Ferromagnetic materials

Details Ferromagnetic materials Ferromagnetic materials

1992-10-19

1995-01-17

Wyszomierski, George

Metal treatment

Stock

Magnetic

420 8, C22C 3800, H01F 104

Patent

active

053823044

DESCRIPTION:

BRIEF SUMMARY
SUMMARY OF THE INVENTION

This invention relates to ferromagnetic materials.
Ferromagnetic materials display a marked increase in magnetisation in an independently established magnetic field. The temperature at which ferromagnetism changes to paramagnetism is defined as one Curie Temperature, T.sub.c.
Ferromagnetic materials may be used for a wide variety of applications such as motors, electromechanical transducers. Most of these applications use ferromagnets made from SmCo.sub.5, (K Strnat et. al. J App Phys 38 p1OO1 1967), Sm.sub.2 Co.sub.17, (W Ervens Goldschmidt Inform 2:17 NR, 48 P3 1979), Nd.sub.2 Fe.sub.14 B (M Sagawa et. al. J App Phys 55 p2083 1984) and AlNiCo or ferrites (B D Cullity, Introduction to Magnetic Materials, Addison Wesley Publishing).
Nd.sub.2 Fe.sub.14 B has one of the highest reported Curie Temperatures of rare earth-iron based alloys at 315.degree. C. The inclusion of iron within an alloy is a well-established method of producing a ferromagnetic material. Iron has been used to dope GaAs in order to produce a material with ferromagnetic properties. I R Harris et. al. (J Crystal Growth 82 p450 1987) reported the growth of Fe.sub.3 GaAs with a T.sub.c of about 100.degree. C. More recently (International Patent Application Number PCT/GB 89/00381) it has been shown to be possible to obtain Curie Temperatures higher than those of Nd.sub.2 Fe.sub.14 B with M.sub.3 Ga.sub.2-x As.sub.x where 0.15.ltoreq..times..ltoreq.0.99 and M may represent Fe is partially substituted by either manganese or cobalt. Where M=Fe, and x=0.15 then the material is characterised by Curie Temperature of about 310.degree. C. Other ferromagnetic materials include that of GB 932,678, where the material has a tetragonal crystal structure and a transition metal composition component range of 61 to 75 %, and an amorphous alloy ferromagnetic filter of the general formula M.sub.x N.sub.y T.sub.z where M is selected as at least one element from iron, nickel and cobalt, N is at least one metalloid element selected from phosphorous, boron. Carbon and silicon and T is at least one additional metal selected from molybdenum, chromium, tungsten, tantalum, niobium, vanadium, copper, manganese. zinc, antimony, tin, germanium, indium, zirconium and aluminum and x has a range of between 60 and 95%.
According to this invention a ferromagnetic material having a B8.sub.2 type crystal structure comprises Fe.sub.60 M.sub.x N.sub.y where M is at least one element from the group of Al, Ga, In and Tl, N is at least one element from the group of P, As, Sb and Bi, where 1.ltoreq..times..ltoreq.39 and where x+y =40 and excluding Fe.sub.60 Ga.sub.x As.sub.y. .
Preferably the ferromagnetic has a composition where M is gallium and N is antimony. This preferred material preferably has a preferred range of x of 3.ltoreq..times..ltoreq.37, and even more preferred range of 20.ltoreq..times..ltoreq.37 and most preferably a range of 30.ltoreq..times..ltoreq.37.
The ferromagnetic material can be produced by methods including casting, which may be carried out in a Czochralski growth furnace. Where constituents of the ferromagnetic material are volatile at the high temperatures required for production, such as eg P and As, then an encapsulation layer is used to stop loss of the volatile constituents. A typical encapsulant is B.sub.2 0.sub.3.
Where homogenisation of the phases within the material is required, then techniques such as annealing or melt spinning may be employed. A typical annealing program is one carried out at a temperature between 600.degree. C. and 900.degree. C. for a time length of between 7 and 21 days.


BRIEF DESCRIPTION OF THE DRAWINGS

This invention will now be described by way of example only, with reference to the accompanying diagram: FIG. 1 is a schematic representation of a casting furnace.


DESCRIPTION OF THE PREFERRED EMBODIMENTS

Production of the ferromagnetic material by casting techniques may be seen in FIG. 1. A pyrolitic boron nitride (PBN) crucible 1 is placed within a furnace 2. The PBN crucible contains melt con

REFERENCES:
patent: 3126346 (1964-03-01), Bither
patent: 5178689 (1993-01-01), Okamura et al.
patent: 5198040 (1993-03-01), Sawa et al.
Moffatt, W. G., et al., "The Structure and Properties of Materials," vol. 1, pp. 46-47, 1964.
Journal of Applied Physics, vol. 55, No. 5, Mar. 1, 1984, M. Sagawa et al, "New Material for Permanent Magnets on a Base of Nd & Fe" pp. 2083-2089.
Journal of Applied Physics, vol. 38, No. 5, Mar. 1967, K. Strnat et al, "A Family of New Cobalt--Base Permanent Magnet Materials", pp. 1001--1002.
Journal of Crystal Growth, vol. 82, No. 3, Mar. 1987, Harris et al, "Phase Identification in Fe-Doped GaAs Single Crystals" pp. 450-458.

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