Interfacial characteristics of a Fe3O4∕Nb(0.5%):SrTiO3 oxide junction
TL;DR: In this article, the temperature dependent Schottky diode characteristics of epitaxial junctions between Nb:SrTiO3 (Nb concentrations: 05%) and Fe3O4 are studied.
Abstract: The temperature dependent Schottky diode characteristics of epitaxial junctions between Nb:SrTiO3 (Nb concentrations: 05%) and Fe3O4 are studied Epitaxial thin films of Fe3O4 were grown on Nb:SrTiO3 substrates by pulsed laser deposition technique The films and heterointerfaces were characterized by x-ray diffraction, Z-contrast transmission electron microscopy, magnetic susceptibility, four-probe in-plane resistivity, and the temperature dependent junction current-voltage (I‐V) characteristics The nonlinear nature of the characteristics is analyzed within the framework of thermionic emission theory Junction parameters such as the Schottky barrier height (ϕB) and ideality factor (η) are extracted The temperature evolution of these parameters shows interesting and systematic trends, with remarkable changes near the Verwey transition (TV=120K) The magnetic field dependence of I‐V characteristic data is also recorded and a spin polarization of ∼80% is estimated for the magnetite electrode
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TL;DR: In this article, the microstructure and magnetic properties of magnetite films on (100)-oriented MgO and SrTiO3 (STO) substrates were investigated. And the growth of high quality Fe3O4 films was confirmed by x-ray diffraction analysis and Raman spectroscopy measurements.
Abstract: A comparable study of the microstructure and magnetic properties was performed for magnetite films deposited on (100)-oriented MgO and SrTiO3 (STO) substrates. The growth of strained high quality Fe3O4 films was confirmed by x-ray diffraction analysis and Raman spectroscopy measurements. The surface morphology and magnetic properties of the two films were found to be obviously different. Moreover, a stripelike magnetic domain structure was observed in the film on STO. Substrate-induced strain is believed to be responsible for these observations, which significantly affects the magnetic anisotropy and the magnetic coupling at the antiphase boundaries in the films.
38 citations
TL;DR: In this paper, the effect of the reverse bias voltage on the temperature dependence of magnetoresistance was investigated and the results were discussed by considering the band structure of the heterojunction.
Abstract: Fe3O4∕SiO2∕Si heterojunction was fabricated by growing Fe3O4 film on an n-typed Si wafer with the native SiO2 buffer layer using the pulsed laser deposition. Transmission electron microcopic study shows the high quality of the heterojunction interfaces and the SiO2 layer is 2.5nm thick. This junction shows a backward diodelike rectifying behavior and an anomalously giant positive magnetoresistance (MR) for the large reverse bias voltages. The temperature dependence of MR shows a peak around the Verwey transition temperature with a maximum MR of 87% under a −2V bias voltage. The results were discussed by considering the band structure of the heterojunction and the effect of the reverse bias voltage.
33 citations
TL;DR: In this paper, the authors examined the magnetic easy-axis directions of stoichiometric magnetite films grown on SrTiO3:Nb by infrared pulsed-laser deposition.
Abstract: We examine the magnetic easy-axis directions of stoichiometric magnetite films grown on SrTiO3:Nb by infrared pulsed-laser deposition. Spin-polarized low-energy electron microscopy reveals that the individual magnetic domains are magnetized along the in-plane ⟨100⟩ film directions. Magneto-optical Kerr effect measurements show that the maxima of the remanence and coercivity are also along in-plane ⟨100⟩ film directions. This easy-axis orientation differs from bulk magnetite and films prepared by other techniques, establishing that the magnetic anisotropy can be tuned by film growth.
32 citations
TL;DR: In this paper, the electrical transport mechanism across the disordered interface between polycrystalline Fe3O4 and amorphous Si layers is tunneling above the Verwey temperature of 120K.
Abstract: Polycrystalline Fe3O4∕amorphous Si heterostructure was prepared by facing-target sputtering and its microstructure and electrical transport properties were studied. The polycrystalline Fe3O4 layer was grown in column structure. The electrical transport mechanism across the disordered interface between polycrystalline Fe3O4 and amorphous Si layers is tunneling above the Verwey temperature [Nature (London) 144, 327 (1939)] of 120K. Nonlinear I‐V characteristics of the Schottky diode reveal thermionic emission∕diffusion mechanism below the Verwey temperature, and Schottky barrier height is 0.27eV, calculated by a standard theory of thermionic emission∕diffusion. Based on a simplified band structure, the spin polarization of the polycrystalline Fe3O4 layer was determined to be ∼45%.
30 citations
TL;DR: In this article, a systematic study of Fe 3 O 4 epitaxial films grown on single-crystalline SrTiO 3 (100) substrates using pulsed laser deposition has been conducted in order to elaborate magnetite films with properties suitable for their integration into spintronics heterostructures.
26 citations
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14,205 citations
TL;DR: The band structure of Mn-based Heusler alloys of the crystal structure (MgAgAs type) has been calculated with the augmented-spherical-wave method.
Abstract: The band structure of Mn-based Heusler alloys of the $C{1}_{b}$ crystal structure (MgAgAs type) has been calculated with the augmented-spherical-wave method. Some of these magnetic compounds show unusual electronic properties. The majority-spin electrons are metallic, whereas the minority-spin electrons are semiconducting.
3,851 citations
TL;DR: In this paper, a theoretical and experimental study has been made of silicon Schottky diodes in which the metal and semiconductor are separated by a thin interfacial film.
Abstract: A theoretical and experimental study has been made of silicon Schottky diodes in which the metal and semiconductor are separated by a thin interfacial film. A generalized approach is taken towards the interface states which considers their communication with both the metal and the semiconductor. Diodes were fabricated with interfacial films ranging from 8 to 26 A in thickness, and their characteristics are related to this model. The effects of reduced transmission coefficients together with fixed charge in the film are investigated. The interpretation of the current-voltage characteristics and the validity of the C−2-V method in the determination of diffusion potentials are discussed.
1,519 citations
TL;DR: Using density-functional calculations, a three-band spinless model Hamiltonian is suggested for the description of the Verwey transition using a Stoner model as well as from calculations within the framework of the local-spin-density approximation to the density- functional theory.
Abstract: Using density-functional calculations, we examine the electronic structure of magnetite in the spinel crystal structure in order to gain insight into the nature of the Verwey transition. The calculated cohesive and magnetic properties are in agreement with experimental results. The magnetic structure is analyzed using a Stoner model as well as from calculations within the framework of the local-spin-density approximation to the density-functional theory. The calculations show a minority-spin band at the Fermi energy consisting of ${\mathit{t}}_{2\mathit{g}}$ orbitals on the Fe(B) sublattice. These results suggest a three-band spinless model Hamiltonian for the description of the Verwey transition. The hopping integrals and the electron interaction parameters entering the model Hamiltonian are calculated using the ``constrained'' density-functional theory. The calculated parameters are consistent with the electronic origin of the Verwey transition.
610 citations
TL;DR: Strong local environment effects arising from neighboring cation charge differences that suggest localization of the low density of minority carriers, leading to effective half-metallic ferromagnetism in the CMR regime are identified.
Abstract: Possible origins of ``colossal magnetoresistance'' (CMR) behavior in the ${\mathrm{La}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Ca}}_{\mathit{x}}$${\mathrm{MnO}}_{3}$ system are studied using the local spin-density method. These calculations allow the quantification of the effects of Mn d--O p hybridization that have been largely neglected in previously published work. As regards the end-point compounds ${\mathrm{CaMnO}}_{3}$ and ${\mathrm{LaMnO}}_{3}$, the very different structural and magnetic symmetries of their ground states are predicted correctly. The distortion from the cubic perovskite structure of the ${\mathrm{LaMnO}}_{3}$ lattice is necessary to produce an antiferromagnetic insulating ground state. The distortion also strengthens the Mn magnetic moments. Application to ferromagnetic and constrained ferrimagnetic phases of ${\mathrm{La}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Ca}}_{\mathit{x}}$${\mathrm{MnO}}_{3}$ in the CMR regime x\ensuremath{\approxeq}1/4--1/3 suggests, as observed, that magnetic coupling switches from antiferromagnetic to ferromagnetic. Hybridization between Mn d states and O p states is found to be strongly spin dependent, because the majority Mn d bands overlap the O p bands while the minority Mn d bands are separated by a gap from the O p bands. Both ferromagnetic and ferrimagnetic orderings are obtained and compared. We identify strong local environment effects arising from neighboring cation charge differences (${\mathrm{La}}^{3+}$ or ${\mathrm{Ca}}^{2+}$) that suggest localization of the low density of minority carriers, leading to effective half-metallic ferromagnetism in the CMR regime. This behavior supports in some respects the popular ``double exchange'' picture of Zener but indicates the Mn d--O p hybridization is much too strong to be considered perturbatively. Half-metallic character promotes the possibility of very large magnetoresistance, and may well be an essential ingredient in the CMR effect.
590 citations