DE2519245A1 - LITHIUM-BASED FERRIMAGNETIC MATERIAL USED AT HIGH FREQUENCIES - Google Patents

Description

173, vol. Haussmann
Paris, France

Our reference: T 1767

Ferrimagnetic material that can be used at maximum frequencies

based on lithium

The invention relates to ferromagnetic materials Lithium base, which is suitable for use at the highest frequencies, especially in the X-band (from 8.2 - 12.4 GHz) for numerous Purposes, particularly in non-reciprocal devices such as phase shifters, circulators and Isolators.

At operating frequencies above 6 GHz, the known materials have at least one major disadvantage. Called be:

Insufficient saturation magnetization for ferrites with a garnet structure ϊ

Dr Ha / Mk

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For ferrites with a spinel structure based on nickel, too high losses, both magnetic and electrical Origin;

for ferrites with spinel structure based on manganese and magnesium, too great a change in the magnetic properties Properties with temperature, associated with a comparatively low Curie point;

for ferrites with spinel structure based on Lithium and aluminum too high dielectric losses.

The invention overcomes these various disadvantages.

The materials according to the invention are lithium ferrites with a spinel structure. They are characterized by that they contain the following oxides in the molar proportions resulting from the following formulas:

(I) Li ₂ O; 5 (1-ε) Fe _£ O ₃ ; α Bi ₂ O ₃ ; ß Mn _{£ 0}

(II) Li ₂ O (1 + y); 2 χ Zn O; 5 (1-ε) Fe ₂ O ₃ (1-0.6 y 0.4 x); Ti O ₂ (4 y + 2x); aBi ₂ O ₃ ; ßMn O ₂

(III) Li ₂ O (1 + y - x); 4 χ Zn O; 5 (1-ε) Fe ₂ O ^ (1-0.6y-0.2x); 4 y Ti O ₂ ; aBi ₂ O ₃ ; ßMn O ₂ .

whereby:

0.001 £ α ^ 0.01
0.05 <β 4 0.25
0.05 <ε 4 0.15
0 ^ χ L · 0.40
0.05 4 y 4 0.29

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The following values are possible for the individual parameters:

α = 0.0028 0, + 10 % β = 0.14 0, + 10 % ε = 0.08 + 10 % ο 4 χ ^ 4th 0.2 <y ^ 25th

These materials can be prepared by a known method for the production of polycrystalline ferrites, for example the following process steps being used come:

a) Oxides or very pure salts are mixed (purity over 99.9%) in the chosen formula corresponding amounts with distilled water or alcohol, with one in the takes account of losses or additions occurring in the following stages;

b) the mixture is crushed a first time for 24 hours in steel bottles containing steel balls;

c) it is dried in a drying oven and then ^{fired at about 800 °} C. in the oven;

d) the product obtained is a second time in aqueous or alcoholic medium under the same conditions as crushed the first time, but now for a longer period of 12 to 24 hours, namely 36 to 48 hours;

e) the powder obtained is dried and sieved;

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f) the powder is shaped, either pressed in a steel mold, which requires the addition of a binder (which must then be ^{removed by heating to 600 °} C.), or by so-called "isostatic" pressing in a rubber mold;

g) it is sintered for 6 to 16 hours under oxygen at a temperature between 950 and 1100 ^° C.

The results achieved with the invention can be seen in a measurement of the most important customary properties:

Among these characteristic properties, the following are mentioned in particular:

The saturation magnetization 4π Mg: A minimum value of 2000 Gauss is required for the stated purposes;

the width of the gyromagnetic resonance line ΔΗ for which the smallest possible value is desired; In practice, however, it can amount to 500 Oersted without being used for the regulation of the permanent magnetic field to which the material is exposed in the intended applications to be disruptive;

the width of the resonance line of the spin wave ΔΗ ^, where this size depends on the magnetic losses and is smaller, the smaller these losses themselves are; a value of a few oersteds corresponds to very low magnetic losses;

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tanδ or the tangent of the loss angle for which a Value on the order of 10 "corresponds to very low dielectric losses.

example 1

The material corresponds to a composition of type II with:

α = 0.0028 β = 0.14 ε = 0.08 x = 0 y = 0.25

The preparation is carried out in conventional manner with a sintering temperature in step c) of 800 ⁰ C and a 6 · hour sintering at 1050 ° C in step g).

The properties measured at 9 GHz are as follows:

4π M ₃ = 2340 Gauss

Δ Η = 458 Oersted ^/ ΔΗ _Κ = 2.5 Oersted , tanS = 1.9 · 1Ο " ⁴

The Curie temperature is approximately 500 ^° C. and the real part of the relative dielectric constant is approximately

Example 2

The material corresponds to a composition of the formula of type III with:

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α = 0.0028 β = 0.14 ε = 0.08 y = 0.25

and χ has values from 0 to 0.25.

The production takes place in the classic way with a sintering temperature of 800 ^° C. and a 6-hour sintering at 1025 ^° C.

The characteristics determined at 9 GHz are as follows:

X Π4 Mq
(Gauss7 ΔΗ
(Oersted) ^ΔΗ Κ "
(Oersted) tan δ ΊΟ 0
0.10
0.15
0.20
0.25 2 274
2,790
2,980
3 145
3,325 477
379
318
270
205 2.5
3.1
3.8
3.4
3.6 4.3
4.0
3.1
3.0
3.0

The Curie temperature varies from 500 C for χ = zero to 364 ° C for χ = 0.25. The real part of the relative dielectric constant is around

Example 3 The material corresponds to a formula of type II with:

α = 0.0028 β = 0.14 e = 0.08 y = 0.25

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and χ has values from 0.1 to 0.4.

The production takes place in the classic way with a sintering temperature of 800 ^° C. and a 6-hour sintering at 1000 ^° C.

The characteristics determined at 9 GHz are as follows:

X 4ttM _s ΔΗ tan5 -10 ^ ⁺ (Gauss) COersted) 0.1 2 267 500 2.3 0.2 2,361 321 2.9 0.3 2 211 273 2.5 0.4 2 111 216 1.6

The Curie temperature varies from 462 ⁰ C for χ = 0.1 to 310 ⁰ C for χ = 0.4. The real part of the dielectric constant is 17.

Example 4

The material corresponds to a compound of the formula of type II with:

α = 0.0028 β = 0.14

ε = 0.08

x = 0

y = 0.20

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The production takes place in the classic way with a sintering temperature of 800 ^° C. and a 6-hour sintering at 1000 ^° C.

The characteristics determined at 9 GHz are as follows:

4π Mg = 2 747 Gauss ΔΗ = 506 Oersted tan6 = 4.2 1Ο ~ ⁴

The Curie temperature is 570 ° C and the real part of the relative dielectric constant is about 17.

In the four above examples, the materials obtained have very low magnetic and dielectric losses in the X-band.

A possible explanation of the nature of the results obtained is given below by the respective roles which the different components play, are analyzed.

The bismuth oxide plays an important role as does the manganese ions. Once the bismuth oxide is a flux, which facilitates sintering and reduces the porosity of the product obtained; the bismuth does not occur into the crystal lattice of the ferrite. On the other hand, the manganese plays a fundamental role in the reduction the dielectric losses. The manganese ion with several valencies forms part of the Kirstall lattice.

The titanium plays a double role in the form of a divalent ion. It facilitates and favors sintering the decrease in saturation magnetization.

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The divalent "zinc ion" plays quite a different role Role, depending on whether it is included in the formula II or III is introduced. It has various preferred locations (octahedral or tetrahedral). In the case of Formula II, it keeps the magnetization constant despite an increase in the titanium content. In the case of formula III, where the titanium content is independent of the zinc content, it allows the saturation magnetization to increase with a simultaneous reduction in the width of the gyromagnetic resonance line.

When using the materials according to the invention for the production of circulators, phase shifters and isolators very low magnetic and dielectric losses are found. For example, one has for a circulator for the X-band measured a coupling loss limited to 0.1 decibels.

The invention is also applicable to the same devices, if these with higher frequencies than those of the X-band work.

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Claims (3)

Claims 1. Ferromagnetic., Poly- • usable at maximum frequencies crystalline ferrites with spinel structure, marked. by one of the following three formulas Composition: (I) Li ₂ O; 5 (1-ε) Fe ₂ O ₃ ; aBi ₂ O ₃ ; ßMn O ₂ (II) Li ₂ O (1 + y); · 2χ Zn 0; 5 (1 - ε) Fe ₂ O ₃ (1 - 0.6 y - 0.4 x); Ti O ₂ (4y + 2x); aBi ₂ O ₃ ; ßMn O ₂ (III) Li ₂ O (1 + y - x); 4 χ ZnO; 5 (1 - ε) Fe ₂ O ₃ (1-0.6 y-0.2 x); 4 y Ti O ₂ ; aBi ₂ O ₃ ; β Mn O ₂ whereby: 0.001 < ■ α ^ - 0.01 0.05 < ß « 0.25 0.05 ^ ε ^ 0.15 0 ^ χ - $ ■ 0.40 0.05 <y <0.29. 2. Ferrite according to claim 1, characterized in that its composition corresponds to the formula I, wherein α = 0.0028 + β = 0.14 + 1056 ε = 0.08 + 10? ό. 3. Ferrite according to claim 1, characterized in that its composition corresponds to the formula II, wherein 509846/1107 α = 0.028 + 10% β = 0.14 + 1096 ε = 0.08 + 10% and χ varies from 0.1 to 0.4 and y from 0.20 to 0.25. Ferrite according to claim 1, characterized in that its composition corresponds to formula III, wherein α = 0.0028 + 1i ß = 0.14 + 10% ε = 0.08 + 10% _and χ varies from 0 to 0.25 and y from 0.20 to 0.25. 509846/1107