Magnetic phase diagram of disordered Ni-Mn near the multicritical point

Abstract

From detailed magnetization data taken under various field-cooling conditions, the magnetic phase diagram of temperature versus composition is determined for disordered Ni-Mn of Mn concentration (x) near 25 at. %. With increasing x, the ferromagnetic Curie-point (${T}_{c}$) line descends and meets the ascending line for the spin-glass reentrance temperature (${T}_{\mathrm{fg}}$) at a multicritical point (MCP) located at x=23.9, T=102 K, from which the spin-glass freezing-temperature (${T}_{g}$) line emerges and reaches a maximum at higher x. The reentrant spin-glass (SG) ordering is accompanied by a net ferromagnetic (FM) moment, thus describing a mixed ferro-spin-glass (FSG) state, which is separated from the normal SG state by a boundary line that extends essentially vertically down in temperature from the MCP. Moreover, it is shown that the SG ordering of the FSG state probably persists into the FM regime above ${T}_{\mathrm{fg}}$, where ${T}_{\mathrm{fg}}$ (like ${T}_{g}$) remains defined operationally by the appearance of irreversible and time-dependent magnetic effects.