Magnetic multilayers: Interlayer coupling in Fe/Cr/Fe

The exchange coupling between neighboring magnetic lavers in multilayer systems consisting of stacks of ferromagnetic layers separated by nonmagnetic metallic layers plays a central role in the properties of these novel artificially structured materials. Here we review the most common techniques for measuring this coupling, namely magneto-optical Kerr effect magnetometry, Brillouin light scattering and ferromagnetic resonance. The theoretical background for interpreting experimental data in trilayers formed by two magnetic layers separated by a nonmagnetic layer is presented, based on a phenomenological model energy including bilinear and biquadratic exchange couplings, as well as surface, in-plane uniaxial and crystalline cubic anisotropy contributions. Accurate quantitative values for the coupling constants and the other magnetic parameters are measured in the prototype system (100) Fe/Cr/Fe grown by sputtering for several Cr spacer thickness. Consistent values are obtained with all three techniques for both the bilinear (J(1)) and biquadratic (J(2)) exchange coupling constants. In most of the Cr thickness range corresponding to the first antiferromagnetic peak, J(2) follows J(1) with a ratio J(2)/\J(1)\ congruent to 0.1. In the range corresponding to the second antiferromagnetic peak J(2) also follows J(1), but with a much larger ratio J(2)/\J(1)\ congruent to 1.0, indicating that the origin of the biquadratic coupling in the two ranges resides in different mechanisms.