Neutron Reflectivity Study in Py/CoO Exchange Bias System

We have studied the permalloy-cobalt monoxide exchange bias system using polarized neutron reflectivity. Both polycrystalline and epitaxial single crystalline (with the (111) and (100) CoO planes at the interface) CoO films were studied. By fitting the reflectivity for both directions of the applied field relative to the cooling field, we are able to obtain both the nuclear and spin depth profiles, as well as locating the pinned spins which are responsible for the exchange bias effect. The pinned spins at the interface can be resolved in the polycrystalline sample, which is consistent with our previous study with resonant soft x-ray reflectivity. One could reasonably have expected a stronger exchange bias effect in the (111) single crystal CoO film, because it has more uncompensated spins at the interface. The neutron reflectivity, however, shows lesser pinned spins. In the presentation, we will show the difference between the magnetic density profiles of the samples involving polycrystalline, (111) and (100) single crystalline CoO films respectively.