Interplay between reversible and irreversible magnetic phase transitions in polycrystallineGd5Ge4

Abstract

Temperature and magnetic field dependent magnetization and heat capacity of polycrystalline ${\mathrm{Gd}}_{5}{\mathrm{Ge}}_{4}$ have been measured. In addition to the antiferromagnetic ordering observed at the N\'eel temperature, ${T}_{N}=128\mathrm{K},$ there is a cusp at $\ensuremath{\sim}17.5\mathrm{K}$ in the low-field zero-field cooled (zfc) $M(T)$ curves, below which the zfc and field-cooled (fc) magnetic data exhibit irreversibility. The zfc and fc magnetization data show a complex mixture of reversible and irreversible behaviors at fields between $\ensuremath{\sim}10$ and $\ensuremath{\sim}18\mathrm{kOe},$ which is correlated to the magnetic field induced transitions between the antiferromagnetic (AFM) and the ferromagnetic (FM) states. The initial zfc $M(H)$ data below a certain temperature exhibit two transitions: a discontinuous metamagnetic-like transition and a continuous magnetic moment rotation process. The anomalies in the isofield and isothermal magnetization data indicate a complex magnetic structure at low temperatures, e.g., a complex canted AFM structure. In addition, magnetic field or temperature induced $\mathrm{AFM}\ensuremath{\leftrightarrow}\mathrm{FM}$ transitions occur under certain conditions. The unusual magnetic behavior is discussed in terms of a possible complex magnetic structure at low temperatures and a martensitic-like structural change induced by the magnetic field