Spin-polarized metastable He study of surface magnetic order in Ho thin films

摘要

A spin-polarized metastable helium beam operating in magnetic fields of up to 5 T has been used to investigate the spin polarization at the surface of thin films of Ho(0001) grown on W(110) substrates. The extreme surface sensitivity of this technique allows a direct probe of the various magnetic structures that form as a function of film thickness, temperature, and applied magnetic field. Evidence for a transition from a conical ferromagnetic structure to a helical antiferromagnetic (AFM) phase is observed at low temperatures with a further transition to paramagnetism at close to the AFM ordering temperature, T_N. In addition, the spin polarization of the 6s CE that mediate the exchange interaction between localized Ho 4f moments (the RKKY interaction) is found to be positive, supporting earlier observations.