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Clarification of the role of magnetic ordering and scattering in two-dimensional electron gas has become increasingly important to understand the transport and magnetic behavior in the LaAlO3 (LAO)/SrTiO3 (STO) heterostructures. In this work, we report the sheet resistance of the LAO/STO heterostructures as functions of temperature, magnetic field, and field orientation. An unexpected resistance minimum was discovered at ∼10 K under a sufficiently high in-plane magnetic field. An anisotropic magnetoresistance (MR) is clearly identified, indicating the presence of magnetic scattering which may be related to the interaction between itinerant electrons and localized magnetic moments in the LaAlO3/SrTiO3 heterostructures. It is believed that the high concentration of oxygen vacancies induced by the ultralow oxygen partial pressure during the deposition process plays a predominant role in the occurrence of the anisotropic MR.

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Co doped ZnO films have been deposited by a laser-molecular beam epitaxy system. X-ray diffraction and UV spectra analysis show that Co effectively substitutes the Zn site. Transmission electron microscopy (TEM) and secondary ion mass spectroscopy analysis indicate that there are no clusters. Co dopants are uniformly distributed in ZnO film. Ferromagnetic ordering is observed in all samples deposited under an oxygen partial pressure, PO2=10-3, 10-5, and 10-7 torr, respectively. However, the magnetization of PO2=10-3 and 10-5 is very small at room temperature. At low temperature, the ferromagnetic ordering is enhanced. Muon spin relaxation (μSR) measurements confirm the ferromagnetism in all samples, and the results are consistent with magnetization measurements. From μSR and TEM analysis, the film deposited under PO2=10-7 torr shows intrinsic ferromagnetism. However, the volume fraction of the ferromagnetism phase is approximately 70%, suggesting that the ferromagnetism is not carrier mediated. Resistivity versus temperature measurements indicate Efros variable range hopping dominates the conductivity. From the above results, we can confirm that a bound magnetic polaron is the origin of the ferromagnetism.

AlO 2 layers and the build-up of triplet coupling of Ti 3d states through oxygen bonds (or possibly vacancies) in the TiO 2 interface plane may be responsible for the observed magnetism. [ 7 ] Theoretical calculation suggests that the robust ferromagnetism is not the intrinsic property of LAO/STO interface and the oxygen vacancy in STO or LAO layer is the origin of ferromagnetism. [ 7 ] In fact, the formation and distribution of oxygen vacancies in LAO/STO have been considered to play a critical role in determining the novel physical phenomena appearing in LAO/STO heterostructures, but the mechanism of the oxygen vacancy effects on the magnetic behaviors of LAO/STO is still unclear.Up to date, there is no universal explanation on the origin of ferromagnetism occurring in LAO/STO heterostructures. A systematic experimental verifi cation for the role of oxygen vacancy on the introduction of magnetic state in LAO/STO heterostructures is eagerly awaited. In this work, we experimentally and theoretically demonstrate that the enhancement of the saturated magnetization of the LAO/STO heterostructures was closely related to the increased density of oxygen vacancies in this particular materials system. Results and DiscussionsAs shown in Figure 1 a, the strong refl ection high energy electron diffraction (RHEED) intensity oscillations are maintained up to 24 oscillations (corresponding to a thickness of ≈9.1 nm), suggesting a layer-by-layer growing mode for our samples. Figure 1 b shows the AFM topographic images of the as-deposited 24 unit cells (uc) LAO thin fi lms with the typical step-fl ow terrace. The average surface roughness value ( R a ) is ≈0.283 nm for the fi lms grown under the oxygen partial pressure of 5 × 10 −8 Torr, suggesting the good surface quality in such a low oxygen processing pressure. Figure 1 c shows the XRD θ -2 θ scan spectra of 24 uc LAO thin fi lms grown under different oxygen partial pressures. Only the strong (00l) refl ections are detected, indicating all the fi lms are highly c -axis oriented. X-ray diffraction (XRD) reciprocal space mapping (RSM) was performed on the sample prepared under the oxygen partial pressure of 5 × 10 −8 Torr. Figure 1 d,e shows the RSM around the (003) and (203) refl ections, respectively. The diffraction peak of the LAO fi lm locates right above that of the substrate as arrowed, i.e., the in-plane lattice parameter of the fi lm is almost the same as that of the substrate, indicating the The discovery of magnetism at the LaAlO 3 /SrTiO 3 heterostructures has attracted a lot of interests in regards to the origin of magnetic properties appearing in this nonmagnetic system. In this paper, the existence of a robust ferromagnetic state in the LaAlO 3 /SrTiO 3 heterostructures is demonstrated. The oxygen vacancy dependence of magnetic phenomena demonstrates the correlation between the magnetic properties and the oxygen vacancies. The strong ferromagnetism can be also manipulated by controlling the partial pressure of oxygen during the fi lm deposition process. The well-...