L1
-FePt nanoparticles (NPs) have great potential in areas of advanced magnetic and catalytic applications. Here, we present a facile control route for synthesis of hard magnetic L1
-FePt NPs in ...which halide ions (Cl
, Br
, or I
) were added to the synthetic process to promote the phase transformation. It is confirmed that the strong ionic binding force between halide ions and Fe
or Pt
ions could facilitate the formation of L1
-FePt phase due to favoring growth of FePt NPs in a more thermodynamically stable way, which enables the formation of an ordered structure. L1
-FePt NPs with the highest coercivity of 8.64 kOe and saturation magnetization of 64.21 emu/g at room temperature can be directly obtained by controlling the amount of the halide ions. In comparison with conventional solution phase reduction methods, the halide ion-assisted method shows enhanced capability to tune the growth of hard magnetic bimetallic NPs, particularly Pt-based bimetallic NPs.
Using a grain-boundary diffusion process (GBDP) involving the electrophoretic deposition (EPD) of submicron TbF3 powder, we substantially increased the coercivity of sintered Nd-Fe-B permanent ...magnets. The experiments used magnets with low heavy-rare-earth (HRE) content (HRE = 1.2 wt%) and a coercivity of 790 kA/m (at 75 °C). After experiencing optimized conditions at 875 °C for 10 h and subsequent annealing at 500 °C for 1 h, the coercivity was increased to 1536 kA/m (at 75 °C). This value is 1.94 times higher than that for a sintered magnet, without post-sintering heat treatment. Furthermore, a vibration test revealed satisfactory adhesion of the TbF3 powder to the surface of the magnet with no detected reduction in coercivity. Using field emission gun scanning electron microscopy (FEG-SEM) with an energy dispersive spectroscope (EDS), we confirmed the formation of various secondary intergranular phases and the core-shell-type microstructure, which increases the coercivity. The Tb content in the magnet, exposed to the EPD-based GBDP, was controlled by inductively coupled plasma optical electron spectroscopy (ICP-OES). The additional Tb detected in the magnet due to the described technology was only 0.12 wt%.
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Magnetic effects of lanthanide bonding Lanthanide coordination compounds have attracted attention for their persistent magnetic properties near liquid nitrogen temperature, well above alternative ...molecular magnets. Gould
. report that introducing metal-metal bonding can enhance coercivity. Reduction of iodide-bridged terbium or dysprosium dimers resulted in a single electron bond between the metals, which enforced alignment of the other valence electrons. The resultant coercive fields exceeded 14 tesla below 50 and 60 kelvin for the terbium and dysprosium compounds, respectively. —JSY
Shape‐programmable soft materials that exhibit integrated multifunctional shape manipulations, including reprogrammable, untethered, fast, and reversible shape transformation and locking, are highly ...desirable for a plethora of applications, including soft robotics, morphing structures, and biomedical devices. Despite recent progress, it remains challenging to achieve multiple shape manipulations in one material system. Here, a novel magnetic shape memory polymer composite is reported to achieve this. The composite consists of two types of magnetic particles in an amorphous shape memory polymer matrix. The matrix softens via magnetic inductive heating of low‐coercivity particles, and high‐remanence particles with reprogrammable magnetization profiles drive the rapid and reversible shape change under actuation magnetic fields. Once cooled, the actuated shape can be locked. Additionally, varying the particle loadings for heating enables sequential actuation. The integrated multifunctional shape manipulations are further exploited for applications including soft magnetic grippers with large grabbing force, reconfigurable antennas, and sequential logic for computing.
A novel magnetic shape‐memory polymer, which is a composite consisting of two types of magnetic particles in an amorphous shape‐memory polymer matrix, integrates multiple shape‐manipulation functions, including untethered rapid reversible shape change, sequential actuation, reprogrammability, and shape locking. Applications including soft magnetic grippers with large grabbing force, sequential logic for computing, and reconfigurable antennas are exploited.
3d transition metal chalcogenides have gradually become candidates for magnetic materials due to their unique d-electronic structures. However, a relatively lower Curie temperature (TC) and ...coercivity (HC) limit their widespread applications. Here, we report a high-temperature organic-solvent-phase method for the synthesis of hexagonal α-Fe1−xCrxSe (0 ≤x ≤ 0.6) alloyed nanosheets with high TC through Cr introduction. Without Cr introduction, FeSe nanosheets appear as a mixture of tetragonal β-FeSe and hexagonal α-FeSe phases with a soft/hard decoupled hysteresis loop of HC∼3.35 kOe at 5 K. With an increase in the Cr content, α-Fe1−xCrxSe gradually becomes dominant. The tetragonal-to-hexagonal phase transition is completed at the optimum doping of Cr (x = 0.4), and α-Fe1−xCrxSe exhibits hard magnetic behavior. The coercivity (HC) can be as high as 15.80 kOe at 5 K and 4.98 kOe at 300 K when the Cr concentration reaches 60%. The synthesis of α-Fe1−xCrxSe alloy provides a potential material for hard magnets. Therefore, the doping-induced phase transition is an effective way to synthesize ideal phase nanomaterials.
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•The α-FeCrSe alloying phase were synthesized by Cr introduction.•α-Fe0.6Cr0.4Se nanosheets shows hard magnetic properties with Hc of 9.66 kOe at 5 K.•Tc of α-FeCrSe alloy is significantly higher than room temperature.•Hc of α-Fe0.4Cr0.6Se is 15.80 kOe at 5 K and 4.98 kOe at 300 K.
We present detailed magnetic properties of (1-x)BaTiO3–xCoFe2O4 (x = 1, 0.5, 0.4, 0.3, 0.2, 0.1, 0.75, 0.05, 0.025) nanocomposites, synthesized through multiple-step chemical synthesis technique. ...Stepwise synthesis and structural optimization of composites include oxalate route synthesis of BaTiO3 with specifically chosen tetragonality followed by mixing in citric acid solution, and a final addition of the precursor for CoFe2O4. Heat treatment temperature were appropriately chosen to obtain composites with distinct spinel and tetragonal perovskite phases. Peak broadening has been observed in composites being a consequence of presence of strain. Main goal of the present work is to investigate magnetic response as a function of temperature for various compositions and to compare them with the magnetic properties of CoFe2O4 nanoparticles. BaTiO3 acts as a barrier for the growth of the CoFe2O4 due to the phase separation between these constituent phases in the composites. The nanoscopic features are consistently observed in the magnetic properties of the composites. These features include increase in coercivity, stronger temperature dependence of coercivity and magnetic irreversibility. CoFe2O4 and BaTiO3 composites exhibit strong temperature dependence with a more than an order of magnitude increase in coercivity at low temperatures.
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•Multiple-step chemical synthesis of (1-x)BaTiO3–xCoFe2O4 nano-composites.•Tetragonality variation through pre-mixing processing.•Sintering led to observation of strain.•Nanoscopic features observed in the magnetic properties e.g. Increase in Hc.•Temperature dependence of coercivity and magnetic irreversibility.
•A good balance between magnetic and mechanical properties is achieved in the HEA.•The Hc of the HEA is much lower than most of the previously reported HEAs.•After rolling and annealing, the plastic ...deformation of the HEA is near to 60%.•The UTS × EL of the annealed HEA is one of the highest values in HEAs.•The present HEA is comprised of a simple and stable FCC solid solution structure.
A novel FeCoNiCr0.2Si0.2 (at. %, thereafter, all mean atomic ratios) high-entropy alloy (HEA) was synthesized. The as-cast HEA exhibits a combination of excellent mechanical and magnetic properties with a large plastic deformation of about 60% and low coercivity (Hc) of about 187.9 A/m, which are prominent in the HEAs reported so far. Based on the large plasticity, rolling and annealing were adopted as a strategy for improving magnetic and mechanical properties of the HEA. The process of rolling followed by annealing leads to the significant enhancement of the yield strength (YS) and ultimate tensile strength (UTS) of alloy rolled at 773 K, increasing to 320 and 920 MPa respectively. Meanwhile the large plasticity and good soft magnetic properties remain. The enhancement mechanism of annealed after rolling was analyzed. Consequently, the optimal balance of magnetic and mechanical properties is achieved. The present work suggests a promising way to develop HEAs with a combination of excellent magnetic and mechanical properties.
A large coercive field (E
) and ultrahigh piezoelectricity are essential for ferroelectrics used in high-drive electromechanical applications. The discovery of relaxor-PbTiO
crystals is a recent ...breakthrough; they currently afford the highest piezoelectricity, but usually with a low E
. Such performance deterioration occurs because high piezoelectricity is interlinked with an easy polarization rotation, subsequently favoring a dipole switch under small fields. Therefore, the search for ferroelectrics with both a large E
and ultrahigh piezoelectricity has become an imminent challenge. Herein, ternary Pb(Sc
Nb
)O
-Pb(Mg
Nb
)O
-PbTiO
crystals are reported, wherein the dispersed local heterogeneity comprises abundant tetragonal phases, affording a E
of 8.2 kV/cm (greater than that of Pb(Mg
Nb
)O
-PbTiO
by a factor of three) and ultrahigh piezoelectricity (d
= 2630 pC/N; d
= 490 pC/N). The observed E
enhancement is the largest reported for ultrahigh-piezoelectric materials, providing a simple, practical, and universal route for improving functionalities in ferroelectrics with an atomic-level understanding.
The recent discovery of intrinsic ferromagnetism in two-dimensional (2D) van der Waals (vdW) crystals has opened up a new arena for spintronics, raising an opportunity of achieving tunable intrinsic ...2D vdW magnetism. Here, we show that the magnetization and the magnetic anisotropy energy (MAE) of few-layered Fe3 GeTe2 (FGT) is strongly modulated by a femtosecond laser pulse. Upon increasing the femtosecond laser excitation intensity, the saturation magnetization increases in an approximately linear way and the coercivity determined by the MAE decreases monotonically, showing unambiguously the effect of the laser pulse on magnetic ordering. This effect observed at room temperature reveals the emergence of light-driven room-temperature (300 K) ferromagnetism in 2D vdW FGT, as its intrinsic Curie temperature TC is ~200 K. The light-tunable ferromagnetism is attributed to the changes in the electronic structure due to the optical doping effect. Our findings pave a novel way to optically tune 2D vdW magnetism and enhance the TC up to room temperature, promoting spintronic applications at or above room temperature.
Full text
Available for:
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Reconfigurable ferromagnetic liquid droplets Liu, Xubo; Kent, Noah; Ceballos, Alejandro ...
Science (American Association for the Advancement of Science),
07/2019, Volume:
365, Issue:
6450
Journal Article
Peer reviewed
Open access
Solid ferromagnetic materials are rigid in shape and cannot be reconfigured. Ferrofluids, although reconfigurable, are paramagnetic at room temperature and lose their magnetization when the applied ...magnetic field is removed. Here, we show a reversible paramagnetic-to-ferromagnetic transformation of ferrofluid droplets by the jamming of a monolayer of magnetic nanoparticles assembled at the water-oil interface. These ferromagnetic liquid droplets exhibit a finite coercivity and remanent magnetization. They can be easily reconfigured into different shapes while preserving the magnetic properties of solid ferromagnets with classic north-south dipole interactions. Their translational and rotational motions can be actuated remotely and precisely by an external magnetic field, inspiring studies on active matter, energy-dissipative assemblies, and programmable liquid constructs.
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