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The perpendicular magnetic anisotropy (PMA) at ferromagnet/insulator interfaces has important technological applications, such as in the fields of magnetic recording and sensing devices. The perpendicular magnetic tunnel junctions (p-MTJs) with strong PMA have recently attracted increasing interest because they offer high stability and device performance toward low energy consumption. Heusler alloys are a large family of compounds that offer promising magnetic properties for developing p-MTJs. However, it is challenging to select appropriate combinations of Heusler ferromagnets and insulators with the desired interfacial properties. Here, we report a systematic high-throughput screening approach to search for candidate Heusler/MgO material interfaces with strong PMA and other desired material properties for spintronic technologies. On the basis of the open quantum material repositories, we developed a series of material descriptors, including formation energy, convex hull distance, magnetic ordering, lattice misfit, magnetic anisotropy constant, cleavage energy, and tunnel magnetoresistance, to filter candidate Heusler/MgO interfaces among the possible 40 000 ternary Heusler compounds. After a comprehensive screening, five full-Heusler compounds, including Co2CrAl, Co2FeAl, Co2HfSn, Fe2IrGa, and Mn2IrGe, and two half-Heusler compounds, PtCrSb and PtMnAs, were found to be promising for designing p-MTJs. This work demonstrates a new way for the high-throughput design of functional material interfaces for spintronic applications via exploiting the open quantum material repositories and developing effective material descriptors along with the large-scale ab initio calculations for material interfaces.

By using first-principles electronic structure calculations, we explored the possibility of producing two-dimensional electron gas (2DEG) in nonpolar/nonpolar AHfO3/SrTiO3(A = Ca, Sr, and Ba) heterostructures. Two types of nonpolar/nonpolar interfaces, (AO)0/(TiO2)0and (HfO2)0/(SrO)0, each with AO and HfO2surface terminations, are modeled, respectively. The polarization domain and resulting interfacial electronic property are found to be more sensitive to the surface termination of the film rather than the interface model. As film thickness increases, an insulator-to-metal transition is found in all the heterostructures with HfO2surface termination: for (AO)0/(TiO2)0interfaces, predicted critical film thickness for an insulator-to-metal transition is about 7, 6, and 3 unit cells for CaHfO3/SrTiO3, SrHfO3/SrTiO3, and BaHfO3/SrTiO3, respectively; for (HfO2)0/(SrO)0interfaces, the critical film thickness is about 7.5, 5.5, and 4.5 unit cells, respectively. In contrast, for the heterostructures with AO surface termination, CaHfO3/SrTiO3exhibits a much larger critical film thickness about 11–12 unit cells for an insulator-to-metal transition; while SrHfO3/SrTiO3and BaHfO3/SrTiO3do not show any polarization behavior even film thickness increases up to 20 unit cells. The strain-induced polarization behavior was well-elucidated from energy versus polarization profile. This work is expected to stimulate further experimental investigation to the interfacial conductivity in the nonpolar/nonpolar AHfO3/SrTiO3HS.

On basis of the first-principles calculations, we have studied the effects of hole doping and biaxial tensile strain on the electronic and magnetic properties of monolayer of platinum diselenide (PtSe2). Due to the large density of states near the valence band edge, this nonmagnetic monolayer semiconductor switches to a ferromagnetic half metal within a small range of hole doping. With an increase of hole density, average magnetic moment per carrier also increases and reaches at its maximum value over a specific range of carrier density, while the system remains in a half metal state before the magnetic moment abruptly begins to fall. We also predict a critical value of biaxial tensile strain (5%) for doped monolayer PtSe2, after which the optimal carrier density becomes constant, while the magnetic moment/carrier gradually increases and the ferromagnetic state of the system becomes more stable with increasing values of strain. This work paves a possible way to engineer the magnetic properties of the two-dimensional nanomaterials.

We studied strain-induced polarization and resulting conductivity in the nonpolar/nonpolar CaZrO3/SrTiO3(CZO/STO) heterostructure (HS) system by means of first-principles electronic structure calculations. By modeling four types of CZO/STO HS-based slab systems, i.e., TiO2/CaO and SrO/ZrO2interface models with CaO and ZrO2surface terminations in each model separately, we found that the lattice-mismatch-induced compressive strain leads to a strong polarization in the CZO film and that as the CZO film thickness increases there exists an insulator-to-metal transition. The polarization direction and critical thickness of the CZO film for forming interfacial metallic states depend on the surface termination of CZO film in both types of interface models. In the TiO2/CaO and SrO/ZrO2interface models with CaO surface termination, the strong polarization drives the charge transfer from the CZO film to the first few TiO2layers in the STO substrate, leading to the formation of two-dimensional electron gas (2DEG) at the interface. In the HS models with ZrO2surface termination, two polarization domains with opposite directions are in the CZO film, which results in the charge transfer from the middle CZO layer to the interface and surface, respectively, leading to the coexistence of the 2DEG on the interface and the two-dimensional hole gas (2DHG) at the middle CZO layer. These findings open a new avenue to achieve 2DEG (2DHG) in perovskite-based HS systems via polarization discontinuity.

Tailoring the two-dimensional electron gas (2DEG) at the n-type (TiO2)0/(LaO)+1interface between the polar LaAlO3(LAO) and nonpolar SrTiO3(STO) insulators can potentially provide desired functionalities for next-generation low-dimensional nanoelectronic devices. Here, we propose a new approach to tune the electronic and magnetic properties in the n-type LAO/STO heterostructure (HS) system via electron doping. In this work, we modeled four types of layer doped LAO/STO HS systems with Sn dopants at different cation sites and studied their electronic structures and interface energetics by using first-principles electronic structure calculations. We identified the thermodynamic stability conditions for each of the four proposed doped configurations with respect to the undoped LAO/STO interface. We further found that the Sn-doped LAO/STO HS system with Sn at Al site (Sn@Al) is energetically most favorable with respect to decohesion, thereby strengthening the interface, while the doped HS system with Sn at La site (Sn@La) exhibits the lowest interfacial cohesion. Moreover, our results indicate that all the Sn-doped LAO/STO HS systems exhibit the n-type conductivity with the typical 2DEG characteristics except the Sn@La doped HS system, which shows p-type conductivity. In the Sn@Al doped HS model, the Sn dopant exists as a Sn4+ion and introduces one additional electron into the HS system, leading to a higher charge carrier density and larger magnetic moment than that of all the other doped HS systems. An enhanced charge confinement of the 2DEG along the c-axis is also found in the Sn@Al doped HS system. We hence suggest that Sn@Al doping can be an effective way to enhance the electrical conduction and magnetic moment of the 2DEG in LAO/STO HS systems in an energetically favorable manner.

The highly mobile two-dimensional electron gas (2DEG) formed at the polar/nonpolar LaAlO3/SrTiO3(LAO/STO) heterostructure (HS) is a matter of great interest because of its potential applications in nanoscale solid-state devices. To realize practical implementation of the 2DEG in device design, desired physical properties such as tuned charge carrier density and mobility are necessary. In this regard, polar perovskite-based transition metal oxides can act as doping layers at the interface and are expected to tune the electronic properties of 2DEG of STO-based HS systems dramatically. Herein, we investigated the doping effects of LaTiO3(LTO) layers on the electronic properties of 2DEG at n-type (LaO)+1/(TiO2)0interface in the LAO/STO HS using spin-polarized density functional theory calculations. Our results indicate an enhancement of orbital occupation near the Fermi energy, which increases with respect to the number of LTO unit cells, resulting in a higher charge carrier density of 2DEG than that of undoped system. The enhanced charge carrier density is attributed to an extra electron introduced by the Ti 3d1orbitals from the LTO dopant unit cells. This conclusion is consistent with the recent experimental findings (Appl. Phys. Lett.2013, 102, 091601). Detailed charge density and partial density of states analysis suggests that the 2DEG in the LTO-doped HS systems primarily comes from partially occupied dyzand dxzorbitals.

The emerging two-dimensional electron gas (2DEG) at the interface between polar LaAlO3(LAO) and nonpolar SrTiO3(STO) provides potential applications in low-dimensional nanoelectronic devices because of its exceptional electron transport property. To form 2DEG in the LAO/STO heterostructure (HS), a minimum thickness of approximately 4 unit cells of LAO is necessary. Herein, we modeled the n-type (TiO2)0/(LaO)+1HS by depositing (LAO)n(n= 4, 5, and 6) thin films on the STO substrate and explored strain effects on the critical thickness for forming 2DEG in the LAO/STO HS-based slab systems using first-principles electronic structure calculations. A vacuum layer was added along the [001] direction on the LAO film to resemble the actual epitaxial growth process of the materials. An insulator-to-metal transition is predicted in unstrained (LAO)n/STO systems when n≥ 5. Our calculations indicate that O 2px/pystates give rise to the surface conductivity, while Ti 3dxystates are responsible for the interfacial conductivity. For the tensilely strained HS system, an increased film thickness of LAO (n≥ 6) is required to form the 2DEG, and a remarkable shift of O 2p orbitals toward higher energy in LAO layers is found, which is caused by the strain-induced change of the electrostatic potential. For the compressively strained HS system, the critical thickness of LAO film for forming 2DEG is between 5 and 6 unit cells of LAO. In addition, our calculations suggest that the interfacial charge carrier density and magnetic moment can be optimized when a moderate tensile strain is applied on the STO substrate in the ab-plane.

Density functional theory based ab initiocalculations are used to investigate the thermodynamic stability, defect formation energies, and electronic properties of isolated neutral and charged vacancies in SrHfO3under various chemical environments. We find that cation defects lead the system into a hole-doped state, while oxygen vacancies yield defect levels near the conduction band minimum. The partial and full Schottky defect reaction energies and mixed electron hole conduction behavior of SrHfO3is also evaluated. Furthermore, various cases for neutral oxygen vacancy clustering are examined for tuning the electrical properties of oxygen deficient SrHfO3. We show that ordered oxygen vacancies in HfO layers are energetically favorable and induce metallicity in this system which emerges due to charge transfer between the vacancy site and the hafnium dangling bond.