title: Dynamical Torque in CoxFe3-xO4 Nanocube Thin Films Characterized by Femtosecond Magneto-Optics: A π-Shift Control of the Magnetization Precession.
abstract: For spintronic devices excited by a sudden magnetic or optical perturbation, the torque acting on the magnetization plays a key role in its precession and damping. However, the torque itself can be a dynamical quantity via the time-dependent anisotropies of the system. A challenging problem for applications is then to disentangle the relative importance of various sources of anisotropies in the dynamical torque, such as the dipolar field, the crystal structure or the shape of the particular interacting magnetic nanostructures. Here, we take advantage of a range of colloidal cobalt ferrite nanocubes assembled in 2D thin films under controlled magnetic fields to demonstrate that the phase, ϕPrec, of the precession carries a strong signature of the dynamical anisotropies. Performing femtosecond magneto-optics, we show that ϕPrec displays a π-shift for a particular angle θH of an external static magnetic field, H. θH is controlled with the cobalt concentration, the laser intensity, as well as the interparticle interactions. Importantly, it is shown that the shape anisotropy, which strongly departs from those of equivalent bulk thin films or individual noninteracting nanoparticles, reveals the essential role played by the interparticle collective effects. This work shows the reliability of a noninvasive optical approach to characterize the dynamical torque in high density magnetic recording media made of organized and interacting nanoparticles.
authors.affiliation: Institut de Physique et Chimie des Matériaux de Strasbourg, UMR 7504, CNRS, Université de Strasbourg , BP 43, 23 rue du Loess, 67034 Strasbourg Cedex 02, France.
authors.forename: Mircea
authors.initials: M
authors.lastname: Vomir
authors.affiliation: SUPA, School of Physics and Astronomy, University of St. Andrews , St Andrews KY16 9SS, United Kingdom.
authors.forename: Robin
authors.initials: R
authors.lastname: Turnbull
authors.affiliation: SUPA, School of Physics and Astronomy, University of St. Andrews , St Andrews KY16 9SS, United Kingdom.
authors.forename: Ipek
authors.initials: I
authors.lastname: Birced
authors.affiliation: SUPA, Department of Physics and Astronomy, University of Glasgow , Glasgow G12 8QQ, United Kingdom.
authors.forename: Pedro
authors.initials: P
authors.lastname: Parreira
authors.affiliation: SUPA, Department of Physics and Astronomy, University of Glasgow , Glasgow G12 8QQ, United Kingdom.
authors.forename: Donald A
authors.initials: DA
authors.lastname: MacLaren
authors.affiliation: SUPA, School of Physics and Astronomy, University of St. Andrews , St Andrews KY16 9SS, United Kingdom.
authors.forename: Stephen L
authors.initials: SL
authors.lastname: Lee
authors.affiliation: SUPA, School of Physics and Astronomy, University of St. Andrews , St Andrews KY16 9SS, United Kingdom.|Elements Chemistry Laboratory, RIKEN , Wako 351-0198, Japan.|Department of Physics, CNRS-Ewha International Research Center, Ewha W. University , Seoul 120-750, Republic of Korea.
authors.forename: Pascal
authors.initials: P
authors.lastname: André
authors.affiliation: Institut de Physique et Chimie des Matériaux de Strasbourg, UMR 7504, CNRS, Université de Strasbourg , BP 43, 23 rue du Loess, 67034 Strasbourg Cedex 02, France.
authors.forename: Jean-Yves
authors.initials: JY
authors.lastname: Bigot
keywords: 2D nanoparticle films; Magnetization dynamics; colloidal magnetic nanoparticles; ferrite nanocubes; magnetic torque; ultrafast magneto-optics