X-ray spectroscopy aids understanding of how magnetic refrigeration works

Scientists at Argonne National Laboratory and Ames Laboratory, Iowa State University, have recently performed X-ray magnetic circular dichroism (XMCD) measurements of giant magnetocaloric material, Gd₅(Ge_1-xSi_x)₄. It was found that germanium becomes magnetic by spin-dependent hybridization between Ge 4p and Gd 5d. This hybridization can change at the germanium-silicon bond-breaking transition, causing the destruction of magnetic ordering and leading to the giant magnetocaloric effect. By combining the experimental results with calculations based on density functional theory, it was concluded that the magnetized germanium orbitals act as "magnetic bridges" in mediating the magnetic interactions across the distant gadolinium ions. For more information, see the paper, "Role of Ge in Bridging Ferromagnetism in the Giant Magnetocaloric Gd₅(Ge_1-xSi_x)₄ Alloys", D. Haskel et al., Phys. Rev. Lett., 98, 247205 (2007).