DE2231941A1 - FERROMAGNETIC MATERIAL AND METHOD FOR MANUFACTURING IT - Google Patents

Description

THOMSON - CSP
173, vol. Haussmann
PARIS 8e / France

Our sign; ! P 1239

Ferromagnetic material and process for its manufacture

The invention relates to new ferromagnetic materials that without substantial reflection the electromagnetic Absorb waves in a wide frequency band around 3000 MHz.

There are ferromagnetic "substances with more or less high magnetic and dielectric losses in an electromagnetic field in the hyperfrequency range known. One knows in particular magnetic substances, which effectively the electromagnetic waves in the range of absorb a few hundred megahertz. At higher frequencies they become less effective because of their permeability is generally low.

Dr. Ha / Gl

209883/0752

Incidentally, there are also non-magnetic materials known, which the electromagnetic waves, in particular absorb at 3000 MHz thanks to their dielectric losses. They have the disadvantage not to be very effective, especially when they are near a metal wall as underneath Under these conditions the electric field is weaker compared to the magnetic field.

Magnetic materials with a relatively complex permeability operating in a wide range of frequencies bind satisfactorily around about 3000 MHz are difficult to obtain. In particular is the real part of their relative permeability is generally less than unity and for applications where if they are close to a metal wall, their absorption capacity is small.

The invention overcomes these difficulties by creating new materials with one at the same time good absorption capacity (due to magnetic and dielectric losses) and good matching to the self-impedance of the air (or vacuum) in a wide frequency range on both sides of 3000 MHz.

According to the invention, polycrystalline ferromagnetic materials having a spinel structure have a general one chemical composition, which is characterized by the following general formula of the polycrystalline material:

N: < -X- y ^c ° x ^Zn y- Si F (
ζ ζ 0 , 10 < x ^ O , 20 0 , 20 y ^ o , 30 0 z ^ O , 05 209883 / 07 52 ^ä 2 ° 4

These substances can be obtained in the following ways:

One chooses and weighs a suitable amount of starting materials consisting of nickel, zinc, iron, silicon and Consist of cobalt oxide (the latter oxide is obtained by calcining cobalt carbonate at 800 ° C), all of these substances are highly pure. The calculation of the amounts of these oxides in particular bears losses Account that occurs during heat treatment and takes into account the introduction of iron during of grinding, so that one has a compound with a stoichiorometric one very close to the desired one Composition received. A first grinding is carried out for about 24 hours in the aqueous phase in cylindric strips Steel containers with steel balls that rotate on their axis. The mixture is then dried in a drying pot dried.

According to one embodiment of the invention, the dry mixture undergoes a heat treatment in an oven subjected at about 105> 0 ° 0. The product obtained is again made according to the method described above Ground for about 48 hours and then dried.

After drying, the powder obtained in this way is with an organic binder such as an aqueous solution of polyvinyl alcohol to form a paste Mixed mass, which is then homogenized, passed through a sieve to obtain granules and then pressed under a pressure of one ton / cm in suitable molds. The pieces thus obtained are then at 600 ° C to drive out the organic

209883/0752

Treated binder. It is then placed in an oven at a temperature not exceeding 1350 ° C, which is maintained for a few hours, burned. This burning occurs either in a stream of air or in a stream of oxygen.

The invention is explained in more detail with reference to the following description in conjunction with the drawing.

In the drawing show:

Pig. 1 the changes in the complex magnetic permeability and the complex dielectric constant for a material with χ and y equal to 0.15 and 0.25, respectively, depending on the change in the variable z, where the frequency of electromagnetic waves is constant and is 2800 IiHz.

Fig. 2 shows the same changes for an analog one Material, however, where ζ = 0, and the frequency varies from 100 to 4000 MHz.

We know that if one denotes the relative complex magnetic permeability with n. (Real part ii .., imaginary part χι _? ) And with ε the relative complex dielectric constant (real part ε-j, imaginary part ε ₂ )> one defines the absorption maximum for electromagnetic waves Insertion of a body made of the ferromagnetic material is obtained if:

- the magnetic and dielectric losses are large, i.e. if at the frequency of the

20 9 R.

waves to be absorbed n ₂ and S _{2 are} quite large, and ju ^ is as large as possible;

- there is a good match between the propagation medium of the incident waves (vacuum or air) and the material, which means that the parameter n is not too small in relation to the parameter ε., and that the parameters tu and ε _{2 are} not too differ greatly, all of these conditions having to be present in a broad frequency band around 3000 MHz.

In Pig. 1 an axis OZ is drawn, on which values of ζ between 0 and 0.05 are plotted on the abscissa; on the ordinate (with a division from 0 to 20 ·) the modules of the quantities jx,, tu, t * , ε _{2 are} plotted depending on the material with the following chemical formula (this formula serves as the basis for the initial weight of the Starting materials):

^Ni O, 6 ^Co O, 15 ^Zn O, 25 - ε ³¹ Z ^ ₂ ° 4

This material was made according to that described above Process made.

These are 'relative "permeabilities and' relative" Dielectric constants (compared to air or vacuum) i.e. by the quotient of the absolute values ε and u and the values εθ and uO in air or vacuum.

The measurements were made at 2800 MHz on from the above defined material produced toroidal bodies measured.

209RR3 / D75?

It is found that αι. is always above 1, while ζ varies from 0 to 0.05, that ε ^ is greater than 10 and that ερ and / U _? are not very different from one another and that they are even equal for ζ = 0.015.

The absorption properties of the material at 2800 MHz can be summarized by saying that the Increases in z, i.e. the small but increasing replacement of silicon for zinc, the magnetic properties barely changed. On the other hand, the increase in ζ causes the dielectric loss to increase.

If ζ = 0 and if you look at the parameters at a If the frequency changes from 100 to about 4000 MHz, the curves of FIG. 1 are obtained. In particular, determines that for the measured sample / U- = about 2 at 2800 MHz. In addition, the absorption and adaptation conditions are by and large good in the frequency range specified above and in particular at around 3000 MHz.

The materials of the invention are useful for forming deposits deposited on a metal surface Absorption layers. In this case, attenuations - of 12 deciwel for an absorbing, Measure a 2 mm thick layer at 2800 MHz, the experiment being carried out in a coaxial line, by placing the material in front of a short circuit.

2098 83/0 75?

Claims (3)

Claims 1.Polycrystalline ferromagnetic material with spinel structure, characterized in that its chemical composition of the general formula ^Ni 1 - χ _r y ^Co x ^Zn y - ζ ^Si z * ^e 2 ° 4 corresponds to, where 0.1 <χ ^ 0.2 0.2 <y <0.3 0 < ζ ^ 0.05 2. Material according to claim 1, characterized in that x = 0.15 y = 0.25 0s £ z <0.05. 3. Method of making a ferromagnetic Materials according to claim 1, wherein one - in the aqueous phase a mixture of very pure oxides of nickel, zinc, iron, silicon and cobalt in the mixes proportions corresponding to the formula according to claim 1, - the mixture thus obtained dries, - incorporates organic binders in the aqueous phase to achieve a paste-like mass, - in molds under a pressure of 1 t / cm this pasty Mass presses, - heated to 650 ° G to remove the organic binder and 209R8 / 1 / 07K? - sinters in an oxidizing environment, characterized in that, that the sintering temperature is at most 1350 ° C. ? D9883 / 075? Blank page