Finite-temperature Theory Of Local Environment Effect Research Articles

Magnetism in amorphous transition metals. II.

Susceptibilities and pressure effects on the magnetic properties of amorphous transition metals have been investigated on the basis of a finite-temperature theory of local-environment effects in amorphous metallic magnetism. Calculated high-field susceptibilities, paramagnetic susceptibilities, effective Bohr-magneton numbers, and the pressure dependence of magnetization, Curie temperature, and spin-glass temperatures are shown to explain various aspects of the magnetism in amorphous and liquid transition metals and alloys as a function of the d electron number. It is demonstrated that these quantities are governed by the electronic structure of amorphous transition metals, in particular, by the main-peak position in the noninteracting density of states for amorphous structure. Moreover, the detailed investigations for susceptibilities, forced-volume magnetostriction, and the T-P phase diagram in the reentrant spin-glass region reveal that the itinerant-electron spin glasses in the Fe-rich amorphous alloys with more than 90 at. % Fe are caused by structural disorder instead of configurational disorder.

New magnetism in amorphous transition metals and alloys

Magnetism of amorphous 3d transition metals is investigated on the basis of the finite-temperature theory of local-environment effects. The simple ferromagnetism of Fe, Co and Ni is shown to be drastically changed by structural disorder. The results explain the recent experimental data for Fe- and Co-rich amorphous alloys.

Finite-temperature magnetism of disordered Fe-Co alloys.

The magnetic properties of disordered Fe-Co alloys have been investigated for both bcc and fcc structures using the finite-temperature theory of local-environment effects. The calculated magnetization, Curie temperature, effective Bohr magneton number, Weiss constant, and high-field susceptibility are shown to explain the concentration dependence of the experimental data. It is found that fcc Fe-Co alloys show ferromagnetic instability at 50 at. % Fe and form a spin-glass state after the disappearance of ferromagnetism at ${c}^{\mathrm{*}}$=78 at. % Fe. This is caused by the nonlinear magnetic coupling between Fe local moments and the local-environment effect on the amplitudes of Fe local moments. Strong local-environment effects around ${c}^{\mathrm{*}}$ are examined in detail with a prediction of the internal-field distribution for $^{57}\mathrm{Fe}$.

Finite-temperature theory of local-environment effects in Fe-Ni alloys.

Magnetic properties of Fe-Ni alloys have been investigated for both fcc and bcc structures on the basis of the finite-temperature theory of local-environment effects (LEE). The temperature and concentration dependencies of various local moments, susceptibilities, and the internal-field distribution function have been calculated. The results are analyzed from the viewpoint of the LEE. The magnetic phase diagram obtained explains the experimental results well; the bcc alloys show a stable ferromagnetism while the fcc has a ferromagnetic instability at about 65 at. % Fe. In particular, the spin-glass state in the fcc phase is theoretically obtained for the first time on the basis of the itinerant-electron model. It is shown to be a new type of itinerant-electron spin glass which arises from the nonlinearity of the magnetic couplings between Fe local moments. The theory predicts also an asymmetric divergence of the high-field susceptibility around the ferromagnetic instability in the fcc lattice.