Bhattacharyya A, Giri S, Majumdar S
Department of Solid State Physics, Indian Association for the Cultivation of Science, 2A&B Raja S C Mullick Road, Jadavpur Kolkata 700 032, India.
J Phys Condens Matter. 2009 Aug 19;21(33):336007. doi: 10.1088/0953-8984/21/33/336007. Epub 2009 Jul 28.
We study the effect of Ga doping at the Ge site of the metamagnetic compound Gd(5)Ge(4). For 5% Ga doping, the resulting alloy (Gd(5)Ge(3.8)Ga(0.2)) shows antiferromagnetic ordering around 130 K, and a thermally driven first order magneto-structural transition at low temperature leading to the ferromagnetic ground state. The alloy shows a noticeable amount of training effect in resistivity when thermally cycled through this first order phase transition (FOPT). The training effect is present in the case of isothermal field cycling. The FOPT region is found to be metastable and extremely sensitive to the applied magnetic field with a clear signature of a metamagnetic transition in the magnetization and resistivity. The metastability is further supported by the large relaxation observed in the resistivity. The giant magnetoresistance observed in the sample is found to be positive near the FOPT, while below the transition it is negative. The resistivity shows irreversibility due to field cycling, which is related to both a field-induced arrested state and some permanent micro-structural changes in the sample.
我们研究了在变磁化合物Gd(5)Ge(4)的Ge位点进行Ga掺杂的影响。对于5%的Ga掺杂，所得合金（Gd(5)Ge(3.8)Ga(0.2)）在约130 K附近呈现反铁磁有序，并且在低温下存在热驱动的一级磁结构转变，导致铁磁基态。当该合金通过此一级相变（FOPT）进行热循环时，其电阻率表现出明显的训练效应。在等温场循环的情况下也存在训练效应。发现FOPT区域是亚稳的，并且对所施加的磁场极其敏感，在磁化强度和电阻率中具有变磁转变的明显特征。电阻率中观察到的大弛豫进一步支持了这种亚稳性。在样品中观察到的巨磁电阻在FOPT附近为正，而在转变温度以下为负。由于场循环，电阻率表现出不可逆性，这与场诱导的停滞状态以及样品中的一些永久性微观结构变化有关。
