Magnetic and Optical properties of artifical superlattice

磁性超晶格包括铁磁层和抗磁层，它们具有诸如巨磁电阻和磁光效应等有趣的性质。另一方面，众所周知，钛氧化物的性质随其金属氧比的变化而敏感。采用活化反应蒸发(ARE)方法制备了不同厚度组合的Fe_3O_4/Mo(M=Mg，Co)超晶格薄膜。用ARE法在α-Al_2O_3(0001)衬底上外延生长了化学计量比和单化学计量比的氧化钛薄膜。主要研究结果如下：1.在(0001)面的α-Al_2O_3和(100)面的氧化镁单晶衬底上生长了(111)和(100)取向的Fe_3O_4/MgO薄膜，证实了薄膜的外延生长和人为调制。在5K下，各薄膜的饱和磁化强度约为85-100emu/g，与Fe_3O_4块体的饱和磁化强度基本一致。在40K以下，随着温度的升高，磁化强度与1/T成正比下降。对于Fe_3O_4/CoO薄膜，CoO层的晶格间距沿生长方向收缩，而Fe_3O_4层的晶格间距增大，这可能是由于这些层之间的晶格失配所致。在(100)和(111)取向的超晶格中，CoO层的磁致伸缩分别引起面内和垂直磁各向异性。Fe_3O_4与CoO层之间的强磁耦合使得CoO层的Neel温度较高，表现为亚铁磁/反铁磁交换各向异性。在(0001)α-Al_2O_3衬底上外延生长了二氧化钛和三氧化二钛薄膜。在(0001)α-Al_2O_3衬底上制备的薄膜是化学计量比为(100)取向的金红石结构的金红石型二氧化钛薄膜，在约400K处有明显的(001)取向的电学转变。

Magnetic superlattices including ferromagnetic and diamagnetic layrs bring interesting properties such as the giant magnetoresistance and the mangneto-optical effects. On the other hand, it is well known that titanium oxides change their properties sensitively with their metal to oxygen ratios.Fe_3O_4/Mo (M=Mg, Co) superlattice films having various thickness combinations of the individual Fe_3O_4 and Mo were prepared by an activated reactive evaporation (ARE) method. Stoichiometric and monstoichiometric titanium oxide films were also epitaxially formed on alpha-Al_2O_3 (0001) substrates by ARE method. The summarized results are as follows :1. Epitaxial growths and artificial modulations of (111) -and (100) -orientated Fe_3O_4/Mgo films deposited on (0001) -faced alpha-Al_2O_3 and (100) -faced Mgo single crystaline substrates, respectively, were confirmed. The saturation magnetization of each film at 5K was about 85-100 emu/g, being nealy consistent with that of the Fe_3O_4 bulk. However, with increasing temperature the magnetizations decreased linearly in proportion to 1/T below 40K.2. For Fe_3O_4/CoO film the lattice spacing along the growth direction was contracted for the CoO layr but expanded for the Fe_3O_4 layr probably due to the lattice mismatch between these layrs. The magnetostriction of CoO layrs induced in-plane and perpendicular magnetic anisotropy in (100) -and (111) -oriented superlattices, respectively. Strong magnetic coupling between Fe_3O_4 and CoO layrs made the Neel temperature of the CoO layr higher and showed the ferrimagnetic/antiferromagnetic exchange anisotropy.3. Titanium di-and sesquioxide films were epitaxially grown on (0001) alpha-Al_2O_3. Films prepared at Po_2*2.0*10^<-4> Torr were stoichiometric (100) -oriented rutile of TiO_2. AtP_<02>=0.6*10^<-4> Torr, on the other hand, (001) -oriented Ti_2O_3 was formed and an electrical transition was clearly detected at about 400K.