Metal treatment – Process of modifying or maintaining internal physical... – Magnetic materials
Patent
1992-05-28
1994-07-12
Sheehan, John P.
Metal treatment
Process of modifying or maintaining internal physical...
Magnetic materials
427130, 427128, 427132, C21D 104
Patent
active
053285239
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
The present invention relates to a composite magnetic material in multilayer sheet form having a high magnetic permeability at high frequency and a low density, as well as to its production process.
This material can be used in magnetic heads for high frequency magnetic recording as a result of its high magnetic stability, as a core for a coil and very high frequency transformer, as an electromagnetic filter or shield used in telecommunications and data processing (shielding of complex circuits, computers, etc.), as a microwave absorber in an anechoic or echo-free chamber for experimental studies, or as an absorbent material in microwave ovens. In the latter application, the material according to the invention is placed on the inner face of the oven door.
Composite materials make it possible to obtain materials with a magnetic permeability and electrical permittivity adapted to each particular application. More specifically, the magnetic material according to the invention is used for equipped anechoic chambers.
The known materials used at present for this purpose are constituted by pyramidal patterns or honeycomb structures having a thickness of a few dozen centimetres and a low surface density between 1 and 5 kg/m.sup.2. Unfortunately, this type of material is limited to a low wavelength range.
In addition, microwave-absorbing material are known in the form of thin films with a thickness of a few centimetres and made from dense materials such as ferrite, or from the dispersion of said dense materials in an appropriate organic binder. This type of material suffers from the disadvantage of being heavy (>10 kg/m.sup.2). These materials have a low magnetic permeability leading to considerable thicknesses and corresponding high weights.
To obviate these disadvantages, the invertor has envisaged producing a composite magnetic material constituted by an alternation of amorphous ferromagnetic layers and electrically insulating layers, each ferromagnetic material layer being formed from several blocks separated from one another by electrically insulating joints. This principle is described in FR-A-2 620 853. Unfortunately the magnetic material described in the latter document cannot at present be produced and its production process is very difficult to carry out.
In particular, the above document teaches the production of 10 micrometer etching lines for a stack of layers having a thickness of 70 to 600 micrometers. However, at present, even when using a laser etching process, the etching line width is at a minimum one or two times the thickness of the stack (or layers) to be etched.
The present invention relates to a composite, multilayer magnetic material making it possible to obviate the disadvantages referred to hereinbefore. In particular, said material has a low density and a high magnetic permeability. Its production process can also be carried out industrially and performed relatively easily.
The material according to the invention simultaneously combines excellent performance characteristics and high production speeds.
More specifically, the invention relates to a composite, multilayer magnetic material having at least one thin, polymer support film, which is mechanically and thermally strong, which is coated on at least one of its faces by a thin deposit of a ferromagnetic amorphous compound, the density d and the permeability .mu. of the composite magnetic material being such that 5.ltoreq..mu./d.ltoreq.100.
According to the invention a ferromagnetic deposit can be provided on each face of the support film. Moreover, according to the envisaged application several support films in each case coated by the ferromagnetic deposit or deposits and joined by an adhesive film can be used. In this stack, the ferromagnetic deposits can be made from the same material or from different materials so as to modify the magnetic permeability spectrum.
Contrary to the case of FR-A-2 620 853, said multilayer material is not subject to delamination.
According to the invention, the volume percentage of metal
REFERENCES:
IEEE Transactions on Magnetics vol. MAG-22, No. 2, Mar., 1986, IEEE, (New York, US), Y. Shimada: "Initial Permeability of Amorphous Single and Multilayered Films", pp. 89-92.
IEEE Translation Journal on Magnetics in Japan, vol. 3, No. 2, Feb. 1988, IEEE, (New York, US), M. Takahashi et al.: "Effect of Local Anistropy Fluctuation on the Permeability of Multilayered Co-Zr-Mo-Ni Amorphous Films", pp. 166-172.
Journal of the Electrochemical Society, vol. 136, No. 6, Jun. 1989, The Electrochemical Society Inc., (Manchester, N.H., US), O. J. Wimmers et al.: "Taper Etching of an Amorphous Soft Magnetic CoNbZr Alloy Using an Interfacial Organosilane Layer", pp. 1769-1772.
Fontaine Jean-Marie
Varoquauz Arnaud
Commissariat a l''Energie Atomique
Sheehan John P.
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