Magnetic anomalies in a new manganocuprate Gd3Ba2Mn2Cu2O12

The manganocuprate compound Gd3Ba2Mn2Cu2O12 (Gd-3222) has been synthesized by the conventional solid state reaction method and its magnetic behavior has been studied by dc and ac magnetization (M) and heat capacity (C) measurements as a function of temperature (T). This compound crystallizes in a tetragonal structure (space group I4/mmm). We find that this compound exhibits three magnetic transitions, around 2.5, 4.8 and 9 K, as inferred from dc and ac magnetic susceptibility (χ) data. However, no evidence for a well-defined λ-anomaly is found in C(T) above 1.8 K, though there is a gradual upturn below about 10 K. An application of a magnetic field results in a peak around 5 K, while ac χ appears to show a very weak frequency dependence below 9 K. The isothermal M curve at 1.8 K exhibits a weak hysteresis without any evidence for saturation even at fields as high as 12 T. These results indicate that this compound possibly undergoes a spin-glass-like freezing at low temperatures, though the exact nature of the magnetic transition at 10 K is not clear. The magnitude of the magnetocaloric effect, as inferred from M and C data, is quite large over a wide temperature range below 50 K peaking around 4 K.