NO751579L - - Google Patents

Description

FERRITE MATERIALS

The present invention relates to a material of the kind which

is stated in claim l's preamble.

The present invention relates to lithium-based ferrimagnetic materials for microwave applications, in particular for band X (8.2-12.4 GHz) applications of various kinds and in particular applications in non-reciprocating devices such as phase shifters, circulators and insulators.

At operating frequencies above 6 GHz, the known materials exhibit at least one significant disadvantage, for example: in the case of ferrites with a garnet structure: insufficient saturation magnetism,

for; case of nickel-based. ferrites with spinel1 structure: for large magnetic and electric iiap,

for manganese-based and magnesium-based ferrites with a spinel structure: too large a variation in the magnetic properties with temperature, in connection with a relatively low courier point,

for lithium-based and aluminum-based ferrites with spinel structure: too large dielectric losses.

The present invention makes it possible to avoid these various disadvantages.

These materials can be obtained by one of the known methods for the production of polycrystalline ferrites, for example comprising the following steps: a) mixing with distilled water or alcohol oxides or salts with high purity (purity exceeding 99.9%), as they

selected amounts of the oxides or salts correspond to the selected I composition, taking into account element loss or enrichmentj

in the following steps,

Ib) crush the mixture for 2-4 hours in a steel vessel containing steel balls, c) oven-dry the mixture and then anneal it in an oven at approx. 800°C, d) a second crushing, in an aqueous or alcoholic environment, of the product obtained, under conditions corresponding to those in the

first crushing operation, but in a period exceeding 12-24 hours, for example 36-48 hours,

e) drying and sifting the obtained powder,

f) forming, either by pressing in a steel mold, which necessitates the incorporation of a binder (which can later be removed by heating to 600°C) or by so-called "isostatic" pressing in a rubber mold, g) sintering in an oxygen atmosphere at a temperature in the range 950-1100°C for a period of 6-16 hours.

The results obtained by the present invention are determined by subjecting samples of the manufactured materials to measurements of the conventionally most significant properties, of these characteristic parameters the following are of particular importance: the saturation magnetism 4itm (a value of at least 200 gauss is necessary to make the material suitable for the intended applications),AH, which gives the width of the gyromagnetic resonance line in relation to the smallest possible necessary value (in practice, a value of 500 orsted will not present serious problems with regard to the adjustment of the permanent magnetic field which the material is subjected to in the intended applications) , Z^H^, which gives the width of the nuclear magnetic resonance line

(spin wave resonance line) -_4 gens to the loss angle (where a value of the order of magnitude 10 corresponds to very small dielectric losses). The material according to the invention is characterized by what is stated in claim 1 characterizing part.

Example I

'A material corresponding to that of formula II, . where:

was produced by a conventional method at a glow temperature of 800°C and a sintering temperature of 1050°C for 6 hours.

The characteristic properties measured at 9 GHz were as follows 4ttms = 23 40 gauss

AH = 458 orsted..

AHK= 2.5 Orsted

tan 6 = 1.9.10<-4>

The courier temperature was approx. 500°C and the real part of the relative dielectric constant was of the order of magnitude 17.

Example 2

A material corresponding to that of formula III, where: where x had the values 0-0.25, was produced by a conventional method at a glow temperature of 800°C and a sintering temperature of 1025°C for 6 hours. The characteristic properties measured at 9 GHz were as follows: The courier temperature varied from 500°C for a zero value of x to 364°c for x =0.25. The real part of the relative dielectric constant was of the order of magnitude 17.

Example 3

A material corresponding to that of formula II, wherein:

where x had values in the range 0.1-0.4, was produced in a conventional manner at a glow temperature of 800°C and a sintering temperature of 1000°C for 6 hours.

The characteristic properties measured at 9 GHz were as follows:

The courier temperature varied from 462 °C for x = 0.1 to 310 °C for x =0.4. The real part of the dielectric constant was of order 17.

I I

Example 4

I The material corresponding to that of formula II, where: i

was produced in a conventional manner with a glow temperature of 800°C and a sintering temperature of 1000°C for 6 hours.

The characteristic properties measured at 9 GHz were. as follows:

4TTM= 2,747 gauss

AH = 506 Orsted

tanS 4.2.IO<-4>

The curing temperature was 570°C and the real part of the dielectric constant was of the order of magnitude 17.

In the above 4 examples, the materials exhibited very low magnetic and dielectric losses in the X band.

A possible explanation for the good results obtained is indicated below, on the basis of the importance of the various components.

Bismuth oxide plays an essential role in the same way as manganese ions. On the other hand, bismuth is a densifying additive that promotes sintering and reduces the porosity of the product obtained, bismuth is not incorporated into the ferrite's crystal lattice. on the other hand, manganese plays a fundamental role in reducing the dielectric losses. The manganese ions in the multivalent state form part of the crystal lattice.

Titanium in the form of a divalent ion plays a dual role.

It promotes sintering and further exhibits a tendency to decrease the saturation magnetism.

I The divalent zinc ion exhibits different effects, depending on whether it is introduced in the conditions indicated in formulas II or III. It occupies different preferred sites (octahedral or tetrahedral). For the case of formula II, the zinc ion will retain the magnetization constant despite the increase in the titanium ratio. In the case of formula III where the titanium ratio is independent of the zinc ratio, it will increase the saturation magnetism at the same time as it reduces the width of the gyromagnetic resonance line.

When using the materials according to the present invention in the manufacture of circulators, phase shifters, insulators etc., very low magnetic and dielectric losses will be achieved. E.g. in an X-band circulator, an insertion loss not exceeding 0.1 decibels was measured.

The invention is equally applicable in the corresponding device

which operate at frequencies exceeding the X-band frequencies.

Claims (4)

1. The ferrimagnetic materials, characterized in that it is a polycrystalline ferrite with a spinel structure, whose composition can be expressed by one of the following three formulas: (I )L i2 0 ; 5(1 - E) Fe2 03 ; Bi2 03 ; on Mn 02 (II) Li 2 0 (1 + y) ; 2x ZnO; 5(1 -£) Fe2 03 (1 _-0.6y - 0.4x) ; Ti02 (4y + 2x) ; <x Bi2 03 j (3Mn02(III) Li20 (1 + y _ x) ; 4x ZnO ; 5(1 -£)Fe2 03 (l - 0.6y-0.2x); 4y TiO 2 ; a-Bi2O3; (3 Mn02 I where 2. The material according to claim 1, characterized in that it satisfies formula (i), in which the parameters have the following values: 3. The material according to claim 1, characterized in that it satisfies the formula (I I) in which the parameters oc, (3 and £ have the following values: and where x has values in the range 0.1-^ 0.4 and y has values in the range 0.20-0.25. 4. The material according to claim 1, characterized in that it satisfies formula (III), in which the parameters oc, (3 and £ have the following values: and x has values in the range 0-0.25 and y has values 0.20-0.25.