CONTROL OF SPIN CONFIGURATION OF MAGNETIC ULTRA-THIN FILMS

巨磁阻（GMR）效应已经在各种各样的材料中被发现。然而，迄今为止关于非晶材料的报道很少。由于非晶磁性薄膜通常具有优异的软磁性能，如低矫顽力、高磁导率和相对较高的电阻率，因此常用于电感式读出头。对于GMR，我们发现使用非晶CoFeB的自旋阀具有相对较大的MR比率，为4%至6%。这些值与晶体NiFe自旋阀相当甚至更大。B含量为0 ~ 10atm的NiO/CoFeB/Cu/CoFeB自旋阀。研究了巨磁阻效应与自由磁层厚度的关系。在自旋阀中，即使自由磁层非常薄到1或0.5 mm，也可以观察到巨磁阻效应。当B含量较低时，随着自由磁层厚度的增加，磁流变率迅速增加，而当B含量较高时，磁流变率在厚度处达到最大值，该厚度与磁性层中电子的平均自由程大致相等。利用Camley - Barnas模型，考虑电子在磁性层与非磁性层界面处的镜面反射，可以一致地解释磁阻比和电阻率的值。

Giant magnetoresistance (GMR) effect has been found in a wide variety of materials. Concerning amorphous materials, however, very little has been reported so far. Since amorphous magnetic films have usually excellent soft magnetic properties, such as low coercivity, high permeability and relatively high resistivity, they have been often applied for inductive readout heads. For the GMR, we found that spin valves using amorphous CoFeB exhibit relatively large MR ratios of 4 to 6%. These values are comparable to or even larger than those of crystalline NiFe spin valves. NiO/CoFeB/Cu/CoFeB spin valves with B content of 0 to 10 atm.% were prepared to investigate the dependence of the giant magnetoresistance effect on the thickness of free magnetic layers. In the spin valves, giant magnetoresistance effects were observed even when the free magnetic layers were very thin down to 1 or 0.5 mm. For lower B content, the MR ratio rapidly increased with the increase of the thickness of free magnetic layers, while for higher B content, the MR ratio exhibited the maximum at the thickness which is roughly equal to the mean free path of electrons in the magnetic layers. By using Camley - Barnas model, the value of the MR ratio and the resistivity can be consistently explained if the specular reflection of electrons is considered at the interface between magnetic and nonmagnetic layers.