روزنامه با شماره پیاپی سال 2011

4

112

115

Magnetic properties and magnetocaloric effects of amorphous and crystalline TbCuAl ribbons are investigated by measuring their ac susceptibilities including a nonlinear term and dc magnetizations. The in-phase third harmonic ac susceptibility χ 3 ′ is found to be negative. It can be well fitted by the expression χ 3 ′ = τ ε 3 γ at high temperatures, indicating a spin-glass behavior in amorphous TbCuAl alloy. Δ T f ( ω ) / [ T f ( ω ) Δ l o g 10 ω ] , a possible distinguishing criterion to judge the presence of a spin-glass behavior is ∼0.011. The frequency-dependent data can be well fitted by the conventional critical slowing down law and the spin-glass transition temperature is obtained to be 20.1 K. The maximum of magnetic entropy change reaches 4.5 J kg−1 K−1 for a field change of 0–50 000 Oe, while the crystalline TbCuAl compound experiences a simple ferromagnetic-to-paramagnetic phase transition. The peak value of magnetic entropy change is obtained at the Curie temperature and reaches 14.4 J kg−1 K−1 for the same field change, which is much larger than that of amorphous TbCuAl alloy.

Acta Tropica

2011

Acta Tropica