Cluster spin glass state caused by antiphase boundaries in NiFeGa alloys

We report an observation of magnetic glassy properties in NiFeGa ferromagnetic shape memory alloys. A cluster spin glass transition was observed at approximately 27 K in Ni50Fe21Ga29. The glassy property originates from the freezing of fine magnetic domains separated by antiphase boundaries (APBs). Due to the pinning effect of the APBs, depression of the magnetization just below the Curie temperature was observed. The pinned domains induce very large saturation fields and a nearly random distribution of magnetization in low field. Based on dynamic magnetic measurements, the frequency dependence of the spin-glass transition was investigated by using the Vogel-Fulcher law and a power law. Below the freezing temperature, an aging phenomenon was observed and described by stretched exponential functions. These theoretical investigations confirm the cluster spin-glass state, which originates from a strong interaction between the frustrated magnetic domains.