Ferromagnetic Resonance in Co hcp and fcc Single Crystal Films on MgO

Epitaxial Co fee and hcp thin films were studied by ferromagnetic resonance (FMR) and magnetization (M) measurements. Fcc Co(001)(50 nm thick) was obtained by rf sputtering on MgO(001), having Co [100] parallel to MgO [100] as observed by x-ray diffraction. Using FMR we determined the cubic anisotropy field, K-l(c)/M (100K < T < 300K), A variation of over 10% of the effective demagnetization field was observed on going from 100K to 300K. Hcp Co (50 nm thick) was grown by incorporating a 20nm Cr(211) buffer layer on MgO(110). X-ray diffraction and FMR results show that the epitaxial relations are Co(10 (1) over bar 0) parallel to MgO(110) and Co [0001] parallel to MgO [001]. From magnetization measurements we obtained the uniaxial anisotropy fields, K-1/M and K-2/M as a function of T.