Multiferroic materials have attracted wide interest because of their exceptional static
and dynamical
magnetoelectric properties. In particular, type-II multiferroics exhibit an ...inversion-symmetry-breaking magnetic order that directly induces ferroelectric polarization through various mechanisms, such as the spin-current or the inverse Dzyaloshinskii-Moriya effect
. This intrinsic coupling between the magnetic and dipolar order parameters results in high-strength magnetoelectric effects
. Two-dimensional materials possessing such intrinsic multiferroic properties have been long sought for to enable the harnessing of magnetoelectric coupling in nanoelectronic devices
. Here we report the discovery of type-II multiferroic order in a single atomic layer of the transition-metal-based van der Waals material NiI
. The multiferroic state of NiI
is characterized by a proper-screw spin helix with given handedness, which couples to the charge degrees of freedom to produce a chirality-controlled electrical polarization. We use circular dichroic Raman measurements to directly probe the magneto-chiral ground state and its electromagnon modes originating from dynamic magnetoelectric coupling. Combining birefringence and second-harmonic-generation measurements with theoretical modelling and simulations, we detect a highly anisotropic electronic state that simultaneously breaks three-fold rotational and inversion symmetry, and supports polar order. The evolution of the optical signatures as a function of temperature and layer number surprisingly reveals an ordered magnetic polar state that persists down to the ultrathin limit of monolayer NiI
. These observations establish NiI
and transition metal dihalides as a new platform for studying emergent multiferroic phenomena, chiral magnetic textures and ferroelectricity in the two-dimensional limit.
Ferroelectric ferromagnets are exceedingly rare, fundamentally interesting multiferroic materials that could give rise to new technologies in which the low power and high speed of field-effect ...electronics are combined with the permanence and routability of voltage-controlled ferromagnetism. Furthermore, the properties of the few compounds that simultaneously exhibit these phenomena are insignificant in comparison with those of useful ferroelectrics or ferromagnets: their spontaneous polarizations or magnetizations are smaller by a factor of 1,000 or more. The same holds for magnetic- or electric-field-induced multiferroics. Owing to the weak properties of single-phase multiferroics, composite and multilayer approaches involving strain-coupled piezoelectric and magnetostrictive components are the closest to application today. Recently, however, a new route to ferroelectric ferromagnets was proposed by which magnetically ordered insulators that are neither ferroelectric nor ferromagnetic are transformed into ferroelectric ferromagnets using a single control parameter, strain. The system targeted, EuTiO3, was predicted to exhibit strong ferromagnetism (spontaneous magnetization, ∼7 Bohr magnetons per Eu) and strong ferroelectricity (spontaneous polarization, ∼10 µC cm−2) simultaneously under large biaxial compressive strain. These values are orders of magnitude higher than those of any known ferroelectric ferromagnet and rival the best materials that are solely ferroelectric or ferromagnetic. Hindered by the absence of an appropriate substrate to provide the desired compression we turned to tensile strain. Here we show both experimentally and theoretically the emergence of a multiferroic state under biaxial tension with the unexpected benefit that even lower strains are required, thereby allowing thicker high-quality crystalline films. This realization of a strong ferromagnetic ferroelectric points the way to high-temperature manifestations of this spin-lattice coupling mechanism. Our work demonstrates that a single experimental parameter, strain, simultaneously controls multiple order parameters and is a viable alternative tuning parameter to composition for creating multiferroics.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
High performance (La0.35Ce0.65)xFe14B (x = 2.0, 2.4, 2.8, 3.2, 3.6, 4.0) ribbons were prepared by melt-spinning method, using industrial La–Ce mischmetal. Phase composition and room temperature ...permanent magnetic properties were investigated. The main phases of all samples crystallize in the tetragonal 2:14:1 type structure. A second-phase appears when x = 3.6 and 4.0, which is La–Ce alloy with a crystal structure of face-centered cubic but not CeFe2. Replacement of CeFe2 by La–Ce alloy enhances the temperature stability of the magnetic material at low temperature. The intrinsic coercivity increases with x monotonously, and the energy product reaches a maximal value of 8.29 MGOe at x = 2.4 when an optimal wheel velocity of 20 m/s was adopted, which is twice of that of Ce2Fe14B. The coercivity mechanism and intergrain exchange coupling were studied by using minor loops. The results indicated that strong pinning effect dominate the magnetization reversal process in all of the rare-earth-rich ribbons. The structure-property relationship was analyzed by using Henkel plots, and intergrian exchange coupling were found in all samples.
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•The (La0.35Ce0.65)xFe14B ribbons were prepared by melt-spinning with mischmetal.•The energy product of (La0.35Ce0.65)2Fe14B is twice lager than that of Ce2Fe14B.•The second-phase appears when x = 3.6 and 4.0, which is La–Ce alloy but not CeFe2.•The strong pinning effect dominate the magnetization reversal process.•The evidence of the existence of exchange coupling interaction was found.
Materials can be transformed from one crystalline phase to another by using an electric field to control ion transfer, in a process that can be harnessed in applications such as batteries, smart ...windows and fuel cells. Increasing the number of transferrable ion species and of accessible crystalline phases could in principle greatly enrich material functionality. However, studies have so far focused mainly on the evolution and control of single ionic species (for example, oxygen, hydrogen or lithium ions). Here we describe the reversible and non-volatile electric-field control of dual-ion (oxygen and hydrogen) phase transformations, with associated electrochromic and magnetoelectric effects. We show that controlling the insertion and extraction of oxygen and hydrogen ions independently of each other can direct reversible phase transformations among three different material phases: the perovskite SrCoO
(ref. 12), the brownmillerite SrCoO
(ref. 13), and a hitherto-unexplored phase, HSrCoO
. By analysing the distinct optical absorption properties of these phases, we demonstrate selective manipulation of spectral transparency in the visible-light and infrared regions, revealing a dual-band electrochromic effect that could see application in smart windows. Moreover, the starkly different magnetic and electric properties of the three phases-HSrCoO
is a weakly ferromagnetic insulator, SrCoO
is a ferromagnetic metal, and SrCoO
is an antiferromagnetic insulator-enable an unusual form of magnetoelectric coupling, allowing electric-field control of three different magnetic ground states. These findings open up opportunities for the electric-field control of multistate phase transformations with rich functionalities.
Cobalt ferrite nano-particles, Co0.9RE0.1Fe2O4, with three different rare earth ions (Nd, Eu, and Gd) were prepared by the chemical co-precipitation method. X-ray diffraction (XRD) analysis, ...transmission electron microscopy (TEM), Fourier Transform Infrared (FTIR), and Vibrating Sample Magnetometry were carried out to study the structural and magnetic properties, respectively. The XRD results revealed that the crystal size is about 22 nm for GdaCo ferrite, which is close to the particle sizes observed from TEM images (20 nm). The FTIR measurements between 350 and 4000 cm-1 confirmed the intrinsic cation vibrations of the spinel structure. The results showed that the RE ions increase both vibrational frequencies and bond strength. The magnetic results showed that the highest magnetic coercivity and the loop area correspond to the GdaCo ferrite, making it suitable for hyperthermia treatment. Also, the Curie point was decreased by the RE ions and had its lowest value for NdaCo ferrite (336 degree C).
•Enriching the application of boron ene in magnetism.•Explored the effect of doping with same family atoms on the system.•Explored the reasons for magnetic quenching in the system
Based on ...first-principles calculations using density functional theory, we studied the effects of Fe, Ru, Os substitutional doping on the magnetic properties of β12 and δ6 borophene systems, and analyzed the stability, charge density, and electronic structure of the systems. The study shows that, except for the phenomenon of magnetic quenching and show paramagnetism in the Os atom-doped δ6 borophene system, and the Ru doped δ6 borophene system showing antiferromagnetism, the other borophene doped Fe, Ru and Os atomic systems show ferrimagnetic properties. The doping of Fe, Ru and Os atoms does not alter the metallic properties of β12 and δ6 borophenes within the scope of the current study. Comparing the three dopants of Fe, Ru and Os, we found out that the Os-doped borophene system is different from the Fe and Ru atom-doped borophene system. The total magnetic moment of the Fe and Ru doped borophene systems is mainly provided by the doping atoms, while the magnetic moment of the β12 borophene system is not conferred by the Os atoms, but by the B atoms that are not covalently bonded to the Os atoms in borophene induced by dopant. One of the reason why the Os atom-doped δ6 borophene system exhibits non-magnetic properties is that the dopant Os atom and the B atomic orbital have strong hybridization and resonance interaction, which makes the Os-B stable covalent bond, resulting in the orbital magnetic moment disappear.
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Magnetic proximity effects are integral to manipulating spintronic
, superconducting
, excitonic
and topological phenomena
in heterostructures. These effects are highly sensitive to the interfacial ...electronic properties, such as electron wavefunction overlap and band alignment. The recent emergence of magnetic two-dimensional materials opens new possibilities for exploring proximity effects in van der Waals heterostructures
. In particular, atomically thin CrI
exhibits layered antiferromagnetism, in which adjacent ferromagnetic monolayers are antiferromagnetically coupled
. Here we report a layer-resolved magnetic proximity effect in heterostructures formed by monolayer WSe
and bi/trilayer CrI
. By controlling the individual layer magnetization in CrI
with a magnetic field, we show that the spin-dependent charge transfer between WSe
and CrI
is dominated by the interfacial CrI
layer, while the proximity exchange field is highly sensitive to the layered magnetic structure as a whole. In combination with reflective magnetic circular dichroism measurements, these properties allow the use of monolayer WSe
as a spatially sensitive magnetic sensor to map out layered antiferromagnetic domain structures at zero magnetic field as well as antiferromagnetic/ferromagnetic domains at finite magnetic fields. Our work reveals a way to control proximity effects and probe interfacial magnetic order via van der Waals engineering
.
Novel core/shell Fe.sub.3O.sub.4/C/polypyrrole (PPy) composites were prepared via facile hydrothermal and chemical oxidative polymerization method. The obtained Fe.sub.3O.sub.4/C/PPy exhibits a dual ...core-shell structure in which an intermediate carbon layer provides excellent electrical connectivity between Fe.sub.3O.sub.4 nanoparticles and PPy polymer. Further, these trilaminar core/shell composites were investigated for EMI shielding material to prevent EMI pollution. The excellent EMI shielding efficiency (> 28) dB was attained for Fe.sub.3O.sub.4/C:PPy (2:8 wt/wt) at thickness 0.8 mm which is mainly governed by absorption. Additional evidence of superior EMI absorption performance is the magnetic property of Fe.sub.3O.sub.4/C:PPy composites. It was observed that magnetic properties of Fe.sub.3O.sub.4/C:PPy composites highly depend on the content and thickness of the shell which influences the spin motion of Fe.sub.3O.sub.4 nanoparticles. Thus, it is anticipated that spin motion plays a decisive role in EMI shielding performance of Fe.sub.3O.sub.4/C/PPy composites.
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