| AVS 66th International Symposium & Exhibition | |
| Complex Oxides: Fundamental Properties and Applications Focus Topic | Wednesday Sessions |
| Session OX+EM+MI+SS-WeM |
| Session: | Electronic and Magnetic Properties of Complex Oxide Surfaces and Interfaces |
| Presenter: | Jeffry Kelber, University of North Texas |
| Authors: | C. Ladewig, University of North Texas F. Anwar, University of North Texas J.A. Kelber, University of North Texas S.Q.A. Shah, University of Nebraska-Lincoln P.A. Dowben, University of Nebraska-Lincoln |
| Correspondent: | Click to Email |
The formation of all-oxide heterostructures comprising multiferroic oxides interfaced with appropriate semiconducting substrates is a promising path towards low power, voltage-switchable spintronics, including non-volatile memory and multi-functional logic devices. At the same time, the necessary scaling of film thicknesses to the nm range can induce structures and properties sharply different than those of the bulk. We report here in situ XPS, LEED, EELS and ex-situ MOKE data on the growth and properties of Cr2O3(0001) on TiO1.7(111) on Al2O3(0001). The data indicate that the presence of O vacancies during film growth can mediate the further growth of oxides with unusual structures and properties. These data show that (a) O vacancies during initial stages of film growth yield a TiO2 film of an unusual crystallographic orientation and structure; and that (b) this leads to growth of an epitaxial Cr2O3 layer exhibiting magnetic ordering above the expected Néel temperature of thin film chromia - indicative of a strained chromia lattice due to epitaxial growth on a substrate with a lattice constant of 5.1 Å, compared to the bulk chromia lattice constant of 4.9 Å. Molecular beam epitaxy (MBE) of Ti at 500 K in 10-6 Torr O2 on Al2O3(0001) initially yields TiO1.7(111) with the structure of corundum phase Ti2O3 (a = b=5.1 Å). Further deposition and annealing in O2 results in stoichiometric TiO2(111), but with the same lattice structure and orientation as Ti2O3(111), and with a total thickness of 5 nm. This is sharply different from the generally observed growth of TiO2(001) on Al2O3(0001). MBE of ~ 1 monolayer of Cr on TiO2(111) yields hexagonally-ordered Cr2O3 and the formation of titania oxygen vacancies. MOKE measurements confirm that this chromia layer is magnetically ordered at 280 to 315 K, likely antiferromagnetically ordered, with exchange bias coupling to the TiO1.7(111) substrate. O vacancies in the TiO2(111) lattice exhibit weak ferromagnetic behavior, as is evident in the In-plane MOKE, enhancing the canting of the magnetism away from the thin film normal, which is expected for the Cr2O3(0001) alone. These data demonstrate that careful control of initial growth conditions and film stoichiometry during oxide MBE can template the subsequent growth of stoichiometric oxide heterostructures with non-bulk like structures and properties.
Acknowledgement: Work at UNL was supported in part by the Semiconductor Research Corporation (SRC) as task 2760.002 and NSF through ECCS 1740136.