High-pressure Moessbauer studies of magnetism in ScFe2 and Sc0.4Ti0.6Fe2 Laves phases

We report on 57Fe-Moessbauer studies of the magnetic properties in ScFe2 and Sc0.4Ti0.6Fe2 performed as a function of pressure and temperature. Both systems crystallize in the C14-type Laves phase structure with two different Fe sites 6h and 2a. The ferromagnetic properties of ScFe2 (TC = 540 K at ambient pressure) change around 30 GPa to antiferromagnetic order of the 6h sites with non-magnetic 2a sites. The ordering temperature is lowed to TN = 300 K at 51 GPa. This pressure-dependent behaviour of ScFe2 resembles that observed within the Sc1-xTixFe2 series as a function of x. In ferromagnetic Sc0.4Ti0.6Fe2 we observe, as a function of temperature and of pressure, an abrupt high-moment to low-moment transmission of the Fe band moments of the 6h sites, accompanied by a rearrangement of the spin directions. In both systems the decrease of the Fe moments is accompanied by a strong increase in the volume coefficient of the isomer shift, originating from a reduced s-electron shielding capability of the d-electrons in the low-moment state. (author)