Study on non-strain single crystal MR junctions using half metallic ferromagnetic thin films.

采用磁控溅射法制备了高质量的单晶钙钛矿铁磁性薄膜(La&lt；0.7&gt；sr&lt；0.3&gt；MnO_3(LSMO)，sr2FeMnO6(SFMO)，sr2CrReO6(SCRO))。利用优质钙钛矿氧化物制备无应变单晶TMR结的条件如下：1)应尽量减少基片与薄膜之间的不匹配。2)为了减小失配，在衬底和薄膜之间生长一层中间层，如Ba0.4&gt；sr&lt；0.6&gt；TiO_3较好。3)氧分压在薄膜生长后的冷却过程中起着重要作用。过小的分压会使薄膜中的氧原子消失，过高的分压会导致非铁磁性氧化物的生成。应优化压力。4)在制造磁流变器件的过程中，由于薄膜的应变和薄膜中氧原子的缺失，导致了薄膜的破坏。…。表面层较多(约40 nm)。有时，由于损坏，在低温下电阻会极大地增加。在氧气气氛中进行90 0℃以上的退火可使损伤得到恢复。在磁流变器件的制作过程中，退火是非常重要的。我们对上述条件进行了优化。在此基础上，观察到LSMO/SrTiO3/LSMO、SFMO/SrTiO3/Co和SrCrReO/MgO/Co结的TMR比分别为：%、14%和114%。利用NbN超导层，在NbN和半金属之间插入绝缘层，用Andreev反射法测量了铁磁性半金属的自旋极化。建立了制备Co2MnGe、Co2MnGa、Co2MnSi等Heusler合金高质量单晶薄膜或择优取向薄膜的方法。在硅衬底上制备了由(100)或(110)择优取向的Co2MnGe薄膜组成的TMR结。通过能带计算和实验，讨论了Co基Heusler合金的半金属性质或Ni基Heusler合金的非半金属性质的来源。较少

The methods to fabricate the high quality and single crystal half metallic perovskite ferromagnetic (La_<0.7>Sr_<0.3>MnO_3 (LSMO), Sr_2FeMnO_6 (SFMO), Sr_2CrReO_6(SCRO)) films were established, where the magnetron sputtering method was employed. The conditions to make the non-strain single crystal TMR junctions using the high quality perovskite oxides are followings. 1) The misfit between substrate and film should be minimized. 2) In order to minimize the mismatching, furthermore, it is better that an intermediate layer such as Ba_<0.4>Sr_<0.6>TiO_3 is grown between substrate and film. 3) The oxygen partial pressure is important in cooling process after growth of the film. Too small partial pressure deletes the oxygen atoms in film and too much pressure make the non ferromagnetic oxides layer. The pressure should be optimized. 4) In the case of argon gas milling in the process of fabrication of MR devices, the film was damaged by the strain and the deletion of oxygen atoms from film su … More rface layer (about 40nm). Sometimes, the electrical resistance was extremely increased at low temperatures due to the damage. The damage was recovered by the annealing above 900℃ in the oxygen atmosphere. It is important to anneal in the fabrication process of MR devices. We optimized the above conditions. Then, the TMR ratios of 64% for LSMO/SrTiO_3/LSMO, 14% for SFMO/ SrTiO_3/Co and 114% for SrCrReO/MgO/Co junctions were observed. The spin polarization of the ferromagnetic half metals was measured by the Andreev reflection method using NbN superconductor layer, inserting an insulator layer between NbN and the half metal. The methods to fabricate the high quality single crystal films or the preferred oriented films of Heusler alloys such as Co_2MnGe, Co_2MnGa, and Co_2MnSi were established. TMR junctions composed by (100) or (110) preferred oriented Co_2MnGe film was fabricated on a Si substrate. The origin of half metallic property of Co-based Heusler alloys or non half metallic property of Ni-based Heusler alloys was discussed by the band calculations and experiments. Less