JP2009206376A - Magnetic material and magnetic memory using the same, and temperature sensor - Google Patents
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Abstract
Description
本発明は、磁気メモリ及び温度センサに好適に利用されうるε−Ｆｅ２Ｏ３系の磁性材料に関する。 The present invention relates to an ε-Fe 2 O 3 -based magnetic material that can be suitably used for a magnetic memory and a temperature sensor.
従来、ナノオーダー粒子でありながら、室温条件下で２０ｋＯｅという巨大な保磁力を発現する磁性材料として、ε−Ｆｅ２Ｏ３の結晶構造体が知られている（例えば、非特許文献１、非特許文献２参照）。 Conventionally, a crystal structure of ε-Fe 2 O 3 has been known as a magnetic material that expresses a huge coercive force of 20 kOe under room temperature conditions while being nano-order particles (for example, Non-Patent Document 1, Non-Patent Document 1, Patent Document 2).
また、巨大な温度ヒステリシス幅を有する材料は、温度に対する磁化量の応答性を利用することにより、磁気メモリや、温度センサなどの材料として応用できる実用的に有意義な材料と考えられている。
ε−Ｆｅ２Ｏ３の結晶構造体は、上述の非特許文献でも開示されているように、巨大な保磁力を有し、またスピン再配列現象を示すため、上述の磁気メモリや温度センサに用いることのできる可能性は考えられていた。しかし、該用途へ利用を図るためには、所望の温度ヒステリシス挙動を示すとともに、必要とされる温度範囲もしくは磁化に対して応答性を有するように調整できることが必要になるが、温度ヒステリシス挙動を調整するための手法に関しては、未だ知見は得られていなかった。 Since the crystal structure of ε-Fe 2 O 3 has a huge coercive force and exhibits a spin rearrangement phenomenon as disclosed in the above-mentioned non-patent document, the above-described magnetic memory and temperature sensor are used. The possibilities that could be used were considered. However, in order to use it for the application, it is necessary to show a desired temperature hysteresis behavior and to be adjustable so as to be responsive to the required temperature range or magnetization. As for the method for adjustment, knowledge has not yet been obtained.
そこで本発明は、温度に対する優れた磁化量応答性を有したε−Ｆｅ２Ｏ３の結晶の構成ならびにかような構造体を主相とする磁性材料並びにそれを用いた磁気メモリ、及び温度センサを提供することを目的とする。 Accordingly, the present invention relates to a composition of ε-Fe 2 O 3 crystal having excellent magnetization response to temperature, a magnetic material having such a structure as a main phase, a magnetic memory using the same, and a temperature sensor. The purpose is to provide.
上記目的を達成するために、請求項１に係る発明は、一般式ε−Ｆｅ２Ｏ３を主相とし、ε−Ｆｅ２Ｏ３結晶のＦｅサイトの一部がＡで置換されたε−ＡｘＦｅ２−ｘＯ３の（０＜ｘ≦０．３０）結晶からなる磁性材料であって、合成時に形状制御剤として２価の金属を添加し、前記Ａを含有した前記ε−ＡｘＦｅ２−ｘＯ３の結晶粒子の平均体積を１００００ｎｍ３以上とし、温度ヒステリシス幅（ΔＴ）が１０Ｋ以上であることを特徴とする。 In order to achieve the above object, the invention according to claim 1 is an ε- in which a general formula ε-Fe 2 O 3 is a main phase and a part of Fe sites of ε-Fe 2 O 3 crystal is substituted with A. A magnetic material composed of (0 <x ≦ 0.30) crystals of A x Fe 2−x O 3 , wherein a divalent metal is added as a shape control agent during synthesis, and the ε-A containing the A The average volume of crystal grains of x Fe 2−x O 3 is 10,000 nm 3 or more, and the temperature hysteresis width (ΔT) is 10K or more.
また、請求項２に係る発明は、前記Ａが、Ｉｎ，Ｓｃ，Ｙ，Ｃｅ，Ｐｒ，Ｎｄ，Ｓｍ，Ｅｕ，Ｇｄ，Ｔｂ，Ｄｙ，Ｈｏ，Ｅｒ，Ｔｍ，Ｙｂ，Ｌｕ，Ｒｕ，Ｒｈ，Ｂｉ，Ａｌ，及びＧａのうちから選択される１種の元素であることを特徴とする。 The invention according to claim 2 is characterized in that A is In, Sc, Y, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Ru, Rh, It is one element selected from Bi, Al, and Ga.
また、請求項３に係る発明は、前記形状制御剤がＢａ，Ｓｒ，及びＣａのうちから選択される１種の元素であることを特徴とする。 The invention according to claim 3 is characterized in that the shape control agent is one element selected from Ba, Sr, and Ca.
また、請求項４に係る発明は、支持体と、前記支持体上に磁性材料を固定してなる磁性層とを備えた磁気メモリであって、該磁性材料として、請求項１ないし３のいずれか一項に記載の粒子を使用することを特徴とする。 According to a fourth aspect of the present invention, there is provided a magnetic memory including a support and a magnetic layer formed by fixing a magnetic material on the support, wherein the magnetic material is any one of the first to third aspects. The particles according to claim 1 are used.
また、請求項５に係る発明は、磁性材料と、前記磁性材料の磁化の強さを測定する測定手段とを備えた温度センサであって、該磁性材料として、請求項１ないし３のいずれか一項に記載の粒子を使用することを特徴とする。 The invention according to claim 5 is a temperature sensor comprising a magnetic material and a measuring means for measuring the magnetization intensity of the magnetic material, wherein the magnetic material is any one of claims 1 to 3. The particles according to one item are used.
本発明に記載の磁性材料は、温度ヒステリシス幅が大きく、すなわち温度応答性に優れるため、磁気メモリあるいは温度センサに好適に利用できる。 Since the magnetic material described in the present invention has a large temperature hysteresis width, that is, excellent temperature response, it can be suitably used for a magnetic memory or a temperature sensor.
以下図面を参照して、本発明の好適な実施形態について説明する。 Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.
（１）磁性材料の概要
本発明は、一般式ε−Ｆｅ２Ｏ３を主相とし、ε−Ｆｅ２Ｏ３結晶のＦｅサイトの一部が少なくとも一種の金属イオンＡで置換されたε−ＡｘＦｅ２−ｘＯ３の（０＜ｘ≦０．３０）と表記されるイプシロン型の磁性酸化鉄粒子からなる磁性材料であって、該結晶粒子の平均体積が１００００ｎｍ３以上とすることにより、温度ヒステリシス幅を増大させることができることを見出した。ここで温度ヒステリシス幅とは、所定の外部磁場において、温度変化させた場合の磁性材料の磁化量の変化を逐次測定し、測定した当該磁化量を温度に対応させてプロットすることにより描いた磁化−温度曲線から算出できるもので、加熱したときのスピン再配列温度（Ｔ１／２↑）と冷却したときのスピン再配列温度（Ｔ１／２↓）との差（ΔＴ：Ｔ１／２↑−Ｔ１／２↓）をいう。尚、スピン再配列温度は、スピン再配列の前後における磁化の最大値と最小値からそれらの中間値を求め、磁化がその中間値をとる温度で定義した。また、ここで平均体積とは、ＴＥＭ（透過型電子顕微鏡）写真からランダムに選んだ２００個の粒子について、粒子の長軸長と短軸長とを計測するとともに形状を観察し、楕円状粒子については回転楕円体形状であると近似して体積を算出し、ロッド状粒子については円柱形状であると近似して体積を算出した値とした。回転楕円体近似の場合は、短軸を回転楕円体における直径とし、円柱近似の場合は、短軸を円の直径、長軸を円柱の高さとした。
(1) Outline of Magnetic Material The present invention has a general formula ε-Fe 2 O 3 as a main phase, and ε- in which a part of Fe site of ε-Fe 2 O 3 crystal is substituted with at least one metal ion A. A magnetic material composed of epsilon-type magnetic iron oxide particles expressed as (0 <x ≦ 0.30) of A x Fe 2−x O 3 , and the average volume of the crystal particles is 10000 nm 3 or more Thus, it has been found that the temperature hysteresis width can be increased. Here, the temperature hysteresis width is the magnetization drawn by measuring the change in the magnetization amount of the magnetic material when the temperature is changed in a predetermined external magnetic field, and plotting the measured magnetization amount corresponding to the temperature. -It can be calculated from the temperature curve, and the difference (ΔT: T 1/2 ) between the spin rearrangement temperature (T 1/2 ↑ ) when heated and the spin rearrangement temperature (T 1/2 ↓ ) when cooled ↑ -T 1/2 ↓ ). The spin rearrangement temperature was defined as the temperature at which the intermediate value was obtained from the maximum value and the minimum value of the magnetization before and after the spin rearrangement, and the magnetization took the intermediate value. In addition, the average volume here refers to an elliptical particle which is obtained by measuring the long axis length and short axis length of 200 particles randomly selected from a TEM (transmission electron microscope) photograph and observing the shape. For, the volume was calculated by approximating that it was a spheroid shape, and the volume was calculated by approximating that it was a cylindrical shape for rod-shaped particles. In the case of spheroid approximation, the minor axis is the diameter of the spheroid, and in the case of cylinder approximation, the minor axis is the diameter of the circle and the major axis is the height of the cylinder.
磁性材料は、上記温度ヒステリシス幅が大きいと、メモリやセンサなどの応用に有効であることが知られている。本発明者らは、ε−Ｆｅ２Ｏ３のＦｅサイトが他種の金属イオンＡにより置換されており、かつ該結晶粒子の平均体積を大きくすると、上記温度ヒステリシス幅を増加することができることを見出すとともに、粒子の有する温度ヒステリシス幅を任意に調整できうることを見いだし、本願発明を完成させた。具体的には、置換可能な金属イオンを例示すれば、Ｉｎ３＋，Ｓｃ３＋，Ｙ３＋，Ｃｅ３＋，Ｐｒ３＋，Ｎｄ３＋，Ｓｍ３＋，Ｅｕ３＋，Ｇｄ３＋，Ｔｂ３＋，Ｄｙ３＋，Ｈｏ３＋，Ｅｒ３＋，Ｔｍ３＋，Ｙｂ３＋，Ｌｕ３＋，Ｒｕ３＋，Ｒｈ３＋，Ｂｉ３＋，Ａｌ３＋及びＧａ３＋のうちから選択される少なくとも１種のイオンを挙げることができる。また、かようなイオンにより置換することで、温度により変化する磁化の変化量の絶対値が大きいものが得られることがわかり、後述するような温度センサや磁気メモリに好適に適用し得ることもわかった。さらに、上記したイオンにより置換することで、スピン再配列温度を上昇させることができるので、後述するような温度センサや磁気メモリに好適に適用し得ることもわかった。 Magnetic materials are known to be effective for applications such as memories and sensors when the temperature hysteresis width is large. The present inventors have found that the temperature hysteresis width can be increased when the Fe site of ε-Fe 2 O 3 is substituted with another type of metal ion A and the average volume of the crystal particles is increased. As a result, it was found that the temperature hysteresis width of the particles can be arbitrarily adjusted, and the present invention was completed. Specifically, examples of substitutable metal ions include In 3+ , Sc 3+ , Y 3+ , Ce 3+ , Pr 3+ , Nd 3+ , Sm 3+ , Eu 3+ , Gd 3+ , Tb 3+ , Dy 3+ , Ho 3+ And at least one ion selected from Er 3+ , Tm 3+ , Yb 3+ , Lu 3+ , Ru 3+ , Rh 3+ , Bi 3+ , Al 3+, and Ga 3+ . In addition, it can be seen that by replacing with such ions, it is possible to obtain a magnet having a large absolute value of the amount of change of magnetization that changes with temperature, and it can be suitably applied to a temperature sensor and a magnetic memory as described later. all right. Furthermore, since the spin rearrangement temperature can be increased by substitution with the above-described ions, it has been found that the present invention can be suitably applied to a temperature sensor and a magnetic memory as described later.
さらに、本発明者らは、後述する逆ミセル法とゾル−ゲル法の組み合わせによりε−ＡｘＦｅ２−ｘＯ３を合成する際、形状制御剤の濃度を増加させることにより、平均体積を増加させることができる、という知見を得た。具体的には、形状制御剤としては、Ｂａ２＋，Ｓｒ２＋，及びＣａ２＋のうちから選択される少なくとも１種の２価のイオンを挙げることができる。尚、この形状制御剤は、結晶粒子の平均体積の増加に寄与するものの、合成により得られる磁性材料には残留しないと考えられる。 Furthermore, when synthesizing ε-A x Fe 2-x O 3 by a combination of the reverse micelle method and the sol-gel method described later, the inventors increased the concentration of the shape control agent to increase the average volume. The knowledge that it can be increased was obtained. Specifically, examples of the shape control agent include at least one divalent ion selected from Ba 2+ , Sr 2+ , and Ca 2+ . In addition, although this shape control agent contributes to the increase in the average volume of a crystal grain, it is thought that it does not remain in the magnetic material obtained by a synthesis | combination.
温度ヒステリシス幅が増加する詳細なメカニズムについては検討中であるが、以下のように考えられる。すなわち、ε−Ｆｅ２Ｏ３の温度変化に伴う磁化量の変化を測定すると、５００Ｋ近傍で磁気相転移を起こしたのち、２００Ｋ以下で磁化が減少する相転移(スピン再配列相転移)が観測される。このときの温度（相転移温度［Ｔｐ］）はＦｅ３＋より原子半径が大きい、例えばＩｎ３＋の置換量を増加させれば、高温側にシフトすることが分かっている。一方、上記相転移は、構造相転移を伴う一次相転移であることにより、温度ヒステリシスが発現するものと考えられる。また、粒子径が大きくなること、すなわち平均体積が大きくなることにより、温度ヒステリシス幅が増大すると考えられる。このように添加する形状制御剤、例えばＢａ２＋の濃度を増加させることにより、温度ヒステリシス幅を増加させることができる。 Although a detailed mechanism for increasing the temperature hysteresis width is under study, it is considered as follows. That is, when the change in the magnetization amount accompanying the temperature change of ε-Fe 2 O 3 is measured, a phase transition (spin rearrangement phase transition) in which the magnetization decreases at 200 K or less after the magnetic phase transition is observed near 500 K is observed. Is done. It has been found that the temperature (phase transition temperature [T p ]) at this time has an atomic radius larger than that of Fe 3+ , for example, if the substitution amount of In 3+ is increased, the temperature shifts to a higher temperature side. On the other hand, the phase transition is considered to exhibit temperature hysteresis due to the primary phase transition accompanied by the structural phase transition. Further, it is considered that the temperature hysteresis width increases as the particle diameter increases, that is, the average volume increases. The temperature hysteresis width can be increased by increasing the concentration of the added shape control agent, for example, Ba 2+ .
上述したように、温度ヒステリシス幅を増加させる効果は、結晶粒子の平均体積が１００００ｎｍ３以上であれば顕著に効果が得られる。結晶粒子の平均体積が１００００ｎｍ３未満では、あらわれる温度ヒステリシス幅は７Ｋ以下であり、大きな温度ヒステリシス幅は認めがたい。これに対し、結晶粒子の平均体積が１００００ｎｍ３以上になると、温度ヒステリシス幅は１４Ｋ以上となり、温度ヒステリシス幅の増加が認められる。 As described above, the effect of increasing the temperature hysteresis width, the average volume of the crystal grains is remarkably effect can be obtained if the 10000 nm 3 or more. The average volume of 10000nm less than 3 crystal grains, appears thermal hysteresis width is at 7K or less, large temperature hysteresis width hardly observed. In contrast, when the average volume of the crystal grains is 10000 nm 3 or more, the temperature hysteresis width becomes more 14K, an increase in the temperature hysteresis width is observed.
また、Ｂａ２＋濃度の、合成時におけるＦｅ３＋濃度とＡ濃度との和に対する比（［Ｂａ２＋］／（［Ｆｅ３＋］＋［Ａ］））が大きいほど、結晶粒子の平均体積を大きくすることができる。すなわち、［Ｂａ２＋］／（［Ｆｅ３＋］＋［Ａ］）が０．１以上、好ましくは０．２以上のとき、結晶粒子の平均体積を増加させる顕著な効果を奏し、好適な温度ヒステリシス幅を有するようになる。 Further, the Ba 2+ concentration, the ratio to the sum of Fe 3+ concentration and A concentration during synthesis ([Ba 2+] / ([ Fe 3+] + [A])) The larger, increasing the mean volume of the crystal grains be able to. That is, when [Ba 2+ ] / ([Fe 3+ ] + [A]) is 0.1 or more, preferably 0.2 or more, it has a remarkable effect of increasing the average volume of crystal grains, and suitable temperature hysteresis. Have a width.
また、上記した磁性材料は、磁気メモリに用いることができる。すなわち、支持体と、前記支持体上に磁性材料を固定してなる磁性層とを備える磁気メモリにおいて、前記磁性材料に、一般式ε−Ｆｅ２Ｏ３を主相とし、ε−Ｆｅ２Ｏ３結晶のＦｅサイトの一部がＡで置換されたε−ＡｘＦｅ２−ｘＯ３の（０＜ｘ≦０．３０）結晶からなり、合成時に形状制御剤を添加することにより、前記Ａを含有した前記ε−ＡｘＦｅ２−ｘＯ３の結晶粒子の平均体積を１００００ｎｍ３以上とした磁性材料を用いることで、前記磁性材料が双安定状態を示す領域、すなわち温度ヒステリシスを示す温度領域において磁性材料の状態を熱や光などで変化させることにより、前記磁性層に情報を記録することができる磁気メモリを得ることができる。 The magnetic material described above can be used for a magnetic memory. That is, in a magnetic memory including a support and a magnetic layer formed by fixing a magnetic material on the support, the magnetic material has a general formula ε-Fe 2 O 3 as a main phase and ε-Fe 2 O. The crystal is composed of ε-A x Fe 2−x O 3 (0 <x ≦ 0.30) crystal in which part of the Fe site of the three crystals is substituted with A, and by adding a shape control agent during synthesis, By using a magnetic material in which the average volume of the ε-A x Fe 2−x O 3 crystal particles containing A is 10,000 nm 3 or more, the magnetic material exhibits a bistable state, that is, exhibits temperature hysteresis. A magnetic memory capable of recording information in the magnetic layer can be obtained by changing the state of the magnetic material with heat or light in the temperature range.
また、かような磁性材料は、温度センサにも用いることができる。すなわち、磁性材料と、前記磁性材料の磁化の強さを測定する測定手段とを備える温度センサにおいて、前記磁性材料に、一般式ε−Ｆｅ２Ｏ３を主相とし、ε−Ｆｅ２Ｏ３結晶のＦｅサイトの一部がＡで置換されたε−ＡｘＦｅ２−ｘＯ３の（０＜ｘ≦０．３０）結晶からなり、合成時に形状制御剤を添加することにより、前記Ａを含有した前記ε−ＡｘＦｅ２−ｘＯ３の結晶粒子の平均体積を１００００ｎｍ３以上とした磁性材料が得られ、前記磁性材料が有するスピン再配列温度における磁気特性の温度依存性を利用して、前記スピン再配列温度を境とした温度変化を検知する温度センサを得ることができる。
（２）磁性材料の製造方法
Such a magnetic material can also be used for a temperature sensor. That is, in a temperature sensor including a magnetic material and a measuring unit that measures the magnetization strength of the magnetic material, the magnetic material has a general formula ε-Fe 2 O 3 as a main phase and ε-Fe 2 O 3. A part of the Fe site of the crystal is composed of (0 <x ≦ 0.30) crystal of ε-A x Fe 2-x O 3 substituted with A, and by adding a shape control agent during synthesis, the A A magnetic material having an average volume of crystal grains of ε-A x Fe 2-x O 3 containing 10000 nm 3 or more is obtained, and the temperature dependence of the magnetic properties at the spin rearrangement temperature of the magnetic material is utilized Thus, a temperature sensor that detects a temperature change with the spin rearrangement temperature as a boundary can be obtained.
(2) Manufacturing method of magnetic material
次に上記した磁性材料の製造方法について説明する。磁性材料は、例えば、以下のように逆ミセル法及びゾルーゲル法を組み合わせて製造することができる。なお、１００ｎｍ以下のシリカ被覆水酸化鉄系化合物粒子が合成できるのであれば、その合成方法は特に限定されない。 Next, a method for manufacturing the above magnetic material will be described. The magnetic material can be produced, for example, by combining the reverse micelle method and the sol-gel method as follows. In addition, the synthesis method is not particularly limited as long as silica-coated iron hydroxide compound particles having a size of 100 nm or less can be synthesized.
具体的には、先ず始めにｎ−オクタンを油相とする溶液の水相に界面活性剤（例えば臭化セチルトリメチルアンモニウム）を溶解することによりミセル溶液を作製する。 Specifically, first, a micelle solution is prepared by dissolving a surfactant (for example, cetyltrimethylammonium bromide) in an aqueous phase of a solution containing n-octane as an oil phase.
次いで、このミセル溶液に、硝酸鉄（ＩＩＩ）と硝酸インジウム（ＩＩＩ）とを溶解すると共に、これに形状制御剤として硝酸バリウムを加える（こうすることでＢａ２＋が反応系内に含まれることになる）ことにより原料溶液を作製する。 Next, iron (III) nitrate and indium (III) nitrate are dissolved in this micelle solution, and barium nitrate is added to the micelle as a shape control agent (by this, Ba 2+ is contained in the reaction system). To prepare a raw material solution.
また、原料溶液の作製とは別に、ｎ−オクタンを油相とする溶液の水相に界面活性剤（例えば臭化セチルトリメチルアンモニウム）を溶解したミセル溶液に、アンモニア水溶液等の中和剤を混合して中和剤溶液を作製する。 Separately from the preparation of the raw material solution, a neutralizing agent such as an aqueous ammonia solution is mixed with a micelle solution in which a surfactant (for example, cetyltrimethylammonium bromide) is dissolved in an aqueous phase of a solution containing n-octane as an oil phase. To produce a neutralizer solution.
次いで、逆ミセル法によって、原料溶液と中和剤溶液とを攪拌混合することにより混合溶液を作製し、これにより混合溶液内において水酸化鉄系化合物粒子の沈殿反応を進行させる。 Next, the mixed solution is prepared by stirring and mixing the raw material solution and the neutralizing agent solution by the reverse micelle method, thereby causing the precipitation reaction of iron hydroxide compound particles to proceed in the mixed solution.
次いで、混合溶液に対して、シラン化合物としてテトラエチルオルトシランの溶液を適宜添加することで、ゾル−ゲル法により水酸化鉄系化合物粒子の表面にシリカによる被覆を施す。このような反応は混合溶液内で行われ、混合溶液内では、ナノオーダーの微細な水酸化鉄系化合物粒子の表面において加水分解が起こり、表面がシリカで被覆された水酸化鉄系化合物粒子（以下、これをシリカ被覆水酸化鉄系化合物粒子と呼ぶ）を作製できる。 Next, the surface of the iron hydroxide compound particles is coated with silica by a sol-gel method by appropriately adding a solution of tetraethylorthosilane as a silane compound to the mixed solution. Such a reaction is carried out in a mixed solution. In the mixed solution, hydrolysis occurs on the surface of the nano-order fine iron hydroxide compound particles, and the iron hydroxide compound particles (the surface is coated with silica) ( Hereinafter, this is referred to as silica-coated iron hydroxide compound particles).
次いで、この製造方法では、図２に示すように、シリカ被覆水酸化鉄系化合物粒子を作製（ステップＳＰ１）した後、シリカ被覆水酸化鉄系化合物粒子を混合溶液から分離して、大気雰囲気下において所定の温度（７００〜１３００℃の範囲内）で焼成処理する（ステップＳＰ２）。この焼成処理により、シリカ被覆水酸化鉄系化合物粒子はシリカ殻内部での酸化反応により、微細なε−Ｆｅ２Ｏ３粒子が生成される。 Next, in this manufacturing method, as shown in FIG. 2, after producing silica-coated iron hydroxide compound particles (step SP1), the silica-coated iron hydroxide compound particles are separated from the mixed solution, And firing at a predetermined temperature (in the range of 700 to 1300 ° C.) (step SP2). By this baking treatment, fine ε-Fe 2 O 3 particles are produced from the silica-coated iron hydroxide compound particles by an oxidation reaction inside the silica shell.
こうしたほぼ単一の形態を有する酸化鉄を選択的に得られるのは酸化反応の際に、水酸化鉄系化合物粒子がシリカにより被覆されていることに起因すると考えられる。また、シリカによる被覆は、粒子同士の焼結を防止する作用を果たす。また、本発明者らの検討によれば、当該物質の温度ヒステリシスの挙動については、ε−Ｆｅ２Ｏ３相に若干の異相（たとえばα−Ｆｅ２Ｏ３相など）が含まれていても温度ヒステリシス挙動には影響が生じないことは確認できている It is considered that the iron oxide having such a substantially single form can be selectively obtained because the iron hydroxide compound particles are coated with silica during the oxidation reaction. In addition, the coating with silica serves to prevent sintering of the particles. Further, according to the study by the present inventors, regarding the behavior of the temperature hysteresis of the substance, even if the ε-Fe 2 O 3 phase contains some foreign phase (for example, α-Fe 2 O 3 phase). It has been confirmed that there is no effect on temperature hysteresis behavior.
上述したように製造工程において原料溶液を作製する際に、ミセル溶液にＩｎ３＋を適量溶解させることにより、ε−Ｆｅ２Ｏ３と同じ結晶構造を有しながら、Ｆｅ３＋サイトの一部が置換されたε−ＩｎｘＦｅ２−ｘＯ３粒子の単相粒子を生成できる。 As described above, when preparing the raw material solution in the manufacturing process, by dissolving an appropriate amount of In 3+ in the micelle solution, a part of the Fe 3+ site is replaced while having the same crystal structure as ε-Fe 2 O 3. Single-phase particles of the produced ε-In x Fe 2 -x O 3 particles can be produced.
次いで、上述した製造工程によって作製したε−ＩｎｘＦｅ２−ｘＯ３粒子からなる熱処理粉体を、ＮａＯＨ水溶液中に添加して所定温度で所定時間攪拌し、これにより得られた沈殿物を回収して洗浄することで、ε−ＩｎｘＦｅ２−ｘＯ３粒子の表面を被覆しているシリカを除去する。次いで、遠心分離装置により遠心分離処理を行う（ステップＳＰ３）。 Next, the heat-treated powder composed of ε-In x Fe 2-x O 3 particles produced by the above-described production process is added to an aqueous NaOH solution and stirred at a predetermined temperature for a predetermined time, and the resulting precipitate is obtained. by washing recovered and, to remove the silica coating the surface of the ε-in x Fe 2-x O 3 particles. Next, a centrifugal separation process is performed by a centrifugal separator (step SP3).
そして、このような回収作業を所定回数（例えば２回）行うことにより（ステップＳＰ４）、ε−ＩｎｘＦｅ２−ｘＯ３粒子の表面を被覆しているシリカを除去する。次いで、ろ過・水洗し、乾燥する。（ステップＳＰ５）。 Then, by performing such a collection operation a predetermined number of times (for example, twice) (step SP4), the silica covering the surface of the ε-In x Fe 2-x O 3 particles is removed. Then, it is filtered, washed with water and dried. (Step SP5).
このようにして、結晶粒子の平均体積が１００００ｎｍ３以上となる磁性材料を作製できる。 In this way, a magnetic material having an average volume of crystal grains of 10,000 nm 3 or more can be produced.
そして、このような磁性材料を用いて成膜対象に薄膜を形成することにより、磁気メモリや温度センサとして機能する磁性材料を形成することができる（ステップＳＰ６）。 A magnetic material that functions as a magnetic memory or a temperature sensor can be formed by forming a thin film on the film formation target using such a magnetic material (step SP6).
本発明は、本実施形態に限定されるものではなく、本発明の要旨の範囲内で種々の変形実施が可能である。例えば、上記した実施形態では、Ｉｎ３＋を含有したε−ＩｎｘＦｅ２−ｘＯ３粒子の合成について、前駆体となる硝酸鉄と硝酸インジウムの超微粒子を逆ミセル法で作製する場合について説明したが、数１００ｎｍ以下の同様の前駆体が作製できれば本発明は逆ミセル法に限らない。また、前記前駆体の超微粒子をゾル−ゲル法にてシリカコーティングした場合について説明したが、本発明はこれに限らず、前駆体にシリカ等の耐熱性を有する皮膜でコーティングできれば足り、例えばアルミナやジルコニアなどでコーティングすることとしてもよい。また、ＡとしてＩｎ３＋を用いた場合について説明したが、本発明はこれに限らず、Ｓｃ３＋，Ｙ３＋，Ｃｅ３＋，Ｐｒ３＋，Ｎｄ３＋，Ｓｍ３＋，Ｅｕ３＋，Ｇｄ３＋，Ｔｂ３＋，Ｄｙ３＋，Ｈｏ３＋，Ｅｒ３＋，Ｔｍ３＋，Ｙｂ３＋，Ｌｕ３＋，Ｒｕ３＋，Ｒｈ３＋，Ｂｉ３＋，Ａｌ３＋及びＧａ３＋のうちから選択される少なくとも１種のイオンを用いることができる。
（３）実施例
ここでは、Ｆｅサイトの一部を置換する元素ＡとしてＩｎを検討した例に関して記載する。
The present invention is not limited to this embodiment, and various modifications can be made within the scope of the gist of the present invention. For example, in the above-described embodiment, the case of producing ultrafine particles of iron nitrate and indium nitrate as precursors by the reverse micelle method is described for the synthesis of ε-In x Fe 2 -xO 3 particles containing In 3+. However, the present invention is not limited to the reverse micelle method as long as a similar precursor of several hundred nm or less can be produced. In addition, the case where the ultrafine particles of the precursor are silica-coated by a sol-gel method has been described. However, the present invention is not limited to this, and it is sufficient if the precursor can be coated with a heat-resistant film such as silica. It may be coated with zirconia or the like. Further, although the case where In 3+ is used as A has been described, the present invention is not limited to this, and Sc 3+ , Y 3+ , Ce 3+ , Pr 3+ , Nd 3+ , Sm 3+ , Eu 3+ , Gd 3+ , Tb 3+ , At least one ion selected from Dy 3+ , Ho 3+ , Er 3+ , Tm 3+ , Yb 3+ , Lu 3+ , Ru 3+ , Rh 3+ , Bi 3+ , Al 3+ and Ga 3+ can be used.
(3) Example Here, it describes about the example which examined In as the element A which substitutes a part of Fe site.
上記した製造方法により、Ｆｅ３＋サイトの一部を前記Ｉｎ３＋と置換して実施例１〜４を合成した。また、比較例として、Ｉｎ３＋を置換していないε−Ｆｅ２Ｏ３試料（比較例１〜４）、及び、形状制御剤としてのＢａ２＋を添加せずにＦｅ３＋イオンサイトの一部を前記Ｉｎ３＋と置換した試料（比較例５，６）を合成した。表１〜表３に合成した各試料の内訳を示す。
ここで、表中、Ｉｎ仕込み量（ｘｍｉｘ）とは、ミセル溶液に溶解したＩｎ３＋の添加量である。また、Ｂａ２＋の濃度は、合成時におけるＦｅ３＋濃度とＩｎ３＋濃度との和に対する濃度の比で表した。Ｉｎ置換量（ｘｏｂｓ）とは、ＩＣＰ−ＭＳ（Ｉｎｄｕｃｔｉｖｅｌｙ Ｃｏｕｐｌｅｄ Ｐｌａｓｍａ Ｍａｓｓ Ｓｐｅｃｔｒｏｍｅｔｅｒ：誘導結合プラズマ質量分析計）により、作製した磁性材料中に含まれるＩｎ３＋の量を測定した結果である。 Here, in the table, the amount of In charged (xmix) is the amount of In 3+ dissolved in the micelle solution. The concentration of Ba 2+ was expressed as a ratio of the concentration to the sum of the Fe 3+ concentration and the In 3+ concentration at the time of synthesis. The amount of In substitution (xobs) is the result of measuring the amount of In 3+ contained in the produced magnetic material by ICP-MS (Inductively Coupled Plasma Mass Spectrometer).
また、Ｘ線回折結晶構造解析の結果を図２〜図４に示す。図２〜図４から明らかなように、全ての試料において主相はイプシロン相であることが分かった。また、一部のサンプルは、数％から１０％程度のアルファ相を含んでいた。表１及び図２に示すようにＩｎ３＋を置換していないε−Ｆｅ２Ｏ３試料を４個（比較例１〜４）、表２及び図３に示すようにＩｎの置換量が０．０４４以下であるε−ＩｎｘＦｅ２−ｘＯ３試料（比較例５、実施例１，２）、及び、表３及び図４に示すようにＩｎ３＋の置換量が０．０７９以下であるε−ＩｎｘＦｅ２−ｘＯ３試料（比較例６、実施例３，４）を得た。 The results of X-ray diffraction crystal structure analysis are shown in FIGS. As apparent from FIGS. 2 to 4, the main phase was found to be the epsilon phase in all the samples. Some samples contained an alpha phase of several percent to 10%. As shown in Table 1 and FIG. 2, four ε-Fe 2 O 3 samples in which In 3+ is not substituted (Comparative Examples 1 to 4), and as shown in Table 2 and FIG. Ε-In x Fe 2-x O 3 sample (Comparative Example 5, Examples 1 and 2) which is 044 or less, and the amount of substitution of In 3+ is 0.079 or less as shown in Table 3 and FIG. An ε-In x Fe 2 -x O 3 sample (Comparative Example 6, Examples 3 and 4) was obtained.
このように得られた各試料のＴＥＭ（透過型電子顕微鏡）写真画像（以下、ＴＥＭ像という）、前記ＴＥＭ像から算出した結晶粒子の平均体積、及び温度ヒステリシスループを図５〜図７に示す。図５〜図７に示すＴＥＭ像から、Ｂａ２＋を添加しなかった比較例１，５，６は、結晶粒子が楕円状ナノ微粒子であるのに対し、Ｂａ２＋を添加した比較例２〜４、実施例１〜４は、結晶粒子がロッド状ナノ微粒子となったことが確認できた。このことから、Ｉｎ３＋を置換した量の多少に関わらず、合成時に添加したＢａ２＋の濃度を上げることにより、結晶粒子の粒径が増加していくことが分かった。この結果をまとめたのが、図８である。すなわち、本図から明らかなように、Ｉｎ３＋を置換した量に関わらず、Ｂａ２＋の濃度［Ｂａ２＋］／（［Ｆｅ３＋］＋［Ｉｎ３＋］）が０．２以上のとき、結晶粒子の平均体積が増加することが確認できた。尚、平均体積は、ＴＥＭ像写真からランダムに選んだ２００個の粒子について、粒子の長軸長と短軸長とを計測するとともに形状を観察し、楕円状粒子については回転楕円体形状であると近似して体積を算出し、ロッド状粒子については円柱形状であると近似して体積を算出した。回転楕円体近似の場合は、短軸を回転楕円体における直径とし、円柱近似の場合は、短軸を円の直径、長軸を円柱の高さとした。 5 to 7 show TEM (transmission electron microscope) photograph images (hereinafter referred to as TEM images), average volumes of crystal grains calculated from the TEM images, and temperature hysteresis loops of the samples thus obtained. . From the TEM images shown in FIG. 5 to FIG. 7, in Comparative Examples 1, 5 and 6 in which Ba 2+ was not added, the crystal particles were elliptical nano fine particles, whereas Comparative Examples 2 to 4 in which Ba 2+ was added. In Examples 1 to 4, it was confirmed that the crystal particles became rod-shaped nanoparticles. From this, it was found that, regardless of the amount of In 3+ substituted, the grain size of the crystal particles increases by increasing the concentration of Ba 2+ added during the synthesis. FIG. 8 summarizes the results. That is, as is clear from the figure, regardless of the amount obtained by replacing an In 3+, concentrations of Ba 2+ [Ba 2+] / ( [Fe 3+] + [In 3+]) when is 0.2 or more, the crystal grains It was confirmed that the average volume of the increased. The average volume of the 200 particles randomly selected from the TEM image photograph is measured for the major axis length and minor axis length of the particle and the shape is observed, and the elliptical particle is a spheroid shape. And the volume was calculated by approximating that the rod-shaped particles were cylindrical. In the case of spheroid approximation, the minor axis is the diameter of the spheroid, and in the case of cylinder approximation, the minor axis is the diameter of the circle and the major axis is the height of the cylinder.
また、温度ヒステリシスループは、比較例１〜４については外部磁場１０００Ｏｅ（７９．６ｋＡ／ｍ）、温度変化±３Ｋ／ｍｉｎで測定し、その他の試料（比較例５，６、及び実施例１〜４）については外部磁場５０００Ｏｅ（３９８．１ｋＡ／ｍ）、温度変化±１Ｋ／ｍｉｎで磁化−温度変化を測定し、その結果から算出した。磁化測定の結果、Ｉｎ３＋を置換した実施例１〜４及び比較例５，６では、２００Ｋ以下において磁化の大幅な減少を伴う相転移(スピン再配列相転移)が観測され、この転移に伴って温度ヒステリシス現象が確認できた。Ｉｎ置換量の狙い値が０．０４３の試料（実施例１，２、比較例５）と、Ｉｎ置換量の狙い値が０．０７５の試料（実施例３，４、比較例６）とにおいて、温度ヒステリシス幅は、結晶粒子の粒径が増加すると大きくなることがそれぞれ確認でき、最大で４７Ｋとなった（実施例２）。この結果をまとめたのが、図９である。すなわち、本図から明らかなように、Ｉｎ３＋を置換した試料において、結晶粒子の平均体積が増加すると、温度ヒステリシス幅を増大させることができ、特に、平均体積が１００００ｎｍ３以上であると温度ヒステリシス幅（ΔＴ）が１４Ｋ以上となり、温度ヒステリシス幅が顕著に増加することが確認できた（表４）。尚、表中Ｔ１／２↓は、冷却したときのスピン再配列温度、Ｔ１／２↑は加熱したときのスピン再配列温度であり、スピン再配列温度は、スピン再配列の前後における磁化の最大値と最小値からそれらの中間値を求め、磁化がその中間値をとる温度で定義した。ＴＰは、冷却したときのスピン再配列温度及び加熱したときのスピン再配列温度の平均値である。
さらに、表５に示すように、Ｉｎ３＋の置換量が増加することに伴い、相転移温度（ＴＰ）が上昇することが分かった。
以上より、ε−Ｆｅ２Ｏ３と同じ結晶構造を有し、Ｆｅ３＋サイトの一部がＩｎ３＋で置換されたε−ＩｎｘＦｅ２−ｘＯ３の（０＜ｘ≦０．３０）結晶からなる磁性材料にあっては、形状制御剤としてＢａ２＋を添加することにより、結晶粒子の粒径を大きくすることができ、これにより、合成して得た前記ε−ＩｎｘＦｅ２−ｘＯ３からなる磁性材料の温度ヒステリシス幅を増加できることが分かった。 As described above, ε-In x Fe 2-x O 3 having the same crystal structure as ε-Fe 2 O 3 and part of Fe 3+ sites substituted with In 3+ (0 <x ≦ 0.30) In a magnetic material made of crystals, by adding Ba 2+ as a shape control agent, the particle size of the crystal particles can be increased, whereby the ε-In x Fe 2− obtained by synthesis is obtained. It was found to be increased the temperature hysteresis width of the magnetic material consisting x O 3.
Claims (5)
該磁性材料として、請求項１ないし３のいずれか一項に記載の粒子を使用する、磁気メモリ。 A support, and a magnetic layer formed by fixing a magnetic material on the support,
A magnetic memory using the particles according to any one of claims 1 to 3 as the magnetic material.
該磁性材料として、請求項１ないし３のいずれか一項に記載の粒子を使用する、温度センサ。 A magnetic material; and a measuring means for measuring the magnetization strength of the magnetic material,
The temperature sensor which uses the particle | grains as described in any one of Claim 1 thru | or 3 as this magnetic material.
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