Magnetic Oxide Thin Films Research Articles

Local environment surrounding Co in MBE-grown Co-dopedHfO2thin films probed by EXAFS

Local structure around Co impurity atoms in $\mathrm{Hf}{\mathrm{O}}_{2}:\mathrm{Co}$ thin films prepared by molecular beam epitaxy has been investigated using the extended x-ray absorption fine structure (EXAFS) technique. These films were found to be ferromagnetic at room temperature. Progressive formation of Co clusters was observed accompanied by interstitial doping of Co in samples with Co concentration of 1%--20% grown at a substrate temperature of $\ensuremath{\sim}700\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$. However, films with a relatively high Co concentration of $\ensuremath{\sim}10%$ can be prepared without clustering of Co metal in a low-temperature growth mode with a substrate temperature $\ensuremath{\sim}100\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$. These low-temperature-grown films were found to be thermally stable up to an annealing temperature of $\ensuremath{\sim}700\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$. Our EXAFS results have therefore verified the feasibility for preparing Co-cluster-free room-temperature-ferromagnetic $\mathrm{Hf}{\mathrm{O}}_{2}:\mathrm{Co}$-diluted magnetic oxide thin films with great potential for possible spintronic applications.

Nanocomposite [formula omitted], [formula omitted] thin films prepared by RF sputtering and revealed by magnetic coupling effects

Magnetic and semi-conducting nanocomposite iron oxide thin films have been prepared under bias polarization, by radio-frequency sputtering of a magnetite target. The nature of the phases obtained in the thin films depends on the bias power density. The increase in power density, from 0 to 110 mW / cm 2 , allows the preparation of magnetite, magnetite/wustite and wustite/ α -iron nanocomposites successively. Magnetic measurements at low temperature show exchange bias for two-phases films even though the minor phase is not detected by grazing angle X-ray diffraction. The exchange bias can reach very high values of about 4300 Oe. Electrical properties at room temperature are interpreted taking into account both the modifications of the film compactness, and the nature of the phases from which they are made.

II : Gas Phase Crystal Growth and Characterization of New Magnetic Oxide Thin Films

II : Gas Phase Crystal Growth and Characterization of New Magnetic Oxide Thin Films

Role of defects in tuning ferromagnetism in diluted magnetic oxide thin films

In order to answer the question of whether there is another source of magnetism that plays an important role in tuning ferromagnetism in diluted magnetic oxide thin films, investigations on magnetic and structural properties of some types of transition-metal-doped semiconductors had been done. Results on Cr-doped ZnO and Ni-doped $\mathrm{Sn}{\mathrm{O}}_{2}$ films fabricated under various conditions implied that structural defects and/or oxygen vacancy, indeed, very much influence the magnetism in those systems. An elimination of defects, as well as filling up oxygen vacancies, might cause certain degradation to the ferromagnetic ordering of some specific types of compounds.

Nano-Scale Heteroepitaxy Control of Magnetic Oxide Thin Films on Ultra-Smooth Sapphire Substrates

AbstractWe have examined the novel heteroepitaxy of magnetic oxide thin films on ultra-smooth sapphire substrates by laser MBE for fabrication of low-dimensional structures. Employing the atomically controlled substrate surfaces with atomic steps and terraces, we demonstrate the deposition of magnetic oxide nanowires (~0.5 nm high and ~20 nm wide) and nanodots of (Mn, Zn) ferrite, Fe3O4 and NiO.

Magnetic oxide thin films

Thin films of manganese or cobalt oxides exhibiting colossal magnetoresistance have been prepared using the same deposition methods as those used in the growth of superconducting cuprates. The thin film morphology, as well as the physical properties of the manganese oxide thin films, is shown to be strongly dependent on thin film growth. Devices, including these manganese oxides, have been grown to achieve a better sensitivity of their colossal magnetoresistance behavior to a magnetic field.

Kinetics, Growth, Structure, and Atmospheric Chemical Vapor Deposition of Ferrimagnetic Iron Oxide Thin Films from Metallorganic Acetyl Acetonate Precursor

Growth of magnetic iron oxide thin films by a chemical vapor deposition process from metallorganic iron acetyl acetonate precursor under atmospheric transport is described. Kinetics of film growth depends on deposition parameters, particularly substrate temperature, gas flow rate, and location of substrate away from the source which is a direct effect of mass transfer and pyrolyzing efficiency of precursor vapor. As‐deposited films essentially have phase which is transformed by a sequential reduction‐oxidation process into and phases as revealed by electron diffraction studies. The modification in the crystalline phase of the as‐deposited film is observed by varying the substrate orientation and Ar to gas‐phase ratios. The phase of iron oxide films in the as deposited form, is realized by using pure Ar as transport gas. Microstructural changes as well as magnetic properties of iron oxide thin films on transformation into different polymorphic crystallographic phases are described.

Growth, magnetic properties and the effect of cobalt addition in metal-organic chemical vapour deposited (MOCVD) gamma iron oxide thin films for magnetic recording applications

The present study aims at investigating MOCVD technique for the deposition of magnetic oxide thin films using volatile metal-organic compounds as source material. A three-step scheme has been described to form γ-Fe2O3 phase starting from α-Fe2O3 films as-deposited in optically heated atmospheric cold wall CVD reactor. Growth of γ-Fe2O3 in a two-step process has been performed by depositing Fe3O4 phase directly by resistively heated low-pressure CVD (LPCVD) technique. Role of substrate temperature in controlling the oxidation leading to direct formation of metastable γ-Fe2O3 phase (single-step scheme) by atmospheric CVD technique has been described. A new mode of introduction of cobalt in the film, namely heterogeneous dispersion of cobalt in the γ-Fe2O3 matrix, has also been described. Crystallographic structure, microstructure and magnetic properties of the films have been studied in detail. Biaxial vector coil and high-temperature magnetic studies were carried out for determining the nature of anisotropy in the γ-Fe2O3 film. Growth of γ-Fe2O3 films in different schemes have been discussed from the studies of growth kinetics in a cold-and hot-wall-type reactor chambers.

Crystal Structure of Amorphous Magnetic Oxide Thin Films in Ni¿Fe¿P System

The crystal structure of magnetic amorphous oxide thin films in the Ni-Fe-P system made by the two source evaporation method was studied. When the amorphous thin films are heated, the magnetization disappears at the Curie temperature (Tc1), but, at almost exactly the same time, crystallization begins and causes the magnetization to once again increase. Finally the magnetization of the crystal line phase disappears at (Tc2). The amorphous oxide films are presumed to possess a magnetic coupling similar to that in nickel ferrite.