Professor Stephen Blundell

Abstract:

Implanted muon spectroscopy shows that magnetic order coexists with superconductivity in TmNi2B2C. The muon response indicates that large amplitude fluctuations of the internal field are superimposed on a relatively small static component. The static field exhibits an unusual temperature dependence which shows no interruption at the superconducting transition and may represent evolution of a staggered or spiral arrangement of Tm moments. The dynamic component changes its spectral density at the superconducting transition and the question arises as to whether this is associated with Ni moment formation and fluctuation. In LuNi2B2C, where the rare earth ion is nonmagnetic, no signature of static order is seen. An intriguing change in the muon response does occur below about 4 K in this material; this seems suggestive of Ni moment fluctuation, although the evidence is not entirely conclusive.

Abstract:

We have used polarized neutron reflection to determine the layer-dependent spin orientations in an antiferromagnetically coupled 100 Angstrom Cr/50 Angstrom Fe/15 Angstrom Cr/50 Angstrom Fe/Si sandwich structure prepared by sputtering. At low field, the net Fe layer magnetic moments align in an asymmetric canted orientation with a near zero total magnetic moment for the sample. At high fields, a canted state, nearly symmetric with respect to the applied field direction is observed and the magnetization in each layer does not reach the bulk saturation value until the layers are ferromagnetically aligned. The behavior is discussed in the context of current theories of exchange coupling. (C) 1996 American Institute of Physics.