Ising thin films with modulations and surface defects

Properties of magnetic films are studied in the framework of Ising models. In particular, we discuss critical phenomena of ferromagnetic Ising films with straight lines of magnetic adatoms and straight steps on the surface as well as phase diagrams of the axial next-nearest neighbour Ising (ANNNI) model for thin films exhibiting various spatially modulated phases.Comment: 6 pages, 4 figures include

Catalytic oxidation of methylene blue by use of natural zeolite-based silver and magnetite nanocomposites

This work reports the synthesis of natural zeolite-based silver and magnetite nanocomposites and their application for the catalytic oxidation of methylene blue in water. The zeolite was impregnated with 5.5 wt.% Fe in the form of magnetite nanoparticles with size of 32 nm, and with 6.4 wt.% Ag in the form of silver oxide and metallic silver nanoparticles with sizes of 42 and 20 nm, respectively. The results showed that physical adsorption contributed to the removal of methylene blue by 25−36% and that Fe3O4@NZU is superior to Ag2O@NZU and Ag0@NZU, leading to 55% removal without oxidant and 97% in the presence of H2O2. However, there is no evidence of significant mineralization of methylene blue. The application of reaction rate models showed that the reaction order changes from zero to first and second order depending on the H2O2 concentration

Paramagnetic gold in a highly disordered Au-Ni-O alloy

Magnetic materials are usually classified into a distinct category such as diamagnets, paramagnets or ferromagnets. The enormous progress in materials science allows one nowadays, however, to change the magnetic nature of an element in a material. Gold, in bulk form, is traditionally a diamagnet. But in a ferromagnetic environment, it can adopt an induced ferromagnetic moment. Moreover, the growth of gold under certain conditions may lead to a spontaneous ferromagnetic or paramagnetic response. Here, we report on paramagnetic gold in a highly disordered Au–Ni–O alloy and focus on the unusual magnetic response. Such materials are mainly considered for plasmonic applications. Thin films containing Au, Ni and NiO are fabricated by co-deposition of Ni and Au in a medium vacuum of 2 × 10−2 mbar. As a result, Au is in a fully disordered state forming in some cases isolated nanocrystallites of up to 4 nm in diameter as revealed by high resolution transmission electron microscopy. The disorder and the environment, which is rich in oxygen, lead to remarkable magnetic properties of Au: an induced ferromagnetic and a paramagnetic state. This can be proven by measuring the x-ray magnetic circular dichroism. Our experiments show a way to establish and monitor Au paramagnetism in alloys

Layering and temperature-dependent magnetization and anisotropy of naturally produced Ni/NiO multilayers

Ni/NiO multilayers were grown by magnetron sputtering at room temperature, with the aid of the natural oxidation procedure. That is, at the end of the deposition of each single Ni layer, air is let to flow into the vacuum chamber through a leak valve. Then, a very thin NiO layer (~1.2nm) is formed. Simulated x-ray reflectivity patterns reveal that layering is excellent for individual Ni-layer thickness larger than 2.5nm, which is attributed to the intercalation of amorphous NiO between the polycrystalline Ni layers. The magnetization of the films, measured at temperatures 5–300K, has almost bulk- like value, whereas the films exhibit a trend to perpendicular magnetic anisotropy (PMA) with an unusual significant positive interface anisotropy contribution, which presents a weak temperature dependence. The power-law behavior of the multilayers indicates a non-negligible contribution of higher order anisotropies in the uniaxial anisotropy. Bloch-law fittings for the temperature dependence of the magnetization in the spin-wave regime show that the magnetization in the multilayers decreases faster as a function of temperature than the one of bulk Ni. Finally, when the individual Ni-layer thickness decreases below 2nm, the multilayer stacking vanishes, resulting in a dramatic decrease of the interface magnetic anisotropy and consequently in a decrease of the perpendicular magnetic anisotropy

'Theory for the enhanced induced magnetization in coupled magnetic trilayers in the presence of spin fluctuations'

Motivated by recent experiments, the effect of the interlayer exchange interaction $J_{inter}$ on the magnetic properties of coupled Co/Cu/Ni trilayers is studied theoretically. Here the Ni film has a lower Curie temperature $T_{C,\rm Ni}$ than the Co film in case of decoupled layers. We show that by taking into account magnetic fluctuations the interlayer coupling induces a strong magnetization for T\gtsim T_{C,\rm Ni} in the Ni film. For an increasing $J_{inter}$ the resonance-like peak of the longitudinal Ni susceptibility is shifted to larger temperatures, whereas its maximum value decreases strongly. A decreasing Ni film thickness enhances the induced Ni magnetization for T\gtsim T_{C,\rm Ni}. The measurements cannot be explained properly by a mean field estimate, which yields a ten times smaller effect. Thus, the observed magnetic properties indicate the strong effect of 2D magnetic fluctuations in these layered magnetic systems. The calculations are performed with the help of a Heisenberg Hamiltonian and a Green's function approach.Comment: 4 pages, 3 figure

Dipolar interaction between two-dimensional magnetic particles

We determine the effective dipolar interaction between single domain two-dimensional ferromagnetic particles (islands or dots), taking into account their finite size. The first correction term decays as 1/D^5, where D is the distance between particles. If the particles are arranged in a regular two-dimensional array and are magnetized in plane, we show that the correction term reinforces the antiferromagnetic character of the ground state in a square lattice, and the ferromagnetic one in a triangular lattice. We also determine the dipolar spin-wave spectrum and evaluate how the Curie temperature of an ensemble of magnetic particles scales with the parameters defining the particle array: height and size of each particle, and interparticle distance. Our results show that dipolar coupling between particles might induce ferromagnetic long range order at experimentally relevant temperatures. However, depending on the size of the particles, such a collective phenomenon may be disguised by superparamagnetism.Comment: 11 pages, 5 figure

Ruthenocuprates RuSr2(Eu,Ce)2Cu2O10: Intrinsic magnetic multilayers

We report ac susceptibility data on RuSr_2(Eu,Ce)_2Cu_2O_(10-y) (Ru-1222, Ce content x=0.5 and 1.0), RuSr_2GdCu_2O_8 (Ru-1212) and SrRuO_3. Both Ru-1222 (x=0.5, 1.0) sample types exhibit unexpected magnetic dynamics in low magnetic fields: logarithmic time relaxation, switching behavior, and `inverted' hysteresis loops. Neither Ru-1212 nor SrRuO_3 exhibit such magnetic dynamics. The results are interpreted as evidence of the complex magnetic order in Ru-1222. We propose a specific multilayer model to explain the data, and note that superconductivity in the ruthenocuprate is compatible with both the presence and absence of the magnetic dynamics.Comment: 9 pages, 11 figures, Revtex; submitted to Phys.Rev.

AR AND CHAMBER MUSIC: MUSICAL KALEIDOSCOPE

DIGI-ORCH is a research project with objectives, on one hand, to design and develop "smart" brochures for concerts and educational programs of the State Conservatory of Thessaloniki (Greece), and, on the other, to develop an innovative system for the visualization of information on smart mobile devices (smartphones and tablets). The application of Augmented Reality (AR) provides free access to the information and content of the above concerts and educational programs, combining the information of a robust data server and an easy-to-use user interface of the smart device in real-time.The pilot implementation of the system in real conditions took place at the beginning of December 2022, in an event held at the facilities of the State Conservatory of Thessaloniki. The event was an evening of Chamber Music entitled Musical Kaleidoscope, with the internationally acclaimed artists Simos Papanas (violin), Dimos Goundaroulis (violoncello), and Vassilis Varvaresos (piano). They performed the Piano Trio no. 3 in G minor, Robert Schumann's opus 110, and the Piano Trio no. 2 in E flat major, Op. 100 D. 929 by Franz Schubert. The concert was attended by over 150 attendees.The paper will present the chaîne-operatoire of the development of the system, from the acquisition of raw data (text, video, image, and sound) to the methodology used to produce the "smart" event brochure and the AR application for the above concert. Essentially, this large amount of information that cannot be assessed by a regular printed concert brochure is included in the smart system and displayed on the mobile device when the user locates the appropriate AR patterns on the surface of the analog concert poster and/or on the pages of the brochure.This information comprised of ie. additional text and images about the composers and their musical projects, about the musicians of the concert (e.g. biographies), their interviews and rehearsals (video) before the concert, information about the State Conservatory of Thessaloniki (text, video, image, and sound), 3D models of musical instruments, 360° of the concert space, etc. diverse multimedia material.</p