Neutron scattering studies of materials near the magnetic phase transition

Abstract

Metals on the verge or just in the weakly magnetic state offer a unique testing ground for current theories of itinerant magnetism. Three investigations of such systems using neutron scattering are outlined in this work. TiBe(_2) is of interest since the random substitution of copperat Be atom sites expands the lattice allowing one to cross the threshold from an incipient to a weakly magnetic state. Small angle neutron scattering studies of spin density fluctuations in TiBe(_1.5) Cu(_0.5) have shown that a single phenomonological model is sufficient to describe the collected integrated intensities above and below the magnetic phase transition temperature. Observations below the transition temperature may be attributed to scattering from damped spin waves. Polarised neutron diffraction studies of a single crystal of ZrFe(_2) are in contradiction with reported band structure calculations of a strong ferrimagnetic ground state. The magnetic distribution in real space around the Fe ions is highly spherical and the form factor closely follows that of free Fe ions in reciprocal space. A small angle neutron scattering investigation of the helical spin wave density wave in MnSi below the magnetic phase transition and spin density fluctuations in the paramagnetic regime under hydrostatic pressure has been performed.