Katsuyoshi Hayashi

A soft magnetic CoNiFe film with high saturation magnetic flux density and low coercivity

Magnetic materials are classed as ‘soft’ if they have a low coercivity (the critical field strength Hc required to flip the direction of magnetization). Soft magnetic materials are a central component of electromagnetic devices such as step motors, magnetic sensors, transformers and magnetic recording heads. Miniaturization of these devices requires materials that can develop higher saturation flux density, Bs, so that the necessary flux densities can be preserved on reducing device dimensions, while simultaneously achieving a low coercivity. Common high-Bs soft magnetic films currently in use are electroplated CoFe-based alloys electroplated CoNiFe alloys and sputtered Fe-based nanocrystalline and FeN films. Sputtering is not suitable, however, for fabricating the thick films needed in some applications, for which electrochemical methods are preferred. Here we report the electrochemical preparation of a CoNiFe film with a very high value of Bs (2.0–2.1u2009T) and a low coercivity. The favourable properties are achieved by avoiding the need for organic additives in the deposition process, which are typically used to reduce internal stresses. Our films also undergo very small magnetostriction, which is essential to ensure that they are not stressed when an external magnetic field is applied (or conversely, that external stresses do not disrupt the magnetic properties). Our material should find applications in miniaturization of electromechanical devices and in high-density magnetic data storage.

New soft magnetic CoNiFe plated films with high B/sub s/=2.0-2.1 T

A CoNiFe film with saturation magnetic flux density (B/sub s/) greater than 2.0 tesla (T) has been prepared for the first time as a soft magnetic film; the coercivity (H/sub c/) of the film is less than 160 A/m (2.0 Oe). This success was achieved by formulating a new plating bath and operating conditions to form fine grains. The film has a low H/sub c/ of less than 160 A/m, a low saturation magnetostriction (/spl lambda//sub s/) of approximately 10/sup -6/, and a high B/sub s/ of 2.0-2.1 T. The present invention is expected to contribute to accelerating the development of not only the technology of high-density magnetic recording but also the field of magnetic materials in general.

Electrochemical preparation of soft magnetic CoNiFeS film with high saturation magnetic flux density and high resistivity

A soft magnetic CoNiFeS film as a write head core material for the next generation was prepared by electrodeposition. In this system, thiourea was used as an additive in the CoNiFe ternary alloy plating bath. The most suitable magnetic properties were obtained at the film composition of (Co 73 Ni 12 Fe 15 ) 99.1 S 0.9 [atomic percent (a/o)] with a high saturation magnetic flux density (B s ) of 1.7 T, a high resistivity (p) of 51 μΩ cm, and a low saturation magnetostriction (λ s ) of 4.4 x 10 -6 . The film consisted of fine minute crystal grains 5 to 10 nm in diameter. The S content of ca. 0.9 a/o is believed to be responsible for the formation of small crystal grains with low coercivity and high resistivity.

Newly developed inductive write head with electroplated CoNiFe film

A newly developed CoNiFe film is investigated from the viewpoint of its application to MR write heads. Film composition is Co/sub 65/Ni/sub 12/Fe/sub 23/, prepared by electroplating to obtain a b.c.c. plus f.c.c. mixed phase at that composition. Films with mixed phases show improved soft magnetic properties (B/sub s/ is 2.0-2.1 T and the magnetostriction coefficient is +1.8/spl times/10/sup -6/ to +7.4/spl times/10/sup -6/) and also show improved corrosion resistance. Performance of a head with a double layer structure of a 0.3 /spl mu/m CoNiFe film and a 4.1 /spl mu/m NiFe film is investigated, and a short throat height is found to give better overwrite performance.

Newly developed conife film to mr head

The new DigaMaxTM digital tape storage system which offers a high capacity and high, variable data rates has been made possible by the development of advanced multitrack data and servo write heads. The track width of 37.5 ,um combined with the minimum bit length of 0.35 p m enables 13 GB of user capacity on 1000 ft of 8 mm wide tape. Eight channel thin film heads allow data rates of 2 MBls at 44 ips. This paper will discuss the design and performance of the servo and data heads. System aspects of DigaMaxTM are described in a separate contribution. For active positioning of the head during writing and reading of data, servo tracks are permanently written deep into the tape over the full tape width using a dedicated multitrack servowriter. The servo tracks are written by a multichannel servo head which consists of upper and lower flux guides with a continuous shared flux guide in between. Fabrication of this stacked writer configuration is possible thanks to the use of planarization techniques. The efficiency and gap length of the servo heads have been optimized to write tracks 2 p m deep into 900 Oe QIC tape. The servo track pattern defines the position of the 192 data tracks and is recorded in one pass. The writer of the data head writes the data in the upper part of the tape, leading the bulk of the servo tracks unaffected. The planarized design of the write head facilitates the fabrication of the read head on top of the write head. The efficiency of the yoke type and read head has been improved to 19% by reducing the distance between the tape bearing surface and the MagnetoResistive Element (MRE), improving the magnetic coupling between the MRE and the magnetic flux guides and by reducing the width of the MRE. This paper will discuss the efficiencies of the data write and read heads, the impulse response of the read head, the track profiles of the servo and data head, and the attenuation of the servo track signals due to overwriting by the data write head.