JP7450353B2 - Magnetite thin film and magnetic tunnel junction device - Google Patents
Magnetite thin film and magnetic tunnel junction device Download PDFInfo
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- SZVJSHCCFOBDDC-UHFFFAOYSA-N iron(II,III) oxide Inorganic materials O=[Fe]O[Fe]O[Fe]=O SZVJSHCCFOBDDC-UHFFFAOYSA-N 0.000 title claims description 59
- 239000010409 thin film Substances 0.000 title description 41
- 230000005291 magnetic effect Effects 0.000 title description 19
- 239000000758 substrate Substances 0.000 claims description 26
- 239000013078 crystal Substances 0.000 claims description 18
- 230000004888 barrier function Effects 0.000 claims description 9
- 239000000203 mixture Substances 0.000 claims description 8
- 239000012212 insulator Substances 0.000 claims description 6
- 230000005415 magnetization Effects 0.000 description 29
- 239000010408 film Substances 0.000 description 14
- 230000000052 comparative effect Effects 0.000 description 13
- 229910002367 SrTiO Inorganic materials 0.000 description 9
- 238000001228 spectrum Methods 0.000 description 8
- 239000002184 metal Substances 0.000 description 5
- 229910052751 metal Inorganic materials 0.000 description 5
- 230000005294 ferromagnetic effect Effects 0.000 description 4
- 239000007789 gas Substances 0.000 description 4
- 238000004519 manufacturing process Methods 0.000 description 4
- 229910020068 MgAl Inorganic materials 0.000 description 2
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 2
- 239000001301 oxygen Substances 0.000 description 2
- 229910052760 oxygen Inorganic materials 0.000 description 2
- 229910018072 Al 2 O 3 Inorganic materials 0.000 description 1
- 238000004813 Moessbauer spectroscopy Methods 0.000 description 1
- 238000003917 TEM image Methods 0.000 description 1
- 238000002441 X-ray diffraction Methods 0.000 description 1
- 229910001566 austenite Inorganic materials 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 238000009792 diffusion process Methods 0.000 description 1
- 238000011156 evaluation Methods 0.000 description 1
- 238000000731 high angular annular dark-field scanning transmission electron microscopy Methods 0.000 description 1
- 238000002017 high-resolution X-ray diffraction Methods 0.000 description 1
- 230000006698 induction Effects 0.000 description 1
- 238000002347 injection Methods 0.000 description 1
- 239000007924 injection Substances 0.000 description 1
- UQSXHKLRYXJYBZ-UHFFFAOYSA-N iron oxide Inorganic materials [Fe]=O UQSXHKLRYXJYBZ-UHFFFAOYSA-N 0.000 description 1
- 238000001755 magnetron sputter deposition Methods 0.000 description 1
- 150000002739 metals Chemical class 0.000 description 1
- 238000000034 method Methods 0.000 description 1
- 230000010287 polarization Effects 0.000 description 1
- 238000005245 sintering Methods 0.000 description 1
- 230000007704 transition Effects 0.000 description 1
- 229910000859 α-Fe Inorganic materials 0.000 description 1
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Description
本発明は、垂直磁化膜を構成するマグネタイト薄膜およびこれを用いた磁気トンネル接合素子に関する。 The present invention relates to a magnetite thin film constituting a perpendicularly magnetized film and a magnetic tunnel junction element using the same.
本出願人により、絶縁体バリア層の両側を、室温以上のキュリー点を有するハーフメタル強磁性酸化物層が挟みこむ構造および面内磁化反転を特徴とする強磁性トンネル接合素子が提案されている（特許文献１参照）。 The present applicant has proposed a ferromagnetic tunnel junction element characterized by a structure in which an insulating barrier layer is sandwiched on both sides by half-metal ferromagnetic oxide layers having a Curie point above room temperature, and in-plane magnetization reversal. (See Patent Document 1).
上記強磁性トンネル接合素子は、外部磁場での磁化反転によるスイッチングを原理とした面内型の第一世代ＭＲＡＭに対応したものであり、ＳＴＴ－ＭＲＡＭなど現状の電流による磁化反転（スピン注入）を原理とした高記憶容量の第三世代垂直磁化型ＭＲＡＭに対応させるためには、ハーフメタル強磁性酸化物層に反磁界エネルギー以上の強い垂直磁気異方性を付与させ垂直磁化層とする必要がある。 The above-mentioned ferromagnetic tunnel junction device is compatible with the first generation in-plane MRAM, which uses the principle of switching by magnetization reversal using an external magnetic field, and is compatible with the current STT-MRAM, which uses magnetization reversal (spin injection) by current. In order to be compatible with the third generation perpendicular magnetization type MRAM with high storage capacity based on the principle, it is necessary to give the half-metal ferromagnetic oxide layer a perpendicular magnetic anisotropy stronger than the demagnetizing field energy to form a perpendicular magnetization layer. be.
しかし、マグネタイトは高キュリー点（８５０Ｋ）を有し、高温相がハーフメタル特性など興味深い電子物性を示すが、立方晶のため反磁界エネルギー以上の強い一軸磁気異方性は得られない。もし整合歪みなどで異方性を制御し垂直磁化膜が得られれば、垂直磁化型ＭＲＡＭなど各種デバイス応用への展開も期待できる。 However, although magnetite has a high Curie point (850 K) and its high-temperature phase exhibits interesting electronic properties such as half-metal properties, it cannot obtain strong uniaxial magnetic anisotropy exceeding demagnetizing field energy because of its cubic crystal structure. If a perpendicularly magnetized film can be obtained by controlling the anisotropy using alignment strain, etc., it can be expected to be applied to various devices such as perpendicularly magnetized MRAM.
そこで、本発明は、垂直磁気異方性の向上を図りうるマグネタイト薄膜およびこれを用いた垂直磁化型磁気トンネル接合素子を提供することを目的とする。 SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a magnetite thin film capable of improving perpendicular magnetic anisotropy and a perpendicular magnetization type magnetic tunnel junction element using the same.
本発明のマグネタイト薄膜は、（１１１）単結晶基板の上に（１１１）配向を有するエピタキシャル層として形成され、厚さ２～５００ｎｍであり、かつ、組成式Ｆｅ3-δ1Ｏ４（２．７×１０
-3 ≦δ１≦０．０１）で表わされることを特徴とする。
The magnetite thin film of the present invention is formed as an epitaxial layer having a (111) orientation on a (111) single crystal substrate, has a thickness of 2 to 500 nm, and has a composition formula of Fe 3-δ1 O 4 ( 2.7 ×10 −3 ≦δ1≦0.01).
本発明の磁気トンネル接合素子は、（１１１）単結晶基板の上に（１１１）配向を有し、組成式Ｆｅ3-δ1Ｏ4（２．７×１０－３≦δ１≦０．０１）で表わされる厚さ２～５００ｎｍのエピタキシャル層として形成された第１のマグネタイト層と、前記第１のマグネタイト層の上に形成された厚さ０．５～２ｎｍのエピタキシャル絶縁体バリア層と、前記エピタキシャル絶縁体バリア層の上に（１１１）配向を有し、組成式Ｆｅ3-δ2Ｏ4（２．７×１０－３≦δ２≦０．０１）で表わされる厚さ２～５００ｎｍのエピタキシャル層として形成された第２のマグネタイト層とを備えていることを特徴とする。 The magnetic tunnel junction device of the present invention has a (111) orientation on a (111) single crystal substrate, and has a compositional formula of Fe 3-δ1 O 4 (2.7×10 −3 ≦δ1≦0.01). a first magnetite layer formed as an epitaxial layer with a thickness of 2 to 500 nm; an epitaxial insulator barrier layer with a thickness of 0.5 to 2 nm formed on the first magnetite layer; As an epitaxial layer having a (111) orientation on an insulating barrier layer and having a thickness of 2 to 500 nm and having a composition formula of Fe 3-δ2 O 4 (2.7×10 −3 ≦δ2≦0.01). A second magnetite layer is formed.
本発明のマグネタイト薄膜は、垂直磁気異方性の増大が図られているために垂直磁化膜として機能しうる。本発明の磁気トンネル接合素子は、一対のマグネタイト層が垂直磁化膜として機能するため、電流によって磁化反転を行う高記憶容量の第三世代垂直磁化型ＭＲＡＭに対応することが可能である。またマグネタイトはスピン分極率１００％のハーフメタルであるため理論的には無限大のＭＲ比（磁気抵抗変化）が期待できるため、高記憶容量ＭＲＡＭに要求される高いＭＲ比にも対応可能である。 The magnetite thin film of the present invention has increased perpendicular magnetic anisotropy and can function as a perpendicularly magnetized film. Since the pair of magnetite layers functions as a perpendicular magnetization film, the magnetic tunnel junction element of the present invention can be used in a third generation perpendicular magnetization type MRAM with a high storage capacity that performs magnetization reversal using an electric current. Furthermore, since magnetite is a half metal with a spin polarization rate of 100%, it can theoretically be expected to have an infinite MR ratio (magnetoresistance change), so it can also support the high MR ratio required for high storage capacity MRAM. .
一般的に酸化物の電子状態は酸素組成に敏感であることが知られており、特にマグネタイトはその固有のＶｅｒｗｅｙ転移がストイキオメトリーからのわずかなずれで転移点が低温側にシフトし消失してしまうため、ハーフメタルなど電子物性の応用には、ストイキオメトリーからの組成ずれである空孔パラメータδ（Ｆｅ3-δＯ4）を十分小さく保つことが重要である。 It is generally known that the electronic state of oxides is sensitive to oxygen composition, and in magnetite in particular, the inherent Verwey transition shifts to the lower temperature side and disappears with a slight deviation from stoichiometry. Therefore, for applications in electronic properties such as half metals, it is important to keep the vacancy parameter δ (Fe 3 - δ O 4 ), which is the compositional deviation from stoichiometry, sufficiently small.
図１に示されている本発明の一実施形態としての磁気トンネル接合素子は、基板１の上に形成された第１のマグネタイト層１１と、第１のマグネタイト層１１の上に形成された絶縁体バリア層２０と、絶縁体バリア層２０の上に形成された第２のマグネタイト層１２と、を備えている。 The magnetic tunnel junction element as an embodiment of the present invention shown in FIG. The structure includes a body barrier layer 20 and a second magnetite layer 12 formed on the insulator barrier layer 20.
基板１は、ＳｒＴｉＯ3（１１１）単結晶基板、ＭｇＯ（１１１）単結晶基板、ＭｇＡｌ2Ｏ4（１１１）単結晶基板またはＳｉ（１１１）単結晶基板など、表面が（１１１）配向を有する単結晶基板により構成されている。第１のマグネタイト層１１は、本発明の一実施形態としてのマグネタイト薄膜であり、基体１の表面に垂直な方向または厚さ方向に（１１１）配向を有し、組成式Ｆｅ3-δ1Ｏ4（０≦δ１≦０．０１）で表わされる厚さ２～５００ｎｍのエピタキシャル層として形成されている。エピタキシャル絶縁体バリア層２０は、厚さ０．５～２ｎｍのＭｇＯ（１１１）、γ－Ｆｅ2Ｏ3（１１１）、α－Ｆｅ2Ｏ3（０００１）、ＳｒＴｉＯ3（１１１）、ＭｇＡｌ2Ｏ4（１１１）、α－Ａｌ2Ｏ3（０００１）により構成されている。第２のマグネタイト層１２は、第１のマグネタイト層１１と同様に、厚さ方向に（１１１）配向を有し、組成式Ｆｅ3-δ2Ｏ4（０≦δ２≦０．０１）で表わされる厚さ２～５００ｎｍのエピタキシャル層として形成されている。 The substrate 1 is a single crystal substrate whose surface has a (111) orientation, such as a SrTiO 3 (111) single crystal substrate, an MgO (111) single crystal substrate, a MgAl 2 O 4 (111) single crystal substrate, or a Si (111) single crystal substrate. It is composed of a crystal substrate. The first magnetite layer 11 is a magnetite thin film as an embodiment of the present invention, has a (111) orientation in the direction perpendicular to the surface of the substrate 1 or in the thickness direction, and has a composition formula of Fe 3-δ1 O 4 It is formed as an epitaxial layer with a thickness of 2 to 500 nm expressed by (0≦δ1≦0.01). The epitaxial insulator barrier layer 20 is made of MgO (111), γ-Fe 2 O 3 (111), α-Fe 2 O 3 (0001), SrTiO 3 (111), MgAl 2 O with a thickness of 0.5 to 2 nm. 4 (111) and α-Al 2 O 3 (0001). Like the first magnetite layer 11, the second magnetite layer 12 has a (111) orientation in the thickness direction, and is represented by the composition formula Fe 3-δ2 O 4 (0≦δ2≦0.01). It is formed as an epitaxial layer with a thickness of 2 to 500 nm.
（実施例） (Example)
（実施例１）
ＳｒＴｉＯ3（１１１）単結晶基板が加熱され、３００～９００℃（例えば６００℃）まで昇温された状態のＳｒＴｉＯ3（１１１）単結晶基板の上に、ＦｅＯ焼結ターゲットが用いられ、かつ、ＡｒガスおよびＯ2ガスの混合ガスが導入される反応性ＲＦマグネトロンスパッタ法により、厚さ４３３ｎｍの実施例１のマグネタイト薄膜が作製された。この際、混合ガスの酸素量は流量比で１～２％に制御された。
(Example 1)
A FeO sintering target is used on the SrTiO 3 (111) single crystal substrate in a state where the SrTiO 3 (111) single crystal substrate is heated and the temperature is raised to 300 to 900° C. (for example, 600° C.), and The magnetite thin film of Example 1 having a thickness of 433 nm was produced by a reactive RF magnetron sputtering method in which a mixed gas of Ar gas and O 2 gas was introduced. At this time, the amount of oxygen in the mixed gas was controlled at a flow rate ratio of 1 to 2%.
（実施例２）
実施例１と同様の作製条件にしたがって、厚さ８７ｎｍの実施例２のマグネタイト薄膜が作製された。
(Example 2)
According to the same manufacturing conditions as in Example 1, a magnetite thin film of Example 2 having a thickness of 87 nm was manufactured.
（実施例３）
実施例１と同様の作製条件にしたがって、厚さ１７ｎｍの実施例３のマグネタイト薄膜が作製された。
(Example 3)
According to the same manufacturing conditions as in Example 1, a magnetite thin film of Example 3 having a thickness of 17 nm was manufactured.
（比較例） (Comparative example)
（比較例１）
基板としてＭｇＯ（１００）単結晶基板が用いられたほか、実施例１と同様の作製条件にしたがって、厚さ１０６ｎｍの比較例１のマグネタイト薄膜が作製された。
(Comparative example 1)
In addition to using an MgO (100) single crystal substrate as a substrate, a magnetite thin film of Comparative Example 1 having a thickness of 106 nm was manufactured according to the same manufacturing conditions as Example 1.
（比較例２）
基板としてＳｒＴｉＯ3（１００）単結晶基板が用いられたほか、実施例１と同様の作製条件にしたがって、厚さ７９ｎｍの比較例２のマグネタイト薄膜が作製された。
(Comparative example 2)
In addition to using a SrTiO 3 (100) single crystal substrate as a substrate, a magnetite thin film of Comparative Example 2 having a thickness of 79 nm was fabricated under the same fabrication conditions as in Example 1.
（評価）
図２Ａ～図２Ｃのそれぞれには、実施例１～３のそれぞれのマグネタイト薄膜を対象として、Ｇｅ（２２０）モノクロメータを用いて得られた高分解能ＸＲＤスペクトルが示されている。図２Ａ～図２Ｃから、実施例１～３のそれぞれのマグネタイト薄膜が、ＳｒＴｉＯ3（１１１）単結晶基板の上に、厚さ方向に（１１１）配向したマグネタイト薄膜（Ｆｅ3Ｏ4薄膜）であること、および、膜厚が大きいほどＦｅ3Ｏ4（１１１）に相当するＸＲＤピークが高いことがわかる。図３には、実施例１のマグネタイト膜とＳｒＴｉＯ3（１１１）単結晶基板の界面付近の高分解能断面ＴＥＭ（ＨＡＡＤＦ－ＳＴＥＭ）像が示されている。マグネタイト膜の原子配列が単結晶基板と同程度に明瞭に観察され、良好な結晶性を保ちつつエピタキシャル成長していることが確認される。
(evaluation)
Each of FIGS. 2A to 2C shows high-resolution XRD spectra obtained using a Ge (220) monochromator for each of the magnetite thin films of Examples 1 to 3. From FIGS. 2A to 2C, each of the magnetite thin films of Examples 1 to 3 is a magnetite thin film (Fe 3 O 4 thin film) with (111) orientation in the thickness direction on a SrTiO 3 (111) single crystal substrate. It can be seen that the larger the film thickness, the higher the XRD peak corresponding to Fe 3 O 4 (111). FIG. 3 shows a high-resolution cross-sectional TEM (HAADF-STEM) image of the vicinity of the interface between the magnetite film of Example 1 and the SrTiO 3 (111) single crystal substrate. The atomic arrangement of the magnetite film was observed as clearly as that of a single crystal substrate, confirming that it was grown epitaxially while maintaining good crystallinity.
図４Ａおよび図４Ｂのそれぞれには、比較例１および比較例２のそれぞれのマグネタイト薄膜のＸＲＤスペクトルが示されている。ＭｇＯ（１００）およびＳｒＴｉＯ3（１００）基板ピークの脇にマグネタイトＦｅ3Ｏ4（４００）ピークが観測され、マグネタイト膜が（１００）配向していることが確認できる。 4A and 4B each show the XRD spectra of the magnetite thin films of Comparative Example 1 and Comparative Example 2, respectively. A magnetite Fe 3 O 4 (400) peak is observed beside the MgO (100) and SrTiO 3 (100) substrate peaks, confirming that the magnetite film is (100) oriented.
図５Ａ～図５Ｃのそれぞれには、実施例１～３のそれぞれのマグネタイト薄膜を対象として、ＶＳＭ（振動試料型磁力計）を用いて得られた膜面垂直方向に磁界印加した磁化曲線（実線）および膜面内方向に印加した磁化曲線（点線）が示されている。垂直方向のヒステリシスループが閉じる５ｋＯｅ以上の磁界において、垂直方向の磁化が面内方向よりも大きくなっており、また保磁力も垂直方向の方が大きいため、垂直磁気異方性が誘起され垂直磁化膜となっていることが確認できる。図５Ａ～図５Ｃから、実施例１のマグネタイト薄膜の垂直方向の飽和磁化が５．９ｋＧであること、実施例２のマグネタイト薄膜の垂直方向の飽和磁化が６．１ｋＧであること、実施例３のマグネタイト薄膜の垂直方向の飽和磁化が５．９ｋＧであること、および、マグネタイト薄膜の膜厚によって垂直方向の飽和磁化がさほど差がないことがわかる。図５Ａ～図５Ｃから、実施例１のマグネタイト薄膜の垂直方向の保磁力が０．５２ｋＯｅであること、実施例２のマグネタイト薄膜の垂直方向の飽和磁化が１．０６ｋＯｅであること、実施例３のマグネタイト薄膜の垂直方向の飽和磁化が０．６５ｋＯｅであること、および、膜厚が２～５００ｎｍの範囲に含まれている８７ｎｍである実施例２のマグネタイト薄膜の垂直方向の保磁力が比較的大きいことがわかる。 5A to 5C show magnetization curves (solid lines) obtained by applying a magnetic field in the direction perpendicular to the film surface obtained using a VSM (vibrating sample magnetometer) for each of the magnetite thin films of Examples 1 to 3. ) and the magnetization curve (dotted line) applied in the in-plane direction of the film. In a magnetic field of 5 kOe or more, where the vertical hysteresis loop closes, the magnetization in the vertical direction is larger than that in the in-plane direction, and the coercive force is also larger in the vertical direction, so perpendicular magnetic anisotropy is induced and perpendicular magnetization occurs. It can be confirmed that it is a film. From FIGS. 5A to 5C, it can be seen that the perpendicular saturation magnetization of the magnetite thin film of Example 1 is 5.9 kG, that the perpendicular saturation magnetization of the magnetite thin film of Example 2 is 6.1 kG, and that Example 3 It can be seen that the perpendicular saturation magnetization of the magnetite thin film is 5.9 kG, and that the perpendicular saturation magnetization does not differ much depending on the thickness of the magnetite thin film. From FIGS. 5A to 5C, it can be seen that the perpendicular coercive force of the magnetite thin film of Example 1 is 0.52 kOe, that the perpendicular saturation magnetization of the magnetite thin film of Example 2 is 1.06 kOe, and that Example 3 The saturation magnetization in the perpendicular direction of the magnetite thin film of Example 2 is 0.65 kOe, and the perpendicular coercive force of the magnetite thin film of Example 2 whose film thickness is 87 nm, which is included in the range of 2 to 500 nm, is relatively You can see that it's big.
図６Ａおよび図６Ｂのそれぞれには、比較例１および比較例２のそれぞれのマグネタイト薄膜について、膜面垂直方向（実線）および膜面内方向（点線）のそれぞれに磁界印加した磁化曲線が示されている。各磁界での磁化は、実施例１～３とは異なり面内方向の方が大きくなっており、膜面内方向が磁化容易軸の面内磁化膜であることが確認できる。ＭｇＯ（１００）基板の場合には基板からの拡散が、ＳｒＴｉＯ3（１００）基板の場合には別配向相の混在が原因となって、（１１１）配向の実施例１～３よりも磁化値が低下している。また、磁気異方性が（１１１）配向よりも小さいため、保磁力も低くなっている。 6A and 6B each show the magnetization curves of the magnetite thin films of Comparative Example 1 and Comparative Example 2 when a magnetic field was applied in the direction perpendicular to the film surface (solid line) and in the in-plane direction (dotted line), respectively. ing. Unlike Examples 1 to 3, the magnetization in each magnetic field is larger in the in-plane direction, and it can be confirmed that this is an in-plane magnetized film whose axis of easy magnetization is in the in-plane direction. In the case of the MgO (100) substrate, diffusion from the substrate is the cause, and in the case of the SrTiO 3 (100) substrate, the magnetization value is higher than that of Examples 1 to 3 with the (111) orientation due to the mixture of other orientation phases. is decreasing. Furthermore, since the magnetic anisotropy is smaller than that of the (111) orientation, the coercive force is also lower.
図７には、実施例２のマグネタイト薄膜を対象として、ＣＥＭＳ（内部転換電子メスバウアー分光）にしたがって得られたＣＥＭＳスペクトルが、ＡサイトおよびＢサイトの分解成分とともに示されている。３：ｘ：１：１：ｘ：３のピーク強度比ｘから得られる磁気モーメントの方向は、ガンマ線入射方向の膜面垂直方向を基準とした角度をθとしてｘの間にｘ＝４ｓｉｎ2θ／（１＋ｃｏｓ2θ）の関係が成立するため、これから求めた角度θは、無磁界中の残留磁化状態の測定であるにも関わらず薄膜の厚さ方向に対して３０o以内であり、およそ５０°以上の（１００）配向の場合と比較し垂直に近く、磁化曲線（図５Ｂ参照）に対応した結果となった。反磁界エネルギー２πＭ2＝１．５×１０6ｅｒｇ／ｃｍ3以上の垂直異方性の誘起が予想される。無反跳分率の影響を考慮し、Ａ、Ｂサイト成分の積分強度比から求まるＦｅ3-dＯ4の空孔パラメータδは２．７×１０－３であり、１０-3オーダーで十分小さく、ストイキオメトリーに近いＦｅ／Ｏ組成であることが確認された。 FIG. 7 shows a CEMS spectrum obtained according to CEMS (internal conversion electron Mössbauer spectroscopy) for the magnetite thin film of Example 2, together with decomposed components at the A site and the B site. The direction of the magnetic moment obtained from the peak intensity ratio x of 3:x:1:1:x:3 is given by x = 4 sin 2 θ between /(1+cos 2 θ) holds, so the angle θ calculated from this is within 30 degrees in the thickness direction of the thin film, and is approximately 50 degrees Compared to the case of a (100) orientation of 0° or more, the result was closer to perpendicular and corresponded to the magnetization curve (see FIG. 5B). Induction of perpendicular anisotropy is expected with demagnetizing field energy of 2πM 2 =1.5×10 6 erg/cm 3 or more. Considering the influence of the no-recoil fraction, the vacancy parameter δ of Fe 3-d O 4 determined from the integrated intensity ratio of A and B site components is 2.7 × 10 -3 , and the order of 10 -3 is sufficient. It was confirmed that the Fe/O composition was small and close to stoichiometry.
１‥基板、１１‥第１のマグネタイト層（マグネタイト薄膜）、１２‥第２のマグネタイト層、２０‥絶縁体バリア層。
1. Substrate, 11.. First magnetite layer (magnetite thin film), 12.. Second magnetite layer, 20.. Insulator barrier layer.
Claims (2)
前記第１のマグネタイト層の上に形成された厚さ０．５～２ｎｍのエピタキシャル絶縁体バリア層と、
前記エピタキシャル絶縁体バリア層の上に（１１１）配向を有し、組成式Ｆｅ3-δ2Ｏ4（２．７×１０-3≦δ２≦０．０１）で表わされる厚さ２～５００ｎｍのエピタキシャル層として形成された第２のマグネタイト層と、を備えていることを特徴とする磁気トンネル接合素子。
An epitaxial layer with a thickness of 2 to 500 nm having a (111) orientation on a (111) single crystal substrate and expressed by the compositional formula Fe 3-δ1 O 4 (2.7×10 -3 ≦δ1≦0.01) a first magnetite layer formed as a layer;
an epitaxial insulator barrier layer with a thickness of 0.5 to 2 nm formed on the first magnetite layer;
On the epitaxial insulator barrier layer, an epitaxial layer having a (111) orientation and having a thickness of 2 to 500 nm and having a composition formula of Fe 3-δ2 O 4 (2.7×10 -3 ≦δ2≦0.01) is formed. a second magnetite layer formed as a layer.
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