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  • 1
    Electronic Resource
    Electronic Resource
    Magnetotransport in magnetic epitaxial metal layers buried in (Ga,Al)As heterostructures (invited) (abstract) : 35th annual conference on magnetism and magnetic materials (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 6117-6117 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Incorporation of magnetic, metallic quantum wells in semiconductors has added new dimensions to epitaxial heterostructures. Magnetotransport experiments explore the interplay of bandstructure, quantum confinement, dimensionality and magnetism. Rare earth monoarsenides, like ErAs, have been grown as buried layers in GaAs. The material is a semimetallic antiferromagnet that exhibits spin-disorder scattering at the Néel point. By diluting the ErAs with ScAs, lattice matching to GaAs can be achieved and these materials exhibit Shubnikov–de Haas (SdH) oscillations. The exchange interaction between the conduction band and the 4f spin deduced from SdH agrees with that derived from spin-disorder scattering. Surprisingly, down to 2 monolayers, quantum confinement does not convert the semimetal into a semiconductor. This is not understood. But, the Neel point can be seen to drop by a factor of two by following the spin-disorder scattering. In the few monolayer regime the magnetotransport can change its character and is more aptly described by bound magnetic polarons. More recently, ferromagnetic, metastable, τ-MnAl layers have also been grown on GaAs. Thin layers of τ-MnAl grow in such a way that the tetragonal axis is perpendicular to the interface. The extraordinary Hall effect and longitudinal magnetotransport confirm that the moment has the desired property of being oriented perpendicular to the interface.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.347785
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  • 2
    Electronic Resource
    Electronic Resource
    Epitaxial relations between in situ superconducting YBa2Cu3O7−x thin films and BaTiO3/MgAl2O4/Si substrates (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 1772-1776 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In situ superconducting YBa2Cu3O7−x films with Tc0 up to 87 K and Jc, 77 K up to 6×104 A/cm2 were prepared on Si substrates with MgAl2O4 and BaTiO3 double-buffer layers. The epitaxial relations between various layers were established by transmission electron microscopy. The MgAl2O4 layer is heavily faulted. The subsequent BaTiO3 layer stops most of the faults, provides a template for the YBa2Cu3O7−x growth, and partially screens off the stress due to different thermal expansion coefficients. The microstructure of the YBa2Cu3O7−x layer is very similar to that of the films deposited directly on SrTiO3, exhibiting a homogeneous heavily faulted single-crystal-like structure free from secondary phases and grain boundaries. The slight degradation of the transport properties is attributed to residual thermal stress.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.346607
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  • 3
    Electronic Resource
    Electronic Resource
    A microstructure based magnetization reversal model in sintered Fe-Nd-B magnets. II. Effect of post sintering treatments (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 5772-5777 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effect of post sintering heat treatments on the intrinsic coercivity of Fe-Nd-B magnets is studied. It is shown that the large anisotropy in thermal expansion coefficients in the a and c directions of the tetragonal unit cell as well as the anisotropy in thermal expansion properties between the matrix and the grain boundary phase, will lead to stresses upon quenching from the sintering temperature. The effect of stresses due to water quenching have been incorporated into the model developed in the companion paper (Part I). This quenching stress manifests itself as a stress anisotropy constant, which opposes the magnetocrystalline anisotropy constant. Thus, the effective anisotropy field, near the interfaces, is reduced from its value in an optimally cooled sample, leading to a lower iHc. It is also shown through step quenching experiments that the effect of quenching stresses can be nullified by cooling slowly to below a specific temperature following which quenching does not influence the intrinsic coercivity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.346946
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  • 4
    Electronic Resource
    Electronic Resource
    The extraordinary Hall effect in coherent epitaxial τ (Mn,Ni)Al thin films on GaAs : 37th Annual conference on magnetism and magnetic materials (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 6399-6401 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Ultrathin coherent epitaxial films of ferromagnetic τ(Mn,Ni)0.60Al0.40 have been grown by molecular beam epitaxy on GaAs substrates. X-ray scattering and cross-sectional transmission electron microscopy measurements confirm that the c axis of the tetragonal τ unit cell is aligned normal to the (001) GaAs substrate. Measurements of the extraordinary Hall effect (EHE) show that the films are perpendicularly magnetized, exhibiting EHE resistivities saturating in the range of 3.3–7.1 μΩ-cm at room temperature. These values of EHE resistivity correspond to signals as large as +7 and −7 mV for the two magnetic states of the film with a measurement current of 1 mA. Switching between the two magnetic states is found to occur at distinct field values that depend on the previously applied maximum field. These observations suggest that the films are magnetically uniform. As such, τ(Mn,Ni)Al films may be an excellent medium for high-density storage of binary information.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.352609
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  • 5
    Electronic Resource
    Electronic Resource
    A microstructure based magnetization reversal model in sintered Fe-Nd-B magnets. I (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 5767-5771 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A microstructure based magnetization reversal model is presented for sintered Fe-Nd-B magnets. The model makes use of a position dependent domain wall energy profile to correlate the intrinsic coercivity, iHc (and the nucleation field) to the magnetocrystalline anisotropy field. The inferences of the model are verified through the study of the effect of Dy and Ce additions on the iHc as well as by examining the temperature dependence of iHc and anisotropy field existing in published literature. It is inferred from this model that selective modifications of the interfaces could lead to appreciable improvements in the magnetic properties.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.346945
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  • 6
    Electronic Resource
    Electronic Resource
    Galvanomagnetic properties of epitaxial MnAl films on GaAs : 35th Annual conference on magnetism and magnetic materials (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 4689-4691 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Single-crystal films of τ-MnAl are grown by molecular-beam epitaxy on GaAs substrates. The extraordinary Hall effect shows a large hysteresis loop, and the magnetization is found to have a substantial component perpendicular to the plane of the film.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.348298
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  • 7
    Electronic Resource
    Electronic Resource
    Thickness dependence of structural and electrical properties in epitaxial lead zirconate titanate films (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 595-602 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have studied the effect of misfit strain on the microstructure and properties of ferroelectric lead zirconate titanate thin films. We have changed the misfit strain by varying the film thickness and studied the thickness effect on the domain formation of epitaxial PbZr0.2Ti0.8O3 (PZT) films grown by pulsed laser deposition on (001) LaAlO3 substrates with La0.5Sr0.5CoO3 (LSCO) electrodes. The nominal thickness of the PZT films was varied from 60 to 400 nm with the LSCO electrode thickness kept constant at 50 nm. X-ray diffraction experiments show that the films relax via the formation of a domains, the fraction of which increase with the ferroelectric film thickness. The c-axis lattice constant of PZT films calculated from the 002 reflection decreases with increasing film thickness and approaches the bulk value of ∼0.413 nm in the films thicker than 300 nm. Cross-sectional transmission electron microscopy images reveal that the a-domain fraction and period increase with increasing film thickness. The relaxation of misfit strain in the film is accompanied by systematic changes in the polarization properties, as well as the switching fields, quantified by the coercive field and the activation field. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.370772
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  • 8
    Electronic Resource
    Electronic Resource
    Imaging three-dimensional polarization in epitaxial polydomain ferroelectric thin films (2002)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 91 (2002), S. 1477-1481 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Voltage-modulated scanning force microscopy (Piezoresponse microscopy) is applied to investigate the domain structure in epitaxial PbZr0.2Ti0.8O3 ferroelectric thin films grown on (001) SrTiO3. By monitoring the vertical and lateral differential signals from the photodetector of the atomic force microscope it is possible to separate out and observe the out-of-plane and in-plane polarization vectors in the thin film individually. The relative orientation of the polarization vectors across a 90° domain wall is observed. Nucleation of new reversed 180° domains at the 90° domain wall is studied and its impact on the rotation of polarization within the a domain is analyzed as a function of reversal time. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1421219
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  • 9
    Electronic Resource
    Electronic Resource
    Influence of contact electrodes on leakage characteristics in ferroelectric thin films (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 90 (2001), S. 375-382 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Electrodes can impact the device performance of ferroelectric capacitors in several ways. The present controlled studies on Pb (Nb, Zr, Ti)O3 with Pt, (La, Sr)CoO3 and SrRuO3 is a clear demonstration of the role of electrodes in impacting the leakage current mechanism of the ferroelectric capacitors and their reliability properties. The oxide electrode capacitors show predominantly nonblocking contact and good fatigue and imprint properties. Pt electrode capacitors show blocking contacts, long term leakage current relaxation, and poor fatigue and imprint properties. The nature of the temperature and voltage dependence of leakage current relaxation in Pt capacitors indicates trapping of charge carriers to be the cause for the observed relaxation. A good correlation between leakage current relaxation and the rate of polarization loss during fatigue and the similarity in their voltage and temperature dependence suggests trapping (of charged carriers/domains, respectively) as common to both phenomena. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1371947
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  • 10
    Electronic Resource
    Electronic Resource
    Columnar defect induced phase transformation in epitaxial La0.7Ca0.3MnO3 films (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 4210-4215 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Epitaxial La0.7Ca0.3MnO3 thin films on the SrTiO3(100) surface have been irradiated with 250 MeV Ag17+ ions at different nominal fluence values in the range of 5×1010–4×1011 ions/cm2, resulting in columnar defects. At low fluences these defects cause changes in material properties that are small and scale linearly with dosage. Above a threshold fluence value ∼3×1011 ions/cm2 dramatic changes are observed, including an order of magnitude increase in the resistivity and 50 K drop in the Curie temperature. Transmission electron microscopy measurements show that the changes are associated with a phase transformation of the undamaged region between the columnar defects. The transformed phase has a diffraction pattern very similar to that seen in charge-ordered La0.5Ca0.5MnO3. We propose that above a critical level of ion damage, strains caused by the presence of the columnar defects induce a charge-ordering phase transition that causes the observed dramatic changes in physical properties. We speculate that a conceptually similar surface-induced charge ordering may be responsible for the "dead layer" observed in very thin strained films, and the dramatic changes in optical properties induced by polishing, and that an impurity-induced charge ordering causes the extreme sensitivity of properties to lattice substitution. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.373054
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