In this work, combining experimental results and first principles calculations, we show that interstitial nitrogen not only serves for inducing tetragonality in α′-Fe
8
N
x
but is also essential for ...achieving a high degree of perpendicular magneto-crystalline anisotropy,
K
. Our results demonstrate that the orbital magnetic moments of the iron atoms above and below N in the direction of magnetization are much more susceptible to the applied magnetic field than their in-plane counterparts, leading to a giant value of
K
as compared to a hypothetical distorted material without N.
(Nd,Dy)-Fe-B core shell model magnets were prepared by co-sintering Nd-Fe-B and (Nd,Dy)-Fe-B powders. The Nd-Fe-B core and partially Dy substituted i.e. (Nd,Dy)-Fe-B shell were identified by SEM. MFM ...measurements of the remanent state revealed a magnetic contrast of core and shell within the same grain. The magnetization reversal of a representative core-shell grain was investigated by in-situ MFM and magneto-optical Kerr microscopy at room temperature in varying magnetic fields. Micromagnetic simulation was carried out in addition to resolve the specific nucleation site for the reversal. It was found that the position of the nucleation site depends critically on the magnetocrystalline anisotropy Kedge in the shell edge which is defined as the defect layer in the shell surface. Low and high Kedge favors the nucleation in the shell and core, respectively. Once the nucleation occurs in the core, the nucleation field or coercivity does not rely on Kedge.
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A systematic study of the dependence of the Grain Boundary Diffusion Process (GBDP) on texture using Dy and Dy-Nd-Cu in microcrystalline sintered and nanocrystalline hot deformed Nd-Fe-B magnets was ...performed. Diffusion parallel or perpendicular to the texture direction, the nominal c-axes orientation in the polycrystals, was investigated. By measuring thin slices from the respective samples, coercivity as a function of (i) magnet thickness and (ii) diffusion depth was obtained showing that GBDP efficiency depends on the diffusion direction, diffusion source as well as the grain morphology originating from the magnet production route. In nanocrystalline hot deformed magnets perpendicular diffusion is superior due to the platelet-like shape of the grains. Microcrystalline sintered magnets consist of equiaxed grains hence the main effects originate in anisotropic lattice diffusion and pole surface hardening. The magnetic properties are correlated with a comprehensive analysis of microstructure, chemistry and magnetization reversal.
•Comparing texture's effect on GBDP in Dy, Dy-Nd-Cu in microcrystalline sintered & nanocrystalline hot deformed magnets.•GBDP efficiency relies on diffusion direction, source, and grain morphology from the magnet production route.•Perpendicular diffusion is more effective in hot deformed (nanocrystalline) magnets due to their platelet-like grain shapes.•Comprehensive analysis links magnetic properties with microstructure, chemistry, and magnetization reversal studies.
Ferromagnetic Fe3Sn, Fe5Sn3 and Fe3Sn2 single crystals were synthesized using the reactive flux technique. Derived from single crystal x-ray diffraction and Transmission Electron Microscopy (TEM), a ...new structural model is proposed for the Fe5Sn3 crystals - the threefold twinning of an orthorhombic unit cell with (3 + 1) dimensional space group Pbcm(α00)0s0. The spontaneous magnetization (Ms) and the anisotropy constants K1 and K2 of Fe3Sn, Fe5Sn3 and Fe3Sn2 single crystals were determined in a wide temperature range using M(H) dependencies and a modified Sucksmith-Thompson technique. Ms and K1 were also evaluated in the framework of Density Functional Theory (DFT) and an overall good agreement was observed between the calculated and experimental results. Furthermore, a critical evaluation of different analytical models for the assessment of magnetocrystalline anisotropy was performed, which are restricted to the analysis of uniaxial magnetic domain patterns, and it is shown that such high-throughput techniques can lead to unrealistic results. Finally, a DFT high-throughput screening of the Fe-Sn phase diagram was used to identify Fe-Sn based phases with potential to be stabilized upon alloying, and their magnetization and magnetocrystalline anisotropy were evaluated. The results show that a similar strong anisotropy as observed in Fe3Sn may also be found in other Fe-Sn based phases, having higher potential to be used as hard magnetic material.
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Multiferroics are promising for sensor and memory applications, but despite all efforts invested in their research no single‐phase material displaying both ferroelectricity and large magnetization at ...room‐temperature has hitherto been reported. This situation has substantially been improved in the novel relaxor ferroelectric single‐phase (BiFe0.9Co0.1O3)0.4–(Bi1/2K1/2TiO3)0.6, where polar nanoregions (PNR) transform into static‐PNR as evidenced by piezoresponse force microscopy (PFM) and simultaneously enable congruent multiferroic clusters (MFC) to emerge from inherent strongly magnetic Bi(Fe,Co)O3 rich regions as verified by magnetic force microscopy (MFM) and secondary ion mass spectrometry. The material's exceptionally large Néel temperature TN = 670 ± 10 K, as found by neutron diffraction, is proposed to be a consequence of ferrimagnetic order in MFC. On these MFC, exceptionally large direct and converse magnetoelectric (ME) coupling coefficients, α ≈ 1.0 × 10−5 s m−1 at room‐temperature, are measured by PFM and MFM, respectively. It is expected that the non‐ergodic relaxor properties which are governed by the Bi1/2K1/2TiO3 component to play a vital role in the strong ME coupling, by providing an electrically and mechanically flexible environment to MFC. This new class of non‐ergodic relaxor multiferroics bears great potential for applications. Especially the prospect of a ME nanodot storage device seems appealing.
Electric field induced magnetoelectric switching of newly discovered multiferroic clusters (MFC) in (BiFe0.9Co0.1O3)0.4–(Bi1/2K1/2TiO3)0.6 ceramics is reported. Both direct and converse coupling is observed, with the highest reported magnetoelectric coupling coefficient, α ≈ 1.0 × 10−5 s m−1 (dE/dH ≈ 1.3 kV (cm Oe))−1. It is proposed that MFCs are both ferroelectric and ferrimagnetic. The unusual and robust magnetic properties are emphasized by an extremely high Néel temperature TN = 670 ± 10 K.
L. F. Henrichs and co‐workers report on page 2111 an electric‐field‐induced magnetoelectric switching in (BiFe0.9Co0.1O3)0.4–(Bi1/2K1/2TiO3)0.6 ceramics, within newly discovered multiferroic clusters ...(MFCs). The MFCs are suggested to be both ferroelectric and ferromagnetic, and ferromagnetic ordering leads to an exceptionally large Néel temperature. The material has potential for applications in sensors and memory devices.
We have characterized the molecular and genomic diversity of the microbiota of the starlet sea anemone Nematostella vectensis, a cnidarian model for comparative developmental and functional biology ...and a year-round inhabitant of temperate salt marshes. Molecular phylogenetic analysis of 16S rRNA gene clone libraries revealed four ribotypes associated with N. vectensis at multiple locations and times. These associates include two novel ribotypes within the ε-Proteobacterial order Campylobacterales and the Spirochetes, respectively, each sharing <85% identity with cultivated strains, and two γ-Proteobacterial ribotypes sharing >99% 16S rRNA identity with Endozoicomonas elysicola and Pseudomonas oleovorans, respectively. Species-specific PCR revealed that these populations persisted in N. vectensis asexually propagated under laboratory conditions. cDNA indicated expression of the Campylobacterales and Endozoicomonas 16S rRNA in anemones from Sippewissett Marsh, MA. A collection of bacteria from laboratory raised N. vectensis was dominated by isolates from P. oleovorans and Rhizobium radiobacter. Isolates from field-collected anemones revealed an association with Limnobacter and Stappia isolates. Genomic DNA sequencing was carried out on 10 cultured bacterial isolates representing field- and laboratory-associates, i.e., Limnobacter spp., Stappia spp., P. oleovorans and R. radiobacter. Genomes contained multiple genes identified as virulence (host-association) factors while S. stellulata and L. thiooxidans genomes revealed pathways for mixotrophic sulfur oxidation. A pilot metatranscriptome of laboratory-raised N. vectensis was compared to the isolate genomes and indicated expression of ORFs from L. thiooxidans with predicted functions of motility, nutrient scavenging (Fe and P), polyhydroxyalkanoate synthesis for carbon storage, and selective permeability (porins). We hypothesize that such activities may mediate acclimation and persistence of bacteria in a N. vectensis holobiont defined by both internal and external gradients of chemicals and nutrients in a dynamic coastal habitat.
In the first part of this work, the microstructural influence on magnetic properties Sr-hexaferrites is investigated. Using a Magnetic Force Microscope (MFM) the domain evolution during magnetization ...from the Thermally Demagnetized State (TDS) and DC field Demagnetized State (DCD) and during demagnetization was investigated in-situ. A surface magnetization was determined from the MFM contrast that quantitatively matched the bulk magnetization determined by Superconducting Quantum Interface Device (SQUID). For the surface magnetization it was found that smaller grains below the critical single domain size reversed their magnetization from Single Domain State (SDS) to the reversed SDS, while larger grains form an intermediate Multi Domain State (MDS). Using a series of minor loops it was determined that the presence of MDS in the bulk is neglectable.
An in-depth analysis of core shell structured Nd-Fe-B grains was carried out using Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), optical Kerr microscopy and MFM. While the core consisted of pure Nd2Fe14B the shell, the composition of the shell was (Nd1-xDyx)2Fe14B. The composition and morphology of the grain boundary was analyzed using TEM. Using MFM the magnetic contrast of core and shell due to the lower saturation magnetization of the Dy substituted species could be correlated to the chemical contrast observed by SEM. The demagnetization of core and shell was observed under in-situ condition using MFM and Kerr microscopy. The results show a uniform demagnetization across core and shell. The time resolution of the Kerr microscope of 43 frames per second is not large enough to resolve an intermediate domain state between SDS and stable MDS within the 23 ms between two frames. In a subsequent micromagnetic simulation the nucleation site was shown to lie either at the grain boundary or in the core depending on the magnetocrystalline anisotropy at the grain boundary defect layer.
The texture dependency of the Grain Boundary Diffusion Process (GBDP) in sintered and hot-deformed Nd-Fe-B magnets was analyzed by creating a global and a local coercivity profile of the diffused samples. While the former method allows a conclusion on how the magnet acts as a whole, the latter allows a more precise resolution of local coercivity. In sintered magnets a slightly higher coercivity improvement was observed for the diffusion perpendicular to the texture axis. A pole hardening effect was observed for diffusion parallel to the texture axis that compensated the higher coercivity improvement for parallel diffusion. In hot deformed magnets on the other hand, no pole hardening effect was observed and a higher coercivity improvement was observed for parallel diffusion. A microstructural investigation showed that this effect could be attributed to the platelet shaped grains in hot deformed magnets. The in-situ demagnetization of hot-deformed magnets was analyzed for different Dy contents.
The composition of different pilot batch Nd-Fe-B magnets by VACUUMSCHMELZE GmbH & Co. KG was determined by Inductively Coupled Plasma – Optical Emission Spectroscopy (ICP-OES). The grain size distribution and orientation was determined using Electron Back Scattered Diffraction (EBSD). The influence of Heavy Rare Earth Elements (HRE) and microstructure engineering on the intrinsic and extrinsic magnetic properties was investigated. A similar minor loop investigation was also done for Nd-Fe-B sintered magnets showing that the vast majority of grains display a single domain like behavior despite being approximately one order of magnitude larger than the critical single domain size. Furthermore the amount of MDS during the demagnetization could be reduced by the addition of HRE.
Multiferroics are promising for sensor and memory applications, but despite all efforts invested in their research no single-phase material displaying both ferroelectricity and large magnetization at ...room-temperature has hitherto been reported. This situation has substantially been improved in the novel relaxor ferroelectric single-phase , where polar nanoregions (PNR) transform into static-PNR (SPNR) as evidenced by piezoresponse force microscopy (PFM) and simultaneously enable congruent multiferroic clusters (MFC) to emerge from inherent ferrimagnetic Bi(Fe,Co)O3 regions as verified by magnetic force microscopy (MFM) and secondary ion mass spectrometry (SIMS). On these MFC, exceptionally large direct and converse magnetoelectric coupling coefficients, at room-temperature, were measured by PFM and MFM respectively. We expect the non-ergodic relaxor properties which are governed by the Bi0.5K0.5TiO3 component to play a vital role in the strong ME coupling, by providing an electrically and mechanically flexible environment to MFC. This new class of non-ergodic relaxor multiferroics bears great potential for applications. Especially the prospect of a ME nanodot storage device seems appealing.
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