Magnetic leverage effects in amorphous heterostructures
Dr Tom Hase (Warwick)
I will discuss our recent use of resonant x-ray scattering to explore the element specific magnetization and structure in amorphous heterostructrues. After introducing the techniques, we will report our recent measurements on amorphous SmCo/CoAlZr tri-layers in which the magnetic properties were tuned through the layer composition and temperature. Experiments were performed as a function of temperature and applied magnetic field with the photon energy tuned to the soft (<1 keV) Sm M4 and M5 as well as Co L3 edges. The tri-layer sample has a magnetically hard SmCo layer which pins the CoAlZr layers whose ordering temperature is controlled by their relative Co:AlZr ratio. When combined in the trilayer, a two-step reversal process is observed in hysteresis loops recorded at the Co edge, but loops probing the Sm moment show a more gradual reversal with a different saturating field. These data suggest a decoupling of the Sm and Co sub-lattices within the SmCo layer. We also find evidence of an exchange bias even at temperatures when the middle CoAlZr layer is expected to be paramagnetic. The presence of exchange bias is evidence of an apparent magnetic inter-layer exchange coupling spanning a 40 nm paramagnetic layer. We argue that the observed decoupling of the sub-lattices and the exchange bias arises from local variations in the magnetic exchange associated with the distribution of atomic species within the amorphous matrix and introduce a toy model based on percolation effects to explain the data.