Transverse and longitudinal spin-fluctuations in INVAR Fe0.65Ni0.35.

ABSTRACT

The presence of spin-fluctuations deep within the ordered state of ferromagnetic [Formula see text] alloy [Formula see text] has long been suspected but seldom directly observed. Inhomogeneities of one type or another have been cited as important in stabilizing [Formula see text] behaviour-either longitudinal spin-fluctuations associated with the [Formula see text]-state (local environment) model or transverse magnetisation arising from non-collinear spin structures. In this study we employ small-angle neutron scattering with neutron polarization analysis to distinguish between the two possibilities. Surprisingly we in fact find evidence of dominant but uncorrelated longitudinal spin-fluctuations coexisting with transverse magnetisation which exists in short-range clusters of size ~[Formula see text]. This finding supports recent first principles calculations of [Formula see text] in which both longitudinal spin-fluctuations and magnetic short-range order are identified as important ingredients in reproducing the equilibrium [Formula see text] lattice.