Biquadratic Exchange Coupling in Sputtered (100) Fe/Cr/Fe

We have used Brillouin light scattering, ferromagnetic resonance, magneto-optical Kerr effect, and magnetoresistance to investigate interlayer exchange coupling in $\mathrm{Fe}\left(40Å\right)/\mathrm{Cr}\left(t\right)/\mathrm{Fe}\left(40Å\right)$ trilayers grown onto MgO(100) in UHV. Unprecedented strong room-temperature biquadratic exchange coupling (BEC) was found for values of the Cr thickness $t$ corresponding to a region where Fe layers are weakly antiferromagnetically coupled. A common feature in both magnetic and transport measurements, which we take as a signature of the BEC, is the presence of sudden discontinuous jumps as the external magnetic field is varied. The results are in excellent agreement with model calculations that coherently take into account the same phenomenological parameters characterizing the anisotropy, Zeeman, and bilinear and biquadratic exchange energies.