Polarized neutron reflectometry from the interface of the heterostructures SiO2(Co)/Si and SiO2(Co)/GaAs

Polarized neutron reflectometry is used to investigate SiO2(Co) granular films (70 at% of Co nanoparticles in SiO2 matrix) deposited on Si and GaAs substrates. The aim of the study is to compare magnetization depth profiles in two systems: in SiO2(Co)/GaAs heterostructure which shows at room temperature giant injection magnetoresistance (IMR) with the system SiO2(Co)/Si which reveals almost no IMR effect. We found that at room temperature and at the same value of external magnetic field mean magnetization in the SiO2(Co)/GaAs sample is much higher than in the case of SiO2(Co)/Si. We also demonstrate that magnetic scattering length density, and hence, magnetization profile strongly depends on the substrate. We show that SiO2(Co)/Si heterostructure is ferromagnetically ordered within the temperature range between 120 and 460 K what could explain a weak IMR.