Electronic and magnetic structures of Fe/Cr/Fe sandwiches and Fe/Cr superlattices

Studies of Exchange Coupling in Fe (001) Whisker/Cr/Fe Structures using BLS and Rheed Techniques

The conditions for an almost perfect growth of smooth Cr (001) films on an iron whisker substrate have been investigated by means of reflection high energy electron diffraction (RHEED). The exchange interaction between 20 Monolayer thick Fe (001) films separated from a bulk whisker Fe (001) substrate by a variable number of Cr (001) Monolayers (ML) has been investigated by means of Brillouin light scattering experiments (BLS). These experiments show unambiguously that the exchange coupling strength between the iron film and the iron whisker can be described by a short wavelength oscillatory term superposed on a slowly varying antiferromagnetic background. The BLS data enabled one to separate the bilinear and the biquadratic contributions to the antiferromagnetic exchange coupling terms. Both the bilinear and the biquadratic coupling strengths exhibited a short period oscillatory dependence on the Cr interlayer thickness (∼2 Monolayers). Maxima in the bilinear antiferromagnetic coupling strength occur for an odd number of Cr Monolayers. This observation is not in agreement with first principles calculations. The first phase inversion has been found to occur between 4 and 5 ML of Cr.

Theory of Magnetoresistance in Magnetic Superlattices

The origin of the giant magnetoresistance observed recently in Fe/Cr, Co/Cu and Co/Cu /NiFe/Cu metallic superlattices is attributed to random exchange potentials at interfaces in the superlattices. Material dependence of the magnetoresistance is studied for Fe/TM and TM/Cu superlattices, where TM's denote 3d-transition metal elements.

Electronic Structure, Magnetic Order and Interlayer Magnetic Couplings in Metallic Superlattices

The general trends for the electronic structure of perfect model superlattices AmBn are calculated using a real-space tight-binding model. The magnetic moments distribution and the interlayer magnetic couplings between ferromagnetic layers Am (A=Fe or Co) coupled by non-magnetic (B=V or Ru), nearly ferromagnetic (B=Pd) or antiferromagnetic (B=Cr) spacer layers Bn are obtained as a function of the spacer thickness n.

In a first part, we present the model we used for the calculation and the crystallographic structure of the considered superlattices (Fe/V, Fe/Cr, Co/Ru and Co/Pd). These considerations will be applied to the non-magnetic and nearly ferromagnetic cases to derive general trends for the magnetic interlayers couplings.

In a second part, we apply the method we presented previously to the superlattices with an antiferromagnetic spacer (Fe3Crn). Using first a “d” band calculation we show that the interlayer coupling energy can be understood in terms of a strong interfacial antiferromagnetic coupling and of a constrained magnetic wall in the Cr layer giving a rapidly oscillating coupling energy. An extension of the previous calculation taking into account the “spd” hybridization does not affect the previous conclusion. Finally we examine the distribution of magnetic moments and the stability of tilted antiferromagnetic Cr layers and we find that this magnetic structure is nearly degenerate with the collinear antiferromagnetic arrangement.