1. Brillouin Light Scattering Studies of Magnetic Multilayers Cyrus Reed, Milton From Department of Physics and Astronomy, Western Washington University What are they? Ultrathin magnetic layers of ferromagnetic material separated by non-magnetic spacer layers. Individual layers are typically 1 to 20 atoms thick. Multilayers are grown by magnetron sputtering or by Molecular Beam Epitaxy Magnetic Multilayers Present uses of Magnetic Multilayers Magnetic Field Sensors Read Heads for computer hard disks Galvanic Isolators Magnetic multilayers: technology of the future? MRAM (Magnetoresistive random access memory): IBM, Honeywell, Motorola, Hewlet Packard all have substantial development activities SPINTRONICS: One possible road to Quantum computing is to use magnetic multilayers to inject spin polarized electrons into semiconductor devices. Brillouin Light Scattering (BLS) The volume of material which BLS probes is a few cubic microns in size. Thus it is ideally suited to magnetic multilayer geometries. BLS provides a way of measuring the magnetic surface anisotropy of magnetic films. Understanding this anisotropy is of key importance in the development of spin- injection contacts in semiconductor devices. BLS is a non-destructive technique which uses laser light to investigate magnetic excitations in a material. Using BLS to characterize a magnetic material: a two-step process Step 2 Fit a model calculation to the data. Model parameters are: Perpendicular anisotropy (K) Interlayer exchange coupling (J) Uniform magnetization in each magnetic film (M) Step 1 When light is scattered from a magnetic sample the light’s frequency will be shifted by magnetic excitations in the material. Measure this frequency as a function of applied magnetic field with a scanning Fabry-Perot Interferometer. Schematic diagram of the BLS apparatus Photo of the scanning interferometer being built at WWU. An example case study: Fe/Pd multilayers Are the excitations present in a Fe/Pd nanostructure compatible with elementary spin-wave theory? What is the magnetic anisotropy imposed on the Fe by the Pd? Is the bulk moment of the Fe atoms affected by the presence of Pd? Questions:Samples used in the study: 6 samples: x=6, 12, 18, 29, 32, and 43 Prepared by magnetron sputtering Dependence of the BLS spectra on applied magnetic field Dependence of BLS spectra on Pd thickness Sample: [Fe 15Å /Pd x ] x 25, Magnetic field = 2kOe Conclusions A single parameter fit to our data yields the correct BLS peak height ratios and field dependence for individual samples. Thus the data is in agreement with simple spin-wave theory. The observed anisotropy parameter depends on Pd thickness. It falls in the range 0.12<K<0.4 ergs/cm 2 The varying K value may be a sign that the moment of the Fe atoms is affected by Pd. Mossbauer spectroscopy and magnetometry experiments are currently being done to test this hypothesis. Acknowledgements: The BLS data presented here was collected by us on apparatus at Simon Fraser University (Vancouver, Canada). Samples were made at the Center for Materials Research at McGill University (Montreal, Canada).Thanks to Li Cheng and Zaven Altounian for sample preparation and structural characterization.