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The 1988 study grew alternating iron/chromium layers by molecular beam epitaxy on gallium arsenide. Magnetization and torque measurements tested the magnetic configuration. An AC electrical resistance measurement passed electric current along the layers while the applied magnetic field changed. Comparing field directions and spacer thicknesses linked the resistance decrease to magnetic saturation. Electron microscopy and surface analysis checked layer formation, while leaving atomic-scale interface roughness unresolved.^[ref]

The independent Jülich study used four-terminal sensing on epitaxial Fe/Cr/Fe strips. A single iron film supplied an anisotropic magnetoresistance comparison. Magneto-optic Kerr effect signals and Brillouin light scattering from spin waves identified the layer alignments, rather than inferring them from resistance alone. Field scans along different magnetic axes connected the optical signatures to the resistance changes.^[ref]

Peter Andreas Grünberg's retrospective explains why the preceding interlayer exchange coupling measurements mattered: coupled spin wave modes supplied signatures of magnetic alignment before that alignment became an electrical signal.^[ref]

A resistance curve alone does not reveal the microscopic direction of every magnetic layer. The optical measurements add a different observable, while the reference film tests an orientation-dependent response that can occur without a multilayer. Sample preparation and cross-checks therefore belong to the physical explanation.

Interlayer exchange coupling is an interaction that favors particular relative orientations of magnetization in different magnetic layers. In a metallic multilayer, spacer electrons can mediate coupling even when a nonmagnetic layer separates the magnets.

A simple model writes energy per area as $E/A=-J{\hat{\mathbf{m}}}_1\cdot {\hat{\mathbf{m}}}_2$. Positive $J$ favors parallel alignment and negative $J$ favors antiparallel alignment. Spacer material and thickness affect the coupling; magnetic-field sweeps can reveal the field needed to overcome it. Correlated interface roughness can instead produce orange-peel coupling, so a preferred alignment alone does not uniquely establish exchange mediation. ^[ref]

The spacer electrons mediate interlayer exchange coupling. Spin-dependent reflection at the two magnetic interfaces changes their electronic energy as the spacer thickness varies. In the oscillatory spacer-mediated exchange picture, Fermi-surface spanning wavevectors produce terms such as $J(t_2)\propto \cos (Q{t}_2+\phi )$ with a decaying envelope; real spacers can have several periods.

Define the coupling energy per area by $E_{\mathrm{ex}}=-J(t_2){\hat{\mathbf{m}}}_1\cdot {\hat{\mathbf{m}}}_2$. $J>0$ favours parallel moments and $J<0$ antiparallel moments. The oscillation period and phase depend on spacer band structure and interface reflection; there is no universal monotone rule or numerical crossover thickness from $t_2$ alone. Roughness and nonuniform thickness average and weaken the coupling. This is conduction-electron-mediated exchange, not a requirement that the nonmagnetic spacer itself be ferromagnetic.

An in-plane magnetic field lowers the Zeeman energy when moments align with it. It competes with antiferromagnetic interlayer exchange coupling; the layers generally cant or switch toward a parallel configuration and ultimately saturate if the field overcomes coupling and magnetic anisotropy. The high-resistance antiparallel state evolves toward the lower-resistance parallel state. The switching path and field scale depend on anisotropy, pinning and coupling strength, which are not numerically specified.