Magnetic properties and magnetic phase diagram of the frustrated Co1-xFexPt3 compounds.

Abstract

The investigation of the magnetic properties of the pseudobinary ${\mathrm{Co}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Fe}}_{\mathit{x}}$${\mathrm{Pt}}_{3}$ L${1}_{2}$ ordered compounds resulting from alloying the ferromagnet ${\mathrm{CoPt}}_{3}$ and the frustrated antiferromagnet ${\mathrm{FePt}}_{3}$ is reported. dc susceptibilities and zero field cooled and field cooled magnetizations as a function of temperature and field (0--35 T) have been investigated. On the Co-rich side (x0.6), the compounds display a long-range ferromagnetic order characterized by the occurrence of two reentrant spin-glass phases (or mixed magnetic phases) at low temperature and magnetic field starting at very low iron concentration. This ferromagnetic region is closed by a multicritical point located around x=0.55 and T=120 K. On the iron-rich side, an antiferromagnetic region with two antiferromagnetic [1/21/20] and [1/200] structures is observed for 1\ensuremath{\ge}x\ensuremath{\gtrsim}0.8. Beyond 0.8 the basic antiferromagnetic order [1/21/20] changes progressively into a spin-glass ordering and the less stable 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 the intermediate region is not totally elucidated, a tentative phase diagram is proposed and discussed comparatively with the previously determined (Fe-Mn)${\mathrm{Pt}}_{3}$ and (Co-Mn)${\mathrm{Pt}}_{3}$ phase diagrams. The occurrence of a spin-glass phase that separates the long-range ferromagnetic region from the antiferromagnetic one is specific to the (Co-Fe)${\mathrm{Pt}}_{3}$ system in agreement with theoretical models. The (Co-Fe)${\mathrm{Pt}}_{3}$ appears as the most frustrated among the three systems considered. \textcopyright{} 1996 The American Physical Society.