Effect of hydrostatic pressure upon the magnetic transitions in the Gd₅(Si_xGe_1−x)₄ giant magnetocaloric compounds: X-ray magnetic circular dichroism study

The pressure dependence of the magnetic transitions in the giant magnetocaloric materials Gd₅(Si_xGe_1−x)₄ (x=0.125,0.5) has been investigated using x-ray magnetic circular dichroism (XMCD) measurements in a diamond anvil cell (DAC). We found that the most notable features of the x-T phase diagram are also present in the P-T phase diagram. These include a nearly linear increase in Curie temperature, T_c, with increasing both x and P up to 275 K, and a discontinuity accompanied by a change in slope, dT_c∕d(x,P), at this temperature. However, the results indicate that a similar volume change results in ∼3 times larger increase in T_c with Si doping than with pressure. Si doping, hence, does more to stabilize ferromagnetic interactions than simply uniformly reducing the unit cell volume.