Magnetic coupling through Cr: Study of spin polarization in Cr and film-growth effects

The interlayer magnetic coupling of polycrystalline Fe/Cr/Fe and ${\mathrm{Ni}}_{80}$ ${\mathrm{Fe}}_{20}$/Cr/${\mathrm{Ni}}_{80}$ ${\mathrm{Fe}}_{20}$ trilayers has been studied with spin-polarized secondary-electron emission (SPSEE) and magneto-optic Kerr effect. The exchange coupling between the two magnetic layers is observed to oscillate between ferromagnetic and antiferromagnetic as a function of Cr spacer thickness. The sign of the coupling depends on the temperature at which the trilayer structures are grown but is not affected by further changes due to contamination or interdiffusion (∼2 atomic layers) at the interface resulting from post deposition thermal cycling up to 450 K. A ${\mathrm{Ni}}_{80}$ ${\mathrm{Fe}}_{20}$/(12 Å Cr)/${\mathrm{Ni}}_{80}$ ${\mathrm{Fe}}_{20}$ structure deposited at T=90 K is antiferromagnetically coupled for T=90–450 K, whereas the same structure deposited at 300 K shows a reversible transition between ferromagnetic and antiferromagnetic coupling as a function of temperature between 180 and 330 K. SPSEE measurements of Cr overlayers on both Ni-Fe and Fe set an upper limit to Cr polarization effects at 2×${10}^{\mathrm{-}3}$, which has important ramifications for theoretical attempts to understand the coupling mechanism.