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Sökning: WFRF:(Magnus Fridrik)

  • Resultat 1-10 av 42
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  • Dahlqvist, Martin, et al. (författare)
  • Magnetically driven anisotropic structural changes in the atomic laminate Mn2GaC
  • 2016
  • Ingår i: Physical Review B. - : AMER PHYSICAL SOC. - 2469-9950 .- 2469-9969. ; 93:1
  • Tidskriftsartikel (refereegranskat)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.
  • Ingason, Arni Sigurdur, et al. (författare)
  • Magnetic Self-Organized Atomic Laminate from First Principles and Thin Film Synthesis
  • 2013
  • Ingår i: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 110
  • Tidskriftsartikel (refereegranskat)abstract
    • he first experimental realization of a magnetic Mn+1AXn (MAX) phase, (Cr0.75Mn0.25)2GeC, is presented, synthesized as a heteroepitaxial single crystal thin film, exhibiting excellent structural quality. This self-organized atomic laminate is based on the well-known Cr2GeC, with Mn, a new element in MAX phase research, substituting Cr. The compound was predicted using first-principles calculations, from which a variety of magnetic behavior is envisaged, depending on the Mn concentration and Cr/Mn atomic configuration within the sublattice. The analyzed thin films display a magnetic signal at room temperature.
  • Leosson, K., et al. (författare)
  • Comparing resonant photon tunneling via cavity modes and Tamm plasmon polariton modes in metal-coated Bragg mirrors
  • 2012
  • Ingår i: Optics Letters. - 0146-9592 .- 1539-4794. ; 37:19, s. 4026-4028
  • Tidskriftsartikel (refereegranskat)abstract
    • Resonant photon tunneling was investigated experimentally in multilayer structures containing a high-contrast (TiO2/SiO2) Bragg mirror capped with a semitransparent gold film. Transmission via a fundamental cavity resonance was compared with transmission via the Tamm plasmon polariton resonance that appears at the interface between a metal film and a one-dimensional photonic bandgap structure. The Tamm-plasmon-mediated transmission exhibits a smaller dependence on the angle and polarization of the incident light for similar values of peak transmission, resonance wavelength, and finesse. Implications for transparent electrical contacts based on resonant tunneling structures are discussed.
  • Magnus, Fridrik, et al. (författare)
  • Sequential magnetic switching in Fe/MgO(001) superlattices
  • 2018
  • Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 97:17
  • Tidskriftsartikel (refereegranskat)abstract
    • Polarized neutron reflectometry is used to determine the sequence of magnetic switching in interlayer exchangecoupled Fe/MgO(001) superlattices in an applied magnetic field. For 19.6 Å thick MgO layers we obtain a 90◦periodic magnetic alignment between adjacent Fe layers at remanence. In an increasing applied field the toplayer switches first followed by its second-nearest neighbor. For 16.4 Å MgO layers, a 180◦periodic alignment isobtained at remanence and with increasing applied field the layer switching starts from the two outermost layersand proceeds inwards. This sequential tuneable switching opens up the possibility of designing three-dimensionalmagnetic structures with a predefined discrete switching sequence
  • Meshkian, Rahele, et al. (författare)
  • A magnetic atomic laminate from thin film synthesis: (Mo0.5Mn0.5)2GaC
  • 2015
  • Ingår i: APL MATERIALS. - : American Institute of Physics (AIP): Open Access Journals / AIP Publishing LLC. - 2166-532X. ; 3:7
  • Tidskriftsartikel (refereegranskat)abstract
    • We present synthesis and characterization of a new magnetic atomic laminate: (Mo0.5Mn0.5)(2)GaC. High quality crystalline films were synthesized on MgO(111) substrates at a temperature of similar to 530 degrees C. The films display a magnetic response, evaluated by vibrating sample magnetometry, in a temperature range 3-300 K and in a field up to 5 T. The response ranges from ferromagnetic to paramagnetic with change in temperature, with an acquired 5T-moment and remanent moment at 3 K of 0.66 and 0.35 mu(B) per metal atom (Mo and Mn), respectively. The remanent moment and the coercive field (0.06 T) exceed all values reported to date for the family of magnetic laminates based on so called MAX phases.
  • Mockuté, Aurelija, et al. (författare)
  • Structural and magnetic properties of (Cr1-xMnx)(5)Al-8 solid solution and structural relation to hexagonal nanolaminates
  • 2014
  • Ingår i: Journal of Materials Science. - : Springer Verlag (Germany). - 0022-2461 .- 1573-4803. ; 49:20, s. 7099-7104
  • Tidskriftsartikel (refereegranskat)abstract
    • Electron microscopy is used to reveal the competitive epitaxial growth of bcc structure (Cr1-x Mn (x) )(5)Al-8 and (Cr1-y Mn (y) )(2)AlC [M (n+1)AX (n) (MAX)] phase during both magnetron sputtering and arc deposition. X-ray diffraction theta-2 theta measurements display identical peak positions of (000n)-oriented MAX phase and (Cr1-x Mn (x) )(5)Al-8, due to the interplanar spacing of (Cr1-x Mn (x) )(5)Al-8 that matches exactly half a unit cell of (Cr1-y Mn (y) )(2)AlC. Vibrating sample magnetometry shows that a thin film exclusively consisting of (Cr1-x Mn (x) )(5)Al-8 exhibits a magnetic response, implying that the potential presence of this phase needs to be taken into consideration when evaluating the magnetic properties of (Cr, Mn)(2)AlC.
  • Moubah, Reda, et al. (författare)
  • Discrete Layer-by-Layer Magnetic Switching in Fe/MgO(001) Superlattices
  • 2016
  • Ingår i: Physical Review Applied. - : American physical society. - 2331-7019. ; 5:4
  • Tidskriftsartikel (refereegranskat)abstract
    • We report on a discrete layer-by-layer magnetic switching in Fe/MgO superlattices driven by an antiferromagnetic interlayer exchange coupling. The strong interlayer coupling is mediated by tunneling through MgO layers with thicknesses up to at least 1.8 nm, and the coupling strength varies with MgO thickness. Furthermore, the competition between the interlayer coupling and magnetocrystalline anisotropy stabilizes both 90 degrees and 180 degrees periodic alignment of adjacent layers throughout the entire superlattice. The tunable layer-by-layer switching, coupled with the giant tunneling magnetoresistance of Fe/MgO/Fe junctions, is an appealing combination for three-dimensional spintronic memories and logic devices.
  • Frisk, Andreas, 1983-, et al. (författare)
  • Tailoring anisotropy and domain structure in amorphous TbCo thin films through combinatorial methods
  • 2016
  • Ingår i: Journal of Physics D. - 0022-3727 .- 1361-6463. ; 49:3
  • Tidskriftsartikel (refereegranskat)abstract
    • We apply an in-plane external magnetic field during growth of amorphous TbCo thin films and examine the effects on the magnetic anisotropy and domain structure. A combinatorial approach is employed throughout the deposition and analysis to study a continuous range of compositions between 7–95 at.% Tb. Magnetometry measurements show that all samples have a strong out-of-plane anisotropy, much larger than any in-plane components, regardless of the presence of a growth field. However, magnetic force microscopy demonstrates that the growth field does indeed have a large effect on the magnetic domain structure, resulting in elongated domains aligned along the imprinting field direction. The results show that the anisotropy can be tuned in intricate ways in amorphous TbCo films giving rise to unusual domain structures. Furthermore the results reveal that a combinatorial approach is highly effective for mapping out these material properties.
  • George, Sebastian, 1990- (författare)
  • Amorphous Magnetic Materials : A Versatile Foundation for Tomorrow’s Applications
  • 2020
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • Amorphous magnetic materials exhibit a number of key differentiating properties with respect to crystalline magnets. In some cases, the differences may simply be in the values of macroscopic properties such as saturation magnetization, coercivity, Curie temperature, and electrical conductivity. Other cases are more fundamental, such as the possibility for many amorphous alloys to be produced with nearly arbitrary composition, something that is not always possible in crystal structures that may only be stable for certain specific compositions.Fundamentally, these properties arise due to the disordered arrangement of atoms in amorphous materials. However, this structure is challenging to probe and characterize, either experimentally or theoretically. A significant contribution of this thesis is the development of a new approach for studying the local atomic structure of amorphous materials, specifically amorphous SmCo and FeZr alloys. The strategy combines extended x-ray absorption spectroscopy (EXAFS) measurements with stochastic quenching (SQ) simulations in a way that provides more information than either method can offer alone. Additionally, this approach offers the potential for identifying any shortcomings in the theoretical models obtained via SQ.Having an accurate model of the atomic arrangement is not, however, a prerequisite for developing technical applications of amorphous magnetic materials. For that, it is sufficient to quantify those macroscopic properties that are relevant for a given application. Such is the value of the magnetic characterization of amorphous TbCo and CoFeZr alloy thin films presented here. Both investigations used methods such as vibrating sample magnetometry (VSM) and magneto-optic Kerr effect (MOKE) measurements to highlight the high tunability of the magnetic properties in these materials, which can be achieved simply by changing the chemical composition.The final portion of this thesis examines what can be achieved by combining amorphous SmCo and TbCo alloys together in bilayer structures. This is a step away from the alloy characterization studies, as it focuses on how new properties can be realized when multiple materials are brought together. MOKE measurements were used to identify the conditions under which the bilayers spontaneously become magnetized parallel to the film plane versus when the TbCo magnetization begins to tilt out of the plane. Further investigation combining x-ray circular magnetic dichroism (XMCD) measurements and micromagnetic simulations provided a depth-resolved model of the magnetization throughout the bilayers in the presence of a broad range of external field strengths and directions. These models also showed that the local magnetization just above and just below the SmCo/TbCo interface can be aligned either parallel or antiparallel to one another simply by varying the TbCo composition. This discovery offers a novel method for controlling the magnetic behavior in these materials, and may well be useful for all-optical switching or spintronics applications where amorphous TbCo alloys have already drawn attention.
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