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We investigate the domain structure of submicrometer sized ferromagnetic stripes exhibiting in-plane and out-of-plane magnetized areas with magnetic force microscopy (MFM). Two simulation approaches are used to calculate the observed MFM response. The first relies on an analytical solution for the stray field of a bar magnet and the subsequent modeling of the sample as an arrangement of bar magnets. The MFM response is calculated for a realistic tip shape incorporating a distribution of magnetic dipoles. The second, numerical approach is based on a discretization scheme, breaking the tip-sample problem up into cells and then calculating the energy of the magnetic tip-sample interaction. The MFM responses obtained for the ferromagnetic stripe structure are compared. A discussion of the advantages and limitations of the two methods is given in terms of precision, computing time, and flexibility. The numerical method offers shorter computing times and greater flexibility, opening the door for realistic three-dimensional MFM response simulations. The advantage of the analytical method is the investigation of small structures, as its precision is higher for the comparable computational effort. [ABSTRACT FROM AUTHOR]

We have studied the domain behavior of submicrometer wide ferromagnetic stripes by magnetic force microscopy (MFM) in the presence of an in situ magnetic field. MFM images in the demagnetized state show alternatingly magnetized domains fully extended across the stripe. Moreover, domain structures are found to exhibit a substructure across the stripe. Increasing fields drive out the domain walls of the complex domains first, leaving the alternating domains behind. The remaining magnetization process aligns increasing parts of the domains along the field direction by gradually shrinking the width of oppositely magnetized domains rather than by flipping larger areas at once. Micromagnetic simulations confirm the observed behavior. The simulations reveal that flipping of the domains occurs only when a magnetic pinning center is involved. [ABSTRACT FROM AUTHOR]

We present an analytic solution for the magnetic field of a bar-shaped permanent magnet. Assuming a constant magnetization, we derive expressions for the stray field in three dimensions. The analytic solutions can be readily applied to field calculation problems for magnetic force microscopy simulations without the need for finite element methods. [ABSTRACT FROM AUTHOR]

Nanoscale chiral skyrmions in noncentrosymmetric helimagnets are promising binary state variables in high-density, low-energy nonvolatile memory. Skyrmions are ubiquitous as an ordered, single-domain lattice phase, which makes it difficult to write information unless they are spatially broken up into smaller units, each representing a bit. Thus, the formation and manipulation of skyrmion lattice domains is a prerequisite for memory applications. Here, using an imaging technique based on resonant magnetic x-ray diffraction, we demonstrate the mapping and manipulation of skyrmion lattice domains in Cu2OSeO3. The material is particularly interesting for applications owing to its insulating nature, allowing for electric field-driven domain manipulation. [ABSTRACT FROM AUTHOR]

Breaking the time reversal symmetry of a topological insulator, for example by the presence of magnetic ions, is a prerequisite for spin-based electronic applications in the future. In this regard Mn-doped Bi2Te3 is a prototypical example that merits a systematic investigation of its magnetic properties. Unfortunately, Mn doping is challenging in many host materials—resulting in structural or chemical inhomogeneities affecting the magnetic properties. Here, we present a systematic study of the structural, magnetic and magnetotransport properties of Mn-doped Bi2Te3 single crystals using complimentary experimental techniques. These materials exhibit a ferromagnetic phase that is very sensitive to the structural details, with TC varying between 9 and 13 K (bulk values) and a saturation moment that reaches 4.4(5) μB per Mn in the ordered phase. Muon spin rotation suggests that the magnetism is homogeneous throughout the sample. Furthermore, torque measurements in fields up to 33 T reveal an easy axis magnetic anisotropy perpendicular to the ab-plane. The electrical transport data show an anomaly around TC that is easily suppressed by an applied magnetic field, and also anisotropic behavior due to the spin-dependent scattering in relation to the alignment of the Mn magnetic moment. Hall measurements on different crystals established that these systems are n-doped with carrier concentrations of ∼ 0.5–3.0 × 1020 cm−3. X-ray magnetic circular dichroism (XMCD) at the Mn L2,3 edge at 1.8 K reveals a large spin magnetic moment of 4.3(3) μB/Mn, and a small orbital magnetic moment of 0.18(2) μB/Mn. The results also indicate a ground state of mixed d4–d5–d6 character of a localized electronic nature, similar to the diluted ferromagnetic semiconductor Ga1−xMnxAs. XMCD measurements in a field of 6 T give a transition point at T ≈ 16 K, which is ascribed to short range magnetic order induced by the magnetic field. In the ferromagnetic state the easy direction of magnetization is along the c-axis, in agreement with bulk magnetization measurements. This could lead to gap opening at the Dirac point, providing a means to control the surface electric transport, which is of great importance for applications. [ABSTRACT FROM AUTHOR]

We present variabl]e-temperature magnetic force microscopy (VT-MFM) studies of epitaxially grown MnAs layers on GaAs(001). In MnAs, a structural and magnetic phase transition occurs at Tc ≈ 40°C from the hexagonal, ferromagnetic α-phase below Tc to the orthorhombic, paramagnetic β-phase above Tc. In the inves- tigated MnAs-GaAs system, both phases coexist over a temperature range of 30 ° C below Tc due to the involved strain. Using MFM we are able to distinguish between the ferromagnetic and the paramagnetic phases by measuring topographic and magnetic contrast of the same sample area. For VT-MFM studies, we have employed a temperature stage that allows heating and cooling in a controlled atmosphere with small thermal drift (for this system, the temperature was varied from below 0°C to above 45°C). The ratio of the ferromagnetic to the paramagnetic phases shows a temperature hysteresis, i.e. the ratio is dependent on whether the sample was heated or cooled to reach the measurement temperature. Detailed studies of the domains and their arrangements over the hysteretic temperature cycle are shown and compared. Mainly three different domain types are found that are dominant in their respective temperature ranges. [ABSTRACT FROM AUTHOR]

The micromagnetic properties of MnAs thin films grown on the (111)B-oriented GaAs surface have been investigated. Compared to films grown on (001) surfaces, these films exhibit completely different domain patterns, as the c axis of the hexagonal unit cell is oriented normal to the surface. In the course of the first order phase transition, ferromagnetic α-MnAs forms a network of quasihexagonal areas separated by β-MnAs. We present an analysis of the micromagnetic properties based on imaging and simulations. We observe closure domains that either appear as a vortex-like state or a stripe structure. [ABSTRACT FROM AUTHOR]

Nanoscale chiral skyrmions in noncentrosymmetric helimagnets are promising binary state variables in high-density, low-energy nonvolatile memory. Skyrmions are ubiquitous as an ordered, single-domain lattice phase, which makes it difficult to write information unless they are spatially broken up into smaller units, each representing a bit. Thus, the formation and manipulation of skyrmion lattice domains is a prerequisite for memory applications. Here, using an imaging technique based on resonant magnetic x-ray diffraction, we demonstrate the mapping and manipulation of skyrmion lattice domains in Cu2OSeO3. The material is particularly interesting for applications owing to its insulating nature, allowing for electric field-driven domain manipulation. [ABSTRACT FROM AUTHOR]

Thin films of MnAs grown on GaAs(0 0 1) show a self-organized structure of coexisting ferromagnetic α- and paramagnetic β-MnAs stripes in the temperature interval from 10 to 40°C. We quantify the magnetic anisotropies of the α-stripes via ferromagnetic resonance and superconducting quantum interference device magnetometry for samples with thicknesses of 57 and 165 nm. The easy axis of magnetization is found to be located perpendicular to the stripe direction, whereas the direction parallel to the stripes is a hard one. While the intrinsic anisotropies show a bulk-like behavior and explain the direction of the hard axis, the key to understanding the direction of the easy axis is given by the demagnetizing fields due to the stripe formation. [Copyright &y& Elsevier]