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Register a new userProbability distribution of substituted Titanium in RT12 (R = Nd, Sm, T = Fe, Co) structures
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We investigated the atomic fill site probability distributions across supercell structures of RT12-xTi (R=Nd, Sm, T=Fe, Co). We use a combined molecular dynamics and Boltzmann distribution approach to extrapolate the probability distributions for Ti substitution from lower to higher temperatures with an equilibrium condition to assess how temperature affects the predictability of the structures fill path. It was found that the Nd and Sm based Fe systems have the highest filling probability path at lower temperatures but the cohesive energy change due to Ti substitution in Sm and Nd based crystals indicates that a more stable system could be achieved with a combination Co and Fe in the transition metal site.
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The epitaxial system Sm/Co(0001) was studied for Sm coverages up to 1 monolayer (ML) on top of ultrathin Co/W(110) epitaxial films. Two ordered phases were found for 1/3 and 1 ML Sm, respectively. The valence state of Sm was determined by means of photoemission and magnetic properties were measured by magneto-optical Kerr effect. We find that 1 ML Sm causes a strong increase of the coercivity with respect to that of the underlying 10 ML Co film. Element-specific hysteresis loops, measured by using resonant soft x-ray reflectivity, show the same magnetic behaviour for the two elements.
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The influence of La and Nd co-substitution on the structural and magnetic properties of BiFeO3 (BFO) thin films was examined. Epitaxial thin films of pure and, La and Nd co-doped BFO on the SrRuO3 buffered single crystal SrTiO3 (001) substrate were deposited using pulsed laser deposition. The structural change in co doped La and Nd BFO thin films which was caused by the changes of force constant in the crystal lattice induced by ionic radii mismatch was investigated. Raman spectroscopy studies manifest the structural change in doped BFO films from rhombohedral to monoclinic distorted phase which is induced by the co substitution of La and Nd. Room temperature magnetic hysteresis curves indicated that saturation magnetization is enhanced in the doped film with saturation magnetization of ~20 emu/cm3. The dielectric and magnetic properties are effectively improved in BLNFO films compared to pure BFO thin films.
The characteristic microstructure of Sm(Co,Fe,Cu,Zr)$_z$ alloys with SmCo$_5$ cell walls in Sm$_2$Co$_{17}$ cells, all intersected by Zr-rich platelets, makes them some of the best performing high-temperature permanent magnets. Plentiful research has been performed to tailor the microstructure at the nanoscale, but due to its complexity many questions remain unanswered about the effect of the individual phases on the magnetic performance at different temperatures. Here, we explore this mechanism effect for three different Sm(Co,Fe,Cu,Zr)$_z$ alloys by deploying high-resolution magnetic imaging via in-situ transmission electron microscopy and three-dimensional chemical analysis using atom probe tomography. We show that their microstructures differ in terms of SmCo$_5$ cell-wall and Z-phase size and density, as well as the Cu concentration in the cell walls, and demonstrate how these features influence the magnetic domain size and density and thus form different magnetic textures. Moreover, we illustrate that the dominant coercivity mechanism at room temperature is domain-wall pinning and show that magnets with a denser cell-wall network, a steeper Cu gradient across the cell-wall boundary, and thinner Z-phase platelets have a higher coercivity. We also show that the coercivity mechanism at high temperatures is domain-wall nucleation at the cell walls. Increasing the Cu concentration inside the cell walls decreases the transition temperature between pinning and nucleation, significantly decreasing the coercivity with increasing temperature. We therefore provide a detailed explanation of how the microstructure on the atomic to nanoscale directly affects the magnetic performance and provide detailed guidelines for an improved design of Sm(Co,Fe,Cu,Zr)$_z$ magnets.
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