SmCo Films Research Articles

Microstructure and magnetic properties of SmCo films

We have studied the role of deposition pressure on the structure and magnetic properties of SmCo films sputtered on Si(1 0 0) substrates. The effect of variation of Sm content on microstructure and magnetic properties was studied as sputter pressure was changed. The films deposited on heated substrates up to 450 °C and the crystalline c-axis is randomly aligned in the film plane. The films showed hard magnetic properties with in-plane anisotropy. Room temperature intrinsic coercive forces i H c, up to 15.5 kOe have been observed and the maximum energy product of SmCo films was estimated at 15.5 MGOe.

On the role of the soft layer in exchange‐spring hard/soft magnetic bilayers

Bilayers of SmCo/NiFe and SmCo/Co with well-defined in-plane uniaxial anisotropy were grown by dc magnetron sputtering on glass substrates. The magnetization reversal process was investigated by magneto-optic Kerr effect from both sides of the samples, obtaining the hard and soft response separately. The NiFe layers turn out to be exchange coupled to the SmCo films and, for soft layer thicknesses above 30 nm, display reversible demagnetization loops expected from exchange-spring magnets. The experimental NiFe magnetization curve is in good agreement with the theoretical curve obtained by minimizing the magnetic energy in the soft film for an ideal hard/soft bilayer. The soft layer critical thickness above which the exchange spring behavior sets up and its presumed independence on soft layer characteristics are discussed, by comparing the two systems under investigation. We find that SmCo/Co does not fulfil the predictions of the currently accepted theories and that the magnetization reversal of the bilayer is dominated by the Co layer. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Scanning Hall probe microscopy with high resolution of magnetic field image

The scanning Hall probe microscope (SHPM) which can be used in magnetic fields up to 15kOe has been developed. A surface magnetic image in the ferromagnetic SmCo5 film was measured under magnetic fields perpendicular to the sample with the SHPM. The observed images describe domain transitions consistent with the magnetization curve.

Temperature dependence of the hysteretic properties in SmCo films

Abstract Results are presented about the hysteretic properties of Cr/SmCo/Cr/Si films grown at room (RT) and high (HT) temperature. The RT-grown, as-deposited films exhibit small RT coercivities whereas in the HT-grown films the as-deposited RT, in-plane coercivity is close to 0.9 T . Flash annealing of the films deposited at RT leads to the development of in-plane and out-of-plane RT coercivities about 1.5 T . The analysis of the thermal dependence of the coercive force of our films allows us to discuss the relationships between their coercivities and their nanostructural characteristics.

Fabrication of Integrated Magneto-Optic Isolator

ABSTRACTIn optical applications, especially in optical communications, protecting light sources from harmful reflected energy is very important. With magneto-optic isolators, these light sources can be protected to extend their lifetimes and performance by blocking back-reflected light. The active element in these optical isolators is a magneto-optical garnet. However, garnet is difficult to integrate with semiconductors due to the high thermal budget usually required to obtain the garnet crystal structure. For example, current isolator garnets cannot be integrated monolithically into a photonic integrated circuit due to the growth process, liquid phase epitaxy, which requires growth temperatures of >900 °C and also garnet substrates. In this work, magneto-optical garnets were grown monolithically by low-temperature reactive RF sputtering, followed by an ultra-short (<15 sec) anneal. The refractive indices of the resulting garnets were measured using Fourier transform infrared (FTIR) spectroscopy. Various rib waveguides were fabricated by both wet etching and reactive ion etching (RIE). The width of the waveguides varied from 2 to 12 μm and the heights were varied from 0.5 to 1.0 μm. Sm-Co thin films were used for integrated biasing magnets. They were deposited on top of claddings of both magnesium oxide and yttrium oxide, all using the same sputtering system that was used to deposit the garnet films. These magnetic films had high enough remanent fields to saturate the garnet waveguides, and they had coercivities of 700 Oe. The Faraday rotations and waveguide losses of the subsequent isolators were measured to be 10 degrees and 0.1 dB/μm at 632 nm, respectively. Although this prototype is promising, optimization of the device designs is ongoing. In summary, this work succeeded in providing the first comprehensive report on etching YIG by RIE, in developing all of the steps required for integrating isolators on non-garnet substrates, and in proving the feasibility of these isolators.

垂直磁気異方性を有するＳｍ−Ｃｏ／Ｃｕ薄膜の作製と磁気特性

In order to prepare Sm-Co films with perpendicular magnetic anisotropy, effects of the substrate temperatures during the preparations of both the Cu underlayer and the Sm-Co layer were studied. The Cu underlayer was varied from (111) preferred- oriented structure to (200) structure due to the substrate temperature. When the Sm-Co layer was prepared at 300°C onto the Cu underlayer with (111) preferred-oriented structure, the X-ray diffraction line from SmCo5 (002) plane was observed and the magnetic easy axis was in the perpendicular direction. The coercivity in the perpendicular direction was about 9.6 kOe and the coercivity in the in-plane direction was about 1.4 kOe.

SmCo박막의 바이어스자계가 CoZrNb박막의 연자성특성에 미치는 효과

To investigate whether the use of hard magnetic film is available to generate bias magnetic field for a magnetoimpedance sensor, the magnetic properties of SmCo hard magnetic films were investigated as a function of their compositions. The saturation magnetization decreased with Sm content increasing in SmCo films. And, the coercive force increased in the extent of Sm content of 28 at%, but decreased as Sm content increased moreover. The bias field effect of SmCo film to amorphous CoZrNb film was investigated with the magnetization corves, permeabilities, and magnetic domain structures of SmCo/CoZrNb multilayers. The bias field of about 60 Oe was observed in the film with 3 mm 0.5 mm, which can be constructed as a MI sensor, and this result strongly indicates that the bias field generated from a hard magnetic film is adequate to enhance the sensitivity of a MI sensor with hard/soft magnetic multilayer structure.

Hysteresis modeling of anisotropic and isotropic nanocrystalline hard magnetic films

In the Hauser model, the magnetic state of a system is obtained by minimizing the so-called total energy function for a statistical set of magnetic domains. In this article, this energetic model of ferromagnetic materials is used in order to calculate hysteresis loops of isotropic and anisotropic nanocrystalline SmCo films at room temperature. A qualitative very good agreement between the calculated and experimental curves is obtained, mainly in the anisotropic case. Also, it has been verified that, under suitable approximations, the free parameters of the model can tie with intrinsic characteristics of the reversal magnetization process.

Hard magnetic Nd-Fe-B and Sm-Co films: influence of the Cr buffer microstructure on the magnetic properties

Hard magnetic Nd-Fe-B and Sm-Co films have been deposited on various substrates with a Cr buffer layer. The morphology of the buffer was modified from a smooth to a rough, meander-like structure. Films deposited on the rough buffers exhibit a significantly higher coercivity. The feasibility of Cr as a diffusion barrier and as an intermediate layer to induce magnetic texture in these systems is discussed.

Effect of rare earth content on microstructure and magnetic properties of SmCo and NdFeB thin films

Thin films of highly anisotropic rare earth intermetallic compounds increasingly come into the focus of interest for application in magnetic miniature devices. We prepared hard magnetic SmCo and NdFeB films by pulsed laser deposition and investigated the influence of rare-earth content on phase formation, microstructure, and magnetic properties. The phase evolution with rare earth content, as observed by x-ray diffraction, shows a distinct difference for the two systems. For SmCo a disordered SmCo7 structure is found at low Sm content and a change in the lattice constants is observed for a Sm-rich sample. Simultaneously, the coercive field improves whereas the magnetic in-plane texture found for Sm-poor films vanishes for higher Sm content. For NdFeB the increase in Nd content leads to an additional Nd phase because of the small homogeneity range. Contrary to the bulk, coercivity is reduced, which can be attributed to a significant increase of grain size and roughness.

Magnetic properties of CoSm thin films with Cr/sub 80/V/sub 20/ and Cr as underlayers

We investigated the static and time-dependent magnetic properties of thin CoSm films (6-14 nm) on CrV underlayers. We measured remanent coercivities of up to 4.5 kOe and viscosity coefficients as low as 8%/decade for 14-nn films with remanent moment thickness product of 0.49 memu/cm/sup 2/. We compared magnetic hardness, interactions, viscosity, and anisotropy with similar films grown on Cr underlayers, and found that CrV constitutes a better underlayer for CoSm thin film media, most probably because of improved epitaxy at the interface and a more favorable interface, microstructure, and topography.

Inter-relation between reversible and irreversible magnetization components in nanocrystalline SmCo films

A study of the experimental behavior of the reversible ( M rev) and the irreversible ( M irr) DCD magnetization components in enhanced-remanence SmCo films was carried out. The evolution of the DCD M rev and M irr components were determined at room temperature by measuring sets of first-order reversal curves from different points on the initial magnetization curve and the demagnetization curve. From these data, M rev( M irr) H i curves were built, H i being the internal field of the sample. Recent studies show that the behavior of the M rev( M irr) curves at a constant internal field can be used as an indicator of the mechanism of reversal magnetization. The non-monotonic behavior showed by these curves at low fields in our material, seems to be associated with an incoherent mechanism of magnetization reversal in the nanograins of SmCo.

Hard magnetic SmCo thin films prepared by pulsed laser deposition

Hard magnetic SmCo films were prepared by pulsed laser deposition in UHV and at moderate background pressures on polycrystalline Al 2O 3. Structure and magnetic properties are discussed for varying Sm-content. The perpendicular anisotropy observed at a deposition pressure of 0.06 mbar is compared with texturing models known for sputtered samples.

Ｓｍ‐Ｃｏ／Ｃｒ薄膜の高保磁力化

In this study, the dependence of the magnetic properties of Sm-Co layers prepared on the Cr underlayers on Sm concentration, sputtering pressure, and power were studied to increase the coercivity of the film and to apply the film to high-density recording media. The film with a coercivity of about 4.5 kOe was prepared by adjusting the conditions. It was confirmed by the analysis of the selected area electron diffraction pattern that the crystal structure in Sm-Co film consists of a mixture of crystallites and amorphous matrix. The D50 of Sm-Co/Cr disk was about 130 kFRPI.

Magnetic properties and underlayer thickness in SmCo/Cr films

SmCo films with a Cr underlayer have been investigated as potentially attractive candidates for high density recording media. Magnetron sputtering was used here to produce Cr/SmCox/Cr films on Si (100) substrates. The magnetic films were deposited at a substrate temperature of 350 °C and an Ar pressure of 5 mTorr. Cr underlayers were deposited both at 25 °C and at 350 °C and exhibited different textures. Layer thicknesses were evaluated using Rutherford backscattering spectroscopy, while SmCo grain size and underlayer texture were determined from a Rietveld analysis of x-ray diffraction data. The magnetic properties were measured with a vibrating sample magnetometer. The resulting films had in-plane coercivities in the range 4–8 kOe. For a SmCo layer with a thickness of 200 nm, the Cr underlayer thickness was varied in the range 75–300 nm to study its effect on intergranular coupling in the films. For thermally demagnetized samples, both magnetizing and demagnetizing remanence curves were measured and used to evaluate switching field distributions and δm plots. The underlayer texture was found to affect magnetic properties more strongly than underlayer thickness.

Nanophase dispersed SmCo films with high remanence and corrosion resistance

Nanophase dispersions of SmCo5 in either an Al or Co matrix have been synthesized by using pulsed laser deposition to deposit the SmCo aggregated grains while simultaneously sputtering either Al or Co. Smooth single phase type hysteresis loops were measured for both types of dispersed systems. SmCo5 plus Al dispersions were made that exhibited room temperature coercivities of 15 kOe with ≈5 at. % Al and decreased to 5.7 kOe with 21 at. % Al. The SmCo5 plus Al dispersions were only marginally affected by heating in air for 30 min to 300 °C. It was possible to make SmCo5 plus Co films with loop squareness of ≈0.83 and with room temperature coercivity ≈10 kOe by using a Co matrix.

Effect of underlayer thickness on magnetic properties of SmCo film

It is well known that the Cr underlayer plays significant role in the magnetic properties of Co alloy film. In this study, the effects of the underlayer materials such as Cr, Mo, W, W/Cr, and Al and their thickness on the magnetic properties of SmCo films were studied. In the x-ray diffraction diagrams of the SmCo/Cr film and the SmCo/Mo film, only (110) line of body-centered-cubic crystal structure was observed, while diffraction lines from SmCo phase could not be observed. The oval shaped grains were observed on the surface of Cr underlayer and the Mo underlayer when the thickness was thicker than 100 nm. The coercivity of the SmCo/Cr film and the SmCo/Mo film with thickness over 100 nm was higher than 3 kOe and the squareness ratio and the coercivity squareness ratio was above 0.8 and 0.9, respectively. These results indicate the Cr underlayer and the Mo underlayer are suitable for SmCo layers in order to increase the coercivity and the SmCo/Cr film and the SmCo/Mo film are good candidates for high density recording media.

Reversible and irreversible magnetization behavior in SmCo films

Recent studies of demagnetization processes in permanent magnets have used two different methods for determining the reversible magnetization, often arriving at conflicting results. In the present work, enhanced-remanence SmCo films have been prepared by DC magnetron sputtering. The evolution of the reversible ( M rev) and irreversible ( M irr) magnetization along the initial magnetization curve and the demagnetization curve of the films was determined using the two methods. In one case, the DCD definition of the reversible magnetization was used to measure the quantity from a set of recoil curves. Alternatively, the moving Preisach model was used to separate the magnetization into its components M rev and M irr. We discuss the different behaviors encountered for the reversible magnetization and the inter-relation function η=(∂ M rev/∂ M irr) Hi and interpret the differences.

Magnetic interaction and thermal stability in CoSm thin films

We report a systematic experimental study of magnetic interactions and thermal stability in very thin films of CoSm fabricated by DC magnetron sputtering on glass substrates, CoSm/Cr films with CoSm thickness 6 to 14 nm yield high remanent coercivities H/sub cr//spl les/3.8 kOe and low remanent moment thickness product, Mr/spl delta/<0.44 memu/cm/sup 2/. The magnetic interactions are dominated by exchange coupling, decreasing with increasing thickness. Thermal stability as measured by magnetic viscosity and dynamic coercivity decreases with film thickness, but according to current criteria, CoSm films of down to a thickness of about 8 nm would be stable.

Soft x-ray absorption of a buried SmCo film utilizing substrate fluorescence detection

Oxygen K-shell x-ray fluorescence was monitored from the MgO substrate of a metallic heterostructure system containing a buried SmCo permanent magnet layer. This fluorescence was utilized as a detector to record transmission yield spectra for the SmCo film at both the Co–L3,2 and Sm–M5,4 absorption edges. Ordinarily, traditional transmission yield spectroscopy in the soft x-ray regime is impossible to perform with films on single-crystal substrates. The measured intensity ratios agree with simulations to confirm the thickness information. The potential and limitations of this technique are discussed in comparison to standard total electron and fluorescence yield techniques and magnetic circular dichroism.