Atom probe study on the bulk nanocomposite SmCo/Fe permanent magnet produced by ball-milling and warm compaction

The microstructure and compositions of the bulk nanocomposite SmCo/Fe permanent magnet were studied using transmission electron microscopy and 3-dimensional atom probe techniques. The excellent magnetic properties were related to the uniform nanocomposite structure with nanometer α-Fe particles uniformly distributed in the SmCo phase matrix. The α-Fe phase contained ∼26 at% Co, and the SmCo phase contained ∼19 at% Fe, confirming that the interdiffusion of Fe and Co atoms between the two phases occurred. The formation of the α-Fe(Co) phase explained why the saturation magnetization of the nanocomposite permanent magnet was higher than that expected from the original pure α-Fe and SmCo₅ powders, which enhanced further the maximum energy product of the nanocomposite permanent magnet.     

Improvement of magnetic intergranular isolation and evaluation of read/write characteristics on SmCo5 perpendicular magnetic thin films

SmCo₅ alloy is a promising candidate for ultra-high-density perpendicular magnetic recording (PMR) media because of its high uniaxial magnetocrystalline anisotropy K_u of more than 1.1×10⁸ erg/cm³. Previously, we successfully achieved high K_u in a sputter-deposited SmCo₅ thin film by introducing a Cu/Ti dual underlayer. However, in order to apply the SmCo₅ films to practical PMR media, it is necessary to decrease medium noise. A granulated magnetic film comprising of small and magnetically decoupled grains is effective in reducing the medium noise. In this paper, we have proposed a new granular film that is fabricated by partial thermodiffusion of Cu between the Sm-Co continuous layer and the Cu underlayer, which is granulated using compositional segregation caused by the addition of Ta₂O₅. We have analyzed the magnetic properties, magnetic domain size, and magnetization reversal process of the proposed SmCo₅ film. The magnetic domain size decreased and the magnetization reversal process changed from the magnetic-wall-motion mode to a coherent rotation mode to some extent on isolation of magnetic grains. The read/write characteristics of granulated SmCo₅ double-layered media were also evaluated. The medium noise decreased and the signal-to-noise ratio increased for the granulated double-layered (PMR) medium.     

A new TiW seed layer for SmCo5 films with perpendicular magnetic anisotropy

A new seed layer TiW is proposed for SmCo₅ films with perpendicular magnetic anisotropy. The influence of a TiW seed layer on the microstructure and the surface morphology of Cu underlayer are studied. The grain size and surface roughness dependence of Cu underlayer on the thickness and the annealing of the TiW seed layer are also investigated. The improvement in the perpendicular magnetic properties of SmCo₅ film from the TiW seed layer is approved. The results show that a 5 nm Ti₃W₇ seed layer improves the microstructure and surface morphology of Cu underlayer, and significantly improves the perpendicular magnetic properties of SmCo₅ film. The diffusion barrier and a high melting point of the TiW seed layer are regarded as the physical mechanism of the improvement for SmCo₅ film with perpendicular magnetic anisotropy.     

Exchange-coupled nanoscale SmCo/NdFeB hybrid magnets

Nanoscale hybrid magnets containing SmCo₅ and Nd₂Fe₁₄B hard magnetic phases have been produced via a novel “in-one-pot” processing route. The grain size of the processed bulk composite materials is controlled below 20 nm. The refinement of the nanoscale morphology leads to effective inter-phase exchange coupling that results in single-phase like magnetic properties. Energy product of 14 MGOe was obtained in the isotropic nanocomposite magnets at room temperature. At elevated temperatures, the hybrid magnets have greatly improved thermal stability compared to the Nd₂Fe₁₄B single-phase counterpart and have substantially increased magnetization and energy products compared to the single-phase SmCo₅ counterpart.     

Giant intrinsic magnetic hardness

Crystallographically partly randomized materials with high magnetic anisotropy exhibit anisotropy and exchange fluctuations. Possibly the most dramatic consequence of these interaction fluctuations is the presence of giant intrinsic magnetic hardness observed, especially at cryogenic temperatures. This magnetic hardness (resistance to demagnetization) is anintrinsic solid state property, quite in contrast with hardness in technologically important materials based on the presence of fine particles or precipitate phases. It introduces rather a further variety in the phenomenology of interaction fluctuation materials such as spin glasses, representing the extreme case of high anisotropy and high moment concentrations. In this paper the phenomenon of strong intrinsic magnetic hardness is reviewed, and some new experimental data are presented for homogeneous pseudobinary regions of composition on the basis of such compounds as SmNi₅, SmCu₅, SmCo₅, TbFe₂ and others. Magnetic hardness in some of these cases reaches the highest values found so far for any class of materials. For instance, maximum values of coercive force of aboutH _c=230 kOe are observed for SmCo_5−xNi_x. Even higher values are extrapolated in other cases. Maximum values ofH _c are observed in materials with ordering temperatures of order 60–200 K. A strong temperature and a weaker time dependence ofH _c is observed and discussed on the basis of theories involving thermal activation of domain propagation. Comparisons are drawn with effects generally observed in magnetically hard materials, and the relationship of intrinsic magnetic hardness to technologically interesting materials is discussed. Tentative conclusions as to the details of the origins of giant intrinsic magnetic hardness are drawn and areas of future interest are indicated. This study was supported by a grant from the National Science Foundation.     

Improvement of magnetic properties and read/write characteristics in SmCo5 perpendicular thin films

An SmCo₅ alloy is a promising candidate for ultra-high density magnetic recording media because of its strong uniaxial magnetocrystalline anisotropy, whose constant, K_u, is more than 1.1×10⁸ erg/cm³. Recently, we successfully obtained high perpendicular magnetic anisotropy for a sputter-deposited SmCo₅ thin film by introducing a Cu/Ti dual underlayer. However, it is necessary to improve magnetic properties and read/write (R/W) characteristics for applying SmCo₅ thin films to perpendicular magnetic recording media. In this study, we focused on reduction of magnetic domain size and change of a magnetization reversal process of SmCo₅ perpendicular magnetic thin films by introducing carbon (C) atoms into the constituent Cu underlayer. The magnetic domain size became small and the ratio of coercivity (H_c) against magnetic anisotropy (H_k) which is an index of the magnetization reversal process was increased by adding C atoms. We also evaluated the R/W characteristics of SmCo₅ double-layered media including C atoms. The medium noise was decreased and signal-to-noise ratio increased by introducing the C. The addition of C into the Cu underlayer is effective for changing the magnetization reversal process, reducing medium noise and increasing SNR.     

Microstructure and magnetic properties studies of SmCo5 thin films grown on MgO and glass substrates

In this work, SmCo₅ thin films are deposited on single crystal MgO (1 0 0) and amorphous glass substrates with a Cr underlayer at 400 °C by sputtering. A comparison study shows that the microstructures and magnetic properties are different in the two SmCo₅ films on the MgO (1 0 0) and glass substrates, respectively. An epitaxial growth of Cr-(2 0 0)〈1 1 0〉/SmCo₅-(1 1 2¯ 0)〈0 0 0 1〉 is achieved on the MgO (1 0 0) single crystal substrate with an average grain size of 20 nm for SmCo₅. On the amorphous glass substrate, no significant crystallographic texture is found in the Cr underlayer. After the deposition of SmCo₅, a weak texture of (1 1 2¯ 0) is observed with an average grain size of 8 nm. High remanence ratio value in this film is probably due to strong exchange coupling. Both SmCo₅ films show high in-plane coercivity, high in-plane anisotropy and remanence enhancement.     

Microstructures and coercivities of SmCox and Sm(Co,Cu)5 films prepared by magnetron sputtering

We have investigated the influence of composition and annealing conditions on the magnetic properties and microstructural features of SmCo_x films that were prepared by sputtering and subsequent annealing. A huge in-plane coercivity of 5.6 T was obtained from an optimally annealed Sm–Co film, which was attributed to the nanometer sized polycrystalline microstructure of the highly anisotropic SmCo₅ phase. Although a high density of planar defects were observed in the films that were annealed at high temperatures, they did not act as strong pinning sites for domain wall motion. The effect of Cu on [SmCo_4.5(9 nm)/Cu(xnm)]₁₀ multilayer thin films was also studied. An appropriate Cu content increased the coercivity.     

Highly anisotropic resin-bonded magnets processed with surfactant-coated SmCo5 nanocrystalline powders

Highly anisotropic SmCo₅ nanocrystalline powders with grain size in the range 5-20 nm were processed through surfactant and magnetic field-assisted milling. The SmCo₅ nanocrystalline powders so obtained by this method possess unusual characteristics such as reduction in particle size, platelet-structure and high remanence values. A possible mechanism for achieving remanence enhancement with the surfactant-coated SmCo₅ powders has been discussed. Besides, the resin-bonded magnets processed with the surfactant-coated SmCo₅ powders showed relatively higher density, induction remanence and energy product with strong anisotropic behavior than those of the magnets processed with the conventionally milled SmCo₅ powders. Maximum values of H_ci (16 kOe), B_r (4.66 kG) and (BH)_max (5.5 MG Oe) were achieved for the resin-bonded magnets processed with the surfactant-coated powders.     

A study on magnetic properties and structure of SmCo5 thin films on Ni-W underlayers

A systematic study on Ni-W alloy underlayers has shown that a highly textured (2 1 1)-Ni₄W can be formed after deposition at room temperature. Highly textured (0 0 0 1)-SmCo₅ with a high out-of-plane coercivity (over 10 kOe) and large perpendicular anisotropy can be obtained after deposition on the (2 2 1)-Ni₄W underlayer probably due to a small mismatch between (2 2 1)-Ni₄W and (0 0 0 1)-SmCo₅. Our study indicates that the surface roughness of the underlayers also plays a crucial role, that a smooth surface is favorable for a good crystallinity and high coercivity of SmCo₅. Moreover, we found that a highly textured Ni-(1 1 1) can be obtained on the top of the (2 1 1)-textured Ni₄W. The film structure of SmCo₅/Ni/Ni₄W may be interesting as the hard/soft double-layered film for perpendicular magnetic recording or for other applications after a further development.     

A magnetic study of magnetoresistive Cu–(SmCo5)–Fe heterogranular alloys

The magnetic interactions between the nanograins in heterogeneous granular Cu–(SmCo₅)–Fe ribbons were evaluated with a classical mean field model to obtain the exchange coupling as well as the magnetic moment per nanoparticle. The samples were subjected to various thermal treatments and a significant magnetoresistive effect was obtained when the optimal annealing conditions had been achieved.     

Layer resolved magnetization reversal study in SmCo5/Fe nanocomposite bilayers

A hard/soft SmCo5/Fe nanocomposite magnetic bilayer system is fabricated on x-ray transparent 100-200 nm thin Si3N4 films by magnetron sputtering.The microscopic magnetic domain pattern and its behaviours during magnetization reversal in the hard and the soft magnetic phases are studied separately by element specific magnetic soft x-ray microscopy at a spatial resolution of better than 25 nm.We observe that the domain patterns for the soft and hard phases show coherent behaviours in varying magnetic fields.We derive local M(H) curves from the images of Fe and SmCo5 separately and find the switches for hard and soft phases to be the same.     

Electronic structure and magnetic properties of metastable SmCo<Subscript>7</Subscript> compound

The electronic density of states, spin-splittings and atomic magnetic moments of SmCO₇-compound have been studied using spin-polarized MS-Xα method. The results show that a few of electrons are transferred to Sm(5d⁰) orbital because of orbital hybridization between Sm and Co atoms in the compound. The exchange interactions between 3d and 5d electrons lead to the magnetic coupling between Sm and Co, and therefore, result in the long-range ferromagnetic order inside the SmCo₇ compound. There are negative exchange couplings occurring at some levels, which weakens the strength of average coupling around Co lattice. So, the Curie temperature and Co-moment of SmCo₇-decrease distinctly compared with pure Co. Compared with SmCo₅ compound, the disordered substitution of Co-Co “dumbbell-atom” pairs for Sm changes the local environment of Co lattice, which makes the 2e site bear negative magnetic moment. The strength of hybridization near Fermi level weakens and the free energy of the compound increases obviously. Thus, SmCo₇ is a metastable compound at room temperature. Considering the localization of 4f electrons and a few of 5d electrons arising from the orbital hybridization, the magnetic moment of Sm atom will be 1.61μ_B in SmCo₇ compound, which is in agreement with the experimental values of Sm³⁺ ion-moment and Sm atom-moment in metals.     

化合物SmCo5的电子结构、自旋和轨道磁矩及其交换作用分析

用自旋极化的MS-Xα方法研究了稀土-过渡族化合物SmCo5₅的电子态密度、自 旋能级劈裂及原子磁矩.研究结果显示，由于化合物中Sm-Co间的轨道杂化效应，使Sm原子原来的5d00空轨道上占据了少量5d电子.由于Co(3d)-Sm(5d)电子间的直接交换作用，导致了Sm-Co间的磁性交换耦合，这是化合物中形成Sm-Co铁磁性长程序的一个重要原因.在SmCo5_{5化合物中存在6个能级呈现负交换耦合，导致了SmCo55化 关键词： 电子结构 自旋极化 原子磁矩 交换耦合}     

Tailoring the structural and magnetic properties of sol-gel derived Sm-Co nanogranular films

In this study, we investigated the microstructure, phase evolution and magnetic properties of nanogranular films of Sm-Co compounds processed by the sol-gel method. By controlling the compositional ratio of Sm:Co precursor concentration, nanogranular films consisting of three distinct hard magnetic phases namely, Sm₂Co₇, SmCo₅ and Sm₂Co₁₇ with coercivity values of 1.78, 2.94 and 2.12 kOe, respectively, were obtained through this technique.     

Structure and the magnetic and magneto-optical properties of Co-Sm-O nanogranular films

The magnetic properties and magneto-optical effects in nanocomposites based on Co-Sm-O films prepared through pulsed plasma sputtering of a SmCo₅ target are investigated. It is shown that, depending on the technological conditions and regimes of subsequent annealing, the films can have different structures from cobalt nanoparticles distributed in the dielectric samarium oxide matrix with a magnetic phase volume of more than 60% to a continuous polycrystalline cobalt film with embedded samarium oxide nanoparticles. The evolution of the spectra of the magneto-optical Kerr effect and the field dependences of the magnetization is studied as a function of the film structure.     

Melt-spun magnetically anisotropic SmCo5 ribbons with high permanent performance

We have succeeded in preparing magnetically anisotropic SmCo₅ ribbons with high permanent performance by single-roller melt spinning at low wheel velocity. The anisotropy is associated with a crystallographic texture formed during melt-spinning process, with the c-axis parallel to the longitudinal direction of the ribbons. The formation of the crystallographic texture is attributed to a directional solidification process resulting from a thermal gradient. A remanence of 9.1 kG, remanence ratio of 0.9, intrinsic coercivity of 16.2 kOe and energy product of 18.2 MGOe at room temperature are obtained in the melt-spun and subsequently annealed SmCo₅ ribbons prepared at 5 m/s.     

Eddy-current-resistant SmCo5/CaF2 magnets produced via high-energy milling in polar and non-polar liquids

Processes of high-energy ball milling of SmCo₅ alloys were compared for three single-liquid environments without using additional surfactants. Both coarsely grained as-cast and nanocrystalline pre-milled SmCo₅ precursors showed tendency toward formation of thin flakes if milled in polar liquids (acetone and ethanol) in a marked contrast to milling in non-polar heptane. CaF₂ dielectric powder added prior to milling in the polar liquids tends to become attached on the flake surfaces. Milling in heptane in the presence of CaF₂ produces flake-like SmCo₅ particles which with increasing the milling time are found to incorporate an increasing amount of CaF₂. The SmCo₅—5 wt% CaF₂ mixtures milled for the optimum time in both the polar and non-polar liquids were successfully hot-pressed into laminated composite magnets having intrinsic coercivity of 25–30 kOe, maximum energy product of approximately 6.5 MG Oe and electrical resistivity of 500–600 μΩ cm, which is more than 7 times the resistivity of conventional Sm–Co magnets.     

The magnetization reversal behaviour for SmCo6.8Zr0.2 and SmCo6.8Zr0.2/α-（Fe,Co） nanocrystalline magnets at low temperature

This paper reports that the SmCo 6.8 Zr 0.2 nanocrystalline permanent magnets and SmCo 6.8 Zr 0.2 /α-(Fe,Co) nanocomposite permanent magnets are successfully produced by mechanical alloying and subsequently annealing at 700 C for 10 minutes.The x-ray diffraction results show that the phase structure of SmCo 6.8 Zr 0.2 nanocrystalline permanent magnets is composed of SmCo 7 phase and SmCo 6.8 Zr 0.2 /α-(Fe,Co) nanocomposite permanent magnets is composed of SmCo 7 and α-(Fe,Co) phases.The mechanism of magnetization reversal is mainly controlled by inhomogeneous domain wall pinning in SmCo 6.8 Zr 0.2 and SmCo 6.8 Zr 0.2 /α-(Fe,Co) magnets.The inter-grain exchange interaction at low temperature is investigated,which shows that the inter-grain exchange interaction of SmCo 6.8 Zr 0.2 /α-(Fe,Co) magnets increases greatly by the decrease of the measured temperature.According to Δm irr-H/H cj,Δm rev-H/H cj and χ irr-H/H cj curves at room temperature and 100 K,the changes of irreversible and reversible magnetization behaviours of SmCo 6.8 Zr 0.2 and SmCo 6.8 Zr 0.2 /α-(Fe,Co) magnets with the decreasing temperature are analysed in detail.The magnetic viscosity and the activation volume of SmCo 6.8 Zr 0.2 and SmCo 6.8 Zr 0.2 /α-(Fe,Co) magnets at different temperatures are also studied.     

SmCo7纳米晶合金晶粒组织热稳定性的热力学分析与计算机模拟

推导出了单相纳米晶合金的晶界过剩体积与晶粒尺寸之间的定量关系, 建立了纳米晶合金的晶界热力学性质随温度和晶粒尺寸发生变化的确定性函数. 针对SmCo₇纳米晶合金, 通过纳米晶界热力学函数计算和分析, 研究了单相纳米晶合金的晶粒组织热稳定性. 研究表明, 当纳米晶合金的晶粒尺寸小于对应于体系中晶界自由能最大值的临界晶粒尺寸时, 纳米晶组织处于相对稳定的热力学状态; 当纳米晶粒尺寸达到和超过临界尺寸时, 纳米晶组织将发生热力学失稳, 导致不连续的快速晶粒长大. 利用纳米晶合金热力学理论与元胞自动机算法相耦合的模型对SmCo₇纳米晶合金在升温过程中的晶粒长大行为进行了计算机模拟, 模拟结果与纳米晶合金热力学模型的计算预测结果一致, 由此证实了关于纳米晶合金晶粒组织热稳定性的研究结论. 关键词： 纳米晶合金热力学 7纳米晶合金')" href="#">SmCo₇纳米晶合金 热稳定性 计算机模拟