TEMPERATURE-DEPENDENCE OF THE CIRCULAR MAGNETIC-X-RAY DICHROISM IN THE INVAR ALLOY FE72PT28

The method of spin-dependent absorption has been used to examine the t emperature dependence of the circular magnetic x-ray dichroism (CMXD) of the (disordered) Invar alloy fcc Fe72Pt28. At the Fe K edge the dif ference of the transmission for the reversed magnetization direction w as determined with an accuracy of 10(-5). By comparing the dichroic ef fects at 110 and at 410 K evidence was found for a temperature-depende nt change of the magnetic absorption profile different from the pure a mplitude reduction due to the reduced magnetization. It indicates a ch ange of the spin splitting in the low-lying unoccupied p states. The p olarization-averaged absorption spectrum shows also a small variation between 4 and 11 eV above the threshold indicating that the p-like ele ctron density drops when the sample is heated. The experimental CMXD p rofiles are compared with spin-polarized band-structure calculations f or ordered Fe3Pt and discussed within the frame of the model of high-s pin-low-spin transitions in the Invar regime.