We have explored the use of a magneto-optical diffraction grating, in the form of a YIG (Y3Fe5O12) continuous film, as a mean of controlling light with mesoscale magnetic textures. The existence of a periodicity for the out-of-plane magnetic component opens up the possibility of using the film as a magneto-optical diffraction grating. For incident light linearly-polarized along the stripe direction, the Faraday rotation yields a polarization profile of the transmitted light characterized by a uniform distribution along the direction parallel to the stripes and a periodic phase-reversal texture along the corresponding orthogonal direction. The interference pattern resulting from the latter gives rise to magnetic Bragg peaks, in good agreement with the Fourier transform of the real-space magnetic domain texture recorded with Kerr microscopy. These results highlight the potential of controlling the scattering of light by employing and tailoring meso-scale magnetic textures.
The antiferromagnetic coupling in [Fe/MgO]N multilayers is found to be strongly depending on the number of bilayer repeats (N). The results support the presence of long range interlayer exchange interactions as well as profound quantum well states defined by the total extension of the Fe/MgO(001) samples.
For a small island of a magnetic material the magnetic state of the island is mainly determined by the exchange interaction and the shape anisotropy. Two or more islands placed in close proximity will interact through dipolar interactions. The state of a large system will thus be dictated by interactions at both these length scales. Enabling internal thermal fluctuations, e.g. by the choice of material, of the individual islands allows for the study of thermal ordering in extended nano-patterned magnetic arrays [1,2]. As a result nano-magnetic arrays represent an ideal playground for the study of physical model systems.
Here we present three different studies all having used magneto-optical imaging techniques to observe, in real space, the order of the systems. The first study is done on a square lattice of circular islands. The remanent magnetic state of each island is a magnetic vortex structure and we can study the temperature dependence of the vortex nucleation and annihilation fields [3]. The second are long chains of dipolar coupled elongated islands where the magnetization direction in each island only can point in one of two possible directions. This creates a system which in many ways mimics the Ising model [4] and we can relate the correlation length to the temperature. The third one is a spin ice system where elongated islands are placed in a square lattice. Thermal excitations in such systems resemble magnetic monopoles [2] and we can investigate their properties as a function of temperature and lattice parameters.
[1] V. Kapaklis et al., New J. Phys. 14, 035009 (2012)
[2] V. Kapaklis et al., Nature Nanotech 9, 514(2014)
[3] E. Östman et al.,New J. Phys. 16, 053002 (2014)
[4] E. Östman et al.,Thermal ordering in mesoscopic Ising chains, In manuscript.
Films of Me-Ce oxide (Me: Ti, Zr, Sn, W) and of Ni-Ce hydroxide were produced by reactive magnetron co-sputtering. Li intercalation in Me-Ce oxide, and H exchange in Ni-Ce hydroxide, were accomplished electrochemically. Electrochromism was quenched in proportion with the Ce content in Me-Ce oxide. Films of Zr-Ce (and to some extent Ti-Ce) oxide were able to serve as fully transparent counter electrodes, of much interest for transparent electrochromic devices. In Ni-Ce hydroxide, the Ce addition enhanced the capacity for charge exchange.
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