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

建立了用磁控溅射法制备高质量单晶半金属钙钛矿铁磁（La_<0.7>Sr_<0.3>MnO_3（LSMO），Sr_2FeMnO_6（SFMO），Sr_2CrReO_6（SCRO））薄膜的方法。使用高质量钙钛矿氧化物制造无应变单晶TMR结的条件如下。1)基底和膜之间的失配应最小化。2)此外，为了减小失配，最好在衬底和薄膜之间生长一个中间层，如Ba_<0.4>Sr_<0.6>TiO_3。3)氧分压在薄膜生长后的冷却过程中是重要的。过小的分压会使薄膜中的氧原子消失，而过大的分压会使薄膜中形成非铁磁氧化层。压力应该优化。4)在制作磁电阻器件的过程中，氩气研磨的情况下，由于薄膜表面的应变和氧原子的缺失， ...更多信息 表面层（约40 nm）。有时候，在低温下，电阻会因为损坏而急剧增加。在900℃以上的氧气氛中退火，损伤得到恢复。在MR器件的制造过程中，退火是很重要的。我们优化了上述条件。LSMO/SrTiO_3/LSMO、SFMO/ SrTiO_3/Co和SrCrReO/MgO/Co结的TMR分别为64%、14%和114%。用Andreev反射法测量了铁磁半金属的自旋极化，在NbN超导层和半金属之间插入绝缘层。建立了制备Co_2MnGe、Co_2MnGa、Co_2MnSi等Heusler合金高质量单晶薄膜或择优取向薄膜的方法。在Si衬底上制备了由（100）或（110）择优取向Co_2MnGe薄膜组成的TMR结。通过能带计算和实验，讨论了钴基Heusler合金半金属性和镍基Heusler合金非金属性的来源。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