The interesting physics and potential memory technologies resulting from topologically protected spin textures such as skyrmions, has prompted efforts to discover new material systems that can host these kind of magnetic structures. Here we use the highly tunable magnetic properties of amorphous Fe/Gd multilayer films to explore the magnetic properties that lead to dipole-stabilized skyrmions and skyrmion lattices that form from the competition of dipolar field and exchange energy. Using both real space imaging and reciprocal space scattering techniques we determined the range of material properties and magnetic fields where skyrmions form.Micromagnetic modeling closely matches our observation of small skyrmion features (~50 to 70nm) and suggests these class of skyrmions have a rich domain structure that is Bloch like in the center of the film and more Néel like towards each surface. Our results provide a pathway to engineer the formation and controllability of dipole skyrmion phases in a thin film geometry at different temperatures and magnetic fields.

A detailed study on the influence of particle size varied from 8 nm to 53 nm on the structural and magnetic properties of La 0.8 Sr 0.2 MnO 3Ϫ␦ has been done. The unit cell volume increases and the microstrain in the compound shows peak formation as the particle size decreases. Nano particles of La 0.8 Sr 0.2 MnO 3Ϫ␦ exhibit superparamagnetism whose blocking temperature has a nonlinear and logarithmic decreasing tendency as function of particle size and applied magnetic field, respectively. Evidence of formation of a magnetically dead layer at the surface has been found and the ratio of the thickness of the dead layer to the particle size increases exponentially with particle size. The coercivity of the nanoparicles increases manifold as particle size varies from 53 nm to 21 nm. In the single domain region the coercivity exhibits a d Ϫ1.125 behavior. The temperature dependence of the saturation magnetization shows strong collective excitation due to the spin wave that varies as T ␣ with ␣Ͼ␣ bulk of 3/2. Thus the spin wave does not follow the Bloch law in the case of nano particles of La 0.8 Sr 0.2 MnO 3Ϫ␦ .

The crystal structure, magnetic and electrical transport properties of the sodium-doped lanthanum manganites La1-xNaxMnO3 (0.07⩽x⩽0.40) have been studied in detail using x-ray powder diffraction, atomic absorption spectroscopy, a SQUID (superconducting quantum interference device) magnetometer and the four-probe resistivity measurement technique. A rhombohedrally distorted perovskite structure has been observed in the range 0.07⩽x⩽0.20. Both the lattice parameter and unit-cell volume decrease with increase in the Na content. A ferromagnetic-to-paramagnetic phase transition associated with a metal-insulator transition is observed for all the La1-xNaxMnO3 compounds. There is a systematic change in both the Mn-O-Mn bond angle and the tolerance factor with Na content. The compositional variation of the magnetic and metal-insulator transition temperatures is explained as due to the distortion of the MnO6 octahedron and increase in the tolerance factor that controls the hopping interaction. In the metallic region a ρ~AT2 behaviour is observed due to the magnon excitation effect. The resistivity shows a field-dependent minimum at low temperature that has been explained as due to the intergrain transport phenomenon.

We have used the unique spatial sensitivity of polarized neutron and soft x-ray beams in reflection geometry to measure the depth dependence of magnetization across the interface between a ferromagnet and an antiferromagnet. The net uncompensated magnetization near the interface responds to applied field, while uncompensated spins in the antiferromagnet bulk are pinned, thus providing a means to establish exchange bias.

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We report the observation of a Skyrmion lattice in the chiral multiferroic insulator Cu2OSeO3 using Cu L3-edge resonant soft x-ray diffraction. We observe the unexpected existence of two distinct Skyrmion sublattices that arise from inequivalent Cu sites with chemically identical coordination numbers but different magnetically active orbitals. The Skyrmion sublattices are rotated with respect to each other, implying a long wavelength modulation of the lattice. The modulation vector is controlled with an applied magnetic field, associating this moirélike phase with a continuous phase transition. Our findings will open up a new class of science involving manipulation of quantum topological states.

We show that properly engineered amorphous Fe-Gd alloy thin films with perpendicular magnetic anisotropy (PMA) exhibit bound pairs of like-polarity, opposite helicity skyrmions at room temperature. Magnetic mirror symmetry planes present in the stripe phase, instead of chiral exchange, determine the internal skyrmion structure and the net achirality of the skyrmion phase. Our study shows that stripe domain engineering in amorphous alloy thin films may enable the creation of skyrmion phases with technologically desirable properties.

In this study we investigate the effects of Ce doping in R1−xAxMnO3 (R=La, Ce, and A=Sr, Ce) on the magnetic and transport properties of this system. For La1−xCexMnO3 (LCMO), an increase in Ce concentration is accompanied by an increase in TC from 225 to 236 K, as well as an increase in the electrical resistivity. An extremely high resistivity is observed in the new system Ce1−xSrxMnO3 (CSMO) which becomes insulating below its Curie temperature of 43 K. A maximum magnetoresistance (MR) ratio of 40% for CSMO and 53% for LCMO is observed. A larger change in resistivity is seen to correspond to an increase in the Ce concentration, however this is offset by an overall resistivity increase which keeps the MR ratio low. The high resistivity may be due to unreacted oxides in the samples. If true, the amount of impurity appears to be proportional to the Ce doping. If this impurity level can be reduced, a significant colossal magnetoresistance effect could be exhibited by these systems.