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In this work, we present the magneto-ionic response to ionic liquid gating in Ta/CoFeB/MgO/HfO2 stacks, where heavy metal dusting layers of Ta, W, and Pt are inserted at the Ta/CoFeB and CoFeB/MgO interfaces. Dusting layers of W inserted at the Ta/CoFeB interface increase perpendicular magnetic anisotropy (PMA) by more than 50%, while no significant changes are seen for Pt. In these samples, gating cannot break the PMA seeded at the CoFeB/MgO interface, only relatively small changes in the coercivity can be induced, about 20% for Ta and Pt and 6% for W. At the CoFeB/MgO interface, a significant quenching of the magnetization is seen when W and Ta dusting layers are inserted, which remains unchanged after gating, suggesting a critical deterioration of the CoFeB. In contrast, Pt dusting layers result in an in-plane anisotropy that can be reversibly converted to PMA through magneto-ionic gating while preserving the polycrystalline structure of the MgO layer. This shows that dusting layers can be effectively used not only to engineer magnetic properties in multilayers but also to strongly modify their magneto-ionic performance. [ABSTRACT FROM AUTHOR]

We present a multi-microscopy study of dislocations in InGaN, whereby the same threading dislocation was observed under several microscopes (atomic force microscopy, scanning electron microscopy, cathodoluminescence imaging and spectroscopy, transmission electron microscopy), and its morphological optical and structural properties directly correlated. We achieved this across an ensemble of defects large enough to be statistically significant. Our results provide evidence that carrier localization occurs in the direct vicinity of the dislocation through the enhanced formation of In-N chains and atomic condensates, thus limiting non-radiative recombination of carriers at the dislocation core. We highlight that the localization properties in the vicinity of threading dislocations arise as a consequence of the strain field of the individual dislocation and the additional strain field building between interacting neighboring dislocations. Our study therefore suggests that careful strain and dislocation distribution engineering may further improve the resilience of InGaNbased devices to threading dislocations. Besides providing a new understanding of dislocations in InGaN, this paper presents a proof-of-concept for a methodology which is relevant to many problems in materials science. [ABSTRACT FROM AUTHOR]

Nucleation of soft magnetic Fe3Si nanocrystals in Cu-free Fe74.5Si15.5Nb3B7 alloy, upon rapid (10?s) and conventional (30?min) annealing, was investigated using x-ray diffraction, transmission electron microscopy, Mössbauer spectroscopy, and atom probe tomography. By employing rapid annealing, preferential nucleation of Fe3Si nanocrystals was achieved, whereas otherwise there is simultaneous nucleation of both Fe3Si and undesired Fe-B compound phases. Analysis revealed that the enhanced Nb diffusivity, achieved during rapid annealing, facilitates homogeneous nucleation of Fe3Si nanocrystals while shifting the secondary Fe-B crystallization to higher temperatures resulting in pure soft magnetic nanocrystallization with very low coercivities of ~10?A/m. [ABSTRACT FROM AUTHOR]

A methodology for the determination of the subsurface line direction of dislocations using scanning tunneling microscopy (STM) images is presented. The depth of the dislocation core is derived from an analysis of the displacement field measured by STM. The methodology is illustrated for dislocations at GaN(10̄10) cleavage surfaces. It is found that the dislocation line bends toward the surface, changing from predominantly edge-type to more screw-type character, when approaching the intersection point. Simultaneously, the total displacement detectable at the surface increases due to a preferred relaxation towards the surface. [ABSTRACT FROM AUTHOR]

The one-dimensional charge density distribution along an electrically biased Fe atom probe needle is measured using a model-independent approach based on off-axis electron holography in the transmission electron microscope. Both the mean inner potential and the magnetic contribution to the phase shift are subtracted by taking differences between electron-optical phase images recorded with different voltages applied to the needle. The measured one-dimensional charge density distribution along the needle is compared with a similar result obtained using model-based fitting of the phase shift surrounding the needle. On the assumption of cylindrical symmetry, it is then used to infer the three-dimensional electric field and electrostatic potential around the needle with ~10 nm spatial resolution, without needing to consider either the influence of the perturbed reference wave or the extension of the projected potential outside the field of view of the electron hologram. The present study illustrates how a model-independent approach can be used to measure local variations in charge density in a material using electron holography in the presence of additional contributions to the phase, such as those arising from changes in mean inner potential and specimen thickness. [ABSTRACT FROM AUTHOR]

Doping mechanisms of Mn in GaAs nanowires (NWs) that have been grown self-catalytically at 600 °C by molecular beam epitaxy (MBE) are investigated using advanced electron microscopy techniques and atom probe tomography. Mn is found to be incorporated primarily in the form of non-magnetic tetragonal Ga0.82Mn0.18 nanocrystals in Ga catalyst droplets at the ends of the NWs, while trace amounts of Mn (22±4 at. ppm) are also distributed randomly in the NW bodies without forming clusters or precipitates. The nanocrystals are likely to form after switching off the reaction in the MBE chamber, since they are partially embedded in neck regions of the NWs. The Ga0.82Mn0.18 nanocrystals and the low Mn concentration in the NW bodies are insufficient to induce a ferromagnetic phase transition, suggesting that it is difficult to have high Mn contents in GaAs even in 1-D NW growth via the vapor-liquid-solid process. [ABSTRACT FROM AUTHOR]

Magnetoelectric (ME) coupling in La0.7Sr0.3MnO3/Pb(Mg1/3Nb2/3)0.7Ti0.3O3 (LSMO/PMN–PT (001)) has been probed in the past years to identify the underlying mechanism behind it. PMN–PT, which is well known for its excellent piezoelectric properties, also exhibits ferroelectricity. This motivates our interest to differentiate which effect is dominant for this 'voltage control of magnetism'. Here, we present results for the ME coupling at different temperatures: 300 K and 80 K. In this article we discuss and explain, how the nature of ME coupling is influenced by different parameters such as magnetic field, electric field, directional dependence (hard axis, easy axis) and temperature. Owing to large lattice mismatch between LSMO and PMN–PT, the strain-mediated coupling is strongly prevalent, however the change in strain behaviour from butterfly loop to linear loop is observed as a function of temperature. ME measurements are performed along hard axis [100] and easy axis [110] of LSMO in the presence of remanent magnetic field which showcases the pure influence of electric field on the system, resulting in a combination of strain- and charge-mediated coupling. The magnetic depth profile is probed by polarized neutron reflectometry as a function of electric field which demonstrates the existence of an interlayer with reduced nuclear scattering length density and reduced magnetic scattering length density at the interface. From transmission electron microscopy, stoichiometric variations are observed due to the presence of Mn3O4 particles at the interface. [ABSTRACT FROM AUTHOR]

We apply off-axis electron holography and Lorentz microscopy in the transmission electron microscope to map the electric field generated by a sharp biased metallic tip. A combination of experimental data and modelling provides quantitative information about the potential and the field around the tip. Close to the tip apex, we measure a maximum field intensity of 82 MV/m, corresponding to a field k factor of 2.5, in excellent agreement with theory. In order to verify the validity of the measurements, we use the inferred charge density distribution in the tip region to generate simulated phase maps and Fresnel (out-of-focus) images for comparison with experimental measurements. While the overall agreement is excellent, the simulations also highlight the presence of an unexpected astigmatic contribution to the intensity in a highly defocused Fresnel image, which is thought to result from the geometry of the applied field. [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]

We study planar defects in epitaxial Co:ZnO dilute magnetic semiconductor thin films deposited on c-plane sapphire (Al2O3), as well as the Co:ZnO/Al2O3 interface, using aberration-corrected transmission electron microscopy and electron energy-loss spectroscopy. Co:ZnO samples that were deposited using pulsed laser deposition and reactive magnetron sputtering are both found to contain extrinsic stacking faults, incoherent interface structures, and compositional variations within the first 3-4 Co:ZnO layers next to the Al2O3 substrate. The stacking fault density is in the range of 1017 cm-3. We also measure the local lattice distortions around the stacking faults. It is shown that despite the relatively high density of planar defects, lattice distortions, and small compositional variation, the Co:ZnO films retain paramagnetic properties. [ABSTRACT FROM AUTHOR]

Large area square arrays of circular cobalt dots, nominally 100 nm in diameter and 20 nm in thickness, were patterned using interference lithography. Magnetic remanent states were measured using off-axis electron holography in the transmission electron microscope (TEM). The results show that the dots are mostly single domain, although vortex states and multidomain configurations are occasionally observed. Significant magnetic interactions between adjacent dots result in variations in their magnetization direction away from the direction of the applied field. The suitability of such dots for data storage applications is discussed. Quantitative magnetic phase measurements were also obtained by applying the transport of intensity equation to images acquired using the Fresnel mode of Lorentz microscopy in the TEM. The consistency between the electron holography and transport of intensity equation (TIE) results is assessed. [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]