Experimental evidence of the formation of a reentrant spin-glass phase in alloying two ferromagnetic CoPt3 and MnPt3 compounds.

Abstract

The magnetic properties and the magnetic phase diagram of the pseudobinary ${\mathrm{Co}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Mn}}_{\mathit{x}}$${\mathrm{Pt}}_{3}$ system resulting from alloying two ferromagnetic ${\mathrm{CoPt}}_{3}$ and ${\mathrm{MnPt}}_{3}$ compounds have been investigated. Structural and microstructural characterizations added to thorough preparation conditions yield well-ordered samples having the L${1}_{2}$ structure, large ordered domains, and a long-range order parameter close to its maximum value. Magnetic properties including ac and dc susceptibilities, zero-field-cooled and field-cooled magnetizations as a function of temperature and field (0--35 T) have been investigated. The resulting magnetic phase diagram displays, below a ferromagnetic region spreading over the whole (0\ensuremath{\le}x\ensuremath{\le}1) concentration range, a reentrant spin-glass phase for 0x0.8, characterized by the coexistence of ferromagnetic and spin-glass orderings. This phase diagram is well described in the theoretical infinite-range model of Gabay and Toulouse. The randomness of the average exchange interaction is suggested to arise from competing magnetic interactions between the positive values of ${\mathit{J}}_{\mathrm{CoCo}}^{2\mathrm{n}\mathrm{d}}$ and ${\mathit{J}}_{\mathrm{MnMn}}^{2\mathrm{n}\mathrm{d}}$ and the negative value of ${\mathit{J}}_{\mathrm{CoMn}}^{2\mathrm{n}\mathrm{d}}$ for 3d atoms in position of second-nearest neighbors. \textcopyright{} 1996 The American Physical Society.