E. Sawatzky

Platinum‐cobalt films for digital magneto‐optic recording

Platinum‐cobalt thin films were prepared by rf sputtering with substrate biasing to contol composition. Contrary to what was expected from equilibrium bulk properties, films deposited at room temperature have the fcc structure, in‐plane magnetization, and low coercivity. At deposition temperatures above about 500 °C the coercivity increases and x‐ray analysis indicates some tetragonal phase. Annealing at 600 °C causes rapid conversion to the tetragonal phase. In the annealed state the films have a large component of magnetization normal to the film plane with typical remanence‐to‐saturation ratios of 0.8 and coercivities of 8 kOe perpendicular to the film plane. The saturation Faraday rotation of annealed films is about 5×105 deg/cm in the visible and near ir. Curie temperatures are in the range 270–430 °C for compositions with 35–44 at.% cobalt. Dynamic read‐write experiments show that this material is an attractive candidate for digital magneto‐optic recording. Problems due to the high Curie‐point and h...

Preparation of Garnet Films by Sputtering

Three different sputtering approaches are described for the synthesis of garnet films in the thickness range of 0–4 μ. The experimental requirements for producing single‐phase, polycrystalline GdIG films are described in some detail, especially in the rf sputtering mode. Unexpectedly large systematic variations in the unit lattice parameter of the garnet structure as a function of film thickness are reported. Possible causes for these systematic structural changes are discussed.

Manganese gallium germanide‐a new ferromagnetic material

A new ferromagnetic ternary compound MnGaGe, isostructural with Mn2Sb, has been prepared by quenching from the melt and subsequent solid‐state reaction. The metallic MnGaGe is tetragonal with lattice constants a = 3.966±0.001 A and c = 5.885±0.001 A. Magnetic measurements show that the Curie temperature is 185 °C and the saturation magnetization corresponds to 1.66μB/Mn atom at 4.2 °K. The easy axis of magnetization coincides with the crystallographic c axis. The new material is thermally stable to 616 °C at which temperature it melts peritectically.

Magnetic and Structural Properties of Epitaxial and Polycrystalline GdIG Films Prepared by rf Sputtering

Magnetic, magneto‐optical, and structural properties of rf‐sputtered gadolinium iron garnet films are presented. The dependence of the Faraday rotation on film structure is explored and the behavior of coercivity and hysteresis loop characteristics with temperature discussed in some detail. The coercive force was found to be independent of structural differences in the various films as monitored by x‐ray and electron diffraction techniques. The high coercivities observed are attributed in part to a strain induced magnetoelastic interaction. Hysteresis loops with squareness ratios of Mr/Ms=1 are obtained from (111)‐oriented films on (111) YAG substrates. Domain patterns are highly temperature stable in the epitaxial films. There is no evidence from magnetic and structural properties in these epitaxially grown films that cation diffusion from substrate to film is involved at crystallization temperatures below about 900°C. The films are considered quite adequate for magneto‐optic memory applications.

Some Magnetic and Structural Properties of Epitaxial Garnet Films Prepared by rf Sputtering

Epitaxial garnet films have been prepared by rf sputtering from a polycrystalline gadolinium iron garnet target onto single‐crystal substrates of YAG. Epitaxy is achieved on all orientations of the substrate, either in situ when depositing at ≥500°C, or during post‐deposition crystallization of amorphous or partially crystallized films deposited at <500°C. The compensation temperature in epitaxial films depends strongly on the deposition temperature. The lowest compensation temperatures are found in films prepared at the highest deposition temperatures. Flims prepared on glass substrates at elevated deposition temperatures are iron deficient and crystallize in at least two phases, Gd3Fe5O12 and GdFeO3. The iron deficiency in these films is assumed to be caused by a variation with temperature in the net cation sticking coefficients. No GdFeO3 phase is found in epitaxial films prepared at the same elevated deposition temperatures, although these films should also be iron deficient. It is believed that they ...

Magneto‐Optical Properties of Sputtered Mn5Ge3 Films

The Faraday rotation and optical absorption of ferromagnetic Mn5Ge3 thin films have been measured in the visible and near infrared. Apart from a gradual rise in optical density in the near uv, the absorption is featureless to 2.5 μ. The Faraday rotation behaves similarly. At 500 mμ the room‐temperature absorption coefficient α and the 5°K saturation rotation F are 3.5×105 cm−1 and 2.1×105 deg/cm, respectively. The rotation decreases with rising temperature and vanishes at 40°C which agrees well with the bulk Curie temperature of 37°C. The in‐plane coercive field Hc decreases monotonically with temperature as Tc is approached. For a 900‐A‐thick film Hc is 260 Oe at 0°C. The dependence of magnetic and magneto‐optical properties on film structure is discussed.

Apparatus for Direct Recording of Magneto‐Optic Rotation and Magnetic Hysteresis

The design and construction of an apparatus for domain observation and for the measurement of magneto‐optic rotation and coercivity of thin magnetic films, by means of the Faraday effect, are described. A spatial resolution of 5 μ is achieved, allowing scanning of magneto‐optic properties across the film. Gas flow cooling and heating of the samples result in a temperature range of −120 to +200°C. A special sampling detector allows continuous recording of magneto‐optic rotation and coercivity as a function of temperature and wavelength.

Magnetic and magneto‐optical properties of sputtered MnGaGe films

The new compound manganese gallium germanide has recently been shown to be a uniaxial ferromagnet with a Curie temperature of 185°C. The easy axis of magnetization coincides with the tetragonal crystallographic c axis. Nearly completely c‐axis‐oriented films with hysteresis loops showing essentially 100% remanence normal to the film plane have been prepared by sputtering. The Curie temperature depends on the film composition. Curie temperatures as low as 110°C have been observed in nonstoichiometric films. These films have a room‐temperature coercivity of 950 Oe compared to ≥2000 Oe for stoichiometric films. At a wavelength of 6328 A the absorption coefficient α (corrected for reflectivity) is 5.8×105 cm−1 and the room‐temperature polar Faraday rotation F is 80 000°/cm. The reflectivity R at normal incidence is 0.47. MnGaGe undergoes no phase changes before melting peritectically at 616°C and the films are stable to oxidation at temperatures well above the Curie point. The low Curie temperature combined w...

Method for Studying Sputtered Particles by Emission Spectroscopy

An f/6.8 scanning spectrometer with a photomultiplier output was used to monitor the presence of particles sputtered from a target surface by ion bombardment. The ion source was a conventional duoplasmatron providing a high density, high energy ion beam. The density of sputtered particles available for analysis was of the order of 108 cm−3. A fraction of these particles was electronically excited by a high density, low energy electron beam, and the emission spectra characteristic of the target material were recorded with either an electrometer or a phase sensitive detector. Some intense atomic copper lines were easily observed when a Cu target was bombarded with 5000 eV Ar+ ions. The intensities of these lines have been analyzed to obtain the sputtering yield and some relative excitation functions for copper. A comparison between the conventional mass spectrometric technique and the present scheme is presented.

Preparation and properties of nonstoichiometric MnAlGe thin films

Films of MnAlGe which are nonstoichiometric have been prepared by rf sputtering. Structural, magnetic, and optical properties of these films have been determined. The Curie temperature of films with excess aluminum has been found to be as low as 190°C. The crystallographic orientation of these films may be adjusted by proper choice of substrate temperature.