Search

We report on a study of thin (500–4000 A) and ultrathin (100–500 A) yttrium–iron–garnet (YIG) films deposited onto amorphous quartz substrates by the pulsed laser deposition technique. The growth conditions of well-formed polycrystalline films have been determined. The crystalline structure and the magnetic behavior of the films are strongly influenced by the processes occurring on the film–substrate interface. Primarily, a strain due to the difference in thermal expansion coefficients of the film and substrate induces a uniaxial anisotropy. Another source of strain are lattice distortions due to oxygen vacancies. The results obtained from x-ray diffraction analysis, magneto-optical, superconducting quantum interference device, vibrating sample magnetometer, and ferromagnetic resonance (FMR) measurements indicate that films thicker than 200 A can be approximated by a two-layer model. One of the layers with a highly distorted structure and low magnetization is located near the surface. The other one, the u...

[Fe2O3/NiO]N multilayer films prepared by pulsed laser deposition display oscillation observed in the magnetization M as a function of N or the number of interfaces i=2N−1 indicating that they are not symmetric. In this work magneto-optic (MO) polar Kerr rotation spectra of some samples in the photon energy range 1.2–4.5 eV are reported. Faraday rotation (FR) was studied at 632.6 and 550 nm laser wavelengths. It shows the oscillations with N in accordance with M. Polar Kerr rotation spectra show a series of peaks which could be assigned to nickel ferrite NiFe2O4 formed at the interfaces between NiO and αFe2O3. The amplitudes change strongly with N as expected from N dependence of FR and M. A simple analytical expression is proposed to explain the complex phase relations among the contributions from individual ferrimagnetic interfaces to the total MO Kerr rotation in the multilayers.

Thin films of BaFeO3-δ have been deposited by pulsed injection metal-organic chemical vapor deposition. The films adopt a pseudocubic structure as a result of the match with the cubic structure of the SrTiO3 substrate and the accommodation of a high density of oxygen vacancies. They display antiferromagnetic behavior at room temperature and high electrical resistance. Furthermore, we observed an ageing effect that may be recovered to some extent by annealing in oxygen atmosphere.

Determining phase transitions has always been a great challenge in material science due to their important fundamental and technological aspects. Recently, iron-based perovskites (RFeO3), exhibiting phase transitions at high temperatures, have attracted much interest for their functional properties at room temperature, such as multiferroicity (BiFeO3) and ultrafast spin dynamics (TmFeO3). In this family of materials, Samarium orthoferrite (SmFeO3) is a weak ferromagnet, ordering at high temperatures and exhibiting an intrinsic spin reorientation transition above room temperature, which is “hidden” in macroscopic magnetization measurements in polycrystalline samples. In the present article, we show that the related magnetic high temperature phase transitions can be studied through their dielectric functions by spectroscopic ellipsometry in situ and without any need for an applied external magnetic field. The presence of this intrinsic spin reorientation transition is demonstrated for textured SmFeO3 films ...

Structural, electrical, and magnetic properties of epitaxial thin films of Fe1.5Ti0.5O3−δ grown by pulsed laser deposition on SrTiO3(001) have been studied. For all the investigated range of preparation conditions, the thin films are single phase. The films prepared using oxygen pressure PO2 above 3×10−7 Torr presents a R(3¯)c symmetry structure. A single phase with the R(3¯) symmetry is obtained for the substrate temperature Ts=730 °C and PO2=2.6×10−7 Torr. This sample showed a ferrimagnetic behavior with Curie temperature Tc above room temperature, with a high magnetic moment of 0.6 μB/formula at 300 K. The film containing the disordered R(3¯)c phase is weakly ferromagnetic, with a spin glass-like signature. Optical properties seem to be governed more by the oxygen vacancies induced during the growth, than by the atomic ordering of titanium.

An understanding of the thin film structure and properties of ilmenite is crucial for the future study of ilmenite-hematite solid solutions for spintronics applications. Here, we report a systematic study of the FeTiO3±δ thin film structure as a function of the deposition parameters during pulsed laser ablation. The films are found to be crystalline and epitaxial on α-Al2O3(0001) substrates for a wide range of substrate temperatures and oxygen pressures. Initial stages of the film growth and in-plane lattice relaxation were investigated. The increase in the a lattice parameter of up to 6% above its bulk value was observed and is most probably due to the buckling of a few ilmenite monolayers at the film/substrate interface because of a significant compressive stress induced on the film by sapphire substrate. In spite of the absence of a diffraction peak corresponding to the ordered R3¯ phase, these films consist of pure ilmenite phase with negligible net magnetization. Film conductivity is tuned over three...

Direct current (dc) electrical transport properties (resistivity and Hall) and spectroscopic ellipsometric measurements have been combined to study high-quality epitaxial thin films of LaNiO3 (LNO) on SrTiO3 (001) substrates. Stoichiometry of LaNiO3 films was changed by varying the oxygen partial pressure between 240 and 420 μbar during the growth in a pulsed laser deposition setup. Structural and temperature-dependent transport properties conform to epitaxial LaNiO3. The ellipsometric data, measured in the 350–850 nm spectral range, are adjusted with a dispersion relation of Drude-Lorentz (DL) type. In addition to the Drude term, only one Lorentz oscillator was used in the modeling for consistency with existing density of states calculations. Increasing oxygen pressure does not induce significant variations of the electronic density, the Hall mobility, or the Drude plasma energy. Neither are the pseudo-cubic lattice parameter and the Lorentz oscillator resonance energy significantly modified. Resistivity...

LaNiO3 thin films have been deposited on SrTiO3 (100) by pulsed laser deposition. Substrate temperature and oxygen pressure have been investigated in the ranges of 640–840°C and 200–600μbars, respectively. The use of LaNiO3 as an electrode requires good electrical, structural, and morphological properties. Optimized deposition parameters were determined to be in the range from 650to700°C for the substrate temperature and in the oxygen pressure range from 300to400μbars. Spectroscopic ellipsometry has been used to study in situ the growth of LaNiO3 at high temperature and variation of the optical constants during the cooling from growth to ambient temperature. The metallic behavior of the LaNiO3 is directly observed from the spectral variation of the ellipsometric parameters, tanΨ and cosΔ. For the initial stages of the film growth a determination of the thickness by ellipsometry is possible until the skin depth is reached. The optical constants, refractive index n and extinction coefficient k, have been ca...

Controlled off-stoichiometric single phase polycrystalline yttrium iron garnet (YIG) thin films have been grown by pulsed laser deposition, adjusting the oxygen partial pressure PO2 between 5 and 400 mTorr. Atomic stoichiometry by RBS shows an oxygen deficiency for PO2 Pstoich. Pstoich=30mTorr refers to films showing magnetic and structural properties of the bulk stoichiometric YIG. Curie temperature Tc and saturation magnetization 4πMs decreased for PO2 Pstoich: Increase of Tc (up to +10%) and of 4πMs (up to +20%) and lattice parameter compression. Microscopic interpretation is given in terms of superexchange interaction and creation and site selectivity of iron vacancies.