Soft Phonons and Magnetic Ordering in the gamma -Phase Transition Metal Alloys Fe/sub 1-X/Pd/sub X/

摘要

Neutron inelastic scattering measurements have been performed on two single crystals of the thermally quenched gamma -phase (fcc) alloy, Fe/sub 1-x/Pd/sub x/ with x = 0.28 and x = 0.37. The x = 0.28 sample which orders ferromagnetically at T/sub c/ = 575 K exhibits a smeared structural transition into an fct phase near T/sub M/ = 265 K. An anomalous dispersion of the (xixi0)TA1 branch due to the decrease of the phonon energy around the GAMMA point develops below T/sub c/. As the temperature decreases, the branch decreases in energy. The anomalous part of the elastic constant, delta (C sub 11 -C sub 12 )/2, follows the same temperature dependence as the square of the magnetization. On the x = 0.37 sample which has no structure transition, the phonon anomaly is much weaker. For both crystals the other branches exhibit normal behavior. (ERA citation 06:034043)