M. Ohkoshi

Cross‐sectional structures and depth profiles in bias sputtered GdCo films

Structures and compositions of sputtered GdCo films were carefully investigated using a carbon‐replica technique and Auger electron spectroscopy. In zero‐bias sputtered films, the columns are clearly observed to develop perpendicular to the substrate, and they become fine with increasing Gd content up to near the compensation composition from pure Co film. For negative‐bias sputtered GdCo films having near compensation composition, the film structures become fine with increasing negative bias up to 200 V. The observed increment of perpendicular anisotropy in this negative bias region was explained by the structural change of the columns (shape anisotropy and stress induced anisotropy). Above 200 V negative bias, the column structures are damaged partially by Ar‐ion‐bombardment, and then the anisotropy decreases due to the damage of columns. The change in the saturation magnetization due to negative bias was interpreted by the change in the film composition; Gd‐content and oxygen.

Effects of Air pressure and substrate bias on magnetic properties and microstructure in amorphous TbCo sputtered films

Effects of Ar pressure and negative substrate bias voltage on magnetic properties and micro-structure in amorphous TbCo sputtered films are investigated. Magnetic properties, especially perpendicular anisotropy, depend strongly on Ar pressure and substrate bias. A perpendicular anisotropy of the order of 106erg/cm3with a rectangular hysteresis loop is induced in the films deposited at 10 mTorr of Ar pressure without bias or in the films deposited with 100-150 V negative bias. In these films, the ordered fiber structure developed perpendicular to the film plane is observed, which is due to the moderate bombardment of energetic species. The large perpendicular anisotropy is associated with the ordered fiber structure.

Change of magnetic properties in compositionally modulated TbCo sputtered films

Compositionally and morphologically modulated TbCo films were prepared on glass substrates by changing negative bias voltage between 0 and 100V or 150V alternately using RF sputtering method. The films having 12 - 36 layers (layer thickness of 250 - 80 A) show high magnetic coercivity and high resistivity to oxidation. In these films, small stable bits can be written magneto-optically.

Electron microscopy of CoCr sputtered films

Abstract The magnetization curling in the CoCr film is found by a high resolution Lorentz microscopy technique. Several grains assemble to form a column, and it is observed to behave as a magnetic cluster. The magnetization reversal process is performed by the rotational switching in the magnetostatically coupled individual cluster.

Perpendicular anisotropy of bias‐sputtered GdCo film

Some important information about the structural change of GdCo sputtered film with substrate bias is obtained by using the replica technique. It is found that the increase in perpendicular magnetic anisotropy for increasing substrate bias is related directly with the ultrafine microstructure of the GdCo film. The relative substrate potential with respect to the Ar plasma depends either on Ar pressure during sputtering or on the external substrate bias. When this relative substrate potential becomes negative by a certain amount, sputtering of surface oxygen and resputtering of Gd in the growing film will be initiated, and consequently the structure of sputter‐deposited film will change. The origin of microscopic perpendicular magnetic anistropy with or without substrate bias is described by a model proposed earlier for Permalloy films. The perpendicular magnetic anisotropy based on this microscopic shape anisotropy model is Ku = 2πMs2(δ/a), where δ is the thickness of the nonmagnetic boundary and ’’a’’ is ...

Perpendicular magnetization in Co-CoO film prepared by reactive RF sputtering

The perpendicular magnetization state is realized in Co-CoO film prepared by reactive RF sputtering in argon-oxygen mixture. With increasing the oxygen partial pressure, saturation magnetization of the deposited film decreases monotonically due to the formation of CoO. The film is composed of fine particles of hcp Co and fcc CoO. The perpendicular magnetic anisotropy energy and the coercivity reach to 3 × 106erg/cm3and 2 kOe, respectively. Above a critical partial pressure of oxygen, the deposited film has no spontaneous magnetization with a Co 3 O 4 single phase. The observed columnar structure in the Co-CoO film becomes fine with increasing the oxygen partial pressure. The exchange anisotropy is found in the Co-CoO film. The perpendicular magnetic anisotropy in the film is likely to be originated from an anisotropic assembly of ferromagnetic Co particles and antiferromagnetic CoO particles.

Oxidation effects on magnetic properties in CoCr sputtered films

Annealing effects on magnetic properties of CoCr sputtered films were investigated. The anneal in air near 400°C causes the considerable increase of the saturation magnetization M s , the perpendicular coercivity H c ( \perp ) and the perpendicular anisotropy K u . These increments were interpreted by the formation of antiferromagnetic Cr 2 O 3 surrounding column boundaries, which was supported by the depth profiles of AES and the spectrum of ESCA. Furthermore, the variations in magnetic properties are fairly suppressed by coating the film surface with a SiO 2 or AlN layer.

Static and dynamic properties of thermonagnetic writing in amorphous TbFe films

Abstract The domain structure in the bit written thermomagnetically is investigated in detail, and also the dynamic process of the flux reversal in the writing is studied experimentally and theoretically. The formation of the domain structure in a written bit is explained consistently.

Hall effect and magnetic properties in GdFe and CoCr sputtered films

Hall and ohmic resistivities of sputtered GdFe and CoCr films were measured at room temperature in the wide range of the film composition. It was suggested that the Hall effect is connected with the side‐jump mechanism in both materials. Especially for ferrimagnetic GdFe films, the Hall effect was reasonably analyzed by assuming that the dominant contribution to the Hall effect is the Fe sublattice magnetic moment.

Microstructure and Exchange Anisotropy of Co-CoO Sputtered Films with Perpendicular Magnetization

In t roduct i on Despite more attention being paid to the application of perpendicular magnetic films in high-density recsording and magneto-opt ical recording, questicions rermain concern inq the origin of perpendicular ar-nisotropy and the mechanism-i of coercivity. This is especially true of sputtered film irn which the columnar struccture, rm 10c r osc(sop i c coosrT_1 it i orn fluctujation, internal stress, and the effects of Ar and oxygen mixing are all interrelated and change simultaneously whern parameters suich as Ar pressure and substrate bias voltage are changed. Multifaceted studies are required tco clarify what role each of these play in perpendicular arnisotropy constant Ku and coercive force Hc. Th1e authors have investigated as the f irst step the effects that mixirng oxygeen in C:o sputtered films has on magnetic anistropy ar-nd film str ucture