Magnetization of ultrathin [Fe1−cNic]n alloy nanojunctions between Fe or Co leads using an Ising EFT-MFT model

The Fe and Ni sublattice magnetizations of ultrathin iron-nickel alloy nanonjunctions [Fe1−cNic] between Fe and Co leads are inspected. For c≤0.4, the alloy has a bcc structure and becomes fcc otherwise. A combined EFT and MFT treatment is used to obtain the sublattice magnetizations of Fe and Ni in the individual layers as a function of temperature and concentration. This is achieved by calculating single site spin correlations within EFT and making use of reliable experimental data such as lattice parameters a, stiffness spin constants D, and Curie temperatures Tc leading to reasonable values of the exchange parameters J. According to our model, the alloys forming the bcc nanojunctions we examine (c=0.0841,0.204,0.268) are ferrimagnetic with the absence of a compensation temperature while those for the fcc structures (c=0.5,0.81) are ferromagnetic. These EFT results feed the MFT calculations for the nanojunction from the interface inwards. The effect of adding several alloy layers to both bcc and fcc types is also considered. The sublattice magnetizations are necessary elements for certain spin dynamic computations, such as ballistic magnon transport across embedded nanojunctions in magnonics.