Bohra Murtaza, Alman Vidya, Showry Arun, Singh Vidyadhar, Diaz Rosa E, Sowwan Mukhles, Grammatikopoulos Panagiotis
Nanoparticles by Design Unit, Okinawa Institute of Science and Technology Graduate University, 1919-1 Tancha Onna-Son, Okinawa 904-0495, Japan.
Mahindra University École Centrale School of Engineering (MEC), Survey Number 62/1A, Bahadurpally Jeedimetla, Hyderabad 500043, Telangana, India.
ACS Omega. 2020 Dec 14;5(51):32883-32889. doi: 10.1021/acsomega.0c03056. eCollection 2020 Dec 29.
Annealing is a valuable method for fine-tuning the ultrasmall magnetic properties of alloy nanoparticles (NPs) by controlling their sizes, modifying their surfaces, and affecting their magnetic interactions. Herein, we study the effect of moderate annealing (450 °C) on strongly interacting NiCr nanoparticle assemblies (0 ≤ atom % Cr ≤ 15) immediately after deposition. Concurrent temperature-dependent electron microscopy and magnetization data demonstrate the interplay of two competing factors, namely, enhanced particle aggregation and element-specific surface segregation, on the magnetic properties, with the former boosting and the latter suppressing them. Strong interparticle interactions can lead to a magnetic response different from that of superparamagnetic particles, namely, from canonical spin-glass (0 atom % Cr) to correlated spin-glass (5-15 atom % Cr) behavior below higher spin-glass transition temperatures (20-350 K). The observation of "" below cryogenic temperatures (≤20 K) is ascribed to the presence of inhomogeneity/defects caused by Cr segregation. This work emphasizes the necessity of taking into account the delicate balance of such competing factors to understand the magnetic properties of nanoparticulate samples.
退火是一种通过控制合金纳米颗粒（NPs）的尺寸、修饰其表面以及影响其磁相互作用来微调其超小磁性能的重要方法。在此，我们研究了中等温度退火（450°C）对沉积后立即形成的强相互作用NiCr纳米颗粒组装体（0≤Cr原子百分比≤15）的影响。同时进行的温度相关电子显微镜和磁化数据表明，两种相互竞争的因素，即增强的颗粒聚集和元素特异性表面偏析，对磁性能产生相互作用，前者增强而后者抑制磁性能。强烈的颗粒间相互作用可导致与超顺磁性颗粒不同的磁响应，即在高于更高的自旋玻璃转变温度（20 - 350 K）时，从典型自旋玻璃（0原子百分比Cr）转变为相关自旋玻璃（5 - 15原子百分比Cr）行为。在低温（≤20 K）下观察到的“”归因于Cr偏析导致的不均匀性/缺陷的存在。这项工作强调了考虑这些相互竞争因素的微妙平衡对于理解纳米颗粒样品磁性能的必要性。
