Effect Of Antiphase Boundaries Research Articles

Regulation of antiphase boundary density in Fe3O4 thin films and its effect on the electrical and magnetic properties

Antiphase boundaries (APBs) widely exist in Fe3O4 thin films and affect significantly their electrical and magnetic properties. Here, effects of APBs on the electrical and magnetic properties of Fe3O4 thin films have been quantitatively investigated by a combined study of pulsed laser deposition, transmission electron microscopy (TEM) and first-principles calculations. It was revealed that the substrates affected greatly the density of APBs in Fe3O4 thin films but did not change the atomic structures of APBs. The APB density in the Fe3O4 (111) thin film grown on the MgO (111) substrate was one order of magnitude larger than that on the Al2O3 (0001) substrate. Atomic-scale TEM characterizations revealed that the APBs in the Fe3O4 thin films on both substrates had three types of atomic structures. Due to the higher APB density in the Fe3O4/MgO thin film, the electrical resistivity at 300 K was two orders of magnitude larger than that of the Fe3O4/Al2O3 thin film. Meanwhile, the saturation magnetization and the coercivity of the Fe3O4/MgO thin film were reduced by 86 % and 35 %, respectively. First-principles calculations suggested that the antiferromagnetic coupling was easily formed at all the three types of APBs, which led to the decrease of spin polarization and the increase of electrical resistance of the Fe3O4 thin films.

Influences of thickness and temperature of low temperature GaAs buffer layer on two-step MOVPE grown GaAs/Ge heterostructures

We investigate influence of GaAs buffer layer (BL) growth parameters such as temperature and thickness on the structural, morphological, crystalline and optical quality of metal organic vapor phase epitaxy (MOVPE) grown heterostructures of GaAs on Ge. It was found that the optimal BL conditions significantly decrease the effects of anti-phase boundaries (APBs) even when grown on offcut Ge substrate by two-step growth technique with AsH3 pre-flow to promote double atomic step formation. It is observed that as the growth temperature increases, the growth rate of the GaAs BL increases, too. Improvement on the structural quality is observed up to BLs temperature of 535 °C, then it decreases. On the other hand, as the different thick BLs, 12, 25, 75 nm are considered, the epilayer grown on the 25 nm thick BL has shown the lowest full width at half maximum (FWHM) value, large photoluminescence peak intensity and internal quantum efficiency (IQE).

Effect of antiphase boundaries on the magnetic properties of La2CoMnO6

We present a comparative study of structural and magnetic properties of the as-grown and annealed samples of double perovskite, La2CoMnO6. The single monoclinic (P21/n) phase has been achieved for both the samples. Electron microscopy highlights the change in morphology of the as-grown and annealed samples, with the annealed sample having more grain boundaries and bigger particle sizes. The annealing in presence of oxygen leads to increase in the population of antiphase boundaries, which is supported by the decreases in the remanent and saturation magnetizations. An analysis of magnetization dynamics by means of AC susceptibility shows four different magnetic transitions, with two high temperature ferromagnetic transitions and two cluster glass-like states emerging at low temperatures, which appear almost identical in both the as-grown and annealed samples.

Magnetoresistance of epitaxial and polycrystalline Fe3O4 films near Verwey transition

We report investigations of magnetoresistance (MR) in epitaxial and polycrystalline Fe3O4 films. MR in epitaxial Fe3O4 films exhibits a local maximum at TV and a large value of −20% at 60 K. Based on a 1D half infinite spin chain model, the fitting parameter, which depends on the volume fraction of electronic scattering boundaries, sharply increases below TV with the decreased temperature. We suppose that the twin boundaries formed below TV facilitate the increase in MR and can act as antiphase boundaries (APBs) where the magnetic moments across twin boundaries are coupled antiferromagnetically. Similar MR behavior in Fe3O4(100) and (111) epitaxial films manifests the independence of MR on the spatial distribution of APBs. The outline of normalized MR in the epitaxial films shows a distinct temperature dependence. The temperature dependence may result from the different electronic transport mechanisms in Fe3O4 films. In a polycrystalline Fe3O4 film, MR comes from the disordered distribution of magnetic moments at grain boundaries. The effects of APBs, twin boundaries, and grain boundaries on MR are discussed in detail.

The effect of antiphase boundaries on the elastic properties of Ni–Mn–Ga austenite and premartensite

The evolution of elastic properties with temperature and magnetic field was studied in two differently heat-treated single crystals of the Ni–Mn–Ga magnetic shape memory alloy using resonant ultrasound spectroscopy. Quenching and slow furnace cooling were used to obtain different densities of antiphase boundaries. We found that the crystals exhibited pronounced differences in the c′ elastic coefficient and related shear damping in high-temperature ferromagnetic phases (austenite and premartensite). The difference can be ascribed to the formation of fine magnetic domain patterns and pinning of the magnetic domain walls on antiphase boundaries in the material with a high density of antiphase boundaries due to quenching. The fine domain pattern arising from mutual interactions between antiphase boundaries and ferromagnetic domain walls effectively reduces the magnetocrystalline anisotropy and amplifies the contribution of magnetostriction to the elastic response of the material. As a result, the anomalous elastic softening prior to martensite transformation is significantly enhanced in the quenched sample. Thus, for any comparison of experimental data and theoretical calculations the microstructural changes induced by specific heat treatment must be taken into account.

Влияние антифазных границ на структурно-энергетические характеристики сплавов системы Cu-Pt

Влияние антифазных границ на структурно-энергетические характеристики сплавов системы Cu-Pt

Effects of substitutional impurity Au and Si atoms on antiphase boundary energies in Ti3Al: A first principles study

Effects of substitutional impurity atoms Au and Si on the energies of antiphase boundaries (APBs) on {1100} and (0001) planes in a Ti3Al intermetallic compound were examined using first principles calculations. Au additions reduce the energies of APBs on both {1100} and (0001) planes by up to more than 40%. The reduction tends to be more remarkable especially when the added Au atom has larger number of Al atoms on its second-nearest neighbor sites rather than on first-nearest neighbor ones. In addition, in the case of Si addition, a significant energy reduction was found only for APBs on (0001) planes, and no remarkable dependence of APB energies on the coordinating atoms was found even for APBs on (0001) planes. These results are crucial to both understanding of the effect of APBs on the impurity diffusivity and predicting the ability of impurity atoms to stabilize antiphase domain structure that increases the strength of Ti3Al dramatically.

Effect of antiphase boundaries on electrical transport properties of Fe3O4 nanostructures

Fe 3 O 4 nanowires have been fabricated based on Fe3O4 thin films grown on α-Al2O3 (0001) substrates using the hard mask and ion milling technique. Compared with thin films, the Fe3O4 nanowire exhibits a slightly sharper Verwey transition but pronounced anisotropic magnetoresistance properties in the film plane at low magnetic field. Detailed bias-dependence study of both the conductance and magnetoresistance curves for both the thin films and nanowires suggests that the electrical conduction in magnetite near and above the Verwey transition temperature is dominated by a tunneling mechanism across antiphase boundaries.

Effects of bond relaxation on the martensitic transition and optical phonons in spontaneously orderedGaInP2

Strong changes of the Raman intensity induced by the martensitic transition in spontaneously ordered ${\mathrm{GaInP}}_{2}$ alloys are explained by the triggering of the atom positions between unrelaxed (zinc-blende bond lengths) and relaxed $({\mathrm{CuPt}}_{B}$ bond lengths) arrangements. We show that these changes reflect a strong dependence of the optical-phonon properties and Raman selection rules of ${\mathrm{CuPt}}_{B}$-ordered ${\mathrm{GaInP}}_{2}$ on bond relaxation. Using analysis of the experimental spectra available in the literature we demonstrate that the relaxed and unrelaxed martensitic states can be detected by exciting different crystallographic planes. A strong effect of antiphase boundaries on the Raman spectra of spontaneously ordered ${\mathrm{GaInP}}_{2}$ is revealed.

Effect of antiphase boundaries on the electronic structure and bonding character of intermetallic systems: NiAl.

The possible origin of the high degree of brittleness, i.e., low ductility, of the NiAl-based alloys in the B2 structure is investigated by all-electron self-consistent total-energy linear-muffin-tin-orbital calculations. Using a supercell approach (with up to 20 atoms/unit cell), the energetics of the two simplest antiphase boundaries (APB's) for NiAl in the B2 structure--namely the 1/2〈111〉 on {110} and 1/2〈111〉 on {112}--are calculated assuming no relaxation at the interface. We find APB energies of the order of 800 mJ/${\mathrm{m}}^{2}$ for both cases. Since the calculated APB energies are very high, 〈111〉 slip is unlikely to occur--as suggested experimentally and by some phenomenological theories. By substituting Ni or Al with V, Cr, or Mn at the APB interfacial planes, remarkably decreased APB energies are obtained. These theoretical results on simplified model systems may suggest a way to decrease the APB energy in order to eliminate one of the possible reasons for the brittleness at ambient temperatures.

An effect of antiphase boundaries on the kinetics of short-range ordering by a vacancy mechanism

In Monte Carlo simulations of chemical short-range ordering on a square lattice, the number of single-atom domains was found to depend on the presence of antiphase boundaries and on the mechanism by which ordering occurred. When antiphase boundaries were present and the ordering occurred by a vacancy mechanism, the number of single-atom domains was found to increase with decreasing temperature, in contrast to thermodynamic predictions. This is understood as a consequence of highly correlated vacancy motions in those regions of the lattice away from antiphase boundaries.

Modeling of Antiphase Boundaries in L12Structures

AbstractThe thermodynamic properties of conservative (111) antiphase boundaries in L12ordered structures are modeled using the tetrahedron approximation of the cluster variation method. The concentration and long-range order parameter profiles are determined as a function of temperature and composition of the bulk alloy. Characteristic wetting transitions, with a macroscopic disordered layer growing from the antiphase boundary as the transition temperature is approached, are found for all cases investigated. The effectof antiphase boundaries on the disordering of ordered alloys and on the gliding of superdislocations are discussed.

Effect of antiphase boundaries on the magnetic properties of Cu-Mn-Al Heusler alloys

Abstract The magnetic properties of Heusler alloys of approximate composition Cu2MnAl have been studied by Lorentz microscopy. as a function of composition, heat treatment and plastic deformation. Magnetic domain walls have been observed to be pinned at antiphase boundaries. The strength of pinning varies with composition and heat treatment, being strongest in alloys in which some of the aluminum has been replaced by copper, and in specimens which have been quenched from above the ordering temperature The pinning is thought to be due to antiferromagnetic coupling between the magnetic moments of manganese atoms on opposite sides of antiphase boundaries. Magnetic domain walls are also pinned at antiphase boundaries produced by the splitting of superlattice dislocations during plastic deformation. The results obtained by Lorentz microscopy provide an explanation for the variations of bulk magnetic properties with composition and heat treatment.

Effect of antiphase boundaries on the lattice parameter of ordered solid solutions with the L12 superstructure

Effect of antiphase boundaries on the lattice parameter of ordered solid solutions with the L12 superstructure

Effect of antiphase boundaries on the thermodynamic properties of the order-disorder transition

Effect of antiphase boundaries on the thermodynamic properties of the order-disorder transition

Mössbauer Studies of Ordered and Cold-Worked Fe–Al Alloys Containing 30 to 50 at. % Aluminum

Fe–Al alloys containing 30 to 50 at. % Al were investigated by Mössbauer spectroscopy. Both ordered alloys, having the CsCl or B2 structure, and alloys severely cold-worked by crushing were studied. At room temperature, all of the ordered alloys exhibit only paramagnetic lines, whereas the crushed alloys exhibit both paramagnetic and ferromagnetic lines, the intensity of the former increasing from 0% to 100% as the Al concentration increased from 30% to 50%. The results can be explained by considering the nearest neighbor configurations of Fe atoms in the ordered and deformed alloys, with slight corrections for next-nearest neighbors. Plastic deformation induces ferromagnetism by creating large numbers of antiphase boundaries across which the number of Fe–Fe nearest-neighbor bonds is significantly greater than in the ordered alloy. The observed percentages of paramagnetic and ferromagnetic material and the average effective field values in the crushed alloys indicate that the average linear dimensions of the antiphase domains are about six atomic distances. In addition, the effects of antiphase boundaries and short-range order produced by heat treatment have been observed in alloys of the DO3 structure (BiF3 type) having less than 25% Al.