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CIC01_Master_Artificially frustrated magnetic metamaterials

SUITABLE FOR physicists, materials scientists, engineers

Frustration is defined as a competition between interactions such that not all of them can be satisfied. Geometrical frustration, which arises from the topology of a well-ordered structure become a topic of considerable interest since it can be induced and tuned in a controlled way. In particular, geometrical frustration among spins in magnetic materials can lead to exotic low temperature states, of great interest for fundamental and applied studies. In the specific, we are interested in the so called “artificial spin ices” (ASIs), which is a class of lithographically created arrays of interacting ferromagnetic nanometre-scale islands. It was introduced to investigate many-body phenomena related to frustration and disorder in a material that could be tailored to precise specifications and imaged directly. From a different viewpoint, ASIs form a metamaterial where the properties are designed in and arise due to the engineering of the mesoscale properties (the size, shape, and placement of the islands). As such, they offer broad scientific and technological perspectives: implementation of statistical mechanics models of theory, model systems for the study of out-of-equilibrium thermodynamics, and prototypes for physical systems that store and process information in unconventional ways, (complex networks and neuromorphic computers). Recently, we demonstrate a method for thermalizing ASIs by heating above the temperature for activation of thermal fluctuations (TB). This thermally induced demagnetization protocol can be repeated as many times as desired on the same sample, and the heating/cooling parameters can be varied at will. Thereby, this approach opens the pathway to the systematic experimental study of thermally induced ordered states in artificial spin-ice systems.

In this project, we will direct our studies towards the design and fabrication of ASIs of various geometries with the purpose of tuning the energy barrier for thermal fluctuation activation via shape and size of the individual nano-elements as well as the constituent material properties. In this way one can achieve an unprecedented tuning of the dipolar interactions during the frustration accommodation in the thermalization process. We will investigate the novel magnetic phases that would emerge from the ground states of frustrated lattices via magnetic imaging, as well as their collective dynamics excited by radio-frequency and pulsed magnetic fields. To these purpose we will use the magnetic force and magneto-optical microscopy tools and the ferromagnetic resonance measurements setup available at nanoGUNE.

Figure

Fig.: Upper panel: possible vertices configurations in a square ASI; vertex configurations of type T1 are the lowest energy (ground state); vertex configurations T2-T4 have higher energy (vertex excitations).
Lower panel:  Scannig electrom microscopy image of sample implementing a square ASI (a), followed by a MFM image after the application of our proposed  thermal demagnetization protocol has (c); the inset shows an area with ground-state ordering (b); these  ground-state ordering regions (T1 vertex type, white contrast)  are separated by lines of vertex excitations (T2 and T3 vertex types, blue and red contrasts) (d).

References and reading list 

  • R. F. Wang et al., Nature 439, 303 (2006)
  • J. P. Morgan, A. Stein, S. Langridge,  and C. H. Marrows, Nature Phys. 7,  75 (2011)
  • J. M. Porro, A. Bedoya-Pinto, A. Berger, and P. Vavassori, New J. Phys. 15, 055012 (2013)
  • E. Nikulina, O. Idigoras, P. Vavassori, A. Chuvilin, and A. Berger, Appl. Phys. Lett. 100, 142401 (2012).
  • T. Verduci, C. Rufo, A. Berger, V. Metlushko, B. Ilic, and P. Vavassori, Appl. Phys. Lett. 99, 092501 (2011).

More information: Nanomagnetism Group

E-mail: p.vavassori@nanogune.eu

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