Magnetic Profile of Ferrimagnetic Fe-Gd Alloy Thin Films with Varying Thickness*

Rare earth (RE) / transition metal (TM) ferrimagnet alloys exhibit an intriguing magnetic compensation of the RE/TM magnetic sublattices as a function of composition and temperature and this tunability of magnetization and electronic structure makes these alloys suitable in spintronics. We developed compositionally fixed Fe_1-xGd_x [DA1] [JS2] [JS3] films with x ≈ 28% that vary in thickness from 100nm to 25nm.  While the composition is fixed in these films, the magnetization compensation temperature T_MagComp, determined from bulk magnetometry, varies from 25K to over 300K.  We utilized polarized neutron reflectometry (PNR) to examine this effect.  As PNR probes the magnetization parallel to the field as a function of depth, it is an ideal technique to investigate the temperature evolution of these films as the magnetic scattering length density (mSLD) changes drastically as the temperature is varied through T_MagComp.  We conducted PNR studies of our Fe-Gd samples as a function of temperature and film thickness.  The PNR scans suggest that large changes in the mSLD occur near the interfaces with the seed and cap layers and the observations indicate that the evolution of the magnetic interfaces is nontrivial.