S. Takei

SmCo/Cr bilayer films for high-density recording media

The magnetic properties of a SmCo layer on a Cr underlayer, which was prepared by various Ar gas pressure (PAr), were studied. A single line appeared in each X-ray diffraction diagram and its intensity became strong when PAr was decreased from 1.06 to 0.13 Pa. The microstructure observed by using atomic force microscopy showed that the surface morphological structure of Cr underlayers depended on PAr and the surface of the Cr underlayer became smoother as PAr was decreased, while the surface and the grain of the SmCo layer on the Cr underlayer were independent of PAr. The grain size of SmCo layers was as small as 30 nm with the surface roughness of about 1 nm. The coercivity, the squareness ratio, and the coercivity squareness ratio of the SmCo layer on the Cr underlayer prepared at 0.13 Pa were 155 kA/m, 0.92 and 0.92, respectively. Those values suggest that an easy axis of magnetization for the SmCo layer is in plane and the switching field distribution is very small. Although the crystal structure of t...

La–Zn substituted hexagonal Sr ferrite thin films for high density magnetic recording

La–Zn substituted M type Sr-ferrite thin films were prepared by conventional rf diode sputtering. The crystallography, surface morphology, magnetic properties, and their temperature dependence were investigated by x-ray diffractometry, atomic force microscopy, and vibrating sample magnetometry. La–Zn substitution reduces the grain growth rate, so that it was possible to obtain fine grains with mean grain size about 12 nm×12 nm. Suitable amount of La–Zn substitution increases the saturation magnetization Ms of the films without changing the magnetocrystalline anisotropy of the material. As a result, the coercivity Hc increases with the increase of the La–Zn substitution. La–Zn substitution also reduces the values of dHc/dT of the films in the vicinity of room temperature.

Magnetic and crystallographic properties of La–Zn substituted Sr-ferrite thin films

La–Zn substituted Sr-ferrite thin films were prepared by rf diode sputtering. The magnetic and crystallographic properties of the films were investigated by vibrating sample magnetometry and x-ray diffractometry. It is found that the texture of the films sensitively depends on the amount of substitution. Both the saturation magnetization Ms and coercivity Hc increase with the increase of La–Zn substitution. The increase of Hc is caused, in part, by the increase of K1 due to the substitution.

Structural and magnetic properties of NdFeB thin films sputtered on W underlayers

The NdFeB thin films are fabricated by a DC magnetron sputtering system. We find W underlayer is favorable to pseudomorphic growth of Nd2Fe14B crystallites with predominant c-axis perpendicular alignment. Through manipulating the sputtering parameters, this kind of pseudomorphic growth can be effective in a certain film thickness range. In our case, the crucial thickness value is estimated to be about 30 nm, which is thick enough for application of the ultra-high density perpendicular magnetic recording media. Beyond this range, misfit dislocation will be formed in the films, the films become more soft due to the formation of soft phases. We also discuss the magnetization reverse mechanism of the interested film with the thickness of 15 nm. Its magnetization reverse process is found to be mainly controlled by magnetization incoherent rotation

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 den...

Synthesis of Nd-Fe-B thin films with high coercive force by cosputtering

NdFeB thin films were prepared by cosputtering of the individual elements and the magnetic properties were studied as a function of the concentration of Nd and B in the films. The dependence of coercive force, saturation magnetization and the energy product (B/sub r//spl times/H/sub c/) on the composition are presented by three dimensional diagrams. High coercive force and high energy product was observed at Nd concentrations slightly higher than the stoichiometric composition. For a fixed composition, a dependence of coercive force as a function of thickness of the film was observed. The microstructure of the films also showed a variation as a function of thickness.

Characteristics of Ba-ferrite thin films for magnetic disk media application

Abstract The Ba–ferrite thin films prepared by sputtering have been found suitable for high density magnetic disk media application for the properties such as their high mechanical hardness and chemical stability, and for the easiness to synthesize the films with perpendicularly oriented easy magnetization axis. A disadvantage of this film in comparison with the currently used CoCrTaPt film is its larger grain size, which is caused by elevated temperature necessary for crystallization. This paper presents the methods of reducing both the temperature of crystallization and the grain size. Considerations have been given to the surface roughness of the films, the size of the grains and their switching (or activation) volume. Magnetic properties and performance characteristics of prepared disk medium with fundamental design idea have been discussed.

Effect of substrate temperature on magnetic properties of strontium ferrite thin films

Strontium hexagonal ferrite (SrM) thin films were prepared by a dc magnetron sputtering system, and the crystal structure and magnetic properties were studied. It was found that crystallization temperature of SrM film was around 500/spl deg/C. Preferential orientation of c-axis was observed at the substrate temperature (Ts) of 550/spl deg/C. The films prepared at Ts of 550/spl deg/C exhibited the maximum coercivity of 3.5 kOe in the perpendicular direction.

Dependence of magnetic properties on magnetic layer thickness in SmCo/Cr films

SmCo/Cr films were prepared with the thickness of SmCo layer varying from 1 to 400 nm, and the dependence of the magnetic properties on SmCo layer thickness was studied. Atomic force microscopy (AFM) measurement revealed that both the Cr underlayer and SmCo/Cr films were very similar in surface morphology with the surface roughness (Ra) of about 6 nm for the SmCo layer thinner than 100 nm. The Cr underlayer contributes to generate small grain size and smooth surface for SmCo layer as well as to improve its magnetic properties. The maximum coercivity was about 3.3 kOe, and the squareness and the coercive squareness in the plane direction were about 0.91 and 0.97, respectively, when the SmCo layer thickness was 40 nm. The diameter of switching unit estimated by the magnetic switching volume was smaller than 30 nm, while AFM observations show a grain size of 50 nm or more. The magnetic properties and the microstructure of SmCo/Cr bilayer films promise to be suitable for high density recording media applications.

Controlling The Magnetization Reversal Mechanism In Co/Pd Multilayers By Underlayer Processing

The effect of various process parameters on the magnetic properties of sputter deposited Co/Pd multilayered films is presented. The coercivity of the films was found to increase logarithmically with the thickness of the Pd underlayer. Various combinations of sputter gas (Ar) pressure during the deposition of the underlayer (P/sub ul/) and during the deposition of the multilayer (P/sub ml/) were studied. Coercivity was found to depend on both P/sub ul/ and P/sub ml/. When P/sub ml/ was kept constant at 3 mTorr, a decrease in coercivity with the increase in P/sub ul/ was observed. And, for a constant P/sub ul/ of 3 mTorr, an increase in coercivity was observed when P/sub ml/ was increased. The magnetization reversal mechanism of these films was found to change from domain wall motion to rotation when P/sub ul/ is increased from 3 mTorr to 18 mTorr or higher. However, the change in the reversal mechanism was not observed with the variation in the preparation conditions of the magnetic layer or the other underlayer process parameters such as the thickness or sputter power.