  We studied the relationship between the lattice constant and magnetism of
L10-ordered FePt under high pressure by means of first-principles calculations
and synchrotron x-ray measurements. Based on our calculations, we found that
the c/a ratio shows an anomaly at ~ 20 GPa and that the Pt magnetic moment is
sharply suppressed at ~ 60 GPa. As for the c/a, we experimentally verified the
anomaly at ~ 20 GPa by powder x-ray diffraction. We also measured the x-ray
magnetic circular dichroism at the Pt L edge up to ~ 20 GPa. Any significant
change of the Pt magnetic moment was not observed, in agreement with the
calculations. These results thus indicate the possibility that novel magnetic
states can be created in L10-ordered FePt by lattice deformation under high
pressure.
