H. Y. Zhang

Anisotropy and Faraday effect in Co spinel ferrite films

Crystalline Co spinel ferrite films were prepared by rf sputtering on glass substrates without buffer layer and annealed at temperatures from 400 to 600 °C for 2 h in air. (100) texture was obtained in these films. The anisotropy constant, magnetic hysteresis loops, and magneto‐optical Faraday spectra of the films were measured. The texture became poor when the films were annealed below 500 °C, but the perpendicular anisotropy constant Ku, squareness ratio R=(Mr/Ms)⊥/(Mr/Ms)∥ increased and showed peak values of 2.2×105 ergs/cm3 and 0.94, respectively, at an annealing temperature Ta=500 °C. For the film annealed at 600 °C (higher than the Curie temperature, 520 °C, of Co spinel ferrite), the texture recovered, but Ku and R dropped. The Faraday rotation spectra of Co spinel ferrite films showed a broad peak centered around 720 nm. The peak value increased monotonically with increasing annealing temperature. These results may be related to the Co ion‐induced anisotropy and Co ion distribution in tetrahedral ...

Magneto-optical properties and anisotropy of cobalt ferrite films with different texture

Abstract Cobalt ferrite films Co x Fe 3− x O 4 ( x =0.3–1.0) of spinel structure with different textures were prepared by rf sputtering. Annealing in a temperature range from 400 to 600°C led to different changes in the texture and magnetic properties. Peaks at 740 nm in Faraday rotation spectra increased with annealing temperature in different ways for different Co composition.

Preparation of YBa2Cu3O7−x superconducting thin films over large area substrates

Using facing targets and off‐axis direct‐current magnetron sputtering, we have prepared high quality YBa2Cu3O7−x (YBCO) superconducting thin films on ZrO2 (100) with Tc≤90 K (R=0) and Jc as high as 1.6×106 A/cm2 (78 K, zero magnetic field) over an area of 70 mm diameter. Over this large area, the fluctuations of Tc and film thickness are from less than +0.9% to −1.3% and from +6.3% to −10%, respectively. In this article, also discussed are the differences between two sputtering modes used in our experiments, one of which gives larger area of superconducting thin film, higher deposition rate, and better thickness uniformity than the other. It is found that the smoothness and the temperature uniformity of the substrate holder are a of extreme importance for the fabrication of large area superconducting thin films. An electroquartz with little deformation during deposition has turned out to be very successful as the substrate holder in our fabrication.

Influence of Bi on magnetic properties of Dy3Fe5O12 garnet film

Abstract Bi 2 DyFe 5 O 12 garnet films were prepared by crystallization of sputtered amorphous films. The magnetic properties and influence of Bi were studied. The substitution of Bi results in the decrease of low-temperature magnetization and compensation temperature and increase of room-temperature magnetization and Curie temperature. This behaviour may be attributed to the influence of the Bi 3+ ions on the superexchange interaction and to the spin polarization of Bi 3+ ions. It was found that the bismuth enhances the effective magnetic moment of Dy 3+ ions.

Magnetic properties of amorphous Bi2DyFe5O12

Amorphous Bi2DyFe5O12 films have been prepared by rf sputtering technique. The magnetic properties, structure and effect of annealing have been investigated. The magnetization increases with increasing magnetic field and is not saturated at a high magnetic field of 65 kOe. In the temperature range 20 K<T<200 K the susceptibility can be described by a Curie-Weiss law with a Weiss constant of θ=−15 K. The effective paramagnetic moment for the iron ion (4.1 μB) is much smaller than the theoretical moment (5.9 μB). Above 200 K the slope in χ−1 vsT curve changes. The Weiss constant and effective paramagnetic moment for the iron ion increase. After annealing above 600°C the amorphous samples crystallize to a single garnet phase with the magnetization of 21 emu/g at 1.5 K and 7.2 emu/g at 300 K, which are the same as those of the bulk Bi2DyFe5O12 garnet ferrites.

The magneto‐optical Kerr effect of trilayer

In this paper the magneto‐optical polar Kerr rotation spectra of trilayers Fe/Ag/Cu, Fe/Cu/Ag, Fe/Au/Cu, and Fe/Cu/Au were measured and calculated. The experimental results coincided well with the calculated results. It was found that for trilayers Fe/Cu/Ag and Fe/Ag/Cu, with a 100 A thickness of the top Fe layer, there were two Kerr rotation peaks in their rotational magneto‐optical Kerr rotation spectra, located near 320 nm (the plasma edge of Ag) and 560 nm (the absorption edge of Cu). For Fe/Cu/Au and Fe/Au/Cu, with a 100 A thickness of the top Fe layer, there was only one Kerr rotation peak, which shifts slightly with the intermediate layer thickness. Trilayers Fe/Au/Cu and Fe/Cu/Au with suitable thickness of the top Fe layer are useful at present for magneto‐optical storage with a read‐out laser of long wavelength; Fe/Ag/Au and Fe/Cu/Ag will be useful in the future for magneto‐optical storage with read‐out laser of short wavelength.

Crystallization of sputtered amorphous oxide films

Amorphous oxide films with a composition of Bi2DyFe5O12 have been prepared by rf sputtering technique. The crystallization process was investigated using x‐ray diffraction, differential thermal analysis, magnetic properties, magnetic resonance spectra, magneto‐optical Faraday spectra, Raman spectra, and infrared reflection spectra. Amorphous oxide films exhibit very small magnetization and Faraday rotation at room temperature. At about 600 °C amorphous films crystallize to a garnet phase. With crystallization the magnetization and Faraday rotation increase rapidly. Raman and infrared spectra studies show the presence of tetrahedral sites in the amorphous films. As the annealing temperature increases, the peaks corresponding to octahedral and dodecahedral sites occur successively. It is of interest to note that amorphous oxide films containing Fe3+ ions show no magnetic resonance spectra at 71 and 300 K. The films annealed above crystallization temperature show a normal resonance spectrum. With increasing ...

New phenomena in FMR and EPR studies of amorphous oxide films and their crystallization

Abstract (BiDy) 3 Fe 5 O 12 films were made in the amorphous state by rf magnetron sputtering from a sintered Bi 2 Dy 1 Fe 5 O 12 ceramic target onto quartz substrates and studied by X-ray diffraction. The films were annealed at temperatures ranging from 500 to 700°C for 1 h in air and also at 650°C for different periods of time from 5 to 60 min. X-ray diffraction was used to determined the phase components of the samples. In the X-ray patterns, the amorphous films had two diffuse broad maxima in X-ray diffraction patterns centred at the double diffraction angles 2 θ =31° and 52°, respectively. The films crystallized at 650°C and all the crystallized samples have a single phase of garnet. The FMR linewidth increased with the decreases in annealing temperature and annealing time. No FMR and EPR of Fe 3+ were observed in the amorphous films even though they contained large amounts of Fe 3+ ions, while the EPR of Fe 3+ was observed in slide glass with the same gain.

Preparation of YBa2Cu3O7−δ thin films by magnetron sputtering with in situ plasma oxidation

Superconducting YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} thin films with surface roughness Ra{similar to}20 A have been successfully prepared by either rf or dc magnetron sputtering. The substrate temperature was kept at 600--670 {degree}C during deposition and a subsequent {ital in} {ital situ} plasma oxidation treatment was performed at 480--520 {degree}C. The films deposited on single-crystal SrTiO{sub 3} (100) exhibited zero resistance at 91 K and had the critical current density of 3{times}10{sup 6} A/cm{sup 2}. In this paper we describe the influences of fabrication conditions on film superconductivity.

Preparation of YBa sub 2 Cu sub 3 O sub 7 minus. delta. thin films by magnetron sputtering with in situ plasma oxidation

Superconducting YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} thin films with surface roughness Ra{similar to}20 A have been successfully prepared by either rf or dc magnetron sputtering. The substrate temperature was kept at 600--670 {degree}C during deposition and a subsequent {ital in} {ital situ} plasma oxidation treatment was performed at 480--520 {degree}C. The films deposited on single-crystal SrTiO{sub 3} (100) exhibited zero resistance at 91 K and had the critical current density of 3{times}10{sup 6} A/cm{sup 2}. In this paper we describe the influences of fabrication conditions on film superconductivity.