Medina J De La Torre, Hamoir G, Velázquez-Galván Y, Pouget S, Okuno H, Vila L, Encinas A, Piraux L
Instituto de Investigaciones en Materiales-Unidad Morelia, Universidad Nacional Autónoma de México. Antigua Carretera a Pátzcuaro No. 8701 Col. Ex Hacienda de San José de la Huerta, C. P. 58190, Morelia, Mexico.
Nanotechnology. 2016 Apr 8;27(14):145702. doi: 10.1088/0957-4484/27/14/145702. Epub 2016 Feb 24.
A large enhancement of the magnetic anisotropy of Ni nanowires (NWs) embedded in anodic aluminium oxide porous membranes is obtained as a result of an induced magnetoelastic (ME) anisotropy contribution. This unusual large anisotropy enhancement depends on the diameter of the NWs and exceeds the magnetostatic (MS) contribution. As a consequence, it leads to effective magnetic anisotropy energies as large as 1.4 × 10(6) erg cm(-3), which are of the same order of magnitude and comparable to the MS energies of harder magnetic materials like Co NWs. Specifically, from ferromagnetic resonance experiments, the magnetic anisotropy of the NWs has been observed to increase as its diameter is decreased, leading to values that are about four times larger than the corresponding value when only the MS anisotropy is present. Our results are consistent with the recently proposed growth mechanism of Ni NWs that proceeds via a poly-crystalline stage at the bottom followed by a single-crystalline stage with texture [110] parallel to the axis of the NWs. A strong correlation between reducing the diameter of the NWs with the decrease of the length of the poly-crystalline segment and the enhancement of the effective magnetic anisotropy has been shown. Magnetization curves obtained from alternating gradient magnetometry experiments show that the average ME anisotropy results from the competition between the magnetic anisotropies of both crystalline segments of the NWs. Understanding the influence of size and confinement effects on the magnetic properties of nanocomposites is of prime interest for the development of novel and agile devices.
由于诱导磁弹性（ME）各向异性的贡献，嵌入阳极氧化铝多孔膜中的镍纳米线（NWs）的磁各向异性得到了极大增强。这种异常大的各向异性增强取决于NWs的直径，并且超过了静磁（MS）贡献。因此，它导致有效磁各向异性能量高达1.4×10⁶尔格/厘米³，这与更硬磁性材料如钴纳米线的MS能量处于同一数量级且相当。具体而言，通过铁磁共振实验观察到，NWs的磁各向异性随着其直径减小而增加，导致的值比仅存在MS各向异性时的相应值大约大四倍。我们的结果与最近提出的镍纳米线生长机制一致，该机制通过底部的多晶阶段，随后是具有[110]织构且平行于纳米线轴的单晶阶段进行。已经表明，NWs直径减小与多晶段长度减小以及有效磁各向异性增强之间存在很强的相关性。从交变梯度磁力测量实验获得的磁化曲线表明，平均ME各向异性源于NWs两个晶体段的磁各向异性之间的竞争。理解尺寸和限制效应对纳米复合材料磁性能的影响对于新型灵活器件的开发至关重要。
