Integration of epitaxial colossal magnetoresistive films onto Si(100) using SrTiO\u3csub\u3e3\u3c/sub\u3e as a template layer

We report on the integration of epitaxial colossal magnetoresistive La0.67Ba0.33MnO films on Si(100) semiconductor using SrTiO3 template layer by pulsed-laser deposition. X-ray diffraction reveals the superior quality of the manganite film that grows epitaxially on heteroepitaxially grown SrTiO3 template layer on Si substrate. The epitaxial films demonstrate remarkable surface morphology, magnetic transition and hysteresis, magnetoresistance, and ferromagnetic resonance, illustrating the ferromagnetic nature of the film and possible device applications at room temperature

Magnetic properties of La\u3csub\u3e0.60\u3c/sub\u3eSr\u3csub\u3e0.40\u3c/sub\u3eMnO\u3csub\u3e3\u3c/sub\u3e thin films on SrTiO\u3csub\u3e3\u3c/sub\u3e and buffered Si substrates with varying thickness

La0.60Sr0.40MnO3 (LSMO) thin films of varying thickness from 12 to 55 nm were deposited using the pulsed-laser deposition technique onto single-crystalline SrTiO3 (STO) and STO-buffered Si substrates. The T c of LSMO films grown on STO-buffered Si substrates decreases faster than films directly grown on STO with decreasing film thickness. The LSMO/STO film with thickness of 55 nm shows T c at about 360 K, which is close to the bulk value, whereas T c LSMO film on STO-buffered Si film of similar thickness is reduced to 320 K. This difference is attributed to the strain and interfacial disorders in LSMO film on STO/Si. The film surface morphology is influenced by the film thickness. Oxygenation of LSMO films on STO-buffered Si affects the T c minimally but improved the overall magnetization of the films due to better oxygenation, which is also the case for postannealing the sample at elevated temperatures. The thermomagnetic history effects observed in LSMO films of STO-buffered Si indicate the presence of inhomogeneity, mostly at the interface, which influences the magnetic properties significantly

Synthesis and magnetic characterizations of manganite-based composite nanoparticles for biomedical applications

We report chemically synthesized highly crystalline lanthanum strontium manganite (LaSrMnO3) and Eu-doped Y2O3 and their composites. The synthesis yields nanoparticles of size 30–40 nm. Magnetic measurements performed on nanoparticles and composites show magnetic transition at about 370 K with a superparamagnetic behavior at room temperature. The ferromagnetic resonance studies of the nanoparticles show large linewidth due to surface strains. The composite nanoparticles also display luminescent behavior when irradiated with ultraviolet light. The manganites as well their composite with the luminescent nanoparticles may be very useful for biomedical applications

Effect of the J–J Interaction of Excited States of the Rare-Earth Ion Pr3+ on Magnetically Polarized Luminescence of Praseodymium-Yttrium Aluminum Garnet

The spectra of luminescence and magnetic circular polarization of luminescence of praseodymium–yttrium aluminum garnet Pr3+ : Y3Al5O12 (PrYAG) are studied in the visible spectral region at temperature T = 300 K. An analysis of spectral dependences of magnetooptical and optical spectra makes it possible to identify optical 4 f–4 f-transitions between Stark sublevels of multiplets 3P0, 3P1, 3Н5, and 3Н6 in PrYAG. It was shown that an important role in the spectrum of the degree of magnetic circular polarization of luminescence of this paramagnetic garnet is played by the effect of quantum-mechanical J–J mixing of states of Stark singlets 3Н5 and 3Н6 of non-Kramer rare-earth ion Pr3+ in the “green” luminescence band related to forbidden 4 f → 4 f transition 3P0 → 3Н5 in the visible spectral region. To interpret the spectra of magnetic circular polarization of luminescence, the energy of experimentally determined Stark sublevels of multiplets under study, their irreducible representations and wave functions determined by numerical simulation of the energy spectrum of the rare-earth ion Pr3+ in the garnet structure are used

Investigation of J – J “Mixing” Mechanism Influence on Optical and Magnetooptical Properties of Praseodymium Yttrium-aluminum Garnet PrYAG

The spectra of the luminescence and magnetic circular polarization of luminescence (MCPL) in the praseodymium yttrium garnet aluminate Pr3+:YAG (PrYAG) have been studied within the visible spectral range at temperature T = 300 K. Analysis of the spectral dependences of the magnetooptical and optical spectra has made it possible to identify the optical 4f → 4f transitions occurring between the Stark sublevels of the 3P0, 3P1 and 3H5, 3H6 multiplets in PrYAG. It has been shown that for this paramagnetic garnet in the MCPL degree spectrum for the “green” luminescence band associated with forbidden 4f→ 4f transitions 3P0 → 3H5 within the visible spectral range, a significant role is being played by the effect of quantum mechanical J - J “mixing” of the energy states of Stark singlets of the 3H5 and 3H6 multiplets of the non-Kramers rare-earth (RE) Pr3+ ion. A parameterized Hamiltonian defined to operate within the entire 4 f(2) ground electronic configuration of Pr3+ was used to model the experimental Stark levels, their irreducible representations (irreps.) and wavefunctions. Nine independent CF parameters, Bqk role= presentation \u3e, were optimized using standard least-squares fitting between calculated and experimental levels. The final fitting standard deviation between 61 calculated-to-experimental levels is 17.86 cm–1

Oxide-based dilute ferromagnetic semiconductors: ZnMnO and Co:TiO\u3csub\u3e2\u3c/sub\u3e

We report on ferromagnetic properties of ZnMnO and Co:TiO2 films grown by pulsed laser deposition with varying growth conditions. We have demonstrated that ZnMnO films show ferromagnetic properties at room temperature. However, oxygen plays a dominant role in the occurrence of ferromagnetism. Introducing carriers into ZnMnO films did not improve the ferromagnetic properties. Our experimental results indicate that the mechanism for ferromagnetism lies, probably, within the perspective of charge transfer between Mn ions through oxygen. On the other hand, our experimental results suggest that the ferromagnetism in Co:TiO2 films is controlled by the presence of small metal Co2+ clusters in the rutile TiO2 matrix, which are mainly present at the interface and on the surface of the films

Ferromagnetic resonance studies in ZnMnO dilute ferromagnetic semiconductors

We report on the ferromagnetic resonance studies on ZnMnO films grown by the pulsed-laser deposition technique. ZnMnO films were annealed in different atmospheres. The films grown and annealed in oxygen demonstrate ferromagnetic behavior at room temperature and below. However, annealing in either nitrogen or argon deteriorates the ferromagnetic response of the films. Further annealing the films in oxygen recovers the ferromagnetic response. Our results suggest that oxygen plays a major role for controlling the ferromagnetic properties in ZnMnO films

Self-assembled nanocrystalline epitaxial manganite films on SrTiO\u3csub\u3e3\u3c/sub\u3e/Si heterostructures

We report the growth and magnetic characterizations of La0.7Ba0.3MnO3 and La0.7Sr0.3MnO3 films on SrTiO3-buffered Si (100) and Si (111) substrates by pulsed-laser deposition. The structural studies show the epitaxial nature of the films. The microscopic studies show that the films consist of nanocrystalline particles. All films display sharp magnetic and electrical transitions associated with the colossal magnetoresistance behavior at and above room temperature, illustrating the superior quality of the films

Ferromagnetism in nanocrystalline epitaxial Co:TiO\u3csub\u3e2\u3c/sub\u3e thin films

We report on the observation of remarkable room-temperature ferromagnetism in nanocrystalline epitaxial Co:TiO2 films grown on sapphire (0001) substrates by a pulsed-laser deposition technique using high-density targets. The films were characterized by x-ray measurements, atomic force microscopy, micro-Raman, electron-paramagnetic resonance, and magnetization studies. The films exhibit three-dimensional islandlike growth that contains nanocrystalline particles. Our experimental results suggest that the remarkable ferromagnetism in Co:TiO2 films is controlled either by the interstitial Co2+ ions or small clusters, which are mainly present at the interface and on the surface of the films. Our work clearly indicates that Co interstitials and nanoclusters cause room-temperature ferromagnetism in Co-doped TiO2