Existence Of Antiphase Boundaries Research Articles

Structural, magnetic, magnetocaloric behavior and magneto-transport, electrical polarization study in 3d based bulk and nano-crystalline multiferroic double perovskite Dy2MnCoO6

In this paper, we report a detailed investigation of the crystal structure, magnetic, magnetocaloric, magneto-transport and electrical polarization properties of a new multiferroic material in the polycrystalline and nanocrystalline form of the Dy2MnCoO6 double perovskite. Both compounds crystallized in the monoclinic structure with P21/n space group. The magnetic properties of both systems are mainly dominant ferromagnetic (FM) and weak antiferromagnetic (AFM). The FM/AFM coupling is related by the competing and combining functions of the radius and the magnetic moments of rare earth ions (i.e. 3d–4f exchange interactions). The reduction of the saturation magnetization in the isothermal magnetization curves can be explained by the existence of anti-phase boundaries and local anti-site defects in the system. Moreover, these materials hold reasonable values of magnetocaloric parameters and the absence of hysteresis makes the system a potential candidate for magnetic refrigeration. These compounds revealed two magnetic phase transitions, according to the appearance of two peaks in the temperature dependence of magnetic entropy change curves. The temperature dependent resistivity data for both the systems display semiconductor nature near room temperature and insulating like behavior at low temperature regime. The variable-range hopping conduction mechanism is used to best understand their transport mechanism. In addition, the electrical polarization loop at low temperature confirms the presence of ferroelectricity for both the studied systems. The decreases polarization under an external magnetic field evidence the weak magnetoelectric coupling. The coexistence of FM ordering with insulating behavior and ferroelectricity at low temperature promises new opportunities and improvements in next generation applications for information storage, spintronic, and sensors.

Epitaxial Growth of Co<sub>0.75</sub>Fe<sub>2.25</sub>O<sub>4</sub>/NiO Bilayer on MgO(001) Substrate

Co x Fe 3−x O 4 (CFO) films epitaxially grown on MgO(001) substrates show perpendicular magnetic anisotropy as high as 10 Merg/cm3[1]. However, magnetization is dependent on thickness. The magnetization per unit area linearly increases with increasing thickness of the films. Although the slope corresponds to the bulk magnetization, the slope intersects the horizontal (thickness) axis, suggesting that a magnetic dead layer exists at the interface/surface of the films. There are several possible reasons for the decrease in magnetization at the interface such as diffusion of Mg from the substrates, existence of anti-phase boundaries (APBs), and so on. In order to prevent the formation of the dead layer and improve the magnetic properties at the interface, we investigated the effect of a NiO insertion layer on the magnetization of CFO films. It has been reported that the insertion layer of NiO prevents Mg diffusion from MgO substrates in Fe 3 O 4 /MgO(001)[2]. Since NiO is isostructural with MgO, we can expect that APBs in CFO films are formed on the NiO insertion layers as well as on the MgO surfaces.

Granular growth of Fe3O4 thin films and its antiphase boundaries prepared by pulsed laser deposition

Fe 3 O 4 thin film prepared by pulsed laser deposition on Si (100) substrate has been investigated by transmission electron microscopy from plane and cross-sectional views. The thin film, which shows a spinel structure as characterized by selected-area diffraction, is about 180 nm thick with granular growth of particle size about 50 nm. High resolution electron microscopy observations indicate reduced thickness of the native SiO2 layer between the thin film and Si due to rastering of the substrate surface by an unfocused laser beam before the deposition. By using a 220 diffraction spot in two beam condition near the 〈001〉 axis of a single Fe3O4 grain, antiphase boundaries (APBs) inside the grains could be clearly resolved. The existence of APBs in the thin film is consistent with the magnetic experiments including an open hysteresis loop and unsaturated magnetization in relatively high magnetic fields. This study suggests that APBs are not unique to Fe3O4 films grown on MgO substrates.

Folding ofX-point phonons and conduction-band valleys in partially CuPt-orderedGa0.52In0.48Pgrown on GaAs

We report the observation of a folded zone-edge phonon mode, in addition to the folded L point mode reported already in Raman scattering from ${\mathrm{Ga}}_{x}{\mathrm{In}}_{1\ensuremath{-}x}\mathrm{P}$ epitaxial layers grown on GaAs and containing two variants of CuPt ordering. This Raman mode becomes observable as a result of resonant enhancement at an electronic transition at 2.25 eV reported previously in electroreflectance measurements. Our results suggest that a folding of the Brillouin zone along the [001] direction occurs in partially ordered ${\mathrm{Ga}}_{x}{\mathrm{In}}_{1\ensuremath{-}x}\mathrm{P}$ samples due to the existence of antiphase boundaries.

A new type of long period superlattice with hexagonal symmetry in AuCd alloys

The existence of a new type of long period superlattice having hexagonal symmetry, whose period is determined by the critical contact of the Brillouin zone boundaries with the Fermi surface, has been established. The ordering of the atoms on the close packed hexagonal plane of these structures is derived from that of the A 3 B type (Cu 3Au type) structure, but the long period is produced in the basal plane by the existence of antiphase boundaries in three directions perpendicular to the close packed plane and making 120° with each other, thus creating the hexagonal symmetry. The stacking of the close packed layers is of either the 2 H or 4 H type. The size of this hexagonal unit cell is found to be between seven and nine times as large as that of the hexagonal unit cell of the disordered close packed lattice, these limiting cases being called the 7 a 0 structure and the 9 a 0 structure respectively. Significantly, the period of this structure is found to respond to a change of e a in a fashion similar to that found in the one dimensional long period superlattice, which has been investigated in detail. In the case of the AuCd alloys the stacking is of the 2 H type and the 7 a 0 structure is identified as Au 72Cd 26 with space group P6 3 mmc , and the 9 a 0 structure as Au 42Cd 12 with P6 3 mcm . The geometry of the Brillouin zone structure indicates that the structure is stabilized by creating superlattice Brillouin zone boundaries at the flat part of the Fermi surface (in the 〈110〉 directions in the case of the fcc structure), as in the case of the one dimensional long period superlattice. Examples of these new structures are found, other than in the AuCd alloys reported here, in AuMg alloys, CuSb alloys, etc. near the A 3B composition range. These structures are usually found among the long period stacking variants of a one dimensional long period superlattice with non variable period ( M = 1, M = 2, etc.), occurring in these alloys.