Study on spin control in N-VI diluted magnetic semiconductor composite structures

我们研究了(1)新型稀释磁性半导体（dms）的制备，(2)利用相变技术制备铁磁性精细结构，(3)对IV-VI复合GeTe基dms及其多结构的磁性能控制和自旋输运现象，并获得了以下结果：(1)采用射频溅射法制备了与三维过渡金属（从Ti到Ni）成分相近（x ~ 0.15）的GeTe基dms。除了Ge_<1-x>Mn_xTe外，Cr和Fe掺杂薄膜还观察到新的铁磁秩序。Fe掺杂薄膜的居里温度为100 K，载流子浓度低于其他铁磁GeTe基dms。(2)在顺磁性非晶Ge_<1-x>Mn_xTe薄膜中，通过聚焦激光束照射（光束光斑尺寸= 1），成功地形成了宽度为1.0 μ m的晶线。2 μ m^2)(3)为了控制上部Ge_<1-x>Mn_xTe层的矫顽力场，制备了Ge_<1-x>Mn_xTe/GeTe/Ge_<1-x>Mn_xTe/MnTe多层膜。在M-H迟滞中观察到中间肩，这表明两个Ge_<1-x>Mn_xTe层有选择性切换。多层膜的磁阻比为4.9%，比单层膜的磁阻比（0.37%）大一个数量级。成功制备了具有相同Mn组成但载流子浓度在10^<19>到10^<21> cm^<-3>范围内的Ge_<1-x>Mn_xTe薄膜。随载流子浓度的增加，自发磁化强度增大，矫顽力场减小。这表明通过控制载流子浓度实现选择性磁化开关的可能性。利用磁输运测量对磁相变进行了研究。与平均场模型相比，海森堡模型的临界指数值更接近海森堡模型

We have studied (1) the preparation of new diluted magnetic semiconductors (DMSs), (2) fabrication of ferromagnetic fine structure using phase change technique, and (3) magnetic property control and spin transport phenomena, for IV-VI compound GeTe based DMSs and its multi-structures, and obtained the following results(1) GeTe based DMSs having the similar composition (x〜0.15) of 3d transition metals (from Ti to Ni) have been prepared by a rf sputtering. Ferromagnetic order was newly observed for Cr and Fe doped films in addition to Ge_<1-x>Mn_xTe. The higher Curie temperature 100 K was obtained for Fe doped film with the lower carrier concentration than the other ferromagnetic GeTe based DMSs(2) The crystalline wire with 1.0 μ m width has been successfully formed in a paramagnetic amorphous Ge_<1-x>Mn_xTe film by irradiating a focused laser beam through the objective lens (beam spot size=l.2 μ m^2). After the irradiation, the ferromagnetic phase of crystalline wires was confirmed by b … More oth the M-H curves and magnetotransport measurements(3) In order to control the coercive field of upper Ge_<1-x>Mn_xTe layer, Ge_<1-x>Mn_xTe/GeTe/Ge_<1-x>Mn_xTe/MnTe multilayers were fabricated. The intermediate shoulder was observed in the M-H hysteresis, which suggested the selective switching in the two Ge_<1-x>Mn_xTe layers. The magnetoresistance ratio in multilayer is 4.9 %, which is one order larger than that in single layer (0.37 %). Ge_<1-x>Mn_xTe films having the same Mn composition but different carrier concentrations ranging from 10^<19> to 10^<21> cm^<-3> have been successfully prepared. The spontaneous magnetization increased and the coercive field decreased with increasing carrier concentration. This suggested the possibility of selective magnetization switching by controlling the carrier concentration. The magnetic phase transition has been investigated using magnetotansport measurements. The values of the critical exponents were close to those for the Heisenberg model than for the mean field model Less