Magnetometry of single ferromagnetic nanoparticles using magneto-optical indicator films with spatial amplification

Published

March 16, 2015

Author(s)

Andrew L. Balk, Carlos M. Hangarter, Samuel M. Stavis, John Unguris

Abstract

We present a magneto-optical imaging technique to rapidly measure two dimensional, sub-micrometer maps of fringe fields from single magnetic nanorods with microtesla sensitivity. Our technique implements an ultrathin, low-coercivity, perpendicularly-magnetized film as an indicator of the stray field of the nanorods. The stray field is manifested as a shift of down-to-up and up-to-down ferromagnetic transitions in the thin film near the nanorods. This measurement is insensitive to many common noise sources, requires no cryogen, and is easily adaptable to different test environments. We first discuss our method to fabricate the high sensitivity indicator film with low energy argon ion irradiation. We then present a high resolution fringe field map from a single nanorod as measured by the indicator film, and discuss the noise limitations. Our data determines a minimum measureable particle diameter of several tens of nanometers for typical transition metals. We then use our method to obtain hysteresis loops from multiple, single nanorods in parallel, and demonstrate that the nominally identical nanorods show polydispersity in coercive field. We discuss future improvements and applications for our indicator film technique.

Citation

Applied Physics Letters

Volume

106

Issue

11

Pub Type

Journals

Download Paper

https://doi.org/10.1063/1.4916205

Keywords

Magnetic nanoparticles, magnetic anisotropy, single particle measurements, nanomagnetism

Citation

Balk, A. , Hangarter, C. , Stavis, S. and Unguris, J. (2015), Magnetometry of single ferromagnetic nanoparticles using magneto-optical indicator films with spatial amplification, Applied Physics Letters, [online], https://doi.org/10.1063/1.4916205 (Accessed December 26, 2024)