PERROMAGNETIC MATERIALS

Abstract: This invention provides a ferromagnetic material Fe60MxNy where M is at least one element selected from A1, Ga, In and Tl, N is at least one element selected from P, As, Sb and Bi, x has a range of 1 </= x </= 39 and x+y = 40 and excluding Fe60GaxASy. A preferred ferromagnetic material is Fe60GaxAsy, preferably when x has a range of 3 </= x </= 37, more preferably when x has a range of 20 </= x </= 37, and even more preferably when x has a range of 30 </= x </= 37. Typically, ferromagnetic materials of this type can be homogenised by annealing or melt spinning. Melt spun Fe60GaxAsy can show Curie Temperatures (Tc) of about 470 DEG C and saturation magnetisations of about 89 emu/g. Typically a ferromagnetic material of the Fe60MxNy has a B82 type structure.

Description: FERROMAGNETIC MATERIALS 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 the Curie Temperature, T c . Ferromagnetic materials may be used for a wide variety of applications such as motors, electromechanical transducers. Most of these applications use ferro agnets made from SmCo , (K Strnat et al J App Phys _& plOOl 1967) , Sπ_ 2 Co 17 - (W Ervens Goldschmidt Inform 2:17 NR, P3 1979) . Nd 2 Fe lή B (M Sagawa et al J App Phys 55 p2083 1984) and AINiCo or ferrites (B D Cullity, Introduction to Magnetic Materials, Addison Wesley Publishing) . Nd 2 Fe lή B has one of the highest reported Curie Temperatures of rare earth-iron based alloys at 3_-5°C The inclusion of iron wthin 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 wth ferromagnetic properties. I R Harris et al (J Crystal Growth __. p4 0 1987) reported the growth of Fe,GaAs with a T. of about 100°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 2 Fe l4 B wth M 3 Ga 2 _ χ As χ where 0.151 x 1 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°C. Other ferromagnetic materials include that of GB 932 • 67δ, where the material has a tetragonal crystal structure and a transition metal composition component range of 61 to 75/-. an an amorphous alloy ferromagnetic filter of the general formula MxNyTz 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 aluminium and x has a range of between 60 and 95/-- According to this invention a ferromagnetic material comprises Fe 6o M..N y where M is at least one element from the group of A, Ga, In and Tl, N is at least one element from the group of P, As, Sb and Bi, where 1 _. x <_.39 and where x+y __ 40 and excluding Fe 6o Ga χ As . Preferably the ferromagnetic has a composition where M is gallium and N is anthimony. This preferred material preferably has a preferred range of x of 31 _- ≤.37. an even more preferred range of 20 i x <37 and most preferrably a range of 30 ≤. x i.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 2 0,. Where homogenisation of the phases wthin the material is required, then techniques .such as annealing or melt spinning may be employed. A typical annealing programme is one carried out a temperature between 600°C and 900°C for a time length of between 7 and 21 days. This invention will now be deseribed by way of example only, wth reference to the accompanying diagram: Figure 1 is a schematic representation of a casting furnace. Production of the ferromagnetic material by casting techniques may be seen in Figure 1. A pyrolitie boron nitride (PBN) crucible 1 is placed within a furnace 2. The PBN crucible contains melt constituents 3 i_- appropriate ratios and typical purity values of 99-999%• With the PBN crucible in the furnace, valves 4 and are closed, valves 6 and 7 are opened, and vacuum pump 8 pumps the furnace down to a vacuum of about 10-3 Torr. When a vacuum of this level is achieved, valves 6 and 7 are closed, the vacuum pump is stopped and valves 4 and 5 are opened. With valves 4 and open, a continuous flow of high purity nitrogen gas is flushed through the furnace 2. The furnace is then heated up as quickly as possible until the melt constituents are molten. Boric oxide 9 forms an upper encapsulating layer on melting and prevents loss of volatile melt constituents. The furnace is maintained at the elevated temprature for about 2 hours in order to facilitate substantially a fully homogeneous mixture of melt constituents. The furnace 2 is then swtched off, wth the PBN crucible 1 and its contents brought down to ambient temperature by furnace cooling in a flowng nitrogen atmosphere. Where homogenisation of the ferromagnetic material is required the production may include an annealing process. A typical annealing programme is to elevate, and maintain, the as cast material to temperature of about 800 β C for about 14 days in a vacuum of about 10-6 Torr. followed by furnace cooling. Table 1 gives, by way of example only, specific compositions where M is gallium and N is antimony with typical saturation magnetisation and T values. It can be seen that for some compositions these values are provided for annealed samples, whilst all samples have typical melt spun values. Table 2 gives typical X-Ray diffraction data concerning lattice constants of ferromagnetic material where M is gallium and N is antimony

Claims: Claims . 1. A ferromagnetic material comprising Fe 6o M χ N where M is at least one element from the group of A, Ga, In and Tl, N is at least one element from the group of P, As, Sb and Bi, where x has a range of 1 <_ x 139. and where x+y = 40 and excluding Fe 6o Ga χ As . 2. A ferromagnetic material according to claim 1 where M is Ga and N is Sb. 3. A ferromagnetic material according to claim 2 where x has a range of 3 i i 37. 4. A ferromagnetic material according to claim 3 where x has a range of 20 l x ≤.37- 5. A ferromagnetic material according to claim 4 where x has a range of 30 i x < 37- 6. A ferromagnetic material according to any of the preceeding claims where the material is homogenised. 7. A ferromagnetic material according to claim 6 where homogenisation is acchieved by annealing. 8. A ferromagnetic material according to claim 7 where annealing is carried at a temperature of between 600"C and 900 β C. 9. A ferromagnetic material according to claim 6 where homogenisation is achieved by melt spinning.

Inventors: COCKAYNE BRIAN, HARRIS IVOR REX, MACEWAN WILLIAM RITCHIE, SMITH NIGEL ANDREW, COCKAYNE, BRIAN, HARRIS, IVOR, REX, MACEWAN, WILLIAM, RITCHIE, SMITH, NIGEL, ANDREW
Applicants: SECR DEFENCE BRIT, THE SECRETARY OF STATE FOR DEFENCE IN HER BRITANNI
Application year: 1991
Main classification: H01F1
IPC codes: C22C38, H01F1