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Papers by Sreenivasulu Vutukuri
Journal of Applied Physics, Apr 15, 2006
Here we show that ordinary band structure codes can be used to understand the mechanisms of coher... more Here we show that ordinary band structure codes can be used to understand the mechanisms of coherent spin-injection at interfaces between ferromagnets and semiconductors. This approach allows the screening of different material combinations for properties useful for obtaining high tunneling magnetoresistance (TMR). We used the Vienna Ab-initio Simulation Code (VASP) to calculate the wave function character of each band in periodic epitaxial Fe(100)|GaAs(100) and Fe(100)|ZnSe(100) structures. It is shown that Fe wave functions of different symmetry near Fermi energy decay differently in the GaAs and ZnSe.
Electrochemical and Solid State Letters, 2008
ABSTRACT We report epitaxial growth of body-centered cubic Fe and face-centered cubic Ni thin fil... more ABSTRACT We report epitaxial growth of body-centered cubic Fe and face-centered cubic Ni thin films on n-type AlGaAs(001) substrates using electrochemical deposition with the cubic axes of Fe oriented parallel to the substrate lattice while the Ni is rotated in-plane 45 degrees. The magnetic properties in either case are dominated by the fourfold crystalline anisotropy, a high remanence, and saturation magnetization values similar to bulk properties. The growth of such ferromagnetic contacts on AlGaAs might find applications in magneto-electronics. (c) 2008 The Electrochemical Society.
IEEE Transactions on Magnetics, Oct 1, 2005
The tunneling current for electrons tunneling between crystalline ferromagnetic electrodes throug... more The tunneling current for electrons tunneling between crystalline ferromagnetic electrodes through an epitaxial crystalline barrier can be calculated from first principles. These calculations show that the wave function symmetry can be exploited to achieve very high tunneling magnetoresistance. For the Fe(100) MgO(100) Fe(100) system, the calculated conductance is much higher and its decrease with MgO thickness is much slower than has been estimated using a simple free electron-barrier model.
Bulletin of the American Physical Society, Mar 6, 2007
Epitaxial ferromagnetic materials grown on semiconductors are potential candidates for new class ... more Epitaxial ferromagnetic materials grown on semiconductors are potential candidates for new class of spintronic devices which can be used as contacts for spin injection. In this respect electrodeposition has proven to be a promising method as it avoids interface because it is a low-energy, room temperature process. Here we report the electrical transport properties of electrodeposited Ni thin films on GaAs(110) substrate. We have performed resistivity and Hall Effect measurements as a function of film thickness. The results show that the thickness dependence of the electrical resistivity follows the Fuchs 1 model. The bulk resistivity at room temperature is close to the reported bulk properties. The low temperature resistivity values are dominated by surface scattering with the bulk resistivity being essentially zero. The low temperature ordinary Hall coefficient R o of the films is almost independent of the film thickness, whereas the spontaneous Hall coefficient R s decreases with increasing film thickness. The spontaneous Hall coefficient scales with the resistivity as R s ∝ ρ 1.3 , indicating a scattering mechanism which is mixture of both skew scattering and side jump scattering. 1. K. Fuchs, Proc. Camb. Phil. Soc. 34, 100 (1938)
Epitaxial ferromagnetic materials grown on semiconductors are potential candidates for new class ... more Epitaxial ferromagnetic materials grown on semiconductors are potential candidates for new class of spintronic devices which can be used as contacts for spin injection. In this respect electrodeposition has proven to be a promising method as it avoids interface because it is a low-energy, room temperature process. Here we report the electrical transport properties of electrodeposited Ni thin films on GaAs(110) substrate. We have performed resistivity and Hall Effect measurements as a function of film thickness. The results show that the thickness dependence of the electrical resistivity follows the Fuchs 1 model. The bulk resistivity at room temperature is close to the reported bulk properties. The low temperature resistivity values are dominated by surface scattering with the bulk resistivity being essentially zero. The low temperature ordinary Hall coefficient R o of the films is almost independent of the film thickness, whereas the spontaneous Hall coefficient R s decreases with increasing film thickness. The spontaneous Hall coefficient scales with the resistivity as R s ∝ ρ 1.3 , indicating a scattering mechanism which is mixture of both skew scattering and side jump scattering. 1. K. Fuchs, Proc. Camb. Phil. Soc. 34, 100 (1938)
In the emerging field of spintronics, along with charge, spin of the electron also plays a vital ... more In the emerging field of spintronics, along with charge, spin of the electron also plays a vital role. This discovery of spin-dependent transport has stimulated wide interest in the design of novel memory and logic devices. In particular, the proposal of spin field effect transistor by Datta and Das has triggered great attention on the issue of integration of ferromagnetic materials with semiconductors. These spintronics devices would require the growth of epitaxial ferromagnetic films with well-defined crystallographic, magnetic and well defined interfaces in order to minimize the influence of disordered grain boundaries. In this respect, electrochemical deposition (ECD) method offers important advantages as it is low-energy, room-temperature deposition process which can limit the interdiffusion between the film and the substrate. First, the work on epitaxial growth of Fe and Ni onto n-AlGaAs(001) and their structural and magnetic properties is reported. Then the magneto-transport ...
Acta Materialia, 2012
ABSTRACT We report the correlation between the crystalline structure, electronic structure and ma... more ABSTRACT We report the correlation between the crystalline structure, electronic structure and magnetic properties of Co2FeAl films as a function of growing temperature both experimentally and theoretically. The Co2FeAl film grown at room temperature is initially in the partially disordered B2 state, but then it gains a much higher ordered structure with increasing growing temperature due to its transition from short-range to long-range crystallographic order by surface diffusion. Electron energy loss spectroscopy measurements reveals that the increase in the I(L3)/I(L2) ratio of Co can be attributed to the enhanced ferromagnetic exchange interaction between neighboring Co atoms and the fact that the Co contribution is more dominant than the Fe contribution. As the growing temperature increases, many more unoccupied 3d states in Co are observed, hence the Gilbert damping constant increases due to a strong spin–orbit interaction. We also present the results of highly accurate quasiparticle self-consistent GW calculations and confirm that Co2FeAl in an ideal L21 structure is indeed a half-metal with a well-defined band gap in the minority spin channel.
Thin Solid Films, 2014
Abstract Epitaxial Ni thin films were prepared on GaAs(110) substrates using electrodeposition. R... more Abstract Epitaxial Ni thin films were prepared on GaAs(110) substrates using electrodeposition. Resistivity and Hall effect measurements were performed as a function of film thickness. The bulk resistivity value at room temperature is close to the literature value for Ni whereas the low temperature bulk resistivity value is of the order of 0.1 μΩcm, indicating a very low intra-layer defect density due to the high quality of the epitaxial growth. The anomalous Hall coefficient varies with the film resistivity as ρ1.3 and thus strongly depends on the film thickness. Such films with very low defect density might serve as model systems for the study of electromigration effects.
Journal of Applied Physics, Apr 15, 2006
Here we show that ordinary band structure codes can be used to understand the mechanisms of coher... more Here we show that ordinary band structure codes can be used to understand the mechanisms of coherent spin-injection at interfaces between ferromagnets and semiconductors. This approach allows the screening of different material combinations for properties useful for obtaining high tunneling magnetoresistance (TMR). We used the Vienna Ab-initio Simulation Code (VASP) to calculate the wave function character of each band in periodic epitaxial Fe(100)|GaAs(100) and Fe(100)|ZnSe(100) structures. It is shown that Fe wave functions of different symmetry near Fermi energy decay differently in the GaAs and ZnSe.
Electrochemical and Solid State Letters, 2008
ABSTRACT We report epitaxial growth of body-centered cubic Fe and face-centered cubic Ni thin fil... more ABSTRACT We report epitaxial growth of body-centered cubic Fe and face-centered cubic Ni thin films on n-type AlGaAs(001) substrates using electrochemical deposition with the cubic axes of Fe oriented parallel to the substrate lattice while the Ni is rotated in-plane 45 degrees. The magnetic properties in either case are dominated by the fourfold crystalline anisotropy, a high remanence, and saturation magnetization values similar to bulk properties. The growth of such ferromagnetic contacts on AlGaAs might find applications in magneto-electronics. (c) 2008 The Electrochemical Society.
IEEE Transactions on Magnetics, Oct 1, 2005
The tunneling current for electrons tunneling between crystalline ferromagnetic electrodes throug... more The tunneling current for electrons tunneling between crystalline ferromagnetic electrodes through an epitaxial crystalline barrier can be calculated from first principles. These calculations show that the wave function symmetry can be exploited to achieve very high tunneling magnetoresistance. For the Fe(100) MgO(100) Fe(100) system, the calculated conductance is much higher and its decrease with MgO thickness is much slower than has been estimated using a simple free electron-barrier model.
Bulletin of the American Physical Society, Mar 6, 2007
Epitaxial ferromagnetic materials grown on semiconductors are potential candidates for new class ... more Epitaxial ferromagnetic materials grown on semiconductors are potential candidates for new class of spintronic devices which can be used as contacts for spin injection. In this respect electrodeposition has proven to be a promising method as it avoids interface because it is a low-energy, room temperature process. Here we report the electrical transport properties of electrodeposited Ni thin films on GaAs(110) substrate. We have performed resistivity and Hall Effect measurements as a function of film thickness. The results show that the thickness dependence of the electrical resistivity follows the Fuchs 1 model. The bulk resistivity at room temperature is close to the reported bulk properties. The low temperature resistivity values are dominated by surface scattering with the bulk resistivity being essentially zero. The low temperature ordinary Hall coefficient R o of the films is almost independent of the film thickness, whereas the spontaneous Hall coefficient R s decreases with increasing film thickness. The spontaneous Hall coefficient scales with the resistivity as R s ∝ ρ 1.3 , indicating a scattering mechanism which is mixture of both skew scattering and side jump scattering. 1. K. Fuchs, Proc. Camb. Phil. Soc. 34, 100 (1938)
Epitaxial ferromagnetic materials grown on semiconductors are potential candidates for new class ... more Epitaxial ferromagnetic materials grown on semiconductors are potential candidates for new class of spintronic devices which can be used as contacts for spin injection. In this respect electrodeposition has proven to be a promising method as it avoids interface because it is a low-energy, room temperature process. Here we report the electrical transport properties of electrodeposited Ni thin films on GaAs(110) substrate. We have performed resistivity and Hall Effect measurements as a function of film thickness. The results show that the thickness dependence of the electrical resistivity follows the Fuchs 1 model. The bulk resistivity at room temperature is close to the reported bulk properties. The low temperature resistivity values are dominated by surface scattering with the bulk resistivity being essentially zero. The low temperature ordinary Hall coefficient R o of the films is almost independent of the film thickness, whereas the spontaneous Hall coefficient R s decreases with increasing film thickness. The spontaneous Hall coefficient scales with the resistivity as R s ∝ ρ 1.3 , indicating a scattering mechanism which is mixture of both skew scattering and side jump scattering. 1. K. Fuchs, Proc. Camb. Phil. Soc. 34, 100 (1938)
In the emerging field of spintronics, along with charge, spin of the electron also plays a vital ... more In the emerging field of spintronics, along with charge, spin of the electron also plays a vital role. This discovery of spin-dependent transport has stimulated wide interest in the design of novel memory and logic devices. In particular, the proposal of spin field effect transistor by Datta and Das has triggered great attention on the issue of integration of ferromagnetic materials with semiconductors. These spintronics devices would require the growth of epitaxial ferromagnetic films with well-defined crystallographic, magnetic and well defined interfaces in order to minimize the influence of disordered grain boundaries. In this respect, electrochemical deposition (ECD) method offers important advantages as it is low-energy, room-temperature deposition process which can limit the interdiffusion between the film and the substrate. First, the work on epitaxial growth of Fe and Ni onto n-AlGaAs(001) and their structural and magnetic properties is reported. Then the magneto-transport ...
Acta Materialia, 2012
ABSTRACT We report the correlation between the crystalline structure, electronic structure and ma... more ABSTRACT We report the correlation between the crystalline structure, electronic structure and magnetic properties of Co2FeAl films as a function of growing temperature both experimentally and theoretically. The Co2FeAl film grown at room temperature is initially in the partially disordered B2 state, but then it gains a much higher ordered structure with increasing growing temperature due to its transition from short-range to long-range crystallographic order by surface diffusion. Electron energy loss spectroscopy measurements reveals that the increase in the I(L3)/I(L2) ratio of Co can be attributed to the enhanced ferromagnetic exchange interaction between neighboring Co atoms and the fact that the Co contribution is more dominant than the Fe contribution. As the growing temperature increases, many more unoccupied 3d states in Co are observed, hence the Gilbert damping constant increases due to a strong spin–orbit interaction. We also present the results of highly accurate quasiparticle self-consistent GW calculations and confirm that Co2FeAl in an ideal L21 structure is indeed a half-metal with a well-defined band gap in the minority spin channel.
Thin Solid Films, 2014
Abstract Epitaxial Ni thin films were prepared on GaAs(110) substrates using electrodeposition. R... more Abstract Epitaxial Ni thin films were prepared on GaAs(110) substrates using electrodeposition. Resistivity and Hall effect measurements were performed as a function of film thickness. The bulk resistivity value at room temperature is close to the literature value for Ni whereas the low temperature bulk resistivity value is of the order of 0.1 μΩcm, indicating a very low intra-layer defect density due to the high quality of the epitaxial growth. The anomalous Hall coefficient varies with the film resistivity as ρ1.3 and thus strongly depends on the film thickness. Such films with very low defect density might serve as model systems for the study of electromigration effects.