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

我们研究了(1)新型稀磁半导体(DMS)的制备，(2)利用相变技术制备铁磁精细结构，(3)对IV-VI化合物Gete基DMS及其多结构的磁性控制和自旋输运现象进行了研究，得到了以下结果：(1)用射频溅射方法制备了具有相似成分(x~0.15)的3D过渡金属(从钛到镍)的Get基DMS。除了Ge&lt；1-x&Gt；MnxTe外，还观察到了新的掺铬和掺铁薄膜的铁磁有序。当载流子浓度较低时，Fe掺杂薄膜的居里温度比其他铁磁性Gete基DMS的居里温度高100K。(2)用聚焦的激光束通过物镜(光束光斑尺寸=1μm^2)，在顺磁性非晶Ge_(1-x)Gt；Mn_xTe薄膜中成功地形成了宽度为1.0μm的晶线。辐照后，用b-…确定了晶丝的铁磁性相。(3)为了控制上层Ge_x&Gt；Mn_xTe层的矫顽场，制备了Ge_&lt；1-x&gt；Mn_xTe/GeTe/Ge_&lt；1-x&gt；Mn_xTe/MnTe多层膜。在M-H磁滞中观察到中间肩部，这表明Ge_(1-x)&Gt；Mn_xTe两层中存在选择性开关。多层膜的磁电阻率为4.9%，比单层膜的磁阻率(0.37%)大一个数量级。已经成功地制备了具有相同Mn组分但不同载流子浓度的Ge_x；1-x；Mn_xTe薄膜，载流子浓度从10^&lt；19&gt；到10^&lt；21&gt；cm；-3。自发磁化强度随载流子浓度的增加而增大，而矫顽场随载流子浓度的增加而减小。这表明了通过控制载流子浓度来实现选择性磁化转换的可能性。用磁输运测量方法研究了磁相变。临界指数的值与海森堡模型相近，而平均场模型的数值要小一些。

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