Revealing giant internal magnetic fields due to spin fluctuations in magnetically doped colloidal nanocrystals

William D. Rice, Wenyong Liu, Thomas A. Baker, Nikolai A. Sinitsyn, Victor I Klimov, Scott A. Crooker

Research output: Contribution to journalArticlepeer-review

33 Citations (Scopus)

Abstract

Strong quantum confinement in semiconductors can compress the wavefunctions of band electrons and holes to nanometre-scale volumes, significantly enhancing interactions between themselves and individual dopants. In magnetically doped semiconductors, where paramagnetic dopants (such as Mn 2+, Co 2+ and so on) couple to band carriers via strong sp-d spin exchange, giant magneto-optical effects can therefore be realized in confined geometries using few or even single impurity spins. Importantly, however, thermodynamic spin fluctuations become increasingly relevant in this few-spin limit. In nanoscale volumes, the statistical fluctuations of N spins are expected to generate giant effective magnetic fields B eff, which should dramatically impact carrier spin dynamics, even in the absence of any applied field. Here we directly and unambiguously reveal the large B eff that exist in Mn 2+ -doped CdSe colloidal nanocrystals using ultrafast optical spectroscopy. At zero applied magnetic field, extremely rapid (300-600â €...GHz) spin precession of photoinjected electrons is observed, indicating B eff â 1/4 15 â '30 T for electrons. Precession frequencies exceed 2 THz in applied magnetic fields. These signals arise from electron precession about the random fields due to statistically incomplete cancellation of the embedded Mn 2+ moments, thereby revealing the initial coherent dynamics of magnetic polaron formation, and highlighting the importance of magnetization fluctuations on carrier spin dynamics in nanomaterials.

Original languageEnglish
Pages (from-to)137-142
Number of pages6
JournalNature Nanotechnology
Volume11
Issue number2
DOIs
Publication statusPublished - Feb 1 2016

ASJC Scopus subject areas

  • Bioengineering
  • Biomedical Engineering
  • Materials Science(all)
  • Electrical and Electronic Engineering
  • Condensed Matter Physics
  • Atomic and Molecular Physics, and Optics

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