29 research outputs found
First-principles calculation of the intersublattice exchange interactions and Curie temperatures of full Heusler alloys Ni2MnX (X=Ga, In, Sn, Sb)
The interatomic exchange interactions and Curie temperatures in Ni-based full
Heusler alloys Ni2MnX with X=Ga, In, Sn and Sb are studied within the framework
of the density-functional theory. The calculation of the exchange parameters is
based on the frozen-magnon approach. Despite closeness of the experimental
Curie temperatures for all four systems their magnetism appeared to differ
strongly. This difference involves both the Mn-Mn and Mn-Ni exchange
interactions. The Curie temperatures, Tc, are calculated within the mean-field
approximation by solving a matrix equation for a multi-sublattice system. Good
agreement with experiment for all four systems is obtained. The role of
different exchange interactions in the formation of Tc of the systems is
discussed.Comment: 6 pages, 4 figure
First-Principles Dynamical Coherent-Potential Approximation Approach to the Ferromagnetism of Fe, Co, and Ni
Magnetic properties of Fe, Co, and Ni at finite temperatures have been
investigated on the basis of the first-principles dynamical CPA (Coherent
Potential Approximation) combined with the LDA (Local Density Approximation) +
Hamiltonian in the Tight-Binding Linear Muffintin Orbital (TB-LMTO)
representation. The Hamiltonian includes the transverse spin fluctuation terms.
Numerical calculations have been performed within the harmonic approximation
with 4th-order dynamical corrections. Calculated single-particle densities of
states in the ferromagnetic state indicate that the dynamical effects reduce
the exchange splitting, suppress the band width of the quasi-particle state,
and causes incoherent excitations corresponding the 6 eV satellites. Results of
the magnetization vs temperature curves, paramagnetic spin susceptibilities,
and the amplitudes of local moments are presented. Calculated Curie
temperatures () are reported to be 1930K for Fe, 2550K for Co, and
620K for Ni; for Fe and Co are overestimated by a factor of 1.8,
while in Ni agrees with the experimental result. Effective Bohr
magneton numbers calculated from the inverse susceptibilities are 3.0 (Fe), 3.0 (Co), and 1.6 (Ni), being in
agreement with the experimental ones. Overestimate of in Fe and Co
is attributed to the neglects of the higher-order dynamical effects as well as
the magnetic short range order.Comment: 10 pages, 13 figure