Magnetic Properties Of Co-Cr Films Research Articles

Perpendicular magnetic properties of CoCr films on GaAs

CoCr films were deposited on three types of GaAs substrates, GaAs(001), GaAs(111), and Al oxide∕GaAs(001). The perpendicular magnetic properties were investigated by magneto-optical Kerr-effect measurements. The direct deposition of the CoCr film on the GaAs substrate did not show any perpendicular magnetic properties. This fact indicates that the lattice distortion influenced by the GaAs lattice suppresses the perpendicular magnetism. The CoCr film on the Al oxide layer showed a tilted squarelike hysteresis loop. The thickness dependence of the hysteresis loop and the magnetic force microscopy showed that the onset thickness of ferromagnetism was 6.5nm. The domain size of the CoCr films monotonously decreases with the increasing thickness (6.5–75nm).

9-8 ICPプラズマ支援マグネトロンスパッタ法で作成したCo-Cr薄膜の磁気特性

9-8 ICPプラズマ支援マグネトロンスパッタ法で作成したCo-Cr薄膜の磁気特性

Perpendicular Co-Cr magnetic recording media prepared by sputtering using ECR microwave plasma

Perpendicular Co-Cr media were deposited on polyimide substrates by sputtering using an electron-cyclotron-resonance microwave plasma in an Ar sputtering gas pressure ranging from 3/spl times/10/sup -2/ to 8/spl times/10/sup -2/ Pa at a target to substrate distance from 170 to 230 mm. The accelerating voltage of the ions which bombard the media surface during deposition drastically affects the crystallographic and magnetic properties of Co-Cr films. Co-Cr media (50 nm in thickness) with good preferred crystal orientation (/spl Delta//spl theta//sub 50/ less than 5 degrees), high perpendicular magnetic anisotropy (H/sub k/ higher than 4 kOe), high perpendicular coercivity (H/sub c/spl perp// over 1400 Oe) and no initial layer were successfully deposited when the ion accelerating voltage was reduced less than about 20 V.

The Influence of Texture on the Magnetic Properties of CoCr Films

The Influence of Texture on the Magnetic Properties of CoCr Films

Domains and domain nucleation in magnetron-sputtered CoCr thin films

CoCr thin films have been of interest for a number of years due to their strong perpendicular anisotropy, favoring magnetization normal to the film plane. The microstructure and magnetic properties of CoCr films prepared by both rf and magnetron sputtering have been examined in detail. By comparison, however, relatively few systematic studies of the magnetic domain structure and its relation to the observed film microstructure have been reported. In addition, questions still remain as to the operative magnetization reversal mechanism in different film thickness regimes. In this work, the magnetic domain structure in magnetron sputtered Co-22 at.%Cr thin films of known microstructure were examined by Lorentz transmission electron microscopy. Additionally, domain nucleation studies were undertaken via in-situ heating experiments.It was found that the 50 nm thick films, which are comprised of columnar grains, display a “dot” type domain configuration (Figure 1d), characteristic of a perpendicular magnetization. The domain size was found to be on the order of a few structural columns in diameter.

Magnetic properties of Co-Cr films and the effects of heat treatment

We have studied the effects of low-temperature sputter preparation and subsequent heat treatment of Co79Cr21 thin films with emphasis on their microstructure and magnetic properties. Preparation at −196 °C resulted in textured films which did not show the presence of magnetic Co-rich regions. The saturation magnetization moment, Ms, of these films was similar to their homogeneous alloy phase. Conventionally sputtered films (substrate temperature>room temperature) had higher values of Ms than films prepared at −196 °C. A 1-h heat treatment at 500 °C in vacuum reduced the Ms of both films. The results suggest rearrangement of atoms through thermal diffusion. For the films sputtered at −196 °C (liquid-nitrogen temperature) an atomistically ordered phase can be proposed based on hexagonal Co which minimizes the presence of nearest Cr-Cr neighbors. This maximizes the moment quenching activity of Cr on Co and reduces the saturation moment over the one of a fully random material for segregated films prepared at higher temperature reductions in Ms can also be due to dilution of Co concentration in Co-rich regions.

Influence of Oxygen Content in Sputtering Targets on Co-Cr Film Properties

It is well known that the magnetic properties of Co-Cr film vary with several sputtering parameters, among which impurities in the sputtering gas and target are very important. However, the effect of impurities in the target has not previously been investigated. In this paper, we describe the effect of oxygen contained in sputtering targets on the magnetic properties of Co-Cr film. For low oxygen concentrations, the H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</sub> and H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> ⊥ of Co-rich magnetic particles were previously thought to be enhanced as the oxygen content was increased. However, with continued increases in oxygen content, the crystal orientation is so markedly degraded that the H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</sub> and H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> ⊥ become too small to enable use as a perpendicular recording medium. This effect is more pronounced for Co-Cr film thicknesses below 0.1 μm. Finally, it is concluded that the oxygen impurity concentration of the target should be as small as possible in order that Co-Cr media with excellent properties can be mass-produced.

THE MAGNETIC ANISOTROPY AND COLUMNAR STRUCTURE OF OBLIQUELY SPUTTERED Co-Cr FILMS

The shape magnetic anisotropy contribution for Co-Cr films, which were normally and obliquely magnetron sputtered was studied. Both Co-Cr films deposited by atoms from one line source and from two line sources showed a columnar structure, and the inclination angle of the column approximately coincided with the angle of the incident beam angle. From the torque curve analysis, magnetocrystalline anisotropy was found to play a principal part in the magnetic anisotropy of Co-Cr films deposited using two line sources. However, in the case of the Co-Cr film sputtered by one line source, not only magnetocrystalline anisotropy but shape magnetic anisotropy due to the columnar structure played an important role in determining the magnetic properties of Co-Cr films.

Preparation and magnetic properties of Co-Cr films by toroidal plasma (TP) type sputtering

A sputtering apparatus which can form a stable toroidal plasma has been developed in order to deposit magnetic films with a homogeneous and dense structure and excellent properties under the conditions of low argon gas pressure, low applied voltage, and low substrate temperature of around 30 degrees C. All Co-Cr films deposited by this apparatus were composed of HCP (hexagonal-close-packed) crystallites with c-axis orientation ranging from 8 degrees to 13 degrees . The saturation magnetization varied from 380 to 780 emu/cc, and perpendicular coercivity varied from 100 to 30 Oe. D/sub 50/ of CoCr/Ni-Fe double layer floppy disks was as high as 50 kBPI. >

Comparison between magneto-optic and VSM measurements of bias-sputtered CoCr films with perpendicular anisotropy

A direct comparison between surface and bulk hysteresis behavior is made on a variety of bias-sputtered CoCr films using magnetooptic and VSM (vibrating sample magnetometer) techniques. The results show that bias sputtering at around -100 V leads to an improvement in the surface as well as the volume magnetic properties of CoCr films. Furthermore, a reversal in the magnitude of surface and volume coercivities is observed when the Cr content of the films exceeds 13 at.% and the film thickness increases above 0.4 mu m. These effects are attributed to the presence of pores on the film surface which affect the demagnetizing factor of the surface with respect to the volume. The magnetooptical rotation signal obtained from the surface and the back of the films is used to assess their respective saturation magnetization and, hence, the extent of Cr solubility or segregation at the two boundaries.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Ｃｏ‐Ｃｒ媒体特性に及ぼすスパッタターゲット内酸素の影響

It is well known that the magnetic properties of Co-Cr film vary with several sputtering parameters, among which impurities of sputtering gas and target are very important. However, the effect of impurities in the target has not previously been investigated. In this paper, we describe the effect of oxygen content in sputtering targets on the magnetic properties of Co-Cr film. In a range of a small amount of oxygen, with increasing oxygen content Hk and Hc(⊥) of Corich magnetic particles was thought to be enhanced. However, with further increase of oxygen content, the crystal orientation was so markedly degraded that the Hk and Hc(⊥) showed too small values for a perpendicular medium. This effect is more severe for thinner Co-Cr film below 0.1μm. Finally, it is concluded that the impurity oxygen content of the target should be as small as possible to realize excellent properties of the Co-Cr medium in a mass production system.

Segregated microstructure growth in sputtered Co-Cr films

The growth process of a latent segregated microstructure called the CP (chrysanthemumlike pattern) has been investigated as a function of film thickness in sputtered Co-21.5 at.% Cr films. As film growth proceeds, each crystallite exhibits CP structure development with a periodical stripe pattern. Only crystallites with Cr-rich cores survive. This is related to Cr segregation at the grain boundaries. The CP structure growth process is explained using a model based on (1) a phase separation process restricted by grain boundary and surface diffusion, and (2) grain boundary Cr enrichment at the latter stage of segregation. The correlation between CP structure growth and the change in magnetic properties strongly indicates that the perpendicularly formed CP structure is responsible for the magnetic properties of Co-Cr films. >

The effect of initial growth layer on magnetic properties of Co-Cr films

The effect of a Ti underlayer, which increases the perpendicular coercive force of Co-Cr films, was investigated. To clarify the cause of this phenomenon, the film-thickness dependence of the magnetic properties was examined. It was found that the coercive force of a Co-Cr film deposited directly on a polymide substrate decreases drastically when it becomes thinner than 50 nm, whereas in the case of Co-Cr film on a Ti underlayer, a high coercive force is maintained even when the film becomes as thin as 20 nm. The film with the underlayer has a distinct uniform columnar structure, whereas the film without it has a 50-nm-thick initial growth layer with no clear structure. Measurements of the temperature dependence of magnetic properties and observations of segregated microstructures indicate that the improvement of magnetic properties by the insertion of the Ti underlayer is mainly due to the improvement of shape anisotropy resulting from the formation of a distinctly segregated microstructure. >

Changes in structure and magnetic properties of Co-Cr films by oblique incident of sputtered particles

The effect of the incident angle of sputtered particles relative to the substrate surface on the magnetic properties and c-axis orientation of Co-Cr films has been investigated using an opposed-targets sputtering apparatus that can operate at a gas pressure as low as 1*10/sup -4/ Torr. The c-axis orientation and magnetic properties of the film depend little on the incident angle below 45 degrees . However, oblique incidence at an angle above 50 degrees leads not only to a significant deterioration of the c-axis orientation but also to a marked decrease in the mean crystallite size, saturation magnetization, and perpendicular magnetic anisotropy energy. Films deposited at large incident angle have a porous structure and large c-axis canting angle. This is caused by the shadowing effect due to the surface roughness of the substrate. Substrate temperature and ion bombardment of the substrate during sputtering also affect the magnetic properties and c-axis orientation of the film but do not improve them significantly. >

Self-epitaxial Co-Cr media: Preferable for fabrication by roll coater sputtering system

A roll coater system was investigated for establishment of a mass production system for Co-Cr perpendicular magnetic recording media. Improvements of the crystal orientation and the magnetic properties of Co-Cr films with new seed layers of Co-Cr itself are first described. In the light of these results, a Co-Cr film with a composition gradient in the growing direction but without any seed layer is proposed and its properties are discussed. It is found that the anisotropy field Hk can be remarkably increased for the film with a composition gradient over that of films with uniform composition. It is concluded that the newly developed Co-Cr film is very suitable for mass production by a roll coater because of its simplified process which requires no sputtering of any seed layers.

Magnetic properties of Co-Cr films on Co-Cr under-layer with various composition

Double layer Co-Cr films with under-layer Co-Cr of various composition and single layer Co-Cr films were continuously prepared by DC magnetron sputtering on PET film, using Co-Cr alloy targets. The dependences of Hc\perp , Hk and Δθ 50 of double layer Co-Cr films on Cr concentration of under-layer film were measured. The anisotropy field Hk of double layer Co-Cr film is higher or lower than that of single layer Co-Cr film in accordance with whether the Cr concentration of under-layer Co-Cr film is higher or lower than that of over-layer Co-Cr film. On the other hand, the dependence of Hc\perp of double layer Co-Cr film on Cr concentration of under-layer Co-Cr film is contrary to that of Hk. The crystal orientation of double layer film depends on that of under-layer film. It seems that double layer film would grow epitaxially on under-layer film.

Effect of the Ti Sublayer on the Structural and Magnetic Properties of Evaporated CoCr Film

A Ti sublayer tends to align the c-axes normal to the film plane and to promote the growth of columnar grains in evaporated CoCr film. The effect of a Ti sublayer on the c-axis orientation may be similar to the effect of epitaxial-growth. The Ti sublayer improves the magnetic properties of CoCr film: the saturation magnetization Ms, the perpendicular magnetic anisotropy constant, the coercivity and the squareness ratio in the perpendicular hysteresis loop increase. The Ti sublayer also serves to limit the reduction in Ms with an increase in temperature. The smaller reduction in Ms with increasing temperature and the increase in Ms which are attributable to the Ti sublayer imply that the Ti sublayer tends to increase the amount of Cr segregation.

Ｃｏ‐Ｃｒ膜の磁気特性に及ぼす基板ガス出しの影響

It has been reported that outgoing gas from a substrate affects the magnetic properties of Co-Cr film during deposition of Co-Cr on the substrate.Therefore, the procedure of degassing a substrate by heating it in a vacuum prior to formation of Co-Cr film is necessary to reduce the amount of outgoing gas if high perpendicular magnetic anisotropy of the Co-Cr film is to be obtained for perpendicular magnetic recording media.Three kinds of polymer substrate were used to study the influence of the degassing procedure on the properties of Co-Cr film deposited on each polymer substrate by changing sputtering Ar pressure. With polyimide film which has high water absorption and high glass transition temperature, the degassing at 100 °C in a vacuum is not sufficient to increase magnetic anisotropy of Co-Cr film. The large amount of outgoing gas from a substrate such as polyimide disturbs the crystal orientation of Co-Cr and reduces the magnetic anisotropy of Co-Cr film. But a comparatively small amount of outgoing gas from a substrate such as PET film prevents Cr atoms from segregating at the columnar boundary and reduces coercive force in the perpendicular direction.

Ｃｏ‐Ｃｒ膜媒体高速スパッタ時における添加ガスの効果

The effects of H2, O2 and N2 additives on the magnetic properties of Co-Cr film were studied for high rate sputtering. O2 and N2 react with Co-Cr to from compounds. N2 addition induces fcc orientation perpendicular to the film plane, and hence causes a drastic decrease of the perpendicular anisotropy field Hk, accompanied by hcp orientation degradation. O2 is most reactive to Co-Cr, but little affects the crystal structure. These effects become less at higher deposition rate for the same introduced pressure. In contrast, H2 does not react with Co-Cr at all, but has a unique role of changing the coercive force without any change of Hk or crystal orientation. The effects of N2 and H2 are concluded respectively equivalent to that of increase and decrease of substrate temperature.

Thickness Dependence of Magnetic Properties in CoCr Film by High-Rate Evaporation

The relation between film thickness and magnetic properties of CoCr films prepared by the high-rate evaporation techinique which is well suited to mass production, as well as the film growth process itself, were investigated. CoCr films were deposited with a web-coater type vacuum evaporation system. The crystallographic orientation of the films becomes stable during initial layer formation process (? 0.02 ?m), but H c? continues to decrease with the increase of film thickness above 0,05 ?m. This corresponds to changes of the film microstructure.