MAGNETIC-PROPERTIES AND MAGNETIC PHASE-DIAGRAM OF THE FRUSTRATED CO1-XFEXPT3 COMPOUNDS

The investigation of the magnetic properties of the pseudobinary Co1-x FexPt3 L1(2) ordered compounds resulting From alloying the ferromagnet CoPt3 and the frustrated antiferromagnet FePt3 is reported. dc suscep tibilities and zero field cooled and field cooled magnetizations as a function of temperature and held (0-35 T) have been investigated. On t he Co-rich side (x<0.6), the compounds display a long-range ferromagne tic order characterized by the occurrence of two reentrant spin-glass phases (or mixed magnetic phases) at low temperature and magnetic fiel d starting at very low iron concentration. This ferromagnetic region i s closed by a multicritical point located around x=0.55 and T=120 K. O n the iron-rich side, an antiferromagnetic region with two antiferroma gnetic [1/21/20] and [1/200] structures is observed for 1 greater than or equal to x>0.8. Beyond 0.8 the basic antiferromagnetic order [1/21 /20] changes progressively into a spin-glass ordering and the less sta ble one [1/200] persists at low temperature up to Fe concentrations as high as 0.6. Although the complex behavior of the iron-rich side in t he intermediate region is not totally elucidated, a tentative phase di agram is proposed and discussed comparatively with the previously dete rmined (Fe-Mn)Pt-3 and (Co-Mn)Pt-3 phase diagrams. the occurrence of a spin-glass phase that separates the long-range ferromagnetic region f rom the antiferromagnetic one is specific to the (Co-Fe)Pt-3 system in agreement with theoretical models. The (Co-Fe)Pt-3 appears as the mos t frustrated among the three systems considered.