Process of preparing magnetic spinel ferrite having accurate predetermined transition temperature

Claim 1

A method of producing a magnetic spinel ferrite having a desired transition temperature within an accuracy of at least 0.1° C. which comprises the steps of: (1) providing a homogeneous oxidic mixture corresponding to the formula: R.sub.(1-x) T x Fe 2 O 4 , which when sintered into a ferrite exhibits a transition temperature which is within about 2° C. of the desired transition temperature, where "R" is an element selected from the iron group, atomic numbers 22-30, the palladium group, atomic numbers 40-48, the platinum group, atomic numbers 72-80 and Li, "T" is a non-magnetic element selected from the group consisting of zinc, yttrium, cadmium, titanium, zirconium and a different R element and "x" is between 0 and 1; (2) adding a quantity "a" of T to said mixture to produce a mixture having a formula R.sub.(1-x) T.sub.(x+a) Fe 2 O 4 , which when sintered into a ferrite exhibits a substantially constant permeability relative to temperature up to the transistion temperature, wherein "a" is from 0.05 to 0.2; (3) introducing by liquid diffusion into the mixture formed in step (2) a quantity "b" of R to provide a formulation R.sub.(1-x+b) T.sub.(x+a) Fe 2 O 4 , which when sintered into a ferrite exhibits a transition temperature within 0.1° C. of the desired transition temperature, where "b" is in the range of 10 -1 to 10 -6 ; (4) forming the resulting mixture of step (3) into a desired shaped article; and (5) sintering the shaped article at a temperature between the melting point of the ferrite and 100° C. less than said melting point to convert the article into said magnetic spinel ferrite having the desired transition temperature within a accuracy of at least 0.1° C.

Claim 2

A method of producing a magnetic spinel ferrite having a desired transition temperature within an accuracy of at least 0.1° C. which comprises the steps of: (1) providing a homogeneous oxidic mixture corresponding to the formula: R.sub.(1-x) T x Fe 2 O 4 , which when sintered into a ferrite exhibits a transition temperature which is within about 2° C. of the desired transition temperature, where "R" is an element selected from the iron group, atomic numbers 22-30, the palladium group, atomic numbers 40-48, the platinum group, atomic numbers 72-80 and Li, "T" is a non-magnetic element selected from the group consisting of zinc, yttrium, cadmium, titanium, zirconium and a different R element and "x" is between 0 and 1; (2) adding a quantity "a" of T to said mixture to produce a mixture having a formula R.sub.(1-x) T.sub.(x+a) Fe 2 O 4 , which when sintered into a ferrite exhibits a substantially constant permeability relative to temperature up to the transistion temperature, wherein "a" is from 0.05 to 0.2; (3) introducing by liquid diffusion into the mixture formed in step (2) a quantity "b" of R to provide a formulation R.sub.(1-x+b) T.sub.(x+a) Fe 2 O 4 , which when sintered into a ferrite exhibits a transition temperature within 0.1° C. of the desired transition temperature, where "b" is in the range of 10 -1 to 10 -6 ; (4) forming the resulting mixture of step (3) into a desired shaped article; and (5) sintering the shaped article at a temperature between the melting point of the ferrite and 100° C. less than said melting point to convert the article into said magnetic spinel ferrite having the desired transition temperature within a accuracy of at least 0.1° C.