Magnetic powder suitable for low-noise media

Abstract

An iron system magnetic powder, and particularly an iron system magnetic powder comprised chiefly of Fe16N2, is provided that has an atomic ratio of total noble metal content to Fe of 0.01-10%. The magnetic powder can be produced by subjecting iron oxy-hydroxide or iron oxide having an atomic ratio of total noble metal content to Fe of 0.01-10% to reduction treatment. The average particle volume of the magnetic powder is preferably 4,000 nm3 or less. The magnetic powder is suitable for fabricating high recording density media of low noise, high output and high C / N ratio that are suitable for use with a GMR head or the like.

Description

FIELD OF THE INVENTION [0001] This invention relates to an iron system magnetic powder for use in high recording density magnetic recording media, particularly to a magnetic powder composed of fine particles that enables production of magnetic recording tape exhibiting outstanding low-noise and high C / N (carrier-to noise) properties. BACKGROUND ART [0002] In order to achieve the increasingly higher recording densities required by today's magnetic recording media, recording wavelengths are being shortened. However, unless the particle size of the magnetic powder is much smaller than the length of the region for recording the short-wavelength signal, a distinct magnetic transition cannot be produced, which, in practical terms, makes recording impossible. Thus, the particles of the magnetic powder have to be sufficiently smaller than the recording wavelength. [0003] Achieving higher recording density also requires increasing the resolving power of the recording signal, so it is also im...

AI Technical Summary

Benefits of technology

[0012] This invention was accomplished in the light of these circumstances and is directed to achieving strong prevention of sintering during reduction without causing the aforesaid problems and, by this, to provide a magnetic powder that enables the design of low-noise, high-output, high C / N, high recording density media suitable for use with GMR and other high-sensitivity heads. SUMMARY OF THE INVENTION

[0013] The inventors conducted detailed experiments with regard to starting powder composition and reduction conditions in order to achieve the aforesaid object. As a result, it was found that a magnetic powder which is excellent in magnetic properties and provides a low-noise medium when used in tape production can be obtained by, at the time of starting powder preparation, incorporating one or more noble metal elements in the starting powder in the form of solid solution or coating, reducing the result under suitable conditions and optionally nitriding the reduced powder, thereby strongly preventing sintering during the reduction.

[0021] This invention provides an iron system magnetic powder obtained by a process that strongly inhibits sintering during reduction treatment at the time of production. When this magnetic powder is compared with a magnetic powder refined by addition of a large amount of Al or other element known to exhibit sinter inhibiting effect (hereinafter called “conventional sinter inhibiting element”), it is found to exhibit markedly improved Hc and as even at the same level of average particle volume. In addition, the magnetic powder of the invention achieves a higher degree of particle refinement at the same level of conventional sinter inhibiting element addition. Moreover, magnetic recording media produced using the refined magnetic powder of the invention in the magnetic layer were found to exhibit pronounced noise reduction effect. This invention can therefore be expected to enable a great improvement in the recording density of magnetic recording media and help to improve the performance of electronic equipment equipped with such media.

Problems solved by technology

However, unless the particle size of the magnetic powder is much smaller than the length of the region for recording the short-wavelength signal, a distinct magnetic transition cannot be produced, which, in practical terms, makes recording impossible.

However, as the particles get smaller, it becomes more and more difficult for the particles to continue to exist as independent particles.

For example, in the case of the metal magnetic powder generally used in a data storage tape, extreme refinement of the particle size makes the powder susceptible to sintering during the reduction stage of the production process.

Sintering increases the average particle volume, which is undesirable because the larger sintered particles become a source of noise, and also degrades the magnetic properties of the powder by deforming the particle shape.

In addition, when the powder is used to produce magnetic tape, the enlarged particles degrade dispersibility and cause loss of surface smoothness.

The magnetic powder therefore becomes unsuitable for use in high recording density media.

Although this makes output less of a concern when using a magnetic powder of low magnetization σs, it aggravates the problem of noise, because when a high-sensitivity head is used even slight noise is detected as large noise to markedly degrade the C / N ratio.

However, efforts made to reduce particle size at the starting powder stage are frequently outweighed by the effects of sintering occurring at the reduction stage of the magnetic powder production process.

In contrast, the average particle volume required by a low-noise medium is 4,000 nm3 or less, preferably 3,000 nm3 or less, but no practical magnetic powder of such adequately small average particle volume has yet been developed.

When particles sinter together at the reduction stage, the presence of large particles locally within the magnetic powder increases particle-induced noise and also adversely affects roughness during tape manufacture.

This makes production of low-noise tape impossible.

The first method of increasing the amount of nonmagnetic sintering inhibitor is undesirable because it increases noise by reducing the number of magnetic particles per unit volume.

The second method is undesirable because lowering the reduction temperature not only has the desired effect of reducing sintering but also simultaneously lowers the particle reduction rate, which leads to problems such as that the proportion of the grain boundary rises because crystal grain growth within the particles is inhibited and the magnetic properties are markedly degraded by the occurrence of magnetic poles and the like owing to increased irregularity of the particle surfaces.

These drawbacks of the conventional methods point up the need for development of a new sintering inhibiting technique that enables particle refinement without degrading magnetic properties.

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