Bersweiler Mathias, Bender Philipp, Peral Inma, Pratami Sinaga Evelyn, Honecker Dirk, Alba Venero Diego, Titov Ivan, Michels Andreas
Department of Physics and Materials Science, Université du Luxembourg, 162A avenue de la Faïencerie, Luxembourg L-1511, Grand Duchy of Luxembourg.
Heinz Maier-Leibnitz Zentrum, Technische Universität München, Garching D-85748, Germany.
J Appl Crystallogr. 2022 Jul 15;55(Pt 4):713-721. doi: 10.1107/S1600576722006355. eCollection 2022 Aug 1.
Shell ferromagnetism is a new functional property of certain off-stoichiometric Ni-Mn-In Heusler alloys, with a potential application in non-volatile magnetic memories and recording media. One key challenge in this field remains the determination of the structural and magnetic properties of the nanoprecipitates that are the result of an annealing-induced segregation process. Thanks to its unique mesoscopic length scale sensitivity, magnetic small-angle neutron scattering appears to be a powerful technique to disclose the microstructure of such annealing-induced nanoprecipitates. In this study, the microstructure of a zero-field-annealed off-stoichiometric NiMnIn Heusler alloy is investigated by unpolarized magnetic small-angle neutron scattering. The neutron data analysis reveals a significant spin-misalignment scattering, which is mainly related to the formation of annealing-induced ferromagnetic nanoprecipitates in an antiferromagnetic matrix. These particles represent a source of perturbation which, due to dipolar stray fields, gives rise to canted spin moments in the surroundings of the particle-matrix interface. The presence of anticorrelations in the computed magnetic correlation function reflects the spatial perturbation of the magnetization vector around the nanoprecipitates. The magnetic field dependence of the zero crossing and the minima of the magnetic correlation function are qualitatively explained using the law of approach to ferromagnetic saturation for inhomogeneous spin states. More specifically, at remanence, the nanoprecipitates act magnetically as one superdefect with a correlation length that lies outside the experimental range, whereas near saturation the magnetization distribution follows each individual nanoprecipitate. Analysis of the neutron data yields an estimated size of 30 nm for the spin-canted region and a value of about 75 nm for the magnetic core of the individual nanoprecipitates.
壳层铁磁性是某些非化学计量比的Ni-Mn-In赫斯勒合金的一种新功能特性，在非易失性磁存储器和记录介质中具有潜在应用。该领域的一个关键挑战仍然是确定由退火诱导偏析过程产生的纳米析出物的结构和磁性。由于其独特的介观长度尺度敏感性，磁小角中子散射似乎是一种揭示此类退火诱导纳米析出物微观结构的有力技术。在本研究中，通过非极化磁小角中子散射研究了零场退火的非化学计量比NiMnIn赫斯勒合金的微观结构。中子数据分析揭示了显著的自旋失准散射，这主要与反铁磁基体中退火诱导的铁磁纳米析出物的形成有关。这些粒子代表了一种扰动源，由于偶极杂散场，在粒子-基体界面周围产生倾斜的自旋矩。计算得到的磁相关函数中反相关的存在反映了纳米析出物周围磁化矢量的空间扰动。利用非均匀自旋态的铁磁饱和趋近定律定性地解释了磁相关函数的零交叉和最小值的磁场依赖性。更具体地说，在剩余磁化强度下，纳米析出物在磁性上表现为一个超缺陷，其相关长度超出了实验范围，而在接近饱和时，磁化分布遵循每个单独的纳米析出物。对中子数据的分析得出，自旋倾斜区域的估计尺寸为30 nm，单个纳米析出物的磁核值约为75 nm。
