Nd28Fe66B6/Fe50Co50双层纳米复合膜的结构和磁性

利用磁控溅射法制备了Nd28F66B6/Fe50Co50双层纳米复合磁性薄膜,研究了其结构和磁性.经873K退火处理15min后,利用x射线衍射仪测定薄膜晶体结构,采用俄歇电子能谱仪估算薄膜厚度和超导量子干涉仪测量其磁性.磁性测量表明,1)该系列薄膜具有垂直于膜面的磁各向异性.从起始磁化曲线和小回线的形状特征可知,矫顽力机制主要是由畴壁钉扎控制.2)对于固定厚度(10nm)层的硬磁相Nd-Fe-B和不同厚度(dFeCo=1-100nm)层软磁相FeCo双层纳米复合膜,剩磁随软磁相FeCo厚度的增加快速增加,而矫顽力则减少.当dFeCo=5nm时,最大磁能积达到160×103A/m.磁滞回线的单一硬磁相特征说明,硬磁相Nd-Fe-B层和软磁相FeCo层之间的相互作用使两相很好地耦合在一起.剩磁和磁能积的提高是由于两相磁性交换耦合所致.     

Nd-Fe-B/FeCo多层纳米复合膜的结构和磁性

制备了Nd₂₈Fe₆₆B₆/Fe₅₀Co₅₀多层纳米复合磁性薄膜，对溅射态和650℃退火处理15 min试样的相成分分析和微结构的观察显示，溅射态薄膜呈非晶态，经650℃退火处理15 min后，薄膜主要相成分为硬磁性Nd₂Fe₁₄B相和软磁性相FeCo(110)相.Nd₂Fe₁₄B相呈柱状，其易磁化c轴垂直于膜面，尺寸约10 nm.在硬磁性相和软磁性相之间存在少量富Nd相和非晶态，富Nd相大小约7 nm.磁性测量和分析表明，1)该系列薄膜退火态具有垂直于膜面的磁晶各向异性.2)对于固定厚度(10 nm)层Nd-Fe-B和不同厚度(t_FeCo=1—100 nm)层FeCo多层纳米复合膜,剩磁随软磁相FeCo 厚度的增加快速增加，而矫顽力则减小.当t_FeCo=5 nm时，最大磁能积达到200 kJ/m³. 3)硬磁相Nd-Fe-B层和软磁相FeCo层之间交换耦合导致剩磁和磁能积增强. 关键词： Nd-Fe-B/FeCo多层纳米复合膜 交换耦合 磁各向异性     

纳米结构SmCo/FeCo多层薄膜的磁性

研究了用磁控溅射方法制备的纳米结构Sm₂₂Co₇₈单层膜、Sm₂₂Co₇₈/Fe₆₅Co₃₅双层膜及Sm₂₂Co₇₈/Fe₆₅Co₃₅/Sm₂₂Co₇₈三层膜的磁性,特别是双层膜及三层膜系统中的Fe₆₅Co₃₅软磁层厚度d对薄膜剩磁比(M_r/M_s)和矫顽力(H_c)的影响.所有样品的磁滞回线测量表明,该系列薄膜的易磁化轴在膜面内.磁滞回线的单一硬磁相特征,说明SmCo硬磁层与FeCo软磁层之间的交换相互作用使两相很好地复合在一起.在双层膜和三层膜中,M_r/M_s随软磁层厚度d的增加单调上升,而矫顽力随d的变化出现一峰值.通过研究ΔM随磁场H的变化,发现随着软、硬磁相界面数的增加,ΔM曲线的正峰数量逐渐减少;负峰数量逐渐增强,负峰的半高宽逐渐减少. 关键词：     

高性能纳米复合永磁材料的模拟计算研究

构造了在软磁相基体中析出规则形状硬磁相的各向同性和各向异性纳米复合永磁材料Pr2Fe14Bα-Fe.利用微磁学的有限元法，模拟计算了样品的磁滞回线.通过对剩磁、矫顽力和最大磁能积与软磁相厚度的关系分析，发现在软磁相厚度为0—12nm的范围内，复合磁体的矫顽力随软磁相厚度的增加而单调下降，而最大磁能积则是在适当的矫顽力和剩磁下达到最高.预计纳米复合Pr2(Fe,Co)14Bα-(Fe,Co)的各向同性磁体的最大磁能积最高可达248kJ/m3，而各向异性磁体则高达784kJ/m3. 关键词： 纳米复合永磁 矫顽力 剩磁 磁能积     

分子束外延生长Fe/Fe50Mn50双层膜的交换偏置

利用表面磁光克尔效应和铁磁共振对分子束外延生长的Fe/Fe₅₀Mn₅₀双层膜的交换偏置场和矫顽力进行了研究,实验结果表明,当反铁磁层厚度小于55nm时 ,不出现交换偏置,而当大于这一厚度时,出现交换偏置;大约在7nm时,达到极大值.随着 反铁磁层厚度的继续增大,偏置场和矫顽力随Fe₅₀Mn₅₀膜厚的增大 而下降.铁磁共振实验结果表明样品的磁性存在单向各向异性.并对上述结果进行了讨论. 关键词： 分子束外延 50Mn₅₀')" href="#">Fe/Fe₅₀Mn₅₀ 双层膜 交换偏置     

CoFe2O4和MnFe2O4纳米复合介质的制备及其磁性研究

采用热分解法制备了分散程度高且平均晶粒尺寸为20 nm的CoFe₂O₄和MnFe₂O₄复合介质.低温磁化曲线测量显示,制备的复合介质具有软-硬磁交换弹性耦合效应,且合成温度以及软磁和硬磁相的成分比例对磁交换弹性耦合的强度有很大的影响.变温磁测量显示,温度为20K时,复合纳米介质的表面自旋冻结效应导致饱和磁化强度显著增加.Henkel测量显示,对分散的CoFe₂O₄和MnFe₂O₄复合介质,磁偶极相互作用占主导作用.     

纳米复合永磁材料中软磁性相交换硬化的研究

本文就纳米复合永磁材料中软磁相被交换硬化问题,从一维模型和三维模拟计算进行了分析研究. 一维和三维各向异性样品研究表明,在相同微结构下,当硬磁相的各向异性降低时,除矫顽力降低外,在磁矩全部反转之前退磁曲线是一样的. 因此,硬磁相各向异性的降低不会导致最大磁能积(BH)_max增大和剩磁增加. 对于三维各向同性样品的模拟计算表明,降低硬磁相的各向异性会使剩磁和(BH)_max都明显降低. 因此,增强硬磁相的各向异性并增大硬磁相晶粒尺寸是提高 关键词： 纳米复合永磁 矫顽力 剩磁 磁能积     

纳米晶复合SrFe12O19γ-Fe2O3永磁铁氧体的制备和交换耦合作用

采用solgel方法制备M型六角锶铁氧体.利用X射线衍射,透射电子显微镜和VSM对纳米晶样品进行了研究.当焙烧温度小于或等于800℃,样品存在复相.在同样条件下,压成薄片的样品呈现了硬磁与软磁SrFe12O19γFe2O3的纳米复合相的磁性交换耦合作用.800℃焙烧的薄片样品的比饱和磁化强度σS为75.6A·m2kg,内禀矫顽力HcJ为478.9kAm,最大磁能积(BH)max为14.9kJm3,而粉末样品相应的分别为75.9A·m2kg,509.6kAm和12.1kJm3.当焙烧温度大于850℃时,只有 关键词： 六角锶铁氧体 纳米复合 交换耦合 磁性     

各向同性纳米结构Fe-Pt薄膜的结构和磁性

采用直流溅射和热处理技术制备了两个各向同性的纳米结构Fe-Pt永磁合金薄膜系列,并研究了它们的结构和磁性.研究表明,在富Fe双相纳米结构Fe-Pt永磁合金薄膜中,仅由硬磁的FePt相与软磁的Fe₃Pt相组成;在同一系列中,随Fe层厚度的增加,饱和磁极化强度和剩磁明显增大.由Kelly-Henkel图研究指出,在上述Fe-Pt纳米结构永磁合金薄膜中,磁相互作用主要由近邻纳米晶粒间的铁磁交换相互作用控制. 关键词： 磁性薄膜 纳米结构 矫顽力     

基于交换耦合模型纳米双相(硬磁/软磁)自旋体系的磁性

采用MonteCarlo方法对由异类自旋组成混合Heisenberg自旋体系进行了数值计算,以模拟和预测基于交换耦合模型纳米双相(硬磁软磁)磁性体系的磁性.区别于以往所报道的那些直接针对硬磁NdFeB与软磁纳米αFe复合磁体的微磁学计算工作,着眼于符合Heisenberg模型的两类完全不同的原子自旋集团(硬磁自旋和软磁自旋)之间的直接交换耦合作用,模拟计算了由这两类自旋组成的复合自旋体系的内禀矫顽力Hc、剩余磁化强度Mr、最大磁能级(M×H)max等宏观磁性参量随软磁自旋集团的尺度和体积百分比、两类自旋集 关键词： Heisenberg模型 MonteCarlo模拟 纳米复合磁体 Nd-Fe-B     

Exchange coupling and remanence enhancement in nanocomposite Nd–Fe–B/FeCo multilayer films

Nd–Fe–B-type hard phase single layer films and nanocomposite Nd₂₈Fe₆₆B₆/Fe₅₀Co₅₀ multilayer films with Mo underlayers and overlayers have been fabricated on Si substrates by rf sputtering. The hysteresis loops of all films indicated simple single loops for fixed Nd–Fe–B layer thickness (10 nm) and different FeCo layer thickness (d_FeCo=1–50 nm). The remanence of these films is found to increase with increasing d_FeCo and the coercivity decrease with increasing d_FeCo. It is shown that high remanence is achieved in the nanocomposite multilayer films consisting of the hard magnetic Nd–Fe–B-type phase and soft magnetic phase FeCo with 20 nm?d_FeCo?3 nm. The sample of maximum energy product is 27 MG Oe for d_FeCo=5 nm at room temperature. The enhancement of the remanence and energy products in nanocomposite multilayer films is attributed to the exchange coupling between the magnetically soft and hard phases.     

Synthetic Co50Pt50/Ru/CoFe hard–soft trilayer in spin valves

The influence of deposition power and seedlayer on the properties of hard magnet Co₅₀Pt₅₀ was studied. Co₅₀Pt₅₀(/Co₉₀Fe₁₀)/Ru/Co₉₀Fe₁₀ trilayer was used as pining/pinned layer in spin valves. The influences of different hard layer, soft layer and free layer on exchange bias, interlayer coupling, and magnetoresistance (MR) ratio were studied. Weak antiferromagnetic interlayer coupling was obtained by adjusting the thickness of hard and soft layers. MR of a spin valve with structure Cr2/CoFe0.5/CoPt4/CoFe0.5/Ru0.8/CoFe2.2/Cu2.05/CoFe2.6/Cu1.1/Ta1 reached 10.68% (unit in nm), which is comparable to those of IrMn-based synthetic spin valves. The increment of the coercivity of the free layer is mainly due to the static magnetic interaction between the hard layer and the free layer.     

Annealing effect of NiO/Co90Fe10 thin films: From bilayer to nanocomposite

Exchange-biased bilayers are widely used in the pinned layers of spintronic devices. While magnetic field annealing (MFA) was routinely engaged during the fabrication of these devices, the annealing effect of NiO/CoFe bilayers is not yet reported. In this paper, the transition from NiO/Co₉₀Fe₁₀ bilayer to nanocomposite single layer was observed through rapid thermal annealing at different temperatures under magnetic field. The as-deposited and low-temperature (<623 K) annealed samples had rock salt (NiO) and face center cubic (Co₉₀Fe₁₀) structures. On the other hand, annealing at 623 K and 673 K resulted in nanocomposite single layers composed of oxides (matrix) and alloys (precipitate), due to grain boundary oxidization and strong interdiffusion in the NiO/CoFe and CoFe/SiO₂ interfaces. The structural transition was accompanied by the reduction of grain sizes, re-ordering of crystallites, incensement of roughness, and reduction of Ni²⁺. When measured at room temperature, the bilayers exhibited soft magnetism with small room-temperature coercivity. The nanocomposite layers exhibited an enhanced coercivity due to the changes in the magnetization reversal mechanism by pinning from the oxides. At 10 K, the increased antiferromagnetic anisotropy in the NiO resulted in enhanced coercivity and exchange bias in the bilayers. The nanocomposites exhibited weaker exchange bias compared with the bilayers due to frustrated interfacial spins. This investigation on how the magnetic properties of exchange-biased bilayers are influenced by magnetic RTA provides insights into controlling the magnetization reversal properties of thin films.     

Fe/SnO2非晶多层膜的磁特性

研究了高频溅射制备的Fe/SnO₂非晶多层膜的磁特性.当SnO₂层厚度d_s固定为5nm时，样品的饱和磁化强度M_s随Fe层厚度d_m的减小而降低，这主要受样品的死层效应和维度效应的影响.另外，在d_m很小时，样品呈现准二维磁性.样品居里温度T_C随d_m的减小单调下降.样品矫顽力H_c随d_m的变化呈现 关键词：     

Nano-sized disorders in hard magnetic grains and their influence on magnetization reversal at artificial Nd/Nd2Fe14B interfaces

We have investigated the effect of lattice disorders near the surface of hard magnetic Nd₂Fe₁₄B grains on coercivity using artificial interfaces created by sputter depositing Nd on polished surface of Nd-Fe-B sintered magnets. The interfacial structure was manipulated by annealing the coated samples at 550 °C in vacuum with and without Ta cap. Nano-beam electron diffraction revealed a few nm thick disordered layer within the Nd₂Fe₁₄B phase at the Nd/Nd₂Fe₁₄B interface of a low coercivity sample, while a high coercivity sample showed a well-defined crystal structure of Nd₂Fe₁₄B near the NdO_x/Nd₂Fe₁₄B interface.     

La0.67Ca0.33MnO3薄膜中的矫顽力随膜厚与衬底的变化

系统研究了衬底为SrTiO3和LaAlO3上的La0.67Ca0.33MnO3薄膜中的矫顽力随厚度和应变的变化。结构分析表明薄膜为（001）方向织构，而且薄膜中的晶粒尺寸随着薄膜厚度的减小而减小。磁测量表明矫顽力先随着膜厚的减小而增加，在t=10-25nm附近到达一极大值。随后，矫顽力随厚度的减小而降低。还得出矫顽力的大小与测量方向有关：t≥25nm (t≤10nm)时，难磁化方向的矫顽力大于（小于）易磁化方向的矫顽力。据此，我们提出：在厚膜（t≥25nm）中，矫顽力变化由畴壁钉扎机制决定；在超薄膜（t≤10nm）中，则与磁畴的形核机制有关。根据t= 5、10、25、400nm的LCMO/STO薄膜的初始磁化曲线，以及t=5，50nm的LCMO/LAO薄膜的小磁滞回线的测量，我们对薄膜中矫顽力机制作了验证，并且还讨论了钉扎和形核机制发生的非均匀区的尺寸。     

Amorphous-crystalline dual-layer structures resulting from metastable liquid phase separation in （Fe50Co25B15Si10）80Cu20 melt-spun ribbons

（Fe50Co25B15Si10）80Cu20 ribbons are prepared by using the single-roller melt-spinning method. A dual-layer structure consisting of a （Fe, Co）-rich amorphous phase and a Cu-rich crystalline phase forms due to metastable liquid phase separation before solidification. The magnetic hysteresis loops of the as-quenched and annealed samples are measured at room temperature. It is indicated that the coercivity of the ribbon is almost zero in the as-quenched state. The crystallization leads to the increase of coercivity and decrease of saturation magnetization.