Magnetization Switching of Single Magnetite Nanoparticles Monitored Optically

arXiv (Cornell University)

Abstract

Magnetic nanomaterials record information as fast as picoseconds in computer memories but retain it for millions of years in ancient rocks. This exceedingly broad range of times is covered by hopping over a potential energy barrier through temperature, ultrafast optical excitation for demagnetization or magnetization manipulation, mechanical stress, or microwaves. As switching depends on nanoparticle size, shape, orientation, and material properties, only single-nanoparticle studies can eliminate ensemble heterogeneity. Here, we push the sensitivity of photothermal magnetic circular dichroism down to individual 20-nm magnetite nanoparticles. Single-particle magnetization curves display superparamagnetic to ferromagnetic behaviors, depending on size, shape, and orientation. Some nanoparticles undergo thermally activated switching on time scales of milliseconds to minutes. Surprisingly, the switching barrier appears to vary in time, leading to dynamical heterogeneity. Our observations will help to identify and eventually control the nanoscale parameters influencing the switching of magnetic nanoparticles, an important step for applications in many fields.

Authors 7

1. S. Adhikari Aachen

   Leiden University

   Affiliation as printed

   Huygens-Kamerlingh Onnes Laboratory , Leiden University ; 2300 RA Leiden , The Netherlands

2. Y. Wang Aachen

   Leiden University · Harbin Institute of Technology

   Affiliation as printed

   Huygens-Kamerlingh Onnes Laboratory , Leiden University ; 2300 RA Leiden , The Netherlands

   School of Mechatronics Engineering , Harbin Institute of Technology ; Harbin 150001 , P. R. China

3. P. Spaeth Aachen

   Leiden University

   Affiliation as printed

   Huygens-Kamerlingh Onnes Laboratory , Leiden University ; 2300 RA Leiden , The Netherlands

4. F. Scalerandi

   Institute for Atomic and Molecular Physics

   Affiliation as printed

   Department of Sustainable Energy Materials , AMOLF ; Science Park 104 , 1098 XG Amsterdam , The Netherlands

5. W. Albrecht

   Institute for Atomic and Molecular Physics

   Affiliation as printed

   Department of Sustainable Energy Materials , AMOLF ; Science Park 104 , 1098 XG Amsterdam , The Netherlands

6. J. Liu

   Harbin Institute of Technology

   Affiliation as printed

   School of Mechatronics Engineering , Harbin Institute of Technology ; Harbin 150001 , P. R. China

7. Michel Orrit Aachen

   Leiden University

   Affiliation as printed

   Huygens-Kamerlingh Onnes Laboratory , Leiden University ; 2300 RA Leiden , The Netherlands