JP4669916B2 - Method for producing magnetic powder for magnetic recording - Google Patents
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本発明は,微粒子で高い磁気異方性を有した高記録密度記録に好適な磁性粉に関する。 The present invention relates to a magnetic powder suitable for high recording density recording having fine magnetic particles and high magnetic anisotropy.
近年,音声情報や映像情報のデジタル化,ハイバンド化に伴い,記録・保存すべき情報量は,増加の一途をたどっている。また情報量が多いが故に,それらの情報が失われたときの被害・損害も大きく,データのバックアップの重要性は情報社会を維持するために,今後も益々高まって行くものと考えられる。他方において,これらの情報を記録保存する装置や媒体に対するダウンサイジング化と大容量化の要求もますます高まっている。 In recent years, the amount of information to be recorded and stored has been steadily increasing along with the digitization and high banding of audio and video information. In addition, since the amount of information is large, the damage and loss when such information is lost is also great, and the importance of data backup is expected to increase in the future in order to maintain the information society. On the other hand, there is an increasing demand for downsizing and increasing the capacity of devices and media for recording and storing such information.
情報記録技術のなかで,磁気記録技術は,その不揮発性,高記録密度,書き込み・読み込み速度,記録容量あたりの価格の低さから,常に情報記録技術の中で中心的な立場にとり続けている。なかでも,磁性粒子を塗料化し,その磁性塗料をフィルムに塗布することにより作成される磁気テープや磁気ディスクは,他の媒体のものと比較して生産性が高く,特に磁気テープは巻き取ったその形状から疑似三次元の記録を行っているので記録量あたりコストはもっとも安く且つリムーバブル性にも優れるから,今後もデータバックアップ用として重要な媒体であり続けると考えられており,記録密度,信頼性,耐久性,低コスト性をより一層向上させることが市場より強く望まれている。 Among information recording technologies, magnetic recording technology has always been at the center of information recording technology due to its non-volatility, high recording density, writing / reading speed, and low price per recording capacity. . Above all, magnetic tapes and magnetic disks made by coating magnetic particles and applying the magnetic coating to the film are more productive than those of other media. Because the shape is recorded in pseudo three-dimensional form, the cost per recording amount is the lowest and the removable property is excellent, so it is considered to continue to be an important medium for data backup in the future. There is a strong demand from the market to further improve performance, durability, and low cost.
磁気記録媒体例えばハードディスク装置の記憶容量は,近年,年率60〜100%のペースで増加している。この原動力の一つに,磁気抵抗効果を示すMR(Magneto-Resistive) 素子を磁気ヘッドに応用したことがあり,この技術が磁気テープにも応用され,記録密度の改善がなされている。この磁気ヘッドを“MRヘッド”と言う。 In recent years, the storage capacity of magnetic recording media such as hard disk drives has been increasing at an annual rate of 60 to 100%. One of the driving forces is the application of an MR (Magneto-Resistive) element exhibiting a magnetoresistive effect to a magnetic head. This technology is also applied to a magnetic tape to improve the recording density. This magnetic head is referred to as an “MR head”.
従来の磁気誘導型ヘッドでは,高い再生出力を得るために,残留磁束密度×磁性層の厚さ(以下,Mr・t )の値が大きいことが必要であった。ところが,MRヘッドの素子は,感度が高く,必要以上に高いMrでは出力が飽和してしまって逆に感度が低下してしまうという現象が起きる。また,磁気記録では,Mr・t/Hcが小さいほど,媒体の単位体積あたりの磁性粒子が多いほど,ノイズが低減することがわかっている。MRヘッドとしては最近よく使用されているものでAMRヘッドがあるが,AMRヘッドよりさらに感度の高いGMRヘッド,TMRヘッドの開発も進んでおり,そのため,ますます,媒体のノイズを下げることが必要とされている。 In the conventional magnetic induction head, in order to obtain a high reproduction output, it is necessary that the value of residual magnetic flux density × magnetic layer thickness (hereinafter, Mr · t) is large. However, the MR head element has a high sensitivity, and if the Mr is higher than necessary, the output is saturated and the sensitivity is lowered. In addition, in magnetic recording, it is known that the smaller the Mr · t / Hc is, the more the magnetic particles per unit volume of the medium are, the more noise is reduced. There is an AMR head that is often used recently as an MR head, but the development of GMR heads and TMR heads with higher sensitivity than AMR heads is also progressing, so it is necessary to further reduce the noise of the media. It is said that.
以上のことをまとめると,短波長領域における高い出力およびC/N比を得るためには,磁性粉としては,以下のことが重要である。
(1) 磁性層厚が一定であるならば,保磁力Hcは高く,飽和磁化量σs は出力が飽和しない適切な範囲で低いこと。言い換えると,他の磁気特性を悪化させずにσs を制御できることが重要である。
(2) 単位体積あたりの磁性粒子数が多いこと。単位体積あたりの粒子数を多くするには,粒子を微粒子化することが必須となる。
In summary, in order to obtain a high output and a C / N ratio in the short wavelength region, the following is important for the magnetic powder.
(1) If the magnetic layer thickness is constant, the coercive force Hc is high and the saturation magnetization σs is low in an appropriate range where the output is not saturated. In other words, it is important to be able to control σs without degrading other magnetic properties.
(2) The number of magnetic particles per unit volume is large. In order to increase the number of particles per unit volume, it is essential to make the particles fine.
このようなことから,短波長領域における高い出力,C/Nを得るために例えば次ぎのような提案が行われている。 For this reason, the following proposals have been made in order to obtain high output and C / N in the short wavelength region.
高密度デジタル記録システムに適した強磁性金属粉末として,例えば特開2001-6147 号公報において,長軸経30〜120nmで,軸比が3〜8,Hcが1000〜4000Oe ,σs が100〜180emu/g の特性を持つ強磁性金属粉末を使用することが記載されている。 As a ferromagnetic metal powder suitable for a high-density digital recording system, for example, in Japanese Patent Application Laid-Open No. 2001-6147, the major axis is 30 to 120 nm, the axial ratio is 3 to 8, Hc is 1000 to 4000 Oe, and σs is 100 to 180 emu. The use of ferromagnetic metal powders with the characteristic of / g is described.
高品質で高い磁気特性を得る提案としては,本願と同一出願人にかかる特開平10-69629号公報において,Coを5〜50 at.%,Alを0.1 〜30 at.%,希土類元素(Yを含む)を0.1 〜10 at.%,周期律表第1a族元素を0.05重量以下,周期律表第2a族元素を0.1%重量以下をFe中に含有し,Hcが1200〜3000Oe ,σs が100〜200emu/g の磁性粉が記載されている。 As a proposal to obtain high quality and high magnetic characteristics, in Japanese Patent Application Laid-Open No. 10-69629 for the same applicant as this application, Co is 5 to 50 at.%, Al is 0.1 to 30 at.%, Rare earth element (Y 0.1 to 10 at.%), 0.05% or less of Group 1a element of the periodic table, 0.1% or less of Group 2a element of the periodic table in Fe, Hc of 1200 to 3000 Oe, and σs of 100-200 emu / g of magnetic powder is described.
同じく本願と同一出願人に係る特開2001-81506号公報には,オキシ水酸化鉄にCo,Al,SiおよびR(RはYを含む希土類元素の少なくとも一種)を含有させた針状粒子であって,Feに対してCoを0越え〜50 at.%含有しかつAlを0.1 〜30 at.%固溶した粒子の表層部に,Si 0.1〜10 at.%とR 0.1〜15 at.%を含む層を被着する磁性粉製造用先駆物質が提案されている。しかし,両公報のいずれに記載されたものも,高出力を必要とするシステムを対象としたものであり,前述の数種のMRヘッド,すなわちAMRヘッド,GMRヘッド,TMRヘッドを用いたシステム用の磁性粉ではなかった。 JP-A-2001-81506, which also belongs to the same applicant as the present application, describes needle-like particles in which iron oxyhydroxide contains Co, Al, Si, and R (R is at least one kind of rare earth elements including Y). In the surface layer portion of the particles containing Co in an amount of more than 0 to 50 at.% And Fe in a solid solution of 0.1 to 30 at.%, Fe 0.1 to 10 at.% And R 0.1 to 15 at. Precursors for the production of magnetic powders with a layer containing% have been proposed. However, those described in both publications are intended for systems that require high output, and for systems using the above-described several MR heads, that is, AMR heads, GMR heads, and TMR heads. It was not a magnetic powder.
一方,σs に関して言えば, Feはσs =214 emu/gであるのに対し鉄系酸化物のうちの磁性体であるマグネタイトは90emu/g ,マグヘマイトは80emu/g であり,ヘマタイトは常磁性体であることから,オキシ水酸化鉄または酸化物を先駆物質とし,最終的に還元処理を得ることにより得られた金属磁性粒子は,粒子表面から酸化させればσs が下がることは明らかである。そのためσs を低減させるためには,最終の徐酸化工程の温度および/または酸素濃度を上げることにより粒子の酸化度を高め,これによって粒子全体のσs を低下させることができる。しかし,この方法で低σs化を図ったものは,酸化が進んでいるため,長軸径が20〜80nmのものでは酸素含有量が25wt%を超えたものとなっている。また,このように粒子表面を酸化させる方法では,酸化を進めていくほど金属コアの軸比が低下して形状磁気異方性が低下し,Hc低下,SFD悪化などの大きな特性悪化を生じてしまう。したがって,過度な粒子の徐酸化処理は高いHcをもつ磁性粉の作成には好ましくはなく,このようなことから,長軸径が20〜80nmのもので,酸素含有量を25wt%より高くして低σs化したものでは,高いHcを示すものは得られていない。 On the other hand, in terms of σs, Fe is σs = 214 emu / g, whereas the magnetic material magnetite of magnetite is 90 emu / g, maghemite is 80 emu / g, and hematite is paramagnetic. Therefore, it is clear that σs can be lowered if metal magnetic particles obtained by using iron oxyhydroxide or oxide as a precursor and finally obtaining a reduction treatment are oxidized from the particle surface. Therefore, in order to reduce σs, it is possible to increase the degree of oxidation of the particles by increasing the temperature and / or oxygen concentration in the final gradual oxidation step, thereby reducing the σs of the whole particles. However, in the case where the σs is reduced by this method, since the oxidation is progressing, the oxygen content exceeds 25 wt% when the major axis diameter is 20 to 80 nm. Further, in this method of oxidizing the particle surface, as the oxidation proceeds, the axial ratio of the metal core decreases and the shape magnetic anisotropy decreases, resulting in significant deterioration of characteristics such as Hc reduction and SFD deterioration. End up. Therefore, the gradual oxidation treatment of excessive particles is not preferable for the production of magnetic powder having high Hc. For this reason, the major axis diameter is 20 to 80 nm and the oxygen content is set higher than 25 wt%. In the case of the low σs, no high Hc is obtained.
また逆に,金属鉄への還元温度を低下させて,粒子の還元率を低下させることによっても,粒子のσs は低下するが,これでは,粒子内の結晶粒子の成長が抑えられて結晶粒界の割合が増えてしまうことや,粒子内にメゾポアやミクロポア等が残ることや,粒子表面の凸凹が増えて磁極が発生する等によって磁気特性は著しく低下する。したがって,過度な粒子の還元率低下は高いHcをもつ磁性粉の作成には好ましくない。これらの理由から,Hcを低下させずにσs を低くする技術の開発が必要である。
これまで上記のような提案がなされているが,今後の高記録密度システムには欠くことのできない高感度な読みとりMRヘッド(AMRヘッド,GMRヘッド,TMRヘッド等)に適した,鉄を主成分とする磁性粉が得られているとは,言い難いのが実情である。 Although the above proposals have been made so far, iron is a main component suitable for high-sensitivity reading MR heads (AMR heads, GMR heads, TMR heads, etc.) that will be indispensable for future high recording density systems. It is difficult to say that the magnetic powder is obtained.
このような要求を満たす磁性粉を工業的に経済的に有利に製造することが求められているところであるが,十分といえるものではない。例えば,高感度読みとりMRヘッドを用いた高記録密度システムに適した磁性粉として,長軸径が80nm以下,σs が90emu/g 以下でありながらHcが2200Oe 以上を同時に満たすような磁性粉は,針状(針状,紡錘状,平針状を含む)のオキシ水酸化鉄や酸化鉄を原料とする鉄を主体とする磁性粉の分野では,実現出来ていなかった。本発明の課題はこれを実現することにある。 There is a demand for industrially and economically producing magnetic powder satisfying such requirements, but this is not sufficient. For example, as a magnetic powder suitable for a high recording density system using a high-sensitivity reading MR head, a magnetic powder having a major axis diameter of 80 nm or less, σ s of 90 emu / g or less and simultaneously satisfying Hc of 2200 Oe or more is It has not been realized in the field of magnetic powder mainly composed of needle-shaped (including needle-shaped, spindle-shaped and flat needle-shaped) iron oxyhydroxides and iron oxide. The object of the present invention is to achieve this.
本発明者らは,前記の課題を解決すべく,針状のオキシ水酸化鉄または酸化鉄を原料とし,これに固溶させる元素や粒子の表層に被着させる元素の種類や添加条件について数多くの試験を行い,またこれら先駆物質の加熱還元や徐酸化工程についても多くの試験を行って,MRヘッドを用いた高記録密度システムに適した磁性粉が得られるかどうかの研究を重ねた結果,Co/Fe=10〜50 at.%の範囲において,Al/(Co+Fe)=5〜50 at.%で且つAlがオキシ水酸化鉄または酸化物に固溶しやすい条件に設定した場合には,さらにはR(希土類元素,Yを含む)のうち条件にあったものを選択し,また適切な乾式処理を行う場合には,後記の実施に示すように,長軸径80nm以下,σs が90emu/g 以下でありながら,酸素含有量が25wt%以下と低く抑えることができ,その結果,Hcが2200Oe 以上を満たす磁性粉が得られることを見い出した。 In order to solve the above-mentioned problems, the inventors of the present invention have used many kinds of elements and addition conditions of needle-like iron oxyhydroxide or iron oxide as a raw material, the elements to be dissolved in this, and the elements to be deposited on the surface layer of particles. As a result of repeated tests to determine whether magnetic powder suitable for high recording density systems using MR heads can be obtained by conducting many tests on the thermal reduction and gradual oxidation processes of these precursors. In the range of Co / Fe = 10 to 50 at.%, When Al / (Co + Fe) = 5 to 50 at.% And Al is easily dissolved in iron oxyhydroxide or oxide, In addition, when R (which includes rare earth elements and Y) that meets the conditions is selected and an appropriate dry treatment is performed, the major axis diameter is 80 nm or less and σs is Although it is 90 emu / g or less, it contains oxygen. Amount can be kept as low as less 25 wt%, as a result, have found that magnetic powder Hc satisfies more 2200Oe is obtained.
すなわち本発明によれば,Co,Al,R(希土類元素,Yを含む)および酸素を下記の範囲で含有したFeを主成分とする針状粒子からなり,
Co/Fe=10〜50 at.%,好ましくは20〜45 at.%,
粒子内部に存在するAl(固溶Alと言う)/(Fe+Co)=5〜50 at.%,好ましくは8〜50 at.%,さらに好ましくは9〜45 at.%,さらに場合によっては9〜40 at.%,
R/(Fe+Co)=2〜25 at.%,好ましくは6〜25 at.%,さらに好ましくは10〜20 at.%,
酸素=25wt%以下,好ましくは22wt%以下,さらに好ましくは17wt%以下,
且つ
針状粒子の平均長軸径=25〜80nm,好ましくは25〜65nm,さらに好ましくは25〜45nm,
飽和磁化量σs=10〜130emu/g ,好ましくは10〜110emu/g ,さらに好ましくは10〜90未満emu/g ,
保磁力Hc=1400〜2800Oe ,好ましくは1900〜2800Oe ,さらに好ましくは2100〜2800Oe ,場合によってはさらに2200〜2800Oe ,
である,特にMR素子磁気ヘッド(AMRヘッド,GMRヘッド,TMRヘッド対応)用の,磁気記録用磁性粉を提供する。
That is, according to the present invention, it consists of needle-like particles mainly composed of Fe containing Co, Al, R (including rare earth elements, Y) and oxygen in the following ranges,
Co / Fe = 10 to 50 at.%, Preferably 20 to 45 at.%,
Al present in the particles (referred to as solid solution Al) / (Fe + Co) = 5 to 50 at.%, Preferably 8 to 50 at.%, More preferably 9 to 45 at.%, And in some cases 9 to 40 at.%,
R / (Fe + Co) = 2 to 25 at.%, Preferably 6 to 25 at.%, More preferably 10 to 20 at.%,
Oxygen = 25 wt% or less, preferably 22 wt% or less, more preferably 17 wt% or less,
And the average major axis diameter of the acicular particles = 25-80 nm, preferably 25-65 nm, more preferably 25-45 nm,
Saturation magnetization σs = 10 to 130 emu / g, preferably 10 to 110 emu / g, more preferably less than 10 to 90 emu / g,
Coercive force Hc = 1400-2800 Oe, preferably 1900-2800 Oe, more preferably 2100-2800 Oe, in some cases 2200-2800 Oe,
In particular, magnetic recording magnetic powders for MR element magnetic heads (compatible with AMR heads, GMR heads, and TMR heads) are provided.
このような磁性粉は,オキシ水酸化鉄中において,全Feに対するCo換算でCo/Fe=10〜50 at.%のCoを含有し,Al/(Fe+Co)=5〜50 at.%のAlを固溶し,そしてR/(Fe+Co)=2〜25 at.%のRを含む層が被着した針状の粒子を製造し,これを酸化性雰囲気下もしくは還元性雰囲気下で適切に加熱して鉄系酸化物を得たあと,この鉄系酸化物を適切に還元ガスにより還元し,酸化性ガスで温度20〜300℃で徐酸化する方法によって製造することができる。 Such a magnetic powder contains Co / Fe = 10 to 50 at.% Co in terms of Co with respect to total Fe in iron oxyhydroxide, and Al / (Fe + Co) = 5 to 50 at.% Al. Is produced, and acicular particles with a layer containing R / (Fe + Co) = 2 to 25 at.% Are produced and heated in an oxidizing atmosphere or a reducing atmosphere appropriately. Then, after obtaining an iron-based oxide, the iron-based oxide can be appropriately reduced with a reducing gas, and then manufactured by a method of gradual oxidation with an oxidizing gas at a temperature of 20 to 300 ° C.
本発明によると,高感度な読みとりMRヘッド(AMRヘッド,GMRヘッド,TMTヘッド等)に適した,鉄を主成分とする磁性粉が提供される。例えば長軸径が80nm以下,σs が90emu/g 未満でありながらHcが2200Oe 以上を同時に満たすような低飽和磁化で高保磁力の磁性粉でも提供が可能であり,高密度磁気記録の分野に多大の貢献をすることができる。 According to the present invention, a magnetic powder containing iron as a main component suitable for a high-sensitivity reading MR head (AMR head, GMR head, TMT head, etc.) is provided. For example, it is possible to provide magnetic powder with low saturation magnetization and high coercive force that has a major axis diameter of 80 nm or less and σs of less than 90 emu / g, but simultaneously satisfies Hc of 2200 Oe or more. Can contribute.
針状のオキシ水酸化鉄または酸化物を先駆物質として金属磁性粉を製造するには,一般にこの先駆物質を加熱還元することによって得られるが,還元後の物質のままでは燃焼性があるため,酸化処理により粒子表層に酸化被膜を作成させている。本発明者らは,前記の課題解決を目的として,針状のオキシ水酸化鉄または酸化鉄の原料形態を種々変化させた実験を行った。 In order to produce metallic magnetic powder using acicular iron oxyhydroxide or oxide as a precursor, it is generally obtained by heating and reducing this precursor, but since the reduced substance remains combustible, An oxide film is formed on the particle surface layer by oxidation treatment. For the purpose of solving the above problems, the present inventors conducted experiments in which the raw material form of needle-like iron oxyhydroxide or iron oxide was variously changed.
以下に先ず,本発明に従う磁性粉を得るための先駆物質の代表的な製造法について説明する。 First, a typical method for producing a precursor for obtaining a magnetic powder according to the present invention will be described.
前記の目的を達成する磁性粉を得るには,まずそのための先駆物質として,オキシ水酸化鉄において,全Feに対するCo換算でCo/Fe=10〜50 at.%のCoを含有し,Al/(Fe+Co)=5〜50 at.%のAlを固溶し,そしてR/(Fe+Co)=2〜25 at.%のRを含む層が被着した針状粒子を製造する。使用するオキシ水酸化鉄は,針状のほか,紡錘状,平針状などのものが使用可能である。 In order to obtain a magnetic powder that achieves the above-mentioned object, first, as a precursor for that purpose, iron oxyhydroxide contains Co / Fe = 10 to 50 at. Acicular particles in which (Fe + Co) = 5 to 50 at.% Al is dissolved, and a layer containing R / (Fe + Co) = 2 to 25 at.% R is deposited are produced. The iron oxyhydroxide used can be a needle shape, spindle shape, flat needle shape, or the like.
ここで,Coの含有量をCo/Feの原子比(百分率)で10 at.%〜50 at.%とするのは,次のような理由による。なお,FeとCoの出入りがそれ以降も起こらなければ(実際には起こらない)先駆物質のCo/Fe比は最終磁性粉のCo/Fe比に対応する。したがって,ここで述べる理由は磁性粉のCo含有量を規定する理由でもある。以下,AlやRについても同様である。 Here, the reason why the Co content is 10 at.% To 50 at.% In terms of Co / Fe atomic ratio (percentage) is as follows. Note that the Fe / Co entry / exit does not occur thereafter (which does not actually occur), the Co / Fe ratio of the precursor corresponds to the Co / Fe ratio of the final magnetic powder. Therefore, the reason described here is also the reason for prescribing the Co content of the magnetic powder. The same applies to Al and R below.
磁性粉の重要なパラメーターであるHcは,その物質の単位体積あたりの飽和磁化量と軸比(長軸長さ/短軸長さ)に関係する。この単位体積あたりの飽和磁化量は,FeとCoの合金組成により決まるもので,そういった意味で,Co/Fe=10〜50 at.%,好ましくは20〜45 at.%に設定する必要がある。また,耐酸化性改善という目的においても,その組成範囲で合金化することが耐酸化性の向上につながる。 Hc, which is an important parameter of magnetic powder, is related to the amount of saturation magnetization per unit volume of the substance and the axial ratio (major axis length / minor axis length). The saturation magnetization amount per unit volume is determined by the alloy composition of Fe and Co. In this sense, Co / Fe = 10 to 50 at.%, Preferably 20 to 45 at.% Must be set. . For the purpose of improving oxidation resistance, alloying within the composition range leads to improvement of oxidation resistance.
Coを含有した磁性粉を作成するためには,ゲーサイトの生成反応であるFeの第一塩水溶液を炭酸アルカリで中和することにより炭酸塩化を起こし(この炭酸塩化は,求める特性により,炭酸アルカリと苛性アルカリの混合物を用いて行ってもよい),空気等で酸化して,α-FeOOHを成長させるさいに,Feの第一塩水溶液にまえもって,水溶性Co塩を添加すればよい。場合によってはα-FeOOHを成長させる途中に水溶性Co塩の溶液を添加してもよく,成長後に水溶性Co塩の溶液を添加してα-FeOOHの表層に被着してもよい。 In order to prepare a magnetic powder containing Co, carbonation is caused by neutralizing an aqueous first salt solution of Fe, which is a goethite formation reaction, with an alkali carbonate. (Alternatively, a mixture of alkali and caustic may be used.) When oxidized with air or the like to grow α-FeOOH, a water-soluble Co salt may be added to the first salt aqueous solution of Fe. In some cases, a water-soluble Co salt solution may be added during the growth of α-FeOOH, or after the growth, a water-soluble Co salt solution may be added to adhere to the surface layer of α-FeOOH.
Alの含有量については,ゲーサイトへのAlの固溶量をAl/(Fe+Co)で5〜50 at.%とするが,これは,焼成・還元工程等の加熱工程時に,焼結防止・形状保持を確保するのにはこの量のAlが必要であることと,さらには高Al含有量のときに後述の希土類金属元素(Yを含む)の被着による焼結防止効果が相乗的に増大すること,さらにはAl固溶量を調整することによってσs を低σs へと調整できることによる。 Regarding the Al content, the solid solution amount of Al in goethite is 5 to 50 at.% In terms of Al / (Fe + Co). This is to prevent sintering during heating processes such as firing and reduction processes. This amount of Al is necessary to ensure shape retention, and further, the effect of preventing sintering due to the deposition of rare earth metal elements (including Y) described later at a high Al content is synergistic. This is because σs can be adjusted to a low σs by adjusting the amount of Al solid solution.
Al固溶量が増えるとσs が低下するが,この関係は単なるAl増量分とσs低下分との比例関係以上にσsの大きな減少がある。これは,Alが固溶することによって内部金属部の格子の歪み等による結晶構造の変化を与える結果,磁化の低減が図られることが主な原因と考えられる。 As the amount of Al solid solution increases, σs decreases, but this relationship has a larger decrease in σs than the proportional relationship between the mere increase in Al and the decrease in σs. The main reason for this is thought to be the reduction of magnetization as a result of the change in crystal structure due to the distortion of the lattice of the internal metal part due to the solid solution of Al.
Alをゲーサイトに固溶させるには,ゲーサイト成長前または成長途中にAlの水溶性塩やアルミン酸塩の水溶液を滴下すればよい。Alを初期に多量に添加しすぎると,ゲーサイトの酸化成長を阻害するため,針状性の崩れたゲーサイトの生成を生じる。そのため,Alは,ゲーサイトの成長中にも添加することが好ましい。 In order to dissolve Al in goethite, a water-soluble salt of Al or an aqueous solution of aluminate may be dropped before or during the growth of goethite. If too much Al is added in the initial stage, the oxidative growth of goethite is inhibited, so that goethite with broken acicularity is generated. Therefore, Al is preferably added during the growth of goethite.
Rの含有量については,R/(Fe+Co)で2〜25 at.%の範囲で含有させる。Rは焼結防止作用を供するが,このためには,先駆物質粒子にR/(Fe+Co)=2〜25 at.%となる量のRすなわち希土類元素(Yを含む)を被着させるのがよい。希土類元素は,好ましくはY,Gd,Ybなどが好ましく,元素量の重たいものほど低σs の領域では磁気特性が良好であることがわかった。たとえば,メタル長軸径が60nmの磁性粉では,σsが100emu/g 以上の領域では,Y等を用いたものが磁気特性が良好であったのに対し,100emu/g 未満の領域では,GdやYbなどの希土類の方が高い磁気特性を示すことがわかった。希土類元素を先駆物質に含有させるには,ゲーサイトの成長途中の反応スラリーに,希土類元素を含有した水溶液を滴下してもよいし,ゲーサイト成長後のスラリーに希土類元素を含有した水溶液を添加してもよい。 About R content, it is made to contain in the range of 2-25 at.% By R / (Fe + Co). R provides an anti-sintering action. For this purpose, R / (Fe + Co) = 2 to 25 at.% Of R, that is, rare earth elements (including Y) are deposited on the precursor particles. Good. The rare earth elements are preferably Y, Gd, Yb and the like, and it has been found that the heavier the element amount, the better the magnetic properties in the region of low σs. For example, in the case of magnetic powder having a metal major axis diameter of 60 nm, the magnetic properties using Y or the like are good in the region where σs is 100 emu / g or more, whereas in the region of less than 100 emu / g, Gd It was found that rare earth such as Yb and Yb showed higher magnetic properties. To include rare earth elements in the precursor, an aqueous solution containing rare earth elements may be added dropwise to the reaction slurry during the growth of goethite, or an aqueous solution containing rare earth elements may be added to the slurry after the goethite growth. May be.
このようにしてオキシ水酸化鉄に前記の量のCoを固溶しRを被着した針状粒子からなる先駆物質を得ることができる。これを既存の技術を用いて酸化性雰囲気下もしくは還元性雰囲気下で250℃〜600℃で加熱脱水することにより鉄系酸化物が得られる。この加熱脱水時の雰囲気中に適量の水蒸気を添加してもよい。 In this way, it is possible to obtain a precursor consisting of needle-like particles in which the above amount of Co is dissolved in iron oxyhydroxide and R is deposited. This is heated and dehydrated at 250 ° C. to 600 ° C. in an oxidizing atmosphere or a reducing atmosphere using an existing technique to obtain an iron-based oxide. An appropriate amount of water vapor may be added to the atmosphere during the heat dehydration.
ついで,この鉄系酸化物を,一酸化炭素,アセチレン,水素等の還元ガスにより250〜650℃の温度範囲で還元を行う。そのさい多段還元を行うこともできる。多段階還元とは,設定された温度範囲内において,或る温度で所定の時間保持することを,その保持温度を変えて,数回繰り返して還元を行うことを意味する。保持温度と時間を適正に制御することにより,磁性粉の特性を変化させることができる。この還元処理の雰囲気として,還元ガスに水蒸気を添加したものを用いるのも好ましい。 Next, this iron-based oxide is reduced in a temperature range of 250 to 650 ° C. with a reducing gas such as carbon monoxide, acetylene, or hydrogen. At that time, multistage reduction can be performed. Multi-stage reduction means that holding for a predetermined time at a certain temperature within a set temperature range is repeated several times by changing the holding temperature. By properly controlling the holding temperature and time, the characteristics of the magnetic powder can be changed. As the atmosphere for the reduction treatment, it is also preferable to use a reducing gas added with water vapor.
加熱還元後に得られたものは合金磁性粒子粉末となるが,そのまま大気中で扱うと発火のおそれがあるため,次の徐酸化工程により,粒子表面に非磁性酸化物層もしくは90emu/g 以下の磁性酸化物層,またはその両方をもつ酸化物層を形成させる。徐酸化工程は,不活性ガスに酸化性ガス量を徐々に増やしながら20〜300℃の温度で所定時間処理することにより,粒子表面に酸化物層を作成する工程である。実際には,還元が終了したあとの粉体を,この徐酸化工程を行う温度まで冷却し,その温度で徐酸化を行うのが好ましい。すなわち,後記の実施例に示すように還元終了後,50〜200℃の或る温度まで冷却し,この温度で弱酸化性ガスによって該粒子表面に酸化物層を形成させて安定化処理するのがよい。この還元終了後の冷却温度が高いほどσs量を低下させることができるが,前述のようにこの温度が高すぎると他の磁気特性が低下することになる。 What is obtained after heat reduction is alloy magnetic particle powder, but if handled in the air as it is, there is a risk of ignition, so the next gradual oxidation process will cause a non-magnetic oxide layer or 90 emu / g or less on the particle surface. An oxide layer having a magnetic oxide layer or both is formed. The gradual oxidation step is a step of forming an oxide layer on the particle surface by performing a predetermined time treatment at a temperature of 20 to 300 ° C. while gradually increasing the amount of oxidizing gas to an inert gas. Actually, it is preferable that the powder after the reduction is cooled to a temperature at which this slow oxidation step is performed, and then the slow oxidation is performed at that temperature. That is, as shown in the examples described later, after the reduction is completed, cooling is performed to a certain temperature of 50 to 200 ° C., and an oxide layer is formed on the particle surface with a weak oxidizing gas at this temperature to perform a stabilization treatment. Is good. The amount of σs can be reduced as the cooling temperature after the reduction is finished, but if the temperature is too high as described above, other magnetic characteristics are deteriorated.
このようにして,Co/Fe=10〜50 at.%,好ましくは20〜45 at.%:Al/(Fe+Co)=5〜50 at.%,好ましくは8〜50 at.%,さらに好ましくは9〜45 at.%,さらに場合によっては9〜40 at.%:R/(Fe+Co)=2〜25 at.%,好ましくは6〜25 at.%,さらに好ましくは10〜20 at.%:の量でCo,AlおよびRを含有し,酸素含有量=25wt%以下,好ましくは22wt%以下,さらに好ましくは17wt%以下であるFeを主成分とした針状の磁性粉であって,針状粒子の平均長軸径=25〜80nm,好ましくは25〜65nm,さらに好ましくは25〜45nm:飽和磁化量σs=10〜130emu/g ,好ましくは10〜110emu/g ,さらに好ましくは10〜90未満emu/g :保磁力Hc=1400〜2800Oe ,好ましくは1900〜2800Oe ,さらに好ましくは2100〜2800Oe ,場合によってはさらに2200〜2800Oe :の諸特性を具備した磁気記録用の磁性粉を得ることができ,このものは,特にMR素子磁気ヘッド用の磁気記録用磁性粉として十分な機能を発揮する。 Thus, Co / Fe = 10 to 50 at.%, Preferably 20 to 45 at.%: Al / (Fe + Co) = 5 to 50 at.%, Preferably 8 to 50 at.%, More preferably 9-45 at.%, Moreover 9-40 at.%: R / (Fe + Co) = 2-25 at.%, Preferably 6-25 at.%, More preferably 10-20 at.%: A needle-like magnetic powder containing Fe as a main component and containing Co, Al and R in an amount of 25 wt% or less, preferably 22 wt% or less, more preferably 17 wt% or less. Average major axis diameter of particle-like particles = 25-80 nm, preferably 25-65 nm, more preferably 25-45 nm: saturation magnetization σs = 10-130 emu / g, preferably 10-110 emu / g, more preferably 10-90 Less than emu / g: Coercive force Hc = 1400-28 A magnetic powder for magnetic recording having various characteristics of 0 Oe, preferably 1900 to 2800 Oe, more preferably 2100 to 2800 Oe, and in some cases 2200 to 2800 Oe can be obtained. It exhibits a sufficient function as a magnetic powder for magnetic recording.
このように飽和磁化量σs が低くても酸素含有量を低く抑えられ,その結果,保磁力Hcの高い金属粒子からなる磁性粉末が得られたのは,焼結防止剤としての固溶Alと,希土類元素の両方を従来よりも多く使用したことで,Al単独,希土類元素単独で増加させたときよりも相乗的に形状保持効果が向上し,当該粒子の形状磁気異方性が高まったことに起因すると本発明者らは考えている。 Thus, even when the saturation magnetization amount σs is low, the oxygen content can be kept low, and as a result, a magnetic powder composed of metal particles having a high coercive force Hc is obtained with solid solution Al as a sintering inhibitor. By using both rare earth elements more than before, the shape retention effect is improved synergistically and the shape magnetic anisotropy of the particles is increased more than when Al alone and rare earth elements are increased alone. The present inventors believe that this is caused by this.
以下に実施例を挙げるが,各粒子の大きさ例えば表中の平均長軸径(単位:nm)はいずれも透過型電子顕微写真から測定した数値の平均値である。また表中の各磁性粒子粉末のCo量,Al量,希土類元素量はICPにより測定した値であり,磁気特性はVSMで測定した値である。Dx(結晶子粒径:単位オングストローム)はX線回折法を用いデバイ−シェラーの式から求めた。また,耐候性(Δσs)は温度60℃,湿度90%RHの環境に1週間保存したときのσsを測定し,保存前の試料のσsに対する低下率%で評価した。
Examples will be described below. The size of each particle, for example, the average major axis diameter (unit: nm) in the table is an average value of values measured from a transmission electron micrograph. Further, the Co amount, Al amount, and rare earth element amount of each magnetic particle powder in the table are values measured by ICP, and the magnetic characteristics are values measured by VSM. Dx (crystallite particle size: unit angstrom) was determined from the Debye-Scherrer equation using an X-ray diffraction method. Further, the weather resistance (Δσs) was measured by measuring σs when stored for 1 week in an environment of
塗膜の特性(テープ特性)については,磁性粉100重量部に対し以下の材料を下記組成となるような割合で配合して遠心ボールミルで1時間分散させて磁性塗料を作製し,この磁性塗料をポリエチレンテレフタレートからなるベースフイルム上にアプリケーターを用いて塗布することにより,磁気テープを作製し,その保磁力Hcxを測定し,またそのヒステリシスループからSFD値を算出した。
磁性粉 100重量部
ポリウレタン樹脂 30重量部
メチルエチルケトン 190重量部
シクロヘキサノン 80重量部
トルエン 110重量部
ステアリン酸 1重量部
アセチルアセトン 1重量部
アルミナ 3重量部
カーボンブラック 2重量部
Regarding the characteristics of the coating film (tape characteristics), the following materials were blended in a proportion of the following composition with respect to 100 parts by weight of the magnetic powder, and dispersed with a centrifugal ball mill for 1 hour to produce a magnetic paint. Was coated on a base film made of polyethylene terephthalate using an applicator to produce a magnetic tape, the coercive force Hcx was measured, and the SFD value was calculated from the hysteresis loop.
[実施例1]
Co/(Fe+Co)=24 at.%のCoと,Al/(Fe+Co)=5 at.%のAlを固溶したゲーサイト63gを純水中2500ml中に入れ,さらに20wt%のNH3水溶液240gを添加し,その後攪拌を行って分散を進める。この分散液中に,Gdが2.0wt%濃度の硫酸ガドリニウム水溶液を165.0g添加し,30分攪拌後に反応終了とする。
[Example 1]
63 g of goethite in which Co / (Fe + Co) = 24 at.% Co and Al / (Fe + Co) = 5 at.% Al were dissolved was put in 2500 ml of pure water, and further 240 g of 20 wt% NH 3 aqueous solution. Is added, followed by stirring to promote dispersion. To this dispersion, 165.0 g of an aqueous gadolinium sulfate solution having a Gd concentration of 2.0 wt% is added, and the reaction is completed after stirring for 30 minutes.
この反応で得られたCo,Al,Gdを含むオキシ水酸化鉄系物質をブフナー漏斗で濾過し,イオン交換水で水洗後,110 ℃大気中で乾燥させる。得られたオキシ水酸化鉄系粉体を 370℃で焼成後,水素還元雰囲気下で平均温度 490℃で還元する。還元終了後 120℃まで冷却し,ついで,0.1%の酸素を含むN2ガスを導入して,表面酸化処理を行った。得られた磁性粉の平均長軸径は57nmであった。この磁性粉の組成, バルク特性およびテープ特性を表1に示した。 The iron oxyhydroxide-based material containing Co, Al, and Gd obtained by this reaction is filtered with a Buchner funnel, washed with ion-exchanged water, and dried in the atmosphere at 110 ° C. The obtained iron oxyhydroxide powder is calcined at 370 ° C and then reduced at an average temperature of 490 ° C in a hydrogen reducing atmosphere. After the reduction, the sample was cooled to 120 ° C., and then N 2 gas containing 0.1% oxygen was introduced to perform surface oxidation treatment. The average major axis diameter of the obtained magnetic powder was 57 nm. Table 1 shows the composition, bulk properties, and tape properties of this magnetic powder.
[実施例2〜5]
ゲーサイト中のAl含有量が以下のとおりのゲーサイトを用いた以外は,実施例1を繰り返した。得られた磁性粉の組成,バルク特性およびテープ特性を表1に示した。
ゲーサイト中のAl含有量
実施例2:Al/(Fe+Co)=10 at.%
実施例3:Al/(Fe+Co)=20 at.%
実施例4:Al/(Fe+Co)=30 at.%
実施例5:Al/(Fe+Co)=45 at.%
[Examples 2 to 5]
Example 1 was repeated except that a goethite having the following Al content in the goethite was used. Table 1 shows the composition, bulk properties, and tape properties of the obtained magnetic powder.
Al content in goethite Example 2: Al / (Fe + Co) = 10 at.%
Example 3: Al / (Fe + Co) = 20 at.%
Example 4: Al / (Fe + Co) = 30 at.%
Example 5: Al / (Fe + Co) = 45 at.%
[実施例6〜10]
ゲーサイト中のAl含有量が以下のとおりのゲーサイトを使用し且つかつガドリニウム水溶液(Gd濃度=2wt%)の添加量をいずれも825.0gに変えた以外は,実施例1を繰り返した。得られた磁性粉の組成,バルク特性およびテープ特性を表1に示した。
ゲーサイト中のAl含有量
実施例6:Al/(Fe+Co)=5 at.%
実施例7:Al/(Fe+Co)=10 at.%
実施例8:Al/(Fe+Co)=20 at.%
実施例9:Al/(Fe+Co)=30 at.%
実施例10:Al/(Fe+Co)=45 at.%
ガドリニウム水溶液の添加量(g)
実施例6:825.0g
実施例7:825.0g
実施例8:825.0g
実施例9:825.0g
実施例10:825.0g
[Examples 6 to 10]
Example 1 was repeated except that a goethite having the following Al content in goethite was used and that the amount of gadolinium aqueous solution (Gd concentration = 2 wt%) was changed to 825.0 g. Table 1 shows the composition, bulk properties, and tape properties of the obtained magnetic powder.
Al content in goethite Example 6: Al / (Fe + Co) = 5 at.%
Example 7: Al / (Fe + Co) = 10 at.%
Example 8: Al / (Fe + Co) = 20 at.%
Example 9: Al / (Fe + Co) = 30 at.%
Example 10: Al / (Fe + Co) = 45 at.%
Addition amount of gadolinium aqueous solution (g)
Example 6: 825.0 g
Example 7: 825.0 g
Example 8: 825.0 g
Example 9: 825.0 g
Example 10: 825.0 g
[実施例11〜15]
ゲーサイト中のAl含有量が以下のとおりのゲーサイトを使用し且つかつガドリニウム水溶液(Gd濃度=2wt%)の添加量をいずれも1375.0gに変えた以外は,実施例1を繰り返した。得られた磁性粉の組成,バルク特性およびテープ特性を表1に示した。
ゲーサイト中のAl含有量
実施例11:Al/(Fe+Co)=5 at.%
実施例12:Al/(Fe+Co)=10 at.%
実施例13:Al/(Fe+Co)=20 at.%
実施例14:Al/(Fe+Co)=30 at.%
実施例15:Al/(Fe+Co)=45 at.%
ガドリニウム水溶液の添加量(g)
実施例11:1375.0g
実施例12:1375.0g
実施例13:1375.0g
実施例14:1375.0g
実施例15:1375.0g
[Examples 11 to 15]
Example 1 was repeated except that a goethite having an Al content in the goethite as shown below was used and the addition amount of the gadolinium aqueous solution (Gd concentration = 2 wt%) was changed to 1375.0 g. Table 1 shows the composition, bulk properties, and tape properties of the obtained magnetic powder.
Al content in goethite Example 11: Al / (Fe + Co) = 5 at.%
Example 12: Al / (Fe + Co) = 10 at.%
Example 13: Al / (Fe + Co) = 20 at.%
Example 14: Al / (Fe + Co) = 30 at.%
Example 15: Al / (Fe + Co) = 45 at.%
Addition amount of gadolinium aqueous solution (g)
Example 11: 1375.0 g
Example 12: 1375.0 g
Example 13: 1375.0 g
Example 14: 1375.0 g
Example 15: 1375.0 g
[比較例1〜12]
比較例1〜12は,AlとGdの両方または一方の含有量を本発明で規定する範囲より少ない量とし,低σs 化のために還元後の表面酸化を強化した例を示すものであり,比較例1〜4の群,比較例5〜8の群および比較例9〜12の群は,それぞれAlとGd量が同一であるが,還元終了後の表面酸化温度を変化させたものである。
[Comparative Examples 1 to 12]
Comparative Examples 1 to 12 show examples in which the content of both or one of Al and Gd is less than the range specified in the present invention, and the surface oxidation after reduction is enhanced to reduce σs, The groups of Comparative Examples 1 to 4, the groups of Comparative Examples 5 to 8, and the groups of Comparative Examples 9 to 12 have the same amounts of Al and Gd, but the surface oxidation temperature after the reduction is changed. .
すなわち,比較例1〜12においては,ゲーサイトのAlの含有量を以下のように変化させ,ガドリニウム水溶液(Gd濃度=2wt%)の添加量を下記のように変化させ,かつ還元終了後の表面酸化温度を下記のように変化させた以外は,実施例1を繰り返した。得られた磁性粉の組成,バルク特性およびテープ特性を表1に示した。
ゲーサイト中のAl含有量
比較例1:Al/(Fe+Co)=3 at.%
比較例2:Al/(Fe+Co)=3 at.%
比較例3:Al/(Fe+Co)=3 at.%
比較例4:Al/(Fe+Co)=3 at.%
比較例5:Al/(Fe+Co)=10 at.%
比較例6:Al/(Fe+Co)=10 at.%
比較例7:Al/(Fe+Co)=10 at.%
比較例8:Al/(Fe+Co)=10 at.%
比較例9:Al/(Fe+Co)=3 at.%
比較例10:Al/(Fe+Co)=3 at.%
比較例11:Al/(Fe+Co)=3 at.%
比較例12:Al/(Fe+Co)=3 at.%
ガドリニウム水溶液の添加量(g)
比較例1:55.0
比較例2:55.0
比較例3:55.0
比較例4:55.0
比較例5:55.0
比較例6:55.0
比較例7:55.0
比較例8:55.0
比較例9:825.0
比較例10:825.0
比較例11:825.0
比較例12:825.0
還元終了後の表面酸化温度(℃)
比較例1:80
比較例2:120
比較例3:160
比較例4:200
比較例5:80
比較例6:120
比較例7:160
比較例8:200
比較例9:80
比較例10:120
比較例11:160
比較例12:200
That is, in Comparative Examples 1 to 12, the Al content of goethite was changed as follows, the amount of gadolinium aqueous solution (Gd concentration = 2 wt%) was changed as follows, and after the reduction was completed. Example 1 was repeated except that the surface oxidation temperature was changed as follows. Table 1 shows the composition, bulk properties, and tape properties of the obtained magnetic powder.
Al content in goethite Comparative Example 1: Al / (Fe + Co) = 3 at.%
Comparative Example 2: Al / (Fe + Co) = 3 at.%
Comparative Example 3: Al / (Fe + Co) = 3 at.%
Comparative Example 4: Al / (Fe + Co) = 3 at.%
Comparative Example 5: Al / (Fe + Co) = 10 at.%
Comparative Example 6: Al / (Fe + Co) = 10 at.%
Comparative Example 7: Al / (Fe + Co) = 10 at.%
Comparative Example 8: Al / (Fe + Co) = 10 at.%
Comparative Example 9: Al / (Fe + Co) = 3 at.%
Comparative Example 10: Al / (Fe + Co) = 3 at.%
Comparative Example 11: Al / (Fe + Co) = 3 at.%
Comparative Example 12: Al / (Fe + Co) = 3 at.%
Addition amount of gadolinium aqueous solution (g)
Comparative Example 1: 55.0
Comparative Example 2: 55.0
Comparative Example 3: 55.0
Comparative Example 4: 55.0
Comparative Example 5: 55.0
Comparative Example 6: 55.0
Comparative Example 7: 55.0
Comparative Example 8: 55.0
Comparative Example 9: 825.0
Comparative Example 10: 825.0
Comparative Example 11: 825.0
Comparative Example 12: 825.0
Surface oxidation temperature after reduction (℃)
Comparative Example 1: 80
Comparative Example 2: 120
Comparative Example 3: 160
Comparative Example 4: 200
Comparative Example 5: 80
Comparative Example 6: 120
Comparative Example 7: 160
Comparative Example 8: 200
Comparative Example 9: 80
Comparative Example 10: 120
Comparative Example 11: 160
Comparative Example 12: 200
[実施例16〜20]
実施例16〜20は希土類金属の種類を変化させたときの特性の変化を示したものである。すなわち実施例16〜20は,それぞれGdに代えてY,La,Ce,Nd,Ybを使用した以外は実施例7を繰り返したものである。これら各希土類元素の水溶液(R濃度=2wt%)の添加量は下記に示すとおりであるが,それらを添加して得られた生成物のR/(Fe+Co)は,約14.7 at.%の一定になるように調整してある。得られた磁性粉の磁性粉の組成, メタル特性,バルク特性およびテープ特性を表1に示した。
[Examples 16 to 20]
Examples 16 to 20 show changes in characteristics when the kind of rare earth metal is changed. That is, Examples 16 to 20 are the same as Example 7 except that Y, La, Ce, Nd, and Yb were used instead of Gd. The amount of each of these rare earth element aqueous solutions (R concentration = 2 wt%) is as shown below. The R / (Fe + Co) of the product obtained by adding them is about 14.7 at.%. It has been adjusted to be constant. Table 1 shows the composition, metal characteristics, bulk characteristics, and tape characteristics of the magnetic powder obtained.
各希土類元素の水溶液の添加量(g)
実施例16(Y添加)= 466.8
実施例17(La添加)=729.0
実施例18(Ce添加)=735.0
実施例19(Nd添加)=757.0
実施例20(Yb添加)=908.0
Amount of aqueous solution of each rare earth element (g)
Example 16 (Y addition) = 466.8
Example 17 (La addition) = 729.0
Example 18 (Ce addition) = 735.0
Example 19 (Nd addition) = 757.0
Example 20 (Yb addition) = 908.0
表1の結果から次のことがわかる。
(1) 実施例1〜15と比較例1〜8との比較
実施例1〜15においては,Al量増加とGd量増加によって低σs 化がはかられていることがわかる。そして,低σs 化が進んでも,実施例1〜15では,Hcが高い位置を保持していることが分かる。この低σs 化は,Al,Gdの含有量の増加により達成されるが,この高Hc化は,表面酸化の強化に頼らない手法による低σs 化であるため,コアの針状性低下が生じず,かつAl,Gd含有量増加によって,焼結防止剤としてのAl,Gdの作用が一層強く現れたことに起因している効果である。また,Al量の増加,Gd量の増加の両方が達成されることによって,それぞれ相乗的な効果が見られ,大きな高Hc化につながっている。よって実施例1〜15では,低σs 化と高Hc化の両立が実現している。
The following can be seen from the results in Table 1.
(1) Comparison between Examples 1 to 15 and Comparative Examples 1 to 8 In Examples 1 to 15, it can be seen that the reduction in σs is achieved by increasing the Al amount and increasing the Gd amount. It can be seen that even in the case of lowering σs, in Examples 1 to 15, the position where Hc is high is maintained. This reduction in σs is achieved by increasing the content of Al and Gd, but this increase in Hc is a reduction in σs by a method that does not rely on the enhancement of surface oxidation, resulting in a decrease in the acicularity of the core. In addition, this effect is due to the fact that the action of Al and Gd as a sintering inhibitor appears stronger due to the increase in the content of Al and Gd. In addition, by achieving both an increase in the Al amount and an increase in the Gd amount, a synergistic effect is observed, leading to a large increase in Hc. Therefore, in Examples 1 to 15, both low σs and high Hc are realized.
これに対して,Al,Gdの両方または一方の含有量が低い比較例1〜8は,表面酸化時の処理温度を上げ,酸化の進行をより一層進ませることで低σs 化を進めているが,この場合には,粒子内部の金属コア部の針状性が大きく崩れてしまうため,Hcの大きな低下を生じている。よって,この比較例1〜8では,低σs と高Hcの両立は不可能となっている。 On the other hand, Comparative Examples 1 to 8 in which the content of either Al or Gd or one of them is low promotes a reduction in σs by raising the treatment temperature during the surface oxidation and further promoting the oxidation. However, in this case, since the acicularity of the metal core portion inside the particle is greatly broken, Hc is greatly reduced. Therefore, in Comparative Examples 1 to 8, it is impossible to achieve both low σs and high Hc.
図1は,実施例と比較例で得られた各磁性粉のHcとσsをプロットしたものであるが,この図からも,比較例のものでは低σs化にともなってHcが低下するのに対し,本発明に従う実施例のものは低σs化が図られても高いHcを有していることが明らかである。 FIG. 1 is a plot of the Hc and σs of each magnetic powder obtained in the example and the comparative example. From this figure, too, in the comparative example, the Hc decreases as the σs decrease. On the other hand, it is apparent that the example according to the present invention has a high Hc even if the σs is reduced.
また図2は,実施例と比較例で得られた各磁性粉の酸素含有量とσsをプロットしたものであるが,比較例では低σs化にともなって酸素含有量が増加しているのに対し,本発明に従う実施例のものは低σs化は酸素含有量に起因するものではないことがわかる。 FIG. 2 is a plot of the oxygen content and σs of each magnetic powder obtained in the examples and comparative examples. In the comparative example, the oxygen content increases as the σs decrease. On the other hand, in the examples according to the present invention, it can be seen that the reduction in σs is not caused by the oxygen content.
(2) 実施例7および実施例16〜20の効果の比較
前記のような低σs化の効果は,希土類元素の種類を変化させても達成されていることがわかる。各希土類元素の含有量( at.%)が一定であることから,低σs 分は,その希土類金属の原子量に関係して,重い原子量ほどより大きな低σs 効果を発揮していることがわかる。Hcについては,希土類金属の種類に影響を受けている。これは,希土類金属の種類によって,焼結防止効果が異なることが起因している。焼結防止効果のより大きな金属としては,Y,Gd,Ybであることが分かる。
(2) Comparison of effects of Example 7 and Examples 16 to 20 It can be seen that the effect of reducing σs as described above is achieved even when the kind of rare earth element is changed. Since the content (at.%) Of each rare earth element is constant, it can be seen that the low σs component exhibits a greater low σs effect for heavier atomic weights in relation to the atomic weight of the rare earth metal. About Hc, it is influenced by the kind of rare earth metal. This is due to the fact that the sintering prevention effect differs depending on the type of rare earth metal. It can be understood that Y, Gd, and Yb are metals having a greater sintering preventing effect.
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JPH06363A (en) * | 1992-06-22 | 1994-01-11 | Hitachi Maxell Ltd | Production of inorganic powder |
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JP2003119502A (en) * | 2001-10-12 | 2003-04-23 | Fuji Photo Film Co Ltd | Ferromagnetic metal powder and magnetic recording medium containing the same |
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JPH06363A (en) * | 1992-06-22 | 1994-01-11 | Hitachi Maxell Ltd | Production of inorganic powder |
JPH07109122A (en) * | 1993-10-07 | 1995-04-25 | Fuji Photo Film Co Ltd | Production of hematite particle and production of ferromagnetic powder for magnetic recording using hematite particle and magnetic recording medium |
JP2000149244A (en) * | 1998-11-13 | 2000-05-30 | Fuji Photo Film Co Ltd | Magnetic recording medium |
JP2002074642A (en) * | 2000-08-29 | 2002-03-15 | Fuji Photo Film Co Ltd | Magnetic recording medium |
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