bisection method used in [4][5][6][7][8][9][10] gives a good agreement with the multidimensional minimization over a wide range of temperatures. Second, through the calculation with the forward and backward changes of temperature, we demonstrate the hysteresis behaviour of the magnetic characteristics.…”

“…Magnetic properties of transition metals and alloys at finite temperatures are usually calculated in the framework of various approximations of the spin-fluctuation theory (SFT) (see, e.g., [1][2][3] and references therein). A number of such approximations were developed in [4,5] and fairly successfully applied first to ferromagnetic metals Fe, Co and Ni [6][7][8] and then to the Invar alloy Fe-Ni [9,10].…”

“…Calculations [4][5][6][7][8][9][10] showed that the solution to the system of equations of the SFT can be unstable at high temperatures, well below the Curie temperature, T C . It is especially pronounced in Fe and Fe-Ni Invar, where spin fluctuations increase sharply in this region.…”

Magnetic properties of Fe–Ni invar calculated in the dynamic non-local approximation of the spin fluctuation theory

“…In the present paper, for the first time we use the dynamic non-local approximation (DNA) of the SFT, developed in [25] and successfully applied to Fe, Co and Ni in [26][27][28], for investigation of the temperature dependence of the magnetic properties of Fe-Ni invar. Our approach is based on a self-consistent quadratic approximation for the free energy of electrons in a random exchange field.…”