Metal treatment – Stock – Magnetic
Patent
1995-04-05
1997-06-03
Sheehan, John
Metal treatment
Stock
Magnetic
420 83, 420121, 252 6254, 148101, 164463, 164477, H01F 1057
Patent
active
056349874
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to magnetic materials and, in particular, to two-phase magnetic materials comprising a mixture of a crystalline phase of an alloy of Fe, B and R, where R is a rare earth element and .alpha.-Fe.
Magnetic materials and permanent magnets are important materials which are used in many fields, including electrical appliances and electronic devices. In view of the increasing requirement for miniaturization and the greater demands placed on electrical appliances and electronic devices there has been an increasing demand for improved magnetic materials and permanent magnets.
EP-A-0101552 describes magnetic materials based on alloys of the type Fe--B--R containing at least one stable compound of the ternary Fe--B--R type, where R is a rare earth element including yttrium, which compound can be magnetized to become a permanent magnet. The amount of rare earth R is generally in the range of from 8 to 30 atomic percent.
EP-A-0108474 describes a magnetically hard alloy composition comprising at least 10 atomic percent of one or more rare earth elements, 0.5 to 10 atomic percent of boron; and iron or mixtures of iron with a transition metal element, the alloy containing a major portion of a magnetically hard, fine crystallites having an average diameter of less than 400 nanometers.
The materials described in the above patents have generally exhibited the highest remanence when the percentage of rare earth present in the alloy is about 12 atomic percent.
Previously, attempts to produce magnetically hard alloy compositions similar to those described in EP-A-0101552 and EP-A-0108474, but comprising less than 10 atomic percent of the rare earth metal, have produced products with a low remanence and energy product, the latter being attributed to the presence of .alpha.-Fe.
Existing theories, such as those developed by Stoner and Wohlfarth, for the expected properties of isotropic permanent magnet materials, indicate that the remanence should not exceed half the value of the saturation magnetisation. For NdFeB, with a saturation of approximately 1.6 Tesla, the remanence should not be greater than 0.8 Tesla. This maximum value would apply to the stoichiometric composition of NdFeB (2:14:1), which corresponds to about 12 atomic percent Nd, and deviation from this value in either direction will reduce the maximum achievable remanence. If the material can be produced such that the material structure is sufficiently fine and uniform, so that significant magnetic interaction occurs between grains then the remanence can be increased to a level above that predicted by the theory.
EP-A-0195219 describes a hard magnetic alloy of the RE-TM-B type where RE is neodymium or praesodymium, TM is a transition metal chosen from iron, cobalt and nickel and B is boron, and optionally at least one modifier of silicon or combinations of silicon with aluminium, or lithium, hydrogen, fluorine, phosphorus, sulfur, germanium and carbon, the alloy consisting of magnetically, substantially isotropic particles of grains of mainly the tetragonal RE.sub.2 Fe.sub.14 B-type phase with other phases being present below the level of detection by X-ray diffraction, said phase having grain sizes in the range of from 10 to 100 nm and a maximum magnetic energy product greater than 119.4 kJ/m.sup.3 (15MG0e) in all directions. Magnetic alloys having these properties have only been prepared according to the teaching of EP-A-0195219, with the addition of at least one modifier to the alloy of the RE-TM-B type.
EP-A-0229946 describes an interacting hard magnetic material, comprising an alloy of a rare earth metal and a transition metal. The magnetic material may also contain boron and a modifier.
We have now developed a method for producing magnetic materials from alloy compositions of the type Fe--B--R containing less than or equal to 12 atomic percent of the rare earth element which have a high remanence and energy product, without the need for any additions.
Accordingly, the present invention provides a method
REFERENCES:
patent: 4802931 (1989-02-01), Croat
patent: 4834811 (1989-05-01), Keem et al.
patent: 4854979 (1989-08-01), Wecker
patent: 4913745 (1990-04-01), Sato
patent: 5056585 (1991-10-01), Croat
patent: 5172751 (1992-12-01), Croat
Buckley Robert A.
Davies Hywel A.
Manaf Azwar
Zhang Pengzhen
Sheehan John
The University of Sheffield
LandOfFree
Magnetic materials and method of making them does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Magnetic materials and method of making them, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Magnetic materials and method of making them will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-388160