NiO和(Pt/Co)多层膜的交换耦合作用及对其矫顽力的影响

研究了用磁控溅射法制备的(Pt/Co)多层膜和绝缘体反铁磁材料NiO之间的磁学和晶体学相互作用。室温下,当NiO覆盖在(Pt/Co)多层膜上面且NiO厚度大于25 nm时观察到了交换偏置,偏置场随NiO厚度的增加而增大。但总体上偏置场(HE)很小,对应NiO厚度为120nm时偏置场不到4000 A·m-1。NiO在(Pt/Co)多层膜下面时没有观察到交换偏置,但是对多层膜的矫顽力和垂直磁各向异性产生了很大影响。(Pt/Co)多层膜的矫顽力随NiO厚度的增加呈现非单调衰减趋势,当NiO厚度为1和3 nm时,矫顽力分别出现极小值和极大值,厚度超过3 nm的NiO使矫顽力单调下降,直至减小到接近零。(Pt/Co)多层膜的垂直磁各向异性随底层NiO厚度的增加逐渐变弱,最后垂直方向变为难轴。矫顽力和垂直磁各向异性的这种变化是由超薄NiO和(Pt/Co)多层膜之间可能存在的邻近效应,弱晶化NiO对(Pt/Co)多层膜(111)织构的影响以及NiO与(Pt/Co)多层膜之间的交换耦合共同作用造成的。     

Nd2Fe14B/α-Fe纳米晶复合永磁材料的计算机模拟研究

采用计算机模拟的方法计算了 Nd2 Fe1 4B/α- Fe纳米晶复合永磁材料的磁性能 ,并对软磁相比例及不规则晶粒对磁性能的影响进行了研究。结果显示 ,当软磁相比例增加时 ,由于软磁相高的饱和磁极化强度以及软硬磁相间的交换耦合作用的影响 ,剩磁逐渐增加 ,但矫顽力则随着软磁相的增加而逐渐下降。不规则晶粒对磁体的剩磁基本没有影响 ,但降低矫顽力。     

Nd2Fe14B/α - Fe/Nd2Fe14B磁性三层膜的微磁学模拟

以Nd2 Fe14B/α - Fe/Nd2 Fe14B三层膜为对象,应用微磁学理论计算了该体系的磁滞回线,并对其磁性能与软磁层厚度的关系进行了分析.结果表明,当软磁层厚度小于临界尺寸(5nm)时,磁滞回线为矩形,三层膜完全耦合；当软磁层厚度为5nm时,最大磁能积可达到最大值642.51 kJ/m3.在所研究的软磁层厚度范围内,随着软磁层厚度的增加,三层膜矫顽力单调下降.     

稀土-Heusler合金Tb-Co_2FeAl垂直磁各向异性薄膜的制备和磁性能的研究

使用磁控溅射方法制备了一系列Tb-Co2FeAl磁性薄膜,研究了两种不同溅射功率以及不同的薄膜厚度对样品的磁性的影响。采用交变梯度磁强计(AGM)对样品磁性能进行表征。结果显示,当Tb靶和Co2FeAl靶的溅射功率分别为5和15 W时,同时表现出平面内各向异性及弱垂直各向异性;而当功率分别为10和30 W时则表现出强垂直磁各向异性,垂直矫顽力Hc=3.3×104A.m-1,且垂直矫顽力的值随着薄膜厚度降低也逐渐减小,当厚度减小到10 nm时,Hc=1×104A.m-1。     

Co／Nb复合添加对Nd2Fe14B／α-Fe纳米晶双相复合永磁体的影响

通过复合添加,采用熔体快淬法制备Nd8　Fe82　Co3　Nb1　B6纳米晶双相复合永磁体,研究了Co,Nb对合金微观组织及磁性能的影响.结果表明,合金元素Co/Nb的复合添加,可降低剩磁和矫顽力的温度系数,增强软、硬磁相的高温稳定性;其次,提高合金的非晶形成能力,在合金的晶化退火处理中促进晶粒细化,改善显微组织,增加两相晶粒间的铁磁交换耦合作用,有利于合金综合磁性能的提高,其最佳磁性能为Br＝1.14 T,Hcj＝320 kA·m-1,(BH)max＝109.3 kJ·m-3.     

NdTbCo/Cr非晶垂直磁化膜的制备及性能

采用射频磁控溅射法在玻璃基片上制备了NdTbCo/Cr非晶垂直磁化膜。探讨了溅射功率与溅射时间对薄膜磁性能的影响,发现当溅射功率为250 W,溅射时间为4 min时,垂直膜面方向矫顽力为272.8 kA.m-1,剩磁矩形比达到0.801,可以较好地满足高密度垂直磁记录的要求。研究了Nd掺杂对薄膜磁性能与磁光性能的影响,发现随着Nd掺杂量的增多,薄膜的矫顽力从413.8下降为210.9 kA.m-1,饱和磁化强度与克尔旋转角则分别从144 kA.m-1和0.2720°上升为252 kA.m-1和0.3258°。温度对NdTbCo/Cr薄膜克尔旋转角的影响也与Nd的掺杂量密切相关。     

Co/Pt多层膜反常霍尔效应的研究

通过磁控溅射方法制备了一系列以Pt为底层的Co/Pt多层膜样品,研究了周期层中Co层厚度、周期层中Pt层厚度、底层厚度和多层膜周期数对样品霍尔效应和磁性的影响。结果表明,多层膜中各层的厚度及周期数对样品的霍尔效应和磁性有重要的影响。通过对样品测试结果的分析发现多层膜的界面效应是影响其宏观性能的主要因素,样品的霍尔电阻和矫顽力随着膜厚和周期数的变化均体现了这一效应。通过优化多层膜各层厚度参数及周期数,获得了最佳样品结构为Pt 1.0 nm/(Co 0.4 nm/Pt 0.8 nm)3,周期层中Co和Pt的最佳厚度分别为0.4和0.8 nm,最佳周期数为3,该样品的霍尔电阻最大,同时样品霍尔曲线的矩形度最好,且矫顽力也较小,通过磁性测量得到其磁各向异性能为2.0×105J·m-3,具有良好的垂直磁各向异性。     

双层复合永磁薄膜磁性能的模拟研究

利用微磁学理论模拟计算了Nd2Fe14B／α-Fe双层复合永磁薄膜的磁滞回线,并对双层膜体系的剩磁、矫顽力与软磁层厚度的关系进行了研究。结果显示,软磁层厚度小于临近尺寸时,磁滞回线为矩形,双层膜完全耦合;软磁层厚度与磁性能的关系表明,随着软磁层厚度的增加,剩磁先增大后减小,而矫顽力单调下降。     

Gdx((Fe83Co17)55Ag45)100-x颗粒膜结构及巨磁电阻效应研究

复合靶以Fe,Co,Ag和Gd按一定比例组成,采用磁控溅射法制备了Gdx((Fe83Co17)55Ag45)100-x(x=0,3.5,5.0,6.5,8.0,9.5)颗粒膜。在室温下,利用X射线衍射仪(XRD)、四探针电阻测试仪、振动样品磁强计(VSM)等方法研究Gd的掺入以及不同退火温度对颗粒膜显微结构、巨磁电阻效应(GMR)和磁性能影响。X射线衍射实验结果表明:薄膜形成了以Ag(111)和FeCo(110)组成的合金结构,且增加稀土Gd的掺入量能促进薄膜基体中FeCo与Ag的相分离。磁电阻测试结果发现:不同成分的Gdx((Fe83Co17)55Ag45)100-x(x=0,3.5,5.0,6.5,8.0,9.5)薄膜样品均随着退火温度升高以及稀土Gd含量增加,颗粒膜巨磁电阻(GMR)效应呈现先增后减的趋势,且饱和场逐渐降低,当x=5.0、退火温度250℃时,Gd5.0((Fe83Co17)55Ag45)95.0薄膜巨磁电阻效应达到最大,GMR值为-14.8%。Gd掺杂后样品磁滞回线的变化表明薄膜的矫顽力较小,矩形比随Gd含量的增加而增加,分析认为Gdx((Fe83Co17)55Ag45)100-x薄膜具有良好的软磁性能。     

添加Cr_3C_2对SmCo_7合金的组织结构及磁性能的影响

采用熔体快淬法制备(SmCo7)100-x(Cr3C2)x(x为摩尔分数,%.x=0～7)合金薄带.通过X射线衍射(XRD)、热磁分析(TMA)、振动样品磁强计(VSM)、扫描电镜(SEM)和透射电镜(TEM)研究Cr3C2添加量x对合金相结构、微观组织和磁性能的影响.结果表明,当Cr3C2含量x由0增加到7时,(SmC07)100-x(Cr3C2)x的矫顽力由33.2 kA/m显著增加到595.7 kA/m,同时主相的晶粒尺寸显著降低,合金形成了1:7 H的土相结构.第二相的结构随Cr3C2含量增加而变化,由2:17 H相逐渐转变为2:17 R相和2:7相.在高Cr3C2含量的合金(x=7)中析出了含有Cr、Co、C的晶间非磁性相,该相通过抑制主相晶粒尺寸的长大及对畴壁的钉轧来提高合金的矫顽力.     

Effect of film thickness on magnetic properties of Cr/SmCo/Cr films

Cr/SmCo/Cr films with different SmCo thickness were deposited on glass substrates by magnetron sputtering,followed by an annealing process at 550 °C for 20 min.Experimental results showed that the SmCo film of 30 nm exhibited two-phase behavior in the demagnetization process,the obvious kink was observed near zero.For the SmCo film of 50 nm,the kink was invisible,and a single phase like behavior was obtained in the demagnetization process.The reversal behavior became consistent in the thicker films.Moreover,the coercivity reduced and the saturated magnetization increased obviously with the increasing thickness.X-ray diffraction results indicated that the average grain size of SmCo 5 in the thicker films were almost 30 nm,but the quantity of SmCo 5 grains increased with the increasing thickness,which enhanced the intergrain exchange coupling(IEC) of the SmCo 5 hard phases.The increase of IEC improved the magnetic properties of SmCo films with increasing thickness.     

Effect of chromium interlayer on magnetic exchange coupling of SmCo/Cr/TbFeCo multilayer thin films

A series of SmCo/Cr/TbFeCo multilayer thin films with perpendicular anisotropy were prepared by RF- magnetron sputtering system, and the effects of Cr interlayer thickness on magnetic properties and interlayer exchange coupling were investigated. It was found that the magnetic properties varied with the thickness of Cr interlayer, especially the values of saturation magnetization Ms and the coercivity Hc fluctuated periodically with the thickness of Cr interlayer. STM images revealed that the variation of coercivity Hc was attributed to the microstructure change of SmCo layer influenced by Cr interlayer, and the variation of Ms was related to interlayer exchange coupling.     

Multilayer Magnets

After experimental evidence of intergrain exchange coupling was reported, nanocomposite magnets with high remanence and large energy products were predicted. However, the experimental values of the maximum magnetic energy product of nanocomposite bulk magnets have been much less than the theoretically predicted ones. We gave a brief review on advances in multilayer magnets. The exchange coupling and remanence enhancement were realized in nanocomposite (Nd,Dy)(Fe,Co,Nb,B)_5,5/α-Fe thin films prepared by sputtering and heat treatments. Well-designed multilayer films consist of magnetically hard Nd₂Fe₁₄B-type phase with the grain size of 40 nm and magnetically soft α-Fe phase existing in the form of the continuous layers. Furthermore, we reported the structural and magnetic properties of anisotropic Nd-Fe-B thin films. The effects of thickness, deposition rates, substrate temperature, annealing temperature were studied. A high maximum energy product of (BH)_max = 270 kJ/m³ was obtained for anisotropic Nd-Fe-B thin films.     

Analysis of Electronic Structures for SmCo5 Compound

The spin-polarized MS-Xα method is employed to study the electronic structure and the magnetic property of the SmCo5 compound.According to the calculated results, the magnetic moment per Sm is 1.29μB in the SmCo5 compound, which agrees with that of experiments.The analyzed result reveals that some negative exchange couplings occurring at six energy levels induce the distinct decrease of Curie temperature and the magnetic moment per Co.The valence electron numbers of 2.48, which are derived from the orbital hybridization from s, p, d and f functions between Sm and Co atoms, are transferred to Sm(5d0) orbital.Therefore, the exchange interactions between 3d ～ 5d electrons lead to the magnetic coupling between Sm and Co, which results in the long-range ferromagnetic-order inside the SmCo5 compound.     

Enhancement in energy product in Sm-Co/Fe exchange coupled magnetic layers with molybdenum interlayers

Trilayers of Sm-Co/Mo/Fe were deposited by DC and RF magnetron sputtering on Si(100) substrate at 650 °C.Effect of very thin Mo interlayers on energy product of magnetic layers was studied.All the samples showed strong exchange coupling and single phase behavior.With increasing Mo interlayer thickness,we observed oscillating behavior of saturation magnetization and energy product.The rise in energy product was observed as 22% for 0.3 nm Mo interlayer as compared to sample without Mo interlayer.     

Magnetic property and microstructure of SmCo magnetic recording films

Cr/SmCo/Cr thin films with Sm concentration of 37.7 at.% were deposited on glass substrates by magnetron sputtering. Meas-urement of magnetic properties showed that the SmCo film possessed good magnetic anisotropy, a high coercivity of 3019 kA/m and low magnetic exchange coupling. Microstructure analysis showed that crystallized SmCo5 magnetic phase, non-magnetic SmCo2 phase and Sm2Co7 phase co-existed ill the film. The non-magnetic SmCo2 phase might function as isolator of SmCo grains, leading to a decrease of magnetic exchange coupling. Moreover, a Cr2)3 oxide layer which could protect the SmCo layer from oxidation formed at the surface of the Cr cap layer.     

Effect of zirconium content on exchange coupling and magnetization reversal of nanocrystalline Nd_(12.3)Fe_(81.7-x)Zr_xB_6 alloy

The effect of Zr content on exchange coupling and magnetization reversal of the Nd12.3Fe81.7-xZrxB6(x=0-3.0) ribbons was systematically investigated.Interaction domains were imaged by magnetic force microscopy(MFM).The strength of interactions determined byWohlfarth's analysis increased first with Zr content x increasing,reached the maximum value at x=1.5,and then decreased with x further increasing.Initial magnetization curves and dependence of coercivity and remanence on applied magnetic field showed that...     

Micromagnetic Simulation of Magnetization Reversal in SmCo5／Sm2Co17 Magnets

A three-dimensional finite element micromagnetic algorithm was developed to study the magnetization reversal of the SmCo5/Sm2Co17 based magnets. The influences of the microstructure and magnetic parameters on the coercivity were studied based on the model consisting of 64 irregular cells according to the experimental microstructure. Numerical results show that the coercivity increases with increasing the 2: 17-type cell size. Large cell boundary thickness leads to small coercivity. The drop of anisotropy constant of 1:5 phase leads to the coercivity reducing, while the effect of exchange constant of 1 : 5 phase on coercivity is contrary to that of exchange constant. The calculated field dependence of coercivity can be predicted by an inhomogeneous domain - wall pinning model. The microstructure parameter was analyzed by comparing the calculated coercivity.     

Nb添加对Nd-Ce-Fe-B合金的磁性能及晶间交换耦合作用的影响

研究了不同含量的Nb添加对(Nd_0.5Ce_0.5)₁₃Fe_82-xNb_xB₅快淬合金的磁性能、物相组成、交换耦合作用及其初始磁化机制的影响.发现Nb添加能抑制α-Fe的形成,显著改善合金的磁性能.当Nb的添加量(原子分数)为0.5%时,合金获得较优的磁性能.随着Nb的添加量(原子分数)从0增加到0.5%,合金的矫顽力由未添加时的777 kA/m提升到900 kA/m, 最大磁能积也从未添加Nb时的64 kJ/m3增加到78 kJ/m3,而合金的剩磁仅由未添加Nb时的0.71 T轻微下降到0.70 T.合金中晶粒间的交换耦合作用随着Nb的添加而增强.合金的初始磁化机制也有了显著地变化.      

Magnetic and magnetostrictive properties of amorphous TbFe/FeAl multilayer thin film

Exchange coupling multilayer thin films, which combined giant magnetostriction and soft magnetic properties, were of growing interest for applications. The TbFe/FeAl multilayer thin films were prepared by dc magnetron sputtering onto glass substrates. The microstructure, magnetic, and magnetostrictive properties of TbFe/FeAl multilayer thin film was investigated at different annealing temperatures. The results indicated that the soft magnetic and magnetostrictive properties for TbFe/FeAl multilayer thin film compared with TbFe single layer film were obviously improved. In comparison with the intrinsic coercivity JHc of 59.2 kA/m for TbFe single layer film, the intrinsic coercivity JHc for TbFe/FeAl multilayer thin films rapidly dropped to 29.6 kA/m. After optimal annealing (350 ℃×60 min), magnetic properties of Hs=96 kA/m and JHc=16 kA/m were obtained, and magnetostrictive coefficient could reach to 574×10-6 under an external magnetic field of 400 kA·m-1 for the TbFe/FeAl multilayer thin film.