JPH0666216B2 - Manufacturing method of bismuth substituted magnetic garnet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magnetic garnet applied to, for example, a Faraday rotation element of an optical isolator, and particularly to a wavelength band (0.8 μm) of 0.8 μm.
The wavelength range of μm is 0.75-0.8 centered on the wavelength of 0.8 μm
(A wavelength range of about 5 μm is generally referred to, and this wavelength range is also referred to in this specification).
Relates to a method for producing a bismuth (Bi) -substituted magnetic garnet with reduced light absorption.

[Outline of Invention]

The present invention, in a method for producing a bismuth-substituted yttrium magnetic garnet, is to reduce or reduce the presence of Fe ²⁺ by specifying the composition so that a high light transmittance is exhibited particularly in the 0.8 μm wavelength band. is there.

[Conventional technology]

For example, semiconductor lasers are widely used for various purposes including recording and / or reading of information on optical disks and magneto-optical disks.

However, when a semiconductor laser is used in this way, there is a disadvantage such as mode hopping noise when there is return light, so that the light emitted from the semiconductor laser should not return to the semiconductor laser as much as possible. In addition, there is an increasing need for an optical isolator that blocks this return light.

This optical isolator has a polarizer (2) and an analyzer (3) arranged with a Faraday rotator (1) in between, as shown in the schematic structure of FIG. Faraday rotator (1)
The magnet (4) applies a magnetic field in the direction of the optical axis so that the plane of polarization of linearly polarized light incident from the light source (5) such as a semiconductor laser through the polarizer (2) is rotated by 45 °. The analyzer (3) has its axial direction selected so that it can pass the polarized light rotated by 45 ° by this Faraday rotator (1), so that the light passing through it irradiates the illuminated surface. Has been done. Then, in this case, when there is reflected light from the irradiated surface (6), that is, return light, this return light again passes through the analyzer (3) and the Faraday rotation element (1), and again at this time. 45 ° rotated polariser (2)
Head to. Therefore, the returning light toward this polarizer (2) has its polarization plane rotated by 90 ° with respect to the incident light in the forward direction, and cannot pass through this polarizer (2). I can't go to (4). As described above, the optical isolator has a light transmitting property in one direction, that is, the forward direction, but has a blocking effect in the opposite direction.

As described above, the optical isolator has a function of blocking light in the reverse direction, but in order to reduce the light loss in the forward direction, it is desired that the Faraday rotator itself has as high a light transmittance as possible. To increase this light transmittance,
The thickness t of the Faraday rotator is desired to be as small as possible, but this thickness t requires a certain thickness to obtain the required rotation angle, in the above example 45 °. . The forward loss L (dB) during 45 ° rotation is (However, α is given by the light absorption coefficient and F is the Faraday rotation ability.) Therefore, in order to make L small, one having a small light absorption coefficient α is required.

This light absorption coefficient α depends on the wavelength and is 1.3
For long wavelength bands such as the μm wavelength band, see VI
The Faraday rotator made of G (yttrium, iron, garnet) has been quite satisfactory.

However, as a light source for the above-mentioned optical disk or magneto-optical disk, a semiconductor laser in the 0.8 μm wavelength band such as AlGaAs semiconductor laser is in the direction of not being used, and the Faraday rotation about the 0.8 μm wavelength band is used. Development of elements is desired.

On the other hand, as a method of growing a magnetic garnet used for such a Faraday rotation element, that is, a rare earth iron garnet, a method of obtaining a crystal film by liquid crystal epitaxy, that is, a GGG (gadolinium gallium garnet) substrate in a raw material melt is used. The method of growing a magnetic garnet film on this substrate by immersing it in the substrate and then pulling up this substrate is excellent in mass productivity. In this case, flux is added to the melt of this liquid crystal epitaxy. To be done. This flux is usually Pb
O is used. However, when this PbO is used as a flux, it is unavoidable that a part of Pb ²⁺ is mixed in the grown crystal film, which makes it difficult to reduce the absorption loss of light. Even in the case of PbO flax, it has been reported that the light absorption can be lowered by controlling the growth temperature of the crystal film (Journal of Applied Physic.
s) Vol.45 P2867 ~ 2873 July 1974) By the way,
Again, this is not effective in the 0.8 μm wavelength band.

Therefore, in order to prevent Pb ^{2+ from} being mixed in, a Bi-substituted magnetic garnet film, that is, a part of the rare earth element, was removed by liquid crystal epitaxy using a melt containing only Bi ₂ O ₃ as a flux.
It is possible to grow a magnetic garnet film substituted with Bi (Journal of Electrochemical Society) Vol.
123 P1248 to 1249 1976).

However, in reality, even if the Bi-substituted magnetic garnet is grown by such a method, the light absorption cannot be sufficiently reduced. This is because the composition of Bi-substituted magnetic garnet is
For example, (▲ Tm ³⁺ _2.3 ▼ ▲ Bi ³⁺ _0.7 ▼) (▲ Fe ³⁺ _4.0 ▼ ▲ Ga ³⁺
_1.0 ▼) O ₁₂ …… (2) is actually ▲ Tm ³⁺ _2.3 ▼ ▲ Bi ³⁺ _0.7 ▼ ▲ Fe ²⁺ _{2δ + δ ′} ▼
▲ Fe ³⁺ _{4.0-2 δ-δ '} ▼ ▲ Ga ³⁺ _1.0 ▼ ▲ P
t ⁴⁺ _{δ ′} ▼ ▲ O ^2-12 _-δ・^{・ ・ It} is considered that divalent Fe ions are generated by the generation of Pt ⁴⁺ and oxygen vacancy δ as shown in (3), which causes optical absorption. Be done. δ'is the amount of Pt mixed (the number of atoms). This Pt mixing is caused by the crucible used for liquid crystal epitaxy.
By being Pt, the Pt of this crucible is generated by diffusing in the melt.

In addition, as a method for obtaining a garnet film having magnetic anisotropy by liquid crystal epitaxy, a report of adding CaCO ₃ to flux (Material Research Bulltein Vol. 11, PP337 to 246, 19)
76), but in this case, the flux is not Bi ₂ O ₃ alone, but Bi ₂ O ₃ together with CeO ₂ / K ₂ O, or SiO ₂
/ Na ₂ O, etc. are added, and the light absorption has not been clarified.

[Problems to be solved by the invention]

As described above, there is a problem in that Bi-substituted magnetic garnet obtained by the conventional method has not sufficiently obtained light absorption in the 0.8 μm wavelength band.

The present invention solves such problems, and
It has a high transmittance in the 8 μm wavelength band and is used as a Faraday rotator element of an optical isolator for preventing return light when a semiconductor laser in the 0.8 μm wavelength band is used as a light source in a recording / reproducing device for optical disks, magneto-optical disks, etc. The present invention provides a method for producing a Bi-substituted magnetic garnet that is suitable for use.

[Means for solving problems]

In the present invention, a bismuth-substituted iron garnet, crystal epitaxial (hereinafter the light absorbing small garnet substrate from Bi ₂ O ₃ and the garnet structure element only consists of melt
LPE) is used to grow a magnetic garnet having the following specific composition.

That is, in the present invention, Y _{3-x- δ1} Bi _x M ^I _δ1 Fe _{5-y- δ2-δ3} M ^II _δ2 M ^III _y Pt
_δ3 O ₁₂ -δ4 X is selected to be 0.5x2.0 and y is set to 0.
Select y2, and select δ ₁ + δ ₂ within ± 15% of the value at which the light absorption in the 0.8 μm wavelength band is minimal. The specification of this ± 15% range is 0.8μ in this range.
This is because it was confirmed that the light absorption in the m wavelength band was within the range of 15% increase from the minimum value, and that the light absorptance in this wavelength band could be remarkably reduced.

Here, δ ₃ is the number of Pt atoms mixed during the manufacturing process, δ
₄ is the number of oxygen vacant seats.

[Action]

In the present invention, a Bi-substituted magnetic garnet in which Fe ²⁺ is not present is formed, and by doing so, an increase in light absorption in the 0.8 μm wavelength band due to the presence of Fe ²⁺ is avoided.

〔Example〕

Example 1 A Bi-substituted magnetic garnet film was grown by LPE on a Sm ₃ Gd ₅ O ₁₂ substrate. This LPE is In the melt of composition, R ₆ defined in (the number of molecules in this formula indicates the number of moles in the melt), the R ₆ is 3.0% and 6.1, respectively.
%, 7.6%, 9.1%, 15.2% CaCO ₃ was added, and magnetic garnet films were prepared by LPE. When the film thickness of the magnetic garnet film was measured from the difference in weight between the grown surface of this magnetic garnet film and the Sm ₃ Gd ₅ O ₁₂ substrate after the growth, the film thickness per one surface of the substrate was 40 to 60 μm. The electrical resistivity ρ of each magnetic garnet film was measured, and the results are shown in Fig. 1. R ₆ has a maximum value near 9%, and the conductivity type of each sample measured by Seebeck effect is the same. As shown in the drawing, the R ₆ was n-type when R ₆ was smaller than about 9%, and the p-type when R ₆ ≧ 9%. Also, the wavelength λ
The result of measuring the light absorption coefficient α ₈₃₀ for light of 830 nm is as shown in FIG. 2, which decreases with addition of Ca ²⁺ ,
R ₆ shows a minimum around 8%. The composition of the magnetic garnet film with the minimum α ₈₃₀ was analyzed by EPMA (electron probe micro analysis). As a result, the composition of this film was Y _2.20 Bi _0.90 Ca _0.044 Fe _4.30 Ga _0.54 Pt _0.014 0 _{12 -} [delta] ₄ Ca divalent, Pt is tetravalent, Y, Bi and Ga is believed to be present in the trivalent. In addition, it is considered that Fe ²⁺ and Fe ⁴⁺ do not exist in the film having such a high resistivity, and it is considered that all Fe ³⁺ exists. Therefore, the oxygen vacancies δ ₄ required for charge compensation of the entire film are estimated to be δ ₄ = 0.015.

That is, the effect of adding Ca ²⁺ is as follows. When not adding Ca ²⁺ is, Fe ²⁺ is generated due to the presence of Pt ⁴⁺ and oxygen vacancies, therefore becomes n-type, resistivity ρ becomes smaller, the light because of the light absorption by the Fe ²⁺ The absorption coefficient α ₈₃₀ is expected to increase (Journal of Applied Physics).
hysics) Vol.41 P1211 (1970)). Then, an amount corresponding Fe ²⁺ of Ca ²⁺ that has entered in the film is reduced by the addition of Ca ^2+, low efficiency ρ increases, the light absorption coefficient alpha ₈₃₀ will decrease.
When this Ca ²⁺ enters the film to compensate for Pt ⁴⁺ and oxygen vacancies, the generation of Fe ²⁺ is suppressed, so the light absorption coefficient α
₈₃₀ is the minimum. However, when Ca ²⁺ is added excessively, Fe ⁴⁺ is generated, which causes the electrical resistivity ρ to decrease again and α ₈₃₀ to increase. Then, in this Example 1, if R ₆ = 8 ± 1%, then at this time,
Ca ²⁺ in the membrane is centered on 0.044 / molecular formula, that is,
± 13% centered on the minimum value of light absorption at λ = 830 nm
Can be kept within the range of.

Example 2 A Bi-substituted magnetic garnet film was grown on a Sm ₃ Gd ₅ O ₁₂ substrate by LPE. This LPE is To the melt of the same composition as described in the previous example. In this case, the R ₆ should be adjusted to 6.1% and 7.6%, respectively.
Magnetic garnet films were prepared by LPE after adding CO ₃ . The film thickness of each of these magnetic garnet films per one surface of the substrate was 4.9 μm when CaCO ₃ was not added, and 40 to 50 μm when CaCO ₃ was added, by the same measurement method as in Example 1. The electrical resistivity ρ was small when CaCO ₃ was not added, and showed n-type by the Seebeck effect measurement.
As shown in the measurement result of the electrical resistivity ρ in FIG.
The value of ρ increased with the addition of CaCO ₃ and exhibited p-type.
Further, the light absorption coefficient α _{830 at} the wavelength λ = 830 nm is
As shown in the figure, a minimum was shown at R ₆ = 6.1%. Incidentally, R
The α _{830 at 6} = 0 has not been measured due to the low richness. According to FIGS. 3 and 4, where R 6 ₌ 6.1% than a little small, charge compensation composition analysis result of the R _{6 =} 6.1% of EPMA considerably closer to _{the, Y 2.18 Bi 0.96 Ca 0.034 Fe} 4.80 Pt It became _0.021 0 _12- δ. Since this film is p-type, it is considered that Fe ⁴⁺ is present, but the amount thereof is considered to be extremely small, so the value of oxygen vacancy δ ₄ is estimated to be about 0.006.

Comparing this Example 2 with Example 1, Ga ₂ O ₃ was contained in the melt.
Oxygen vacancy δ ₄ changes depending on whether or not there is, and therefore it is difficult to predetermine the amount of CaCO ₃ required for charge compensation. However, both Pt ₄₊ and oxygen vacant seats,
Since Fe ₂₊ is generated, the charge can be compensated and the absorption can be reduced by adding an appropriate amount of CaCO ₃ .

Thus, the light absorption coefficient α ₈₃₀ can be lowered by adding Ca ²⁺ . That is, according to the present invention, Bi ₂ O
_Since LPE is grown with the single flux of ₃ ,
Unlike the case of using the conventional PbO flux described at the beginning, the divalent ion Pb ²⁺ cannot be unintentionally incorporated into the film, so that, for example, as in the above-described embodiment, Ca _{When 2+} ions are not added, n-type conduction is always caused by generation of Fe ₂₊ , and light absorption is high, but Ca ²⁺ can suppress generation of Fe ₂₊ .

In the above-mentioned example, when only Ca ²⁺ is added as the divalent ion, that is, M ^II is omitted in the above formula (1) (δ ₂
= 0), is a case of adding only Ca ₂₊ of M ^I, reliably Ca ²⁺ of M ²⁺ as a divalent ^{ion, Sr 2+, Ba 2+, M} II of Be
Generation of Fe ²⁺ can be suppressed and the light absorption coefficient α ₈₁₀ can be reduced by adding at least one of ²⁺ and Mg ²⁺ . In this case, Be ²⁺ , Mg ²⁺ (that is, M ^II ) substitutes for Fe and is incorporated into the film, and Ca ²⁺ , Sr ²⁺ , Ba ²⁺ substitutes for Y and is incorporated. However, the effect of suppressing the generation of Fe ²⁺ is the same.

In addition, the above-mentioned phenomenon can be expected to have the same effect by adding Ca ²⁺ even when other trivalent Al is used instead of Ga substituting Fe. In this case, since the segregation coefficient of Ca ²⁺ generally changes depending on the composition of the melt, the Ca ²⁺ amount that gives the minimum absorption coefficient is considered to be different from that in Example 1, but the Ca ²⁺ amount It was confirmed that the minimum value is always obtained by the selection, and that a remarkable decrease in light absorption can be obtained by adding ± 15% Ca ²⁺ before and after the Ca ²⁺ amount giving this minimum value.

〔The invention's effect〕

As described above, according to the present invention, a Bi-substituted magnetic garnet having a small optical absorption in the 0.8 μm wavelength band is obtained by solving the problems of Pt due to incorporation from a crucible and Fe ²⁺ due to oxygen vacancies. Therefore, by using this as a Faraday rotation element of an optical isolator, for example, when a semiconductor laser in the wavelength band of 0.8 μm is used, the return light blocks this and a stable operation is performed in the semiconductor laser. Since it can have a high transmittance, that is, a low light loss, the recording / recording of various information on an optical disk, a magneto-optical disk, etc.
It can be used for a reproducing light source system and has a great practical advantage.

[Brief description of drawings]

1, 2 and 3 and 4 are measurement curve diagrams of the resistivity ρ and the light absorption coefficient α used in the explanation of the present invention, and FIG. 5 can be applied to the Bi-substituted magnetic garnet according to the present invention. It is a block diagram of an optical isolator. (1) is a Faraday rotator, (2) is a polarizer, (3) is an analyzer, (4) is a magnet, (5) is a light source, and (6) is a surface to be irradiated with light.

 ─────────────────────────────────────────────────── --- Continuation of the front page (72) Inventor Toshiro Yamada 6-735 Kita-Shinagawa, Shinagawa-ku, Tokyo Sony Corporation (56) References JP-A-56-80106 (JP, A) JP-A-SHO 57-167608 (JP, A) JP-A-60-261051 (JP, A)

Claims (1)

[Claims] 1. A _{Y3 -x- δ1} Bi _x M ^I _δ1 Fe _{5-y- δ2-δ3} M ^II _δ2 M ^{III is} _prepared by liquid phase epitaxial growth using a melt consisting of Bi ₂ O ₃ and a magnetic garnet constituent element only. _y Pt
_δ3 O _{12- δ4} The above x is selected to be 0.5x2.0, the above y is selected to be 0y2, and the above δ ₁ + δ ₂ is 0.
± 1 around the value where the light absorption in the 8 μm wavelength band is minimal
A method for producing a bismuth-substituted magnetic garnet, which comprises obtaining a bismuth-substituted magnetic garnet selected in a range of 5%.