Heat capacity of Ni-doped Bi2Sr2CaCu2O8 single crystals

The specific heat of Ni-doped Bi2Sr2CaCu2O8 crystals has been measured betw een 0.035 and 2 K in magnetic fields up to 9 T. Both pure and doped samples display identical low-temperature nuclear Schottky anomaly tails at T < 20 0 mK. The difference between the specific heat of the Ni-doped sample and t hat of the pure one is a broad peak centered at about 1 K. Applied magnetic fields move the peak to higher temperatures, which is consistent with spin glass-like behavior of the impurity atoms. Freezing of magnetic impurities may be related to the observation of a second low-temperature transition i n several of the Ni-doped samples. (C) 2000 Elsevier Science B.V. All right s reserved.