Search for noncollinear moments at Permalloy/copper interfaces

Recent first-principles electronic structure calculations have shown a tendency for atomic moments near interfaces between Permalloy (e.g., Ni80Fe20) and Cu to become noncollinear with the bulk magnetization direction. One signature of noncollinear moments should be a differential susceptibility at high fields (i.e., above the nominal saturation field) corresponding to a twisting of the noncollinear moments against the exchange fields in the material. We have measured the differential susceptibility for a series of sputtered Permalloy/Cu multilayers and compared it with the bulk (thick Permalloy) film. We have identified a magnetic contribution due to noncollinear moments at the interfaces corresponding to 0.1-0.3 monolayers. Further, we show that the temperature dependence of the differential susceptibility is not consistent with paramagnetic moments, supporting the idea that exchange-driven noncollinearity is present. (C) 2003 American Institute of Physics.