| 1. |
- Arnalds, Unnar B., et al.
(author)
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A new look on the two-dimensional Ising model : thermal artificial spins
- 2016
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In: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 18
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Journal article (peer-reviewed)abstract
- We present a direct experimental investigation of the thermal ordering in an artificial analogue of an asymmetric two-dimensional Ising system composed of a rectangular array of nano-fabricated magnetostatically interacting islands. During fabrication and below a critical thickness of the magnetic material the islands are thermally fluctuating and thus the system is able to explore its phase space. Above the critical thickness the islands freeze-in resulting in an arrested thermalized state for the array. Determining the magnetic state we demonstrate a genuine artificial two-dimensional Ising system which can be analyzed in the context of nearest neighbor interactions.
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| 2. |
- Dahlqvist, Martin, et al.
(author)
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Magnetically driven anisotropic structural changes in the atomic laminate Mn2GaC
- 2016
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In: Physical Review B. - : AMER PHYSICAL SOC. - 2469-9950 .- 2469-9969. ; 93:1
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Journal article (peer-reviewed)abstract
- Inherently layered magnetic materials, such as magnetic M(n+1)AX(n) (MAX) phases, offer an intriguing perspective for use in spintronics applications and as ideal model systems for fundamental studies of complex magnetic phenomena. The MAX phase composition M(n+1)AX(n) consists of M(n+1)AX(n) blocks separated by atomically thin A-layers where M is a transition metal, A an A-group element, X refers to carbon and/or nitrogen, and n is typically 1, 2, or 3. Here, we show that the recently discovered magnetic Mn2GaC MAX phase displays structural changes linked to the magnetic anisotropy, and a rich magnetic phase diagram which can be manipulated through temperature and magnetic field. Using first-principles calculations and Monte Carlo simulations, an essentially one-dimensional (1D) interlayer plethora of two-dimensioanl (2D) Mn-C-Mn trilayers with robust intralayer ferromagnetic spin coupling was revealed. The complex transitions between them were observed to induce magnetically driven anisotropic structural changes. The magnetic behavior as well as structural changes dependent on the temperature and applied magnetic field are explained by the large number of low energy, i.e., close to degenerate, collinear and noncollinear spin configurations that become accessible to the system with a change in volume. These results indicate that the magnetic state can be directly controlled by an applied pressure or through the introduction of stress and show promise for the use of Mn2GaC MAX phases in future magnetoelectric and magnetocaloric applications.
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| 3. |
- Palonen, Heikki, et al.
(author)
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The magnetization profile induced by the double magnetic proximity effect in an Fe/Fe0.30V0.70 superlattice
- 2019
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In: Applied Physics Letters. - : AMER INST PHYSICS. - 0003-6951 .- 1077-3118. ; 115:1
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Journal article (peer-reviewed)abstract
- The double magnetic proximity effect (MPE) in an Fe/Fe0.30V0.70 superlattice is studied by a direct measurement of the magnetization profile using polarized neutron reflectivity. The experimental magnetization profile is shown to qualitatively agree with a profile calculated using density functional theory. The profile is divided into a short range interfacial part and a long range tail. The interfacial part is explained by charge transfer and induced magnetization, while the tail is attributed to the inhomogeneous nature of the FeV alloy. The long range tail in the magnetization persists up to 170% above the intrinsic ordering temperature of the FeV alloy. The observed effects can be used to design systems with a direct exchange coupling between layers over long distances through a network of connected atoms. When combined with the recent advances in tuning and switching, the MPE with electric fields and currents, the results can be applied in spintronic devices. Published under license by AIP Publishing.
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| 4. |
- Rodrigues, Debora C. M., et al.
(author)
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Magnetic anisotropy in permalloy : hidden quantum mechanical features
- 2018
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In: Physical Review B. - 2469-9950 .- 2469-9969. ; 97:22
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Journal article (peer-reviewed)abstract
- By means of relativistic, first principles calculations, we investigate the microscopic origin of the vanishingly low magnetic anisotropy of Permalloy, here proposed to be intrinsically related to the local symmetries of the alloy. It is shown that the local magnetic anisotropy of individual atoms in Permalloy can be several orders of magnitude larger than that of the bulk sample and 5–10 times larger than that of elemental Fe or Ni. We furthermore show that locally there are several easy axis directions that are favored, depending on local composition. The results are discussed in the context of perturbation theory, applying the relation between magnetic anisotropy and orbital moment. Permalloy keeps its pronounced soft ferromagnetic nature due to the exchange energy to be larger than the magnetocrystalline anisotropy. Our results shine light on the magnetic anisotropy of permalloy and of magnetic materials in general, and in addition enhance the understanding of pump-probe measurements and ultrafast magnetization dynamics.
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| 5. |
- Östman, Erik, et al.
(author)
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Interaction modifiers in artificial spin ices
- 2018
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In: Nature Physics. - : NATURE PUBLISHING GROUP. - 1745-2473 .- 1745-2481. ; 14:4, s. 375-379
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Journal article (peer-reviewed)abstract
- The modification of geometry and interactions in two-dimensional magnetic nanosystems has enabled a range of studies addressing the magnetic order(1-6), collective low-energy dynamics(7,8) and emergent magnetic properties(5,9,10) in, for example, artificial spin-ice structures. The common denominator of all these investigations is the use of Ising-like mesospins as building blocks, in the form of elongated magnetic islands. Here, we introduce a new approach: single interaction modifiers, using slave mesospins in the form of discs, within which the mesospin is free to rotate in the disc plane(11). We show that by placing these on the vertices of square artificial spin-ice arrays and varying their diameter, it is possible to tailor the strength and the ratio of the interaction energies. We demonstrate the existence of degenerate ice-rule-obeying states in square artificial spin-ice structures, enabling the exploration of thermal dynamics in a spin-liquid manifold. Furthermore, we even observe the emergence of flux lattices on larger length scales, when the energy landscape of the vertices is reversed. The work highlights the potential of a design strategy for two-dimensional magnetic nano-architectures, through which mixed dimensionality of mesospins can be used to promote thermally emergent mesoscale magnetic states.
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| 6. |
- Östman, Erik, et al.
(author)
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Ising-like behaviour of mesoscopic magnetic chains
- 2018
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In: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 30:36
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Journal article (peer-reviewed)abstract
- We demonstrate an experimental realization of the short range magnetic order in a one-dimensional Ising chain using fabricated mesospins. We confirm an excellent agreement between the experimental findings and simulations obtained using the original Ising model. In particular, we are able to show that the thermal behaviour of the mesoscopic Ising chain dominates over the thermal behaviour of the individual mesospins themselves, confirming that fabricated mesospins can be viewed as artificial magnetic atoms.
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