DE2042950A1 - Process to achieve any anisotropy constants in the case of solid ferrites with a garnet structure - Google Patents

Description

20Λ2950

DipUng. HOP5T AUER

Afnr.liier: Philip- '. ο - .. »■ .- ^ --'- ^ - S GmbH.
Akia: ¹ ^

Philips Patentverwaltung GmbH., 2 Hamburg 1, Mönckebergstr.

"Process for achieving any anisotropy constants in single-crystal ferrites with a garnet structure"

The invention relates to a method for achieving "any anisotropy constants" in single-crystal ferrites with a garnet structure of the composition A, B ^ ^e 5-z ^ z ° 12 ' ^νοΓ · * · ^η A = yttrium and / or at least one rare earth metal, B = Calcium and C is a cation with an ionic radius similar to iron and 0 <y <1 and 0 <ζ <1.5. Cations with an ionic radius similar to iron are, for example, aluminum, gallium, indium, magnesium, silicon, scandium, titanium, Zircon and Vanadium in question.

Such single-crystal ferrites with garnet structure have anisotropy constant K ^ and K ₂ ^au ^> the size and \ sign of the specified compositions depend. For pure yttrium iron garnet ^(Y 3 ^Fe 5 ° - | ^ 2 ^is K ₁ = -6.1Cr [erg / cm ^ ^ J, and K ₂ O The anisotropy constants of the other compositions are not changed as desired, but the size and sign. without changing the magnetization at the same time.

In practice, however, there is a need for monocrystalline

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Ferrites with a garnet structure with anisotropy constants of a certain size and sign. The invention lies Therefore, the object of the invention is to provide a method with which, in the case of single-crystal ferrites with a garnet structure practically any anisotropy constant can be achieved.

According to the invention, this is achieved in a method of the type mentioned at the beginning in that iridium and / or ruthenium is added to the starting mixture for the production of single crystals in an amount corresponding to 0.01 to 0.8 atom% of the end product.

The incorporation of small amounts of iridium and / or ruthenium has practically no effect on the saturation magnetization of the garnet, but to a large extent the anisotropy constants K 1 and K ₂ . Starting from a composition with a certain saturation magnetization, desired anisotropy constants can be obtained by adding small amounts of iridium and / or ruthenium.

It should also be mentioned that it is known from the "Zeitschrift für angewandte Physik", 1967, pages 190 to 193 is to add small amounts of ruthenium or iridium to polycrystalline yttrium iron garnets (YIG), whereby the spin wave line width changes. Body made of polycrystalline yttrium-iron garnets but there is no anisotropy towards the outside.

The invention will now be explained in more detail with reference to the compositions given in the table below.

In the table, the compositions of the shell made according to the invention are indicated as well as the measured thereon anisotropy constant K ₁ and K ₂ at 20 ⁰ C. The analysis accuracy for x, y and ζ is +0.05 atom%.

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O
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The single crystal bodies with the compositions given in the table were made in a manner known per se grown in an auxiliary melt, e.g. B. according to one in "Journal of Crystal Growth" 3, 4 (1968), pages 463 to 466, described procedure.

As can be seen from the table, the anisotropy constants can be reduced by adding iridium and / or ruthenium change in wide areas.

The registration also relates to the use of single crystals produced by the method according to the invention.

Ferrite single crystals with anisotropy constants K ^ = Kg = O produced by the above process are preferably suitable as a ferrimagnetic in microwave filters. The ferromagnetic resonance is used in such filters. In addition to the saturation magnetization in single crystals, this depends essentially on the anisotropy constants, which in turn are temperature-dependent. In order to minimize the temperature dependence of the resonance frequency in a range around room temperature hold, the single crystals used should have anisotropy constants with a value of zero. This can be achieve in the garnets produced by the above process by adding iridium and / or ruthenium. In addition, this addition gives you an exact proportionality between the resonance frequency and the magnetic field H (f = / H).

Another important use of ferrite single crystals produced by the above process is Magnetic layers in single-wall domain memories. One distinguishes here between 1. so-called bubble memories

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(See "IEEE Transactions on Magnetics", Vol. Mag-5, No. 3, Sept. 1969, pages 544 to 553, and pages to 561, as well as DOS 1 910 584) and 2. thermo-magneto-optical storage systems (see "IEEE Transactions on Magnetics ", Vol. Mag-5, No. 4, Dec. 1969, pages 700 to 716).

1. Bubble storage devices have thin magnetic layers (10 to 100 μm) in which cylindrical domains (bubbles) occur. They can be used as storage material. The movement of the cylindrical domains within the layers takes place through a magnetic field. The anisotropy field of the thin layers is perpendicular to the λ layer surface. It is particularly important here to keep the diameter of the domains as small as possible in order to obtain a high storage density. The optimal diameter d is between 1 μm and 10 μm. d is primarily dependent on the magnetization and the anisotropy. For 1 / um <d <10 / um, the magnetization 4 TT Μ _σ must be between 80 and 1200 Gauss and an effective anisotropy field, which is related to the anisotropy constant, between 100 and 10 000 Oerstedt. All ferrites known to date have the property that either the effective anisotropy field is too large (e.g. hoxagonal ferrites with the composition ^ aAl Fe.> 2_ _x 0-ig) or the magnetization ü is too small (e.g. orthoferrite of the composition MFeO ,, where M is a rare earth metal).

The magnetization of grenades according to the invention can be achieved by substituting z. B. aluminum or gallium as desired can be set. If you also add some iridium and / or ruthenium according to the invention, so can the effective anisotropy field can also be set so that

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that one arrives in the desired range of the domain diameter.

2. In the similarly constructed thermo-magneto-optical storage systems, the writing takes place, i. H. the Extinguishing a domain by heating it with a laser beam that was known to be deflected. B. more digital Light deflector). The magnetic material is in a small magnetic field, which at the working temperature is not sufficient to change the magnetization to be able to d. H. is smaller than the coercive force. On the small spot hit by the laser beam (z. B. 10 χ 10 / um) but the coercive force is smaller than the applied field due to the heating, so that the magnetization can be changed. After cooling down, the new state remains because now the coercive force is great again.

The reading can be done with the same laser, which works with a lower power, so that none significant heating of the illuminated spot occurs. Through the magneto-optical Kerr or Faraday effect the light intensity of the continuous or reflected beam depends on the magnetization state and can be registered with an electro-optical detector (photodiode, photomultiplier).

_{Garnets (e.g. Gd, FecO 12} ) are already known as magnetic materials for these storage systems. An important requirement, however, is that the coercive force decreases sharply with temperature in a small temperature range. The garnets produced by the method described above can be used here with advantage, in particular Gd-Fe garnets substituted with Ga. at

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if the iridium or ruthenium doping is not too small, the anisotropy increases sharply at any temperature T to, whereby the general course of the anisotropy - steady decrease down to zero at Curie temperature - is obtained remain. The change in anisotropy dK / dT can therefore be greatly increased. The same goes for that too Change in coercive force dH / dT, because the coercive force increases essentially proportionally with the anisotropy.

Patent claims:

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Claims (3)

Patent claims: Any 1. A method for achieving anisotropy in single-crystal ferrite having a garnet structure of the composition A, B ^Fe "j_ _z ^c _z O ^ 2 ^'wor ^ ^{n A =} yttrium and / or at least one rare earth metal, B = calcium and C is a cation having a similar ion radius like iron and 0 <y <. 1 and 0 < ζ <1.5, characterized in that iridium and / or ruthenium is added to the starting mixture for the production of single crystals in an amount corresponding to 0.01 to 0.8 atom% of the end product. 1. Use of prepared by the method according to claim 1 Ferrite single crystals as a magnetic layer in single-wall domain memories. 3. Use of ferrite single crystals produced by the method according to claim 1 with anisotropy constants K ₁ = Kp = 0 as a ferromagnetic in microwave filters. 209810/1586