Anisotropic Magnetic Resonance in Random Nanocrystal Quantum Dot Ensembles

António J S Almeida; Ayaskanta Sahu; David J Norris; Gleb N Kakazei; Haripriya Kannan; Martin S Brandt; Martin Stutzmann; Rui N Pereira

doi:10.1021/acsomega.0c00279

Anisotropic Magnetic Resonance in Random Nanocrystal Quantum Dot Ensembles

ACS Omega. 2020 May 13;5(20):11333-11341. doi: 10.1021/acsomega.0c00279. eCollection 2020 May 26.

Authors

António J S Almeida^{1

2}, Ayaskanta Sahu^{3

4}, David J Norris³, Gleb N Kakazei⁵, Haripriya Kannan⁴, Martin S Brandt⁶, Martin Stutzmann⁶, Rui N Pereira¹

Affiliations

¹ i3N-Institute for Nanostructures, Nanomodelling and Nanofabrication, Department of Physics, University of Aveiro, 3810-193 Aveiro, Portugal.
² NanoElectronics Group, MESA+ Institute for Nanotechnology, University of Twente, 7522 NB Enschede, The Netherlands.
³ Optical Materials Engineering Laboratory, ETH Zurich, 8092 Zurich, Switzerland.
⁴ Department of Chemical and Biomolecular Engineering, New York University, Brooklyn, 11201 New York, United States.
⁵ Departamento de Física e Astronomia, IFIMUP and IN-Institute of Nanoscience and Nanotechnology, Universidade do Porto, 4169-007 Porto, Portugal.
⁶ Walter Schottky Institut and Physik-Department, Technische Universität München, Am Coulombwall 4, 85748 Garching, Germany.

Abstract

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.