GREAT MAGNETIC ENTROPY CHANGE IN La(Fe, M)13 (M=Si, Al) WITH Co DOPING

Very large magnetic entropy change Δ S_M, which originates from a fully reversible second-order transition at Curie temperature T_C, has been discovered in compounds La(Fe, Si)₁₃, La(Fe, Al)₁₃ and those with Co doping. The maximum change ΔS_M\approx19 J·kg^-1·K^-1, achieved in LaFe_11.4Si_1.6 at 209K upon a 5T magnetic field change, exceeds that of Gd by more than a factor of 2. The T_C of the Co-doped compounds shifts to higher temperatures. ΔS_M still has a considerable large magnitude near room temperature. The phenomena of very large ΔS_M, convenience of adjustment of T_C, and also thesuperiority of low cost, strongly suggest that the compounds La(Fe, M)₁₃ (M=Si, Al) with Co doping are suitable candidates for magnetic refrigerants at high temperatures.     

MgB2超导块材的非线性磁弛豫性质的研究

在32－34K温度和0．5T初始磁场中，MgB2超导块材的磁弛豫性质通过剩余磁化强度M随时间t的变化进行了研究，在初始阶段，M－lnt明显偏离线性，磁通运动接近Zeldov时数模型，足够长的时间后，M-lnt呈现很好的线性，磁通运动符合Anderson-Kim模型。     

熔融织构块材和单晶YBa2Cu3O7在63～75K的磁弛豫性质

本文研究了熔融织构块材和单晶YBa2Cu3O7在液氮温区63～75K的磁弛豫性质.在此温区常数ωa是与温度相关的，平均有效结合能作为电流密度的函数和Zeldov模型一致.     

高温超导体中磁通涡旋的量子隧道效应——TIBaCaCuO化合物磁弛豫…

本报道了ＴＩＢＡＣａＣｕＯ超导体（２２１２，２２２３单相，多晶及薄膜材料）中磁弛豫现象的实验结果，从实验上证实了能量运动由热激活到非热激活机制的转变，实验中得到与温度无关的磁弛豫速率与由通量运动量子隧道效应理论计算结果相一致，同时讨论了各向异性和磁场对磁通的量子漂移速率的影响。     

CURRENT-DEPENDENT POSITIVE MAGNETORESISTANCE IN Ga-DOPED La0.5Ca0.5MnO3

The magnetic and transport properties of the Ga-doped charge-ordering state La_0.5Ca_0.5MnO₃ have been studied. A current-dependent large positive magnetoresistance (1080%) at 5 K was observed. These observations are interpreted in terms of the spin-dependent tunnelling process between ferromagnetic clusters embedded in an antiferromagnetic matrix.