Thermal dependence of the longitudinal spin fluctuations in YMn2

Abstract

Below 100 K, YMn2 orders antiferromagnetically with a long period spiral structure. The transition to the paramagnetic state is first order accompanied by a 5 % reduction in volume. Above TN the uniform susceptibility increases with temperature. The addition of 10 % Al suppresses the transition temperature and the susceptibility becomes Curie-Weiss. On the basis of bulk measurements it has been proposed that the volume change in YMn2 is associated with the collapse of the Mn moment and that the paramagnetic properties are characterized by strong longitudinal spin fluctuations. The magnetic properties of Y(Mn0.9Al0.1) 2 are believed to be of a local nature. Using polarized neutrons and polarization analysis the paramagnetic scattering from the two compounds has been investigated as a function of temperature up to 300 K. The results obtained on YMn2 reveal substantial scattering at all temperatures which remains strongly enhanced about the staggered antiferromagnetic wave vector. Moreover the amplitude of the long wavelength components of the spin fluctuations increases with increasing temperature. Therefore YMn2 represents an excellent system for studying itinerant antiferromagnetism. In the case of Y(Mn0.9Al0.1)2 the enhanced scattering becomes weaker as the temperature is raised as expected for local behaviour