Onset of magnetic order in fcc-Fe films on Cu(100)

Exchange bias driven by Dzyaloshinskii-Moriya interactions

The exchange bias effect in a compensated IrMn3/Co(111) system is studied using multiscale modeling from ab initio to atomistic spin model calculations. We evaluate numerically the out-of-plane hysteresis loops of the bilayer for different thicknesses of the ferromagnetic layer. The results show the existence of a perpendicular exchange bias and an enhancement of the coercivity of the system. To identify the origin of the exchange bias, we analyze the hysteresis loops of a selected bilayer by tuning the different contributions to the exchange interaction across the interface. Our results indicate that the exchange bias is primarily induced by Dzyaloshinskii-Moriya interactions, while the coercivity is increased mainly due to a spin-flop mechanism.

Magnetic ordering in Fe/Co sandwiches on Cu(100)

We investigate magnetic correlations and local magnetic moments at finite temperatures of some Fe and Co multilayers on Cu(100) substrates, such as Co(m)Fe(n)Co(m)/Cu(100) and Fe(m)Co(n)Fe(m)/Cu(100). We use an ab initio mean-field theory of magnetic fluctuations for layered materials based on the first-principles local spin-density functional theory implemented through the screened Korringa-Kohn-Rostoker method. We find that the presence of Fe layers in the neighbourhood of a Co layer always leads to a reduction in the magnetic moment of the Co atoms, whereas that of the Fe atoms is enhanced. Of particular interest is the lack of local moment formation on the single fcc-Co layer sandwiched between two fcc-Fe layers. However, a Co layer completely immersed in a Cu environment remains ferromagnetic. The Curie temperature of the Co(m)Fe(n)Co(m)/Cu(100) system oscillates as the Fe layer thickness is increased whereas that of the Fe(m)Co(n)Fe(m)/Cu(100) system increases almost monotonically with Co layer thickness.

Temperature dependent magnetic anisotropy in metallic magnets from an ab initio electronic structure theory: L1(0)-ordered FePt

Using a first-principles, relativistic electronic structure theory of finite temperature metallic magnetism, we investigate the variation of magnetic anisotropy K with magnetization M in metallic ferromagnets. We apply the theory to the high uniaxial K material, L1(0)-ordered FePt, and find its magnetic easy axis perpendicular to the Fe/Pt layers for all M and K to be proportional to M2 for a broad range of values of M. For small M, near the Curie temperature, the calculations pick out the easy axis for the onset of magnetic order. Our ab initio results for this important magnetic material agree well with recent experimental measurements, whereas the single-ion anisotropy model fails to give the correct qualitative behavior.