Patent ID: 12222588

DESCRIPTION OF EMBODIMENTS

(Configuration of Nanogranular Structure Material)

A nanogranular structure material (secondary nanogranular structure material) as one embodiment of the present invention schematically shown inFIG.1is a nanogranular structure material in which metal oxide nanoparticles11are dispersed in a matrix12consisting of a fluorine compound. For example, a nanogranular structure material has a composition represented by L-M-F—O, where L is one or more elements selected from Fe, Co, and Ni, M is at least one or more elements selected from Li, Be, Mg, Al, Si, Ca, Sr, Ba, Bi, and rare earth elements, F is fluorine, and O is oxygen.

The atomic ratio of L is within the range of 0.03 to 0.50, the atomic ratio of M is within the range of 0.03 to 0.30, the atomic ratio of F is within the range of 0.06 to 0.65, and the atomic ratio of O is within the range of 0.04 to 0.50. The total atomic ratio of L and O is within the range of 0.07 to 0.88. The total atomic ratio of M and F is within the range of 0.12 to 0.93. The metal oxide nanoparticles11have a composition mainly represented by L-O. The matrix12consists mainly of a fluorine compound having a composition represented by M-F. The total atomic ratio of L, M, F, and O amounts to one.

The light transmittance of the nanogranular structure material for light in the wavelength region of 1000 to 1675 nm is within the range of 40% or more at an optical path length of 1 μm.

The Faraday rotation angle of the nanogranular structure material for light in the wavelength region of 500 to 680 and 720 to 1000 nm in the visible light region is within 0.1 deg/μm or more as an absolute value.

The Faraday rotation angle of the nanogranular structure material for light in the wavelength region of 1350 to 1650 nm, which is the optical communication wavelength band, is within 0.1 deg/μm as absolute value.

(Method for Producing Nanogranular Structure Material)

A method for producing a nanogranular structure material having the configuration shown inFIG.1will be described. First, a primary nanogranular structure material is produced (STEP 1). The primary nanogranular structure material is produced by, for example, a sputtering method or an RF sputtering method (for example, refer to Patent Literature 1). Sputtering is performed by using a composite target in which chips of a fluorine compound are evenly arranged on a disk of a magnetic metal or the alloy thereof, or using a target of a magnetic metal or the alloy thereof simultaneously with a target consisting of a fluorine compound. Ar gas is used for sputtering deposition. The film thickness of the nanogranular structure material is controlled by adjusting the deposition time, and the film is formed to a thickness of, for example, approximately 0.3 to 5 m. A substrate is indirectly water cooled or maintained at any temperature within the temperature range of 100 to 800° C. The sputtering pressure during deposition is controlled to be within the range of 1 to 60 mTorr. Sputtering power is controlled to be within the range of 50 to 350 W.

This produces a primary nanogranular structure material in which magnetic metal nanoparticles are dispersed in a matrix formed of a fluorine compound. For example, a primary nanogranular structure material has a composition represented by L-M-F, where L is one or more elements selected from Fe, Co, and Ni, M is at least one or more elements selected from Li, Be, Mg, Al, Si, Ca, Sr, Ba, Bi, and rare earth elements, and F is fluorine. The atomic ratio of M is within the range of 0.01 to 0.40, the atomic ratio of F is within the range of 0.02 to 0.70, and the total atomic ratio of M and F is within the range of 0.03 to 0.97. The primary nanogranular structure material has a nanogranular structure in which metal nanoparticles having the composition represented by L are uniformly distributed in a matrix formed of a fluoride having a composition represented by M-F.

The particle size of the metal nanoparticles is, for example, within the range of 1 to 50 nm or within the range of 1 to 20 nm. The particle size distribution of the metal nanoparticles (and thus the particle size distribution of the metal oxide nanoparticles11in the secondary nanogranular structure material) can be adjusted by changing the deposition conditions and/or the deposition composition.

The primary nanogranular structure material is heat-treated in an oxygen-containing atmosphere at a temperature range of 300 to 800° C. to produce a secondary nanogranular structure material (STEP 2).

Example and Comparative Examples

(Sample 1 (Comparative Example 1))

In Sample 1, Fe and Co were selected as L, Ba was selected as M, and a primary nanogranular structure material represented by Fe44Co32Ba13F11was produced as sample 1. The sample 1 is produced by, for example, a sputtering method or an RF sputtering method (for example, refer to Patent Literature 1). Sputtering is performed by using a composite target in which chips of a fluorine compound are evenly arranged on a disk of a magnetic metal or the alloy thereof, or using a target of a magnetic metal or the alloy thereof simultaneously with a target consisting of a fluorine compound. Ar gas is used for sputtering deposition. The film thickness of the nanogranular structure material is controlled by adjusting the deposition time, and the film is formed to a thickness of, for example, approximately 0.3 to 5 μm. A substrate is indirectly water cooled or maintained at any temperature within the temperature range of 100 to 800° C. The sputtering pressure during deposition is controlled to be within the range of 1 to 60 mTorr. Sputtering power is controlled to be within the range of 50 to 350 W.

(Sample 2 (Comparative Example 2))

As shown by the dashed line inFIG.2, the sample 1 was gradually heated from about 50° C. to about 600° C. over about 3 hr in a vacuum, heat-treated at about 600° C. for about 1 [hr], and then gradually cooled to about 80° C. over about 4 hr to produce sample 2. The composition of the sample 2 was represented by Fe44CO32Ba13F11.

(Sample 3 (Example))

In a mixed gas atmosphere of Ar gas and O2gas (the partial pressure of O2gas was about 1% of the mixed gas), the sample 1 was heat-treated in a temperature change manner as shown by the dashed line inFIG.2to produce sample 3 as a secondary nanogranular structure material having the composition represented by Fe23Co17Ba8F6O46. The pressure of the mixed gas of Ar gas and O2gas was controlled at about 30 mTorr as shown by the solid line inFIG.2.

The upper part ofFIG.3shows the XRD analysis result of the sample 1 (primary nanogranular structure material), and the lower part ofFIG.3shows the XRD analysis result of the sample 3 (secondary nanogranular structure material). It is found fromFIG.3that the peak derived from Fe and Co that constitute the metal nanoparticles present in the sample 1 does not exist in the sample 3, and instead there is a peak derived from CoFe2O4that constitutes the metal oxide nanoparticles. This means that the primary nanogranular structure material is heat-treated in an oxygen-containing atmosphere, whereby the metal nanoparticles contained in the primary nanogranular structure material were oxidized and changed to metal oxide (composite metal oxide) nanoparticles in the secondary nanogranular structure material.

It is found fromFIG.3that the height of the peak derived from BaF2constituting the matrix present in the sample 1 is lower in the sample 3. This means that the primary nanogranular structure material is heat-treated in an oxygen-containing atmosphere, whereby the matrix constituting the primary nanogranular structure material is deteriorated and changed into the matrix of the secondary nanogranular structure material.

InFIG.4, the wavelength dependence of the light transmittance (optical path length of 1 μm) of the sample 1 is shown by a dashed line, and the wavelength dependence of the light transmittance of the sample 3 is shown by a solid line. It is found fromFIG.4that with respect to light in the wavelength region of 1000 to 1675 nm for optical communication, the light transmittance of the sample 1 is 0.5 to 1.0% (optical path length of 1 μm), whereas the light transmittance of the sample 3 is 58 to 81% (optical path length of 1 μm), which is significantly higher than the sample 1.

FIG.5shows the wavelength dependence of the Faraday rotation angle θFof the sample 3 when the magnetic field applied to the sample 3 is 10 kOe. It is found fromFIG.5that the Faraday rotation angle θFof the sample 3 shows: a tendency to gradually increase as the wavelength increases from λ=400 nm; a tendency to gradually decrease after showing a maximum value of about 2.5 deg/μm at λ=about 530 nm; a tendency to gradually decrease after turning from a positive value to a negative value at λ=about 700 nm; a tendency to gradually increase after showing a minimum value of about −1.5 deg/μm at λ=about 750 to 800 nm; a tendency to gradually decrease after showing a maximum value of about 0 deg/μm at λ=about 1300 nm; a tendency to gradually increase after showing a minimum value of about −1.0 deg/μm at λ=about 1480 nm; and a tendency to gradually increase after turning from a negative value to a positive value at λ=about 1650 nm.

The absolute value of the Faraday rotation angle of the nanogranular structure material for light in the wavelength region of 500 to 680 and 720 to 1000 nm in the visible light region is within 0.1 deg/μm or more. In addition, the absolute value of the Faraday rotation angle of the nanogranular structure material for light in the wavelength region of 1350 to 1650 nm, which is the optical communication wavelength band, is within the range of 0.1 deg/μm or more.

Table 1 summarizes the heat treatment conditions for each of samples 1 to 3, the Faraday rotation angle, and the light transmittance at a wavelength λ=1550 nm with an optical path length of 1 μm. It may be noted that samples 4 to 11 shows in Table 1 are prepared by using the method described herein. As shown in Table 1, the nanogranular structure materials of samples 4 to 11 are represented by Fe8Co5Ba13F46O28, Fe17Co12Ca10Ba4F18O39, Fe10Co7Ba8Ca7Y5F23O40, Fe9Co8Al13Ba5F38O27, Fe14Co10Li3Mg12F25O36, Fe12Co10Ni5Be5Ba10F22O36, Fe16Co11Ba9Si3F23O39, and Fe19Co15Ba10Sr4Bi4F38O10, respectively. As discussed hereinabove, sample 3 is represented by Fe23Co17Ba8F6O46. Thus, for samples 3 to 11, the atomic ratio of L is within a range of 0.13 to 0.40, the atomic ratio of M is within a range of 0.08 to 0.20, the atomic ratio of F is within a range of 0.06 to 0.46, and the atomic ratio of O is within a range of 0.1 to 0.46. Further, for samples 3, 5, 6 and 9, the atomic ratio of L is within a range of 0.17 to 0.40, the atomic ratio of M is within a range of 0.08 to 0.20, the atomic ratio of F is within a range of 0.06 to 0.23, and the atomic ratio of O is within a range of 0.36 to 0.46.

TABLE 1Faraday rotationTransmittanceTreatment after depositionangle at 1550 nmat 1550 nmSample 1No (As Depo)4deg./μm0.9%Sample 2600° C. × 1 h (in vacuum)5.1deg./μm1%Sample 3600° C. × 1 h (Ar + 1%O (30 mTorr))−0.9deg./μm80%Sample 4Fe8Co5Ba13F46O28−0.13deg./μm80%Sample 5Fe17Co12Ca10Ba4F18O39−0.72deg./μm74%Sample 6Fe10Co7Ba8Ca7Y5F23O40−0.50deg./μm70%Sample 7Fe9Co8Al13Ba5F38O27−0.40deg./μm75%Sample 8Fe14Co10Li3Mg12F25O36−0.75deg./μm47%Sample 9Fe12Co10Ni5Be5Ba10F22O36−0.67deg./μm70%Sample 10Fe16Co11Ba9Si3F23O39−0.91deg./μm55%Sample 11Fe19Co15Ba10Sr4Bi4F38O10−1.0deg./μm41%
(Application)

Magneto-optical materials having the Faraday effect are often used in optical isolators. The nanogranular structure material according to the present invention is a thin film material with a thickness on the order of submicron, and has a large Faraday effect with a minute size. The use of the present material allows miniaturization and integration of optical isolators, and allows application to optical integrated circuits and the like.

REFERENCE SIGNS LIST

11: Metal oxide nanoparticles,12: Matrix