Magnetic properties and exchange coupling of Nd-Ce-Fe-B nanocomposite films
Magnetic properties and exchange coupling of Nd-Ce-Fe-B nanocomposite films
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Nd-Ce-Fe-B纳米复合薄膜的磁性能及交换耦合
DOI：
10.7498/aps.66.157502
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发表时间：
2017-08-05
影响因子：
1
通讯作者：
Li Wei
中科院分区：
文献类型：
--
作者：
Sun Ya-Chao;Zhu Ming-Gang;Li Wei
20世纪80年代初，发展了软硬磁纳米双相永磁材料，并提出了交换耦合模型。理论最大磁能积可达120 MGOe（1 Oe = 7.9：5.7.75A/m）。然而，大量的实验研究结果总是令人失望的理论计算，但以往的研究表明，在硬磁相也存在着很强的交换耦合，它可以改善磁体的磁性能。采用直流溅射法在Si基片上制备了Ta（50 nm）/NdFeB（100 nm）/Ta（2 nm）/NdCeFeB（100 nm）/Ta（2 nm）/NdFeB（100 nm）/ Ta（40 nm）纳米复合多层膜。在室温下溅射50 nm的Ta底层和40 nm的覆盖层，以分别使RE 2Fe 14 B晶粒的易磁化轴与膜平面垂直的方向对准并防止磁性膜氧化。2nm的Ta间隔层用于抑制不同磁性层之间的元素扩散。NdFeB和NdCeFeB磁性薄膜分别在630 ℃和610 ℃下沉积，然后在645-705 ℃下原位快速热退火30 min。薄膜的微观结构和形貌通过X射线衍射仪、原子力显微镜和磁力显微镜进行表征。用振动样品磁强计测量了薄膜的磁性能，研究了退火温度对薄膜磁性能和晶体结构的影响。结果表明，随着退火温度的升高，薄膜的磁性能逐渐提高，但当温度达到695 ℃以上时，薄膜的磁性能急剧恶化。当退火温度为675 ℃时，在垂直于Nd-Ce-Fe-B薄膜平面的方向上施加磁场时，薄膜的矫顽力H-ci达到10.1kOe，剩磁4（pi）M（r垂直于）为5.91kG（1G = 103/（4pi）A/m）。X射线衍射结果表明，硬磁相（2：1 ~ 4：1相）的晶粒几乎沿着衬底法线（c轴方向）生长，当然也存在一定的取向差。通过对Nd-Ce-Fe-B薄膜的磁化反转过程的研究发现，随着外加磁场的增加，Mrev的最小值向Mirr减小的方向移动，这与畴壁弯曲模型相似。这表明薄膜中存在较强的局域畴壁钉扎。此外，剩磁曲线表明，在685 ℃退火后的Nd-Ce-Fe-B薄膜的磁化反转过程中，钉扎型机制确实不占主导地位。此外，还研究了不同退火温度下薄膜的Henkel图。据信，非零Δ（m）是由于磁体中粒子之间的相互作用。测量结果表明，Nd-Ce-Fe-B薄膜中存在较强的磁交换耦合效应。
In the early 1980 s, the soft and hard magnetic nano-two-phase permanent magnet materials were developed and exchange coupling model was put forward. Moreover, the theoretical maximum magnetic energy product could reach 120 MGOe (1 Oe = 7 9 : 5 7 7 5 A/m). However a great many of experimental research results are always disappointing for theoretical calculation, but previous studies have shown that there exists also a strong exchange coupling in hard magnetic phase, which can improve the magnetic property of magnet.In this paper, nanocomposite Ta(50 nm)/NdFeB(100 nm)/Ta(2 nm)/NdCeFeB(100 nm)/Ta(2 nm)/NdFeB(100 nm)/ Ta(40 nm) multilayer films with Ta underlayers and coverlayers are fabricated on Si substrates by direct current sputtering. A 50 nm Ta underlayer and a 40 nm coverlayer are sputtered at room temperature to align the easy axis of the RE2Fe14B grains to the direction perpendicular to the film plane and to prevent the magnetic film from oxidizing, respectively. The 2 nm Ta spacer layer serves as suppressing the diffusion of elements between different magnetic layers. The NdFeB and NdCeFeB magnetic film are deposited at 630 degrees C and 610 degrees C, respectively, and then they are followed by in situ rapid thermal annealing at 645-705 degrees C for 30 min. The microstructures and morphologies of the films are characterized by X-ray diffractometry with Cu K-alpha radiation, atomic force microscope, and magnetic force microscope. The magnetic properties of the films are measured with vibrating sample magnetometer.The influences of annealing temperature on magnetic property and crystal structure of the film are investigated. The results show that the magnetic property of the film improves gradually with the increase of annealing temperature, but deteriorates sharply when the temperature reaches above 695 degrees C. When the annealing temperature is 675 degrees C, the coercivity H-ci of the film reaches 10.1 kOe and the remanence 4(pi)M(r perpendicular to) is 5.91 kG (1 G = 10 3 /(4 pi) A/m), with a magnetic field applied to the direction perpendicular to the plane of the Nd-Ce-Fe-B thin film. The X-ray diffraction results show that the grains of the hard magnetic phase (2 : 1 4 : 1 phase) grow almost along the substrate normal (c-axis direction), of course, with a certain misorientation. Through the magnetization reversal process of the Nd-Ce-Fe-B thin film, it is found that the minimum value of M rev moves in the direction of decreasing M irr as the applied magnetic field increases, which is similar to the domain wall bowing model. This indicates that there is a strong local domain wall pinning in the film. Moreover, the remanence curve shows that the pinning type mechanism is indeed not dominant in the magnetization reversal process of the Nd-Ce-Fe-B thin film after annealing at 685 degrees C. In addition, Henkel plots are also investigated in the films at different annealing temperatures. It is believed that nonzero delta(m) is due to the interaction between particles in the magnet. It can be stated based on the measuring results that there exists a strong magnetic exchange coupling effect in the Nd-Ce-Fe-B thin film.