Anomalous Magnetic Properties of Tb/Cr/Ta Film Above Curie Temperature
Magnetic properties of Tb/Cr/Ta film, for which the Curie temperature (TC) of ferromagnetic Tb is much lower than the Néel temperature (TN) of antiferromagnetic Cr, have been investigated. An apparent TC beyond that of pure Tb film was observed. The origin of this enhancement of TC is due to a magnetic proximity effect between Tb and Cr. In the temperature range of TC < T < TN, the coercivity HC and exchange bias field HE of the film show unusual temperature dependence. As the temperature increases from TC to TN, HE still exists and its sign changes from negative to positive with a low cooling field. At T > TN, HE turns to vanish. The coercivity HC exists not only at TC < T < TN, but also above TN. These unusual results can be discussed in terms of the pinned uncompensated spins and rotatable uncompensated spins in the interface. Additionally, the magnitude of the cooling field has a strong effect on HE, which probably results from the competition between the exchange coupling energy at the Tb/Cr interface and the Zeeman energy of the Cr surface magnetization.