Almeida António J S, Sahu Ayaskanta, Norris David J, Kakazei Gleb N, Kannan Haripriya, Brandt Martin S, Stutzmann Martin, Pereira Rui N
i3N-Institute for Nanostructures, Nanomodelling and Nanofabrication, Department of Physics, University of Aveiro, 3810-193 Aveiro, Portugal.
NanoElectronics Group, MESA+ Institute for Nanotechnology, University of Twente, 7522 NB Enschede, The Netherlands.
ACS Omega. 2020 May 13;5(20):11333-11341. doi: 10.1021/acsomega.0c00279. eCollection 2020 May 26.
Magnetic anisotropy critically determines the utility of magnetic nanocrystals (NCs) in new nanomagnetism technologies. Using angular-dependent electron magnetic resonance (EMR), we observe magnetic anisotropy in isotropically arranged NCs of a nonmagnetic material. We show that the shape of the EMR angular variation can be well described by a simple model that considers magnetic dipole-dipole interactions between dipoles randomly located in the NCs, most likely due to surface dangling bonds. The magnetic anisotropy results from the fact that the energy term arising from the magnetic dipole-dipole interactions between all magnetic moments in the system is dominated by only a few dipole pairs, which always have an anisotropic geometric arrangement. Our work shows that magnetic anisotropy may be a general feature of NC systems containing randomly distributed magnetic dipoles.
磁各向异性在新的纳米磁性技术中对磁性纳米晶体（NCs）的应用起着关键作用。通过角相关电子磁共振（EMR），我们在非磁性材料的各向同性排列的NCs中观察到了磁各向异性。我们表明，EMR角变化的形状可以通过一个简单模型很好地描述，该模型考虑了随机位于NCs中的偶极子之间的磁偶极-偶极相互作用，这很可能是由于表面悬空键所致。磁各向异性源于这样一个事实，即系统中所有磁矩之间的磁偶极-偶极相互作用产生的能量项仅由少数偶极对主导，而这些偶极对总是具有各向异性的几何排列。我们的工作表明，磁各向异性可能是包含随机分布磁偶极子的NC系统的一个普遍特征。
