US3043776A - Ferromagnetic oxidic material - Google Patents

Ferromagnetic oxidic material Download PDF

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US3043776A
US3043776A US728849A US72884958A US3043776A US 3043776 A US3043776 A US 3043776A US 728849 A US728849 A US 728849A US 72884958 A US72884958 A US 72884958A US 3043776 A US3043776 A US 3043776A
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Jonker Gerard Heinrich
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US Philips Corp
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    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/01—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics
    • C04B35/26—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics based on ferrites
    • C04B35/2608—Compositions containing one or more ferrites of the group comprising manganese, zinc, nickel, copper or cobalt and one or more ferrites of the group comprising rare earth metals, alkali metals, alkaline earth metals or lead
    • C04B35/2616—Compositions containing one or more ferrites of the group comprising manganese, zinc, nickel, copper or cobalt and one or more ferrites of the group comprising rare earth metals, alkali metals, alkaline earth metals or lead containing lithium
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/01—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics
    • C04B35/26—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics based on ferrites
    • C04B35/2608—Compositions containing one or more ferrites of the group comprising manganese, zinc, nickel, copper or cobalt and one or more ferrites of the group comprising rare earth metals, alkali metals, alkaline earth metals or lead
    • C04B35/2625—Compositions containing one or more ferrites of the group comprising manganese, zinc, nickel, copper or cobalt and one or more ferrites of the group comprising rare earth metals, alkali metals, alkaline earth metals or lead containing magnesium
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/01—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics
    • C04B35/26—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics based on ferrites
    • C04B35/2608—Compositions containing one or more ferrites of the group comprising manganese, zinc, nickel, copper or cobalt and one or more ferrites of the group comprising rare earth metals, alkali metals, alkaline earth metals or lead
    • C04B35/2633—Compositions containing one or more ferrites of the group comprising manganese, zinc, nickel, copper or cobalt and one or more ferrites of the group comprising rare earth metals, alkali metals, alkaline earth metals or lead containing barium, strontium or calcium

Definitions

  • Ciaims. (Cl. 252-625)
  • My invention relates to ferromagnetic oxidic materials, which have valuable electromagnetic properties and methods of making the same.
  • the materials according to the invention have a saturation magnetization of the same order of magnitude as that of ferromagnetic ferrites having the crystal structure of the mineral spinel, the so-called "spinel structure, and like the ferrites, most materials according to the invention have a high specific resistance. Many of them can be formed as ferromagnetic bodies for'use atr high frequencies, frequently up to 20() mc./s. and upwards.
  • Ferromagnetic ferrites having spinel structure exhibit an initial permeability which is not independent of frequency, but there is afrequency range in which the initial permeability decreases with increasing frequency.
  • This Patented .italy 10, 1962 fice . styled to be built up and from which these materials can decrease in initial permeability usually begins at a lower I frequency when the material has a higher initial permeability at low frequency (see H. G. Beljers and l. L. Snoek, Philips Technical Review, l1, pages 313-322, 1949- 1950).
  • the initial permeability is constant up to a much higher frequency than with ferromagnetic ferritos having spinel structure which have the same value for the initial permeability at low frequency. Since the use of ferromagnetic cores in a frequency rangey in which the structure, the crystal anisotropy is given to a rst approximation by the expression:
  • FIG. l is a ternary phase diagram showing the compositions according to the invention.
  • FIG. 2 is a portion of the ternary phase diagram of FIG. 1 which shows the compositions according to the invention
  • FIG. 3 is a portion of the ternary phase diagram which shows one class of compositions according to the inven- K tion;
  • FIG. 4 is a portion of the ternary phase diagram which Y are ferromagnetic.
  • AO in which A represents at least one of the bivalent metals Ba, Sr, Pb and Ca
  • Fe2O3 and MeO in which Me represents at least one of the bivalent metals Fe, Mn, Co, Ni, Zn, Mg, Cu or the bivalent com- Plex.
  • Point 1 infFIG. 1 corresponds to the compoundAFe2O4, in which A represents at least one of the bivalent metals Ba, Sr, Pb and Ca. These compounds are not ferromagnetic.
  • Point 2 in FIG. 1 corresponds to the compounds with the formula MeO.Fe2O3 or MeFe2O4, in which Me represents at leastone of the bivalent metals Fe, Mn, Co, Ni, Zn, Mg, Cu or the bivalent complex
  • Me represents at leastone of the bivalent metals Fe, Mn, Co, Ni, Zn, Mg, Cu or the bivalent complex
  • These compounds have a cubic crystal structure corresponding to that of the mineral spinel, the so-called spinel structure.
  • ZnFe2O4 all of them Many of these materials have a high value for the initial permeability, which, however, as previously mentioned, is not independent of frequency. It is possible, for each material, to indicate a frequency range in which the initial permeability decreases with increasing frequency and this decrease begins at a lower frequency as the material has a higher value for the initial permea bility lat low frequency.
  • Fe203 in a given form in the spinel lattice dissolves in an amount which is dependent upon the temperature used in the manufacture. Therefore, not only the formula but also the formula MeO.(l-[x)Fe2O3 wherein, for example, x 0.5 indicates the composition of these ferrites having spinel structure, which for this example corresponds to the line 2 3 in FIG.-1.
  • FIG.l 2 shows part of the diagram of FIG. l and the compositions of lthe materials according to the invention may also be represented therein.
  • the angular points of this diagram are constituted by AFe2O4 (in which A representsat least one of the bivalent metals Ba, Sr, Pb and Ca), Fe203 and MeFeZO., (in Which Me represents at least one of the biva-len-t metals Fe, Mn, Co, Ni, Zn, Mg, Cu or vthe hivalent complex Li++pe+++ 2 AS the une z s in FIG. 1, the une 2 3 ⁇ in FIG. 2 corresponds to ferrites having spinel structure and having a composition corresponding to the formula MEO. 1 -l-x)
  • Point 5 in FIG. 2 corresponds to the 'compounds of the bivalent metalsFe, Mn, Co, Ni, Zn, Mg or the ⁇ bivalent complex r 4Li+ 1:e+++
  • Point 7 in FIG. 2' corresponds to the compound 2AO.2MeO.6Fe2O3 or A2M2Fe12022, ⁇ wherein A represents Ba, for at most one-half Sr, for at most one-,quarter Pb and/or for lat most one-quarter Ca, while Me represents at least one of the bivalent metals Fe, Mn, Co, Ni, Zn, Mg and Cu.
  • These ferromagnetic materials have a rhombohedral crystal structure, the elementary cell of which can be described in the lhexagonal crystal system by a .c-axis of about 43.5 A. land ⁇ an a-axis of about 5.9 A.
  • lAll these materials are built up of crystals having a preferred plane of magnetization at right angles to the hexagonal c-axis, and lthese materials have comparatively high'values for the initial permeability' also at vfreqencies up to 200mc./s. and higher.
  • Point 8 in FIG. 2 corresponds to -the compounds 3AO.2MeO.12Fe2O3 or A3Me2Fe24O41 ⁇ , wherein A represents Ba, for at most 1A; partV Sr, for at most 1/s part Pb and/or for at most 1A@ part Ca, while Me represents at leas-t ⁇ one of the bivalent metals Fe, Mn, Co, Ni, Zn, Mg, Cu orithe bivalent complex Li+lFe+++
  • These ferromagnetic materials have a crystal structure, the elementary cell of which can be kdescribed in the hexagonal crystal system by ya c-axis of about 52.3 A.
  • Point 9 in FIG. 2 corresponds to the compounds LAOlMeQlSFez'OS or A4Me2Fe36O0, in which A represents Ba, for at most 1/s part Sr, for at most Ms part Pb Such is the case at room temperature if MeV Furthermore, there are AO.2MeO.8Fe2O3 tor AMezFelOz-l, in which A represents at yleast one of the bivalent metals Ba, Sr, Pb and for at most LVs part Ca, while Me represen-ts at least one y and/or for at most 3A0 part- Ca, while Me represents at least 'one of the bivalent metals Fe, Oo, Ni, Zn, Mg and for at most %0 part Mn or Cu.
  • These ferromagnetic materials have a. rhombohedral crystal structure, the elementary cell of which can ⁇ be described in the hexagonal crystal system by a c-axis of about 113.1 A. and an aaxis of about 5.9 A. Part of these materials is built up i Such is the case at room temperature if Me represents Co, for at least ?/10 part, which is, however, still slightly dependent ⁇ upon the other bivalent metals represented by Me.
  • the crystals of the other partof the materials havea preferredY direction 'of magnetization parallel to the hexagonal c-axis.
  • Point Y10 in FIG. 2 corresponds to the compounds 2AO.2MeO.l4Fe2O3 or A2Me2Fe28O46, in which A represents at leas-t one of the bivalent metals Ba, Sr, Pb and for at most 2/s part Ca, while Me represents at least one ofthe bivalent metals Fe, Mn, Co, Ni, Zn, Mg or the bivalent complex
  • These ferrom-agentic materials have a rhombohedral crystal structure, the elementarycell of which can be described in the hexagonal crystal system by a c-axis of about 84.1 A. and an a-axis of about 5.9 A.
  • Part of these materials is built up of crystals having a preferred plane of magnetization at right angles to the hexagonal c-axis and these materials have comparatively high values for the initial permeability also at frequencies up to 200 mc./s. andy upwards. Such isthe case at room temperature if Me represents Co, for at least one-half, which is, however, still slightly dependent upon the other bivalent metals represented by Me.
  • the crystals of the other part of the materials have a preferred direction of magnetization parallel to Vthe hexagonal c-axis. Furthermore, there are compounds having the same crystal structure and corresponding ferromagnetic properties.
  • composition of these compounds may be regarded to be derived from the said compounds by substituting therein Fe+++ for at most one-half of Me in :a ratio corre- 2-21 mol percent of AO 5-45 mol percent of MeO 52-83 mol percent of Fe2O3v in which A represents at least one of the bivalent metals Ba, Sr, Pb and Ca and Me represents at least one of the bivalent metals Fe, Mn, Co, Ni, Zn, Mg, Cu or the bivalent complex Li++Fe+++ 2 and consist principally of at least two ferromagnetic crystal phases belonging to the ⁇ group formed by the following six members: f
  • the cubic crystal structure of the mineral spinel The hexagonal crystal structure having a c-axis of about 32.8 A. and an a-axis of about 5.9 A.,
  • the hexagonal crystal ystructure having a c-axis of about 43.5 A. and an a-axis of about 5.9 A.
  • Ihe hexagonal crystal structure having a -axis of abouty 52.3 A. and an a-axis of about 5.9 A.
  • the hexagonal crystal structure having a c-axis of about 113.1 A., ⁇ and an a-'axis of about 5.9 A.,.and
  • the hexagonal crystal structure having a c-axis of about 84.1 A. and an a-axis of about 5.9 A.
  • the range compromising the compositions of the materials according to 8-21 mol percent of AO 5-21 mol percent of MeO 58-83 mol percent of Fe203 The range comprising the compositions o-f thesematen'als is shown in FIG. 2.
  • the crystals of the above-mentioned hexagonal crys- ⁇ tal phases have either a preferred plane of magnetization at right angles to the hexagonal c-axis or a preferred direction of magnetization .parallel to the hexagonal c-axis.
  • the following identification test for example, may
  • This slide is arranged between the poles of an electromagnet so that the lines of magnetic force are at right angles to the surface of the slide.
  • the magnetic field strength is increased so that the particles of the powder rotate in the field in ⁇ a manner, such that either the preferred direction or lthe preferred plane of magnetization becomes approximately parallel to the direction of the lines of magnetic force.
  • the materials according to the invention may contain at the same time hexagonal crystal phases having a preferred plane of magnetization at right angles to the hexagonal c-axis and hexagonal crystal phases having .a preferred direction of magnetization parallel to the hexagonal c-axis.
  • those materials according to the invention are preferable which have the same crystal anisotropy with regard tothe hex-agonal crystal phases.
  • the hexagonal crystal phases of which have a preferred plane of magnetization at right angles to the hexagonal c-axis have ⁇ an initial permeability which is constant to a much higher frequency than with ferromagnetic ferrites having spinel structure which have the Same value for the initial permeability at low frequency.
  • the hexagonal crystal phases of which have a preferred direction of magnetization parallel to the hexagonal c-axis afford new possibilities for the manufacture, for example, of ⁇ ferromagnetic bodies having permanent magnetic properties and ferromagnetic bodies for use inmicro-wave equipment.
  • the ferromagnetic compounds having a cubic Vcrystal structure corresponding to that of the mineral spinel are substantially all important on laccount of their value for the initial permeability. Oonsequently, in a physical sense, they are more similar to the above-mentioned hexagonal crystal phases having a preferred plane of magnetization than to the above-mentioned hexagonal crystal phases having apreferred direction ⁇ of magnetization. Consequently, of the materials according to the invention, in which the cubic crystal phase having a structure of that of the mineral spinel is present, those are preferable which contain hexagonal crystal phases having a preferred plane of magnetization.
  • Ferromagnetic compounds having the cubic spinel structure are preferrred for which the losses at the frequency at which the material is useable because of the properties of the hexagonal crystal phases, has not increased to a high value.
  • Those compounds are ones which have a comparatively low value for the initial permeability at low frequency.
  • the hexagonal crystal phases of the materials according to the invention have a preferred plane of the magnetization at room temperature if these materials are of the following composition:
  • FIG. 3 represents the same diagram as FIG. 2.
  • the materials according to the invention having a cornposition ⁇ corresponding to 8-21 mol percent of AO y mol percentof COO 0-(21-y) mol percent of Me() 58-83 mol percent of Fe203 wherein 7y2l, contain substantially hexagonal crystal ⁇ l 15 to 2l mol percent of AO z mol percent :of CoO 4 to (2l-z) mol pencent of MeO 58 to'78 mol percent of Fe203 wherein 322g 17. These materials contain substantially hexagonal crystal phases. This range of compositions is represented in FIG. 4, which shows the same diagnam t as FIG. 2.
  • FIG. 5 shows the same 'diagnam as FIG. 2.
  • a preferred direction of magnetization at room temperature occurs in the hexagonal crystal phases of ma- FIG. 5.
  • D represents at least one of the bivalent metals Fe, Mn,
  • the lmaterials Kaccording to the invention are manufacturedby heatingtsintering) a finely-divided mixture of the component meta-l oxides of the materials chosen approximately in ⁇ the correct proportion, It is, ofcourse, possible for one or more ofthe constituent metal oxides to vbe replaced wholly or in part by compounds converting into metal oxides upon heating, for example, carbonates, oxalates :and aCetateS. Furthermore, the component metal-oxides may be replaced Wholly or in part by one or more compounds .ofwat least one of the component metal oxides, for example, BaFemOlg.
  • the term correct proportion is to be understood in this case to mean Ea ratio of the amounts of metals in the initial mix- Y tureV equal to that in the materials to be manufactured in the manufacture of ferromagnetic ferrites with spinel structure (inter alia I. I. Went and E. W. Gorter, Philips Technical Review, 13 page 183, 1951-1952).
  • the temperature of the sintering process or the nal sintering process is chosen between about 1000ov C. and about 1450'c C. and preferably between 1200 C. and 1350 C.
  • Bodies consisting of the ferromagnetic materials previously ⁇ described may be obtained by sinterng the initial mixture of the metal oxides or the like right from the beginning inthe desired form' and Aalso by pulverizing-.the reaction product of ⁇ the presintering process, giving it the desired shape, if .desired ⁇ after the addition of a binder, which may -be followed by 1a subsequent -sintering or hardening treatment.
  • EXAMPLE I A mixture consisting of barium carbonate, zinc oxide and ferric oxide in a ratio at 17.6 mol percent of BaO, 11.8 mol percent of ZnO and 70.6 mol percent of Fe203, which corresponds to the compound Ba3Zn2Fe24O41, was mixed with ethyl alcohol in a ball 'mill for l hour and subsequently presintered at 1000 C. in air for 15 hours. The reaction product was ground with ethyl alcohol in a ball mill for 1 hour. Subsequently, after drying, part of the product, to which a small amount of an organic binder had been added, -was pressed to form rings. These rings were sintered in oxygen atV 1200 C. Vfor 2 hours.
  • the density of these rings was 3.57 g./cm.3.
  • the remaining part ofthe product was presintered at 1000 C. and ground, was again presintered in air at 1200 C. for 2 hours.
  • This reaction product was ground with ethylalcoy hol in a ball mill for 11/2 hours and subsequently, after drying, the product, to which a small amount of an organic binder had been added, was pressed to form rings which Were sintered in oxygen at 1260? C. for 2 hours.
  • the density of these rings was 3.73 g./crn.3
  • An X-ray examination revealed that all rings consisted of crystals, the elementary cell of which can be described in the hexagonal crystal system by a c-axis of about 52.3 A. and an a-axis of about 5.9 A.
  • rings were manufactured from an initial mixture corresponding to .18.1 mol percent of BaO, 13.8 mol percent of ZnO and 68.1 mol percent of Fe203.
  • the rings were sintered at 1200 C. and had a density of 3.92 g./cm.3.
  • An X-ray examination reveals that all these rings contain two hexagonal crystal phases, one, the principal, having a c-axis of about v52.3 A. and an a-axis of about y5.9 A., and a second, present in small quantity, having a c-axis of about 43.5 A. and an a-axis of about 5 .9 A.
  • EXAMPLE II A mixture consisting of barium carbonate, cobalt carbonate and ferric oxide in a ratio of 17.6 mol percent of BaO, 11.8 mol percent of CoO and 70.6 mol percent of Fe203 which corresponds to the compound Ba3Co2Fe24O41 was presintered twice in the manner indicated in Example 9 10 t I and pressed intol rings. These rings where sintered in ⁇ in the"hexa'gonal crystal system by a '-axis of about 32.8 oxygen at 1220 C. for 2 hours. The density of these A. and an a-axis of about 5.9 A. y rings was 4.14 g./cm.3.
  • rings were .manufactured from that the rings consisted ofcrystals, the elementary cell initial mixtures correspondirigto of which can be described in the hexagonal crystal system by a c-axis of about 52.3 A. and an a-axis of about 5.9 A.
  • rings were manufactured ⁇ from an initial mixture corresponding to 18.1 mol percent of BaO, 13.8 mol percent of ZnO and 68.1 mol vpercent of Fe2O3.
  • the density of these rings was 5.25 g./cm.3 and, 10 ⁇ according to an X-ray exam-ination, the rings were found rto contain two hexagonal crystal phases, one, theprincipal, having a c-axis of about 52.3 A. and an a-axis of CID-3 and 4-6 g/Cm-3.
  • lSPeCVelY- A11 X-fay examina* about 5 9 A and another, .present in small quantity, tion revealed that all of the rings contained two hexagonal having a c-axis of about 43.5 A. and an a-axis of about 15 crystal phases.
  • EXAMPLE contains the metals in quantities corresponding to 17.2 molrpercent of BaO, 12.2 mol percent of CoO and 70.6 mol percent of Fe203 (or about the compound Ba3Co2Fe24O41) was ground with ethyl alcohol in a ball carbonate and ferric oxide in ratios of mm for 1hour and Subsequently after drying the Prod" 25 18.5 mol percent of BaO, 14.8 mol ⁇ percent of ZnO and uct, to which ⁇ a small amount of an organic binder had 66] m01 percent of F6203, been @dded Was pressed to fofm Hugs'. These Hugs 18.5 mol percent of BaO, 11.1 mol-percent of Zn'O, 3.7 mol were.
  • crystal phases, one, the principal, having a c-axis of about 45 all rings contained two hexagonal crystal phases, one 52,3 A, and an a-axis 0f about 5,9 A, and another, preshaving ia c-iaxis ⁇ orf about 52.3 A. 'and ian a-axi-s of about ent in small quantity, having a c-axis of about 43.5 A. 5.9 A. ⁇ and another having a cfaxis of about 43.5 A. and and an d axis 0f about 5 9 A, an a-axis of about 5.9 A.
  • Rings were manufactured, in the manner indicated in presint'crin'g process took place in air at 1000 C. for 15'hoursand the rings were sintered in oxygen at 1250" C. for 2 hours.
  • Example I from ybarium carbonate, zinc ox'ide, cobaltl 13 having a c-axis of about 43.5 A. and an a-axis of about 5.9 A.
  • ⁇ It was determined in the above-described manner that all hexagonal crystal phases which occur in this example in which a has. a value up to 1.0, b has a value up to 0.7, c has a value up to V0.6, Me is a bivalent ion selected from the group consisting of Fe++, Co++, -Ni++, Zn++, Mg++, R is a bivalent ion selected from the group conhave a referred lane of magnetization at right ang-les h to the hxagonal axis 5 sistmg of Mn++ and Cu++, d has a val-ue up to 0.6, sa1d Properties of these rings are specified in Table 3.
  • a ferromagnetic material having a composition corresponding to about 2 to 21 mol percent of AO, 5 to 45% of MeO, and about 52 to 83% of Fe2O3 in which A is a metal selected from the group consisting of barium, strontium, lead and calcium, and Me is a bivalent ion selected from the group consisting of Fedra, Mn++, Co++, Ni++, Zn++, Mg++, Cu++, and the bival'ent complex and consisting essentially of at least two crystal phases selected from the group of compositions consisting of:
  • Ba3 a b GSI'aPbbCanMe2Fe24IHO41 in which a has a value up to 1, b has a value up to 0.6, and c has a value up to 0.3, Me is a bivalent ion selected fromV the group Fe+ Mn++, Co++, Ni++, Zn++, Mg'H', Cu++, and the bivalent complex Li++pe+++ 2 said crystals having a c-axis of about 52.3 A. and an a-axis of about 5.9 A. in the hexagonal system; n
  • a ferromagnetic material as defined in claim 3 in which the material is the fired reaction product of about 2 to 21 mol percent of AO, about x mol percent of CoO, up to about (45-x) mol percent of MeO, and about 52 to 83 mol percent of -Fe203, wherein x has a value of at least 7 and not more than 45.
  • a ferromagnetic material as defined in claim 4 in which the material is the fired reaction product of about 8 to 21 mol percent of AO, about y mol percent of CoO, up to (2l-y) mol percent of MeO', and about 58 to 83 mol percent of Fe203, wherein y is at least 7 and not more than 21.
  • a ferromagnetic material as defined in claim 4 in which the material is the fired reaction product of about 15 to 21 mol percent of AO, z mol percent of C00, 4 to (2l-z) mol percent of MeO, and about 58 to 78 mol percent of Fe203, wherein z is at least 3 and not more than 17.
  • a ferromagnetic material as defined in claim 5 in which the material is the fired reaction product of about 15 8 to 19 mol percentV of AO, a m01 percent of C00-, (5-a) to (2O-a) m01 percent of DO, and 69 -to 83 mol percent of Fe203, wherein a is at least-5 and D is a'bivalent ion yselected from the group consisting of Fe++, Mn++, Ni++,

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Cited By (2)

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US3114714A (en) * 1960-06-23 1963-12-17 Philips Corp Ferromagnetic material
US4278556A (en) * 1978-05-19 1981-07-14 Tdk Electronics Co., Ltd. Process for producing flexible magnets

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Also Published As

Publication number Publication date
NL108776C (ja) 1964-07-15
CH398823A (de) 1966-03-15
FR1204540A (fr) 1960-01-26
DE1185104B (de) 1965-01-07
GB880865A (en) 1961-10-25
BE566891A (ja) 1958-10-17

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