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Complex morphology is observed in the GaAs:Bi cap layer of Ga(As,Bi) films grown on GaAs(001) substrates by low-temperature (LT) molecular beam epitaxy (MBE). The microstructure is dominated by the presence of V-shaped domains in the LT-GaAs cap layer and by the (unintentional) inhomogeneous incorporation of Bi from the underlying Ga(As,Bi) layer growth. Aberration-corrected scanning transmission electron microscopy techniques enabled two types of domain to be identified: (i) twinned domains and (ii) Bi-rich atomically ordered domains with triple periodicity. The observed microstructure is discussed in the context of LT-MBE growth in combination with the presence of a small amount of Bi, which seemingly alters adatom diffusivity. Surface processes and (surface) kinetic factors play a key role in the resultant morphology and explain the appearance of both types of domains. [ABSTRACT FROM AUTHOR]

We report a study of the magnetic domain structure of nanocrystalline thin films of nickel-zinc ferrite. The ferrite films were synthesized using aqueous spin-spray coating at low temperature (∼90 °C) and showed high complex permeability in the GHz range. Electron microscopy and microanalysis revealed that the films consisted of columnar grains with uniform chemical composition. Off-axis electron holography combined with magnetic force microscopy indicated a multigrain domain structure with in-plane magnetization. The correlation between the magnetic domain morphology and crystal structure is briefly discussed. [ABSTRACT FROM AUTHOR]

We have used electron holography to investigate the local magnetic behavior of isolated ferromagnetic nanowires (NWs) in their remanent states. The NWs consisted of periodic magnetic layers of soft, high-saturation magnetization CoFeB alloys, and non-magnetic layers of Cu. All NWs were fabricated by pulsed-potential electrodeposition in nanoporous alumina membranes. The NW composition and layer thicknesses were measured using scanning transmission electron microscopy and energy dispersive spectroscopy. The magnetization of individual NWs depended upon the thicknesses of the layers and the direction of an external magnetic field, which had been applied in situ. When the CoFeB was thicker than the diameter (50 nm), magnetization was axial for all external field directions, while thinner layers could be randomized via a perpendicular field. In some cases, magnetization inside the wire was detected at an angle with respect to the axis of the wires. In thinner Cu/CoFeB (<10 nm each) multilayer, magnetic field vortices were detected, associated with opposing magnetization in neighbouring layers. The measured crystallinity, compositions, and layer thicknesses of individual NWs were found to be significantly different from those predicted from calibration growths based on uniform composition NWs. In particular, a significant fraction of Cu (up to 50 at. %) was present in the CoFeB layers such that the measured magnetic induction was lower than expected. These results will be used to better understand previously measured effective anisotropy fields of similar NW arrays. [ABSTRACT FROM AUTHOR]

Magnetic remanent states in a rectangular array of 75×280-nm2 NiFe/Cu/Co thin-film pseudo-spin-valve elements are studied using off-axis electron holography in the transmission electron microscope (TEM). An approach based on focused ion-beam milling is used to minimize damage to the magnetic properties of the elements during preparation for TEM examination in plan-view geometry. Experimental electron holographic phase images are used to measure the switching fields of the Co and NiFe layers in each of three adjacent elements separately, and comparisons with micromagnetic simulations are used to infer the true magnetic thicknesses and widths of the layers. Demagnetizing fields are included in the discussion of the results, and the possibility that the conclusions may be affected by the procedure used to analyze the holograms is discussed. [ABSTRACT FROM AUTHOR]

We report a study of the magnetic switching behavior of nanoscale Co rings using off-axis electron holography. Arrays of 10 nm thick polycrystalline Co rings with 400 nm outer diameter (OD) and different inner diameter (ID) were fabricated by electron-beam lithography. The switching behavior of the rings was studied for different OD/ID ratios, and two kinds of reversal mechanism were identified. For OD/ID of 400 nm/250 nm and 400 nm/50 nm, the reversal started from the so-called onion (bidomain) state, proceeding to a stable vortex state, and finally to the reversed onion state. For intermediate OD/ID of 400 nm/150 nm, the reversal was instead accomplished via rotation of head-to-head domain walls around the rings to the reversed onion state without formation of a vortex state. The OD/ID ratio of the rings thus played the most important role in determining the switching process. Irrespective of the reversal mechanism, the coercive field of the rings and the range of the field needed to reverse their magnetization, both increased as the inner ring diameter was increased (i.e., narrower ring). The significance of different contributions to the total energy in causing these differences in switching behavior is briefly discussed. [ABSTRACT FROM AUTHOR]

Provides information on a study wherein an asymmetrical triangular quantum well was grown by molecular-beam epitaxy using a digital alloy composition grading methods. Methods; Results; Conclusion.