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  • Open Access

Theoretical Analysis of Inertia-like Switching in Magnets: Applications to a Synthetic Antiferromagnet

Satadeep Bhattacharjee, Anders Bergman, Andrea Taroni, Johan Hellsvik, Biplab Sanyal, and Olle Eriksson

  • Department of Physics and Astronomy, Box 516, 75120, Uppsala University, Uppsala, Sweden

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Phys. Rev. X 2, 011013 – Published 29 March, 2012

DOI: https://doi.org/10.1103/PhysRevX.2.011013

Abstract

The magnetization dynamics of a synthetic antiferromagnet subjected to a short-magnetic-field pulse has been studied by using a combination of first principles calculations and atomistic spin-dynamics simulations. We observe switching phenomena on the time scale of tens of picoseconds, and inertia-like behavior in the magnetization dynamics. We explain the latter in terms of a dynamic redistribution of magnetic energy from the applied-field pulse to other possible energy terms, such as the exchange interaction and the magnetic anisotropy, without invoking concepts such as the inertia of an antiferromagnetic vector. We also demonstrate that such dynamics can also be observed in a ferromagnetic material where the incident-field pulse pumps energy to the magnetic anisotropy.

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Applying a magnetic field to magnetic material, you can switch the direction of the magnetic moment of the material. This concept is central to data-storage technologies based on magnetic materials. Naturally, fast switching speeds, which can lead to high data recording rates, are highly desired. Over the last few years, a number of methods have been demonstrated to achieve ultrafast switching on the time scales of subpicoseconds. One of the more promising of these experiments used a short laser pulse to induce the switching in an antiferromagnetic material and observed, unexpectedly, oscillatory magnetic switching that continued long after the pulse was turned off. What is then the mechanism behind this observation? The group who made the observation explained it by invoking both the notion of magnetic “inertia”—an analogue to the mass of a particle—and the importance of the antiferromagnetic nature of the material. In this theoretical paper, we reexamine the observed phenomenon at a microscopic level and provide an understanding that is both more fundamental and more general than the concept of magnetic inertia.

Our approach starts with a microscopic description of the dynamics of atomistic spins, the parameters in which are directly derived from first-principles calculations. The primary model system we have investigated is a synthetic antiferromagnet of a Fe/Cr/Fe trilayer. While the atomic spins in each of the layers couple to each other ferromagnetically, the spins in neighboring layers interact antiferromagnetically. Using atomistic spin-dynamics simulations, we have explored the relative roles, and the time evolutions, of the different magnetic-energy terms, in particular, the antiferromagnetic exchange interaction and the magnetic-anisotropy terms. Our results clearly indicate that a time-dependent redistribution of the energy imparted on the spins by the magnetic field pulse into these different energy terms under the inherent nonlinearity of the microscopic spin dynamics is responsible for the oscillatory magnetic switching observed. Moreover, this understanding, and our additional simulations of a ferromagnetic system, also lead to the conclusion that such transient switching dynamics is possible and should be observable in ferromagnetic systems, too, when the dynamic interplay between the different energy terms governing the magnetization dynamics becomes significant enough.

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Phys. Rev. X 2, 011013– Published 29 March, 2012
  • Received 3 September 2011
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This article is available under the terms of the Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

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