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1.
Nanoscale ; 2020 Apr 01.
Artigo em Inglês | MEDLINE | ID: mdl-32236236

RESUMO

Topological semimetals, including topological nodal point semimetals (TNPSs), topological nodal line state semimetals (TNLSs), and topological nodal surface semimetals (TNSSs), featuring zero-dimensional (0D), one-dimensional (1D), and two-dimensional (2D) topological elements (TEs), respectively, have attracted widespread attention in recent years. In this work, based on first-principles calculations, we propose for the first time that three different (0D, 1D, and 2D) TEs are simultaneously present in a synthetic compound, HfIr3B4, with a P63/m type structure. In detail, HfIr3B4 hosts a Dirac point (DP) state at the K point, a TNL state in the kz = 0 plane, and a 2D TNS state in the kz = π plane, respectively. All sorts of topological elements, 0D, 1D, and 2D TEs, coexisting in the P63/m type HfIr3B4, provide an ideal platform to study the rich fermionic states and their related physical properties in this type of compound. In addition, because the 0D, 1D, and 2D TEs of HfIr3B4 are equally distributed in different energy ranges relative to the Fermi level, an approach is proposed to utilize individual TEs to build on-demand devices.

2.
Phys Chem Chem Phys ; 22(7): 4235-4239, 2020 Feb 21.
Artigo em Inglês | MEDLINE | ID: mdl-32043095

RESUMO

In inorganic-organic perovskites, the three-dimensional arrangement of the organic group results in more subtle balance of charge, spin and space, thereby providing an attractive route toward new multiferroics. Here we report the existing of multiple ferroic orderings in inorganic-organic layered perovskites with relative strong hydrogen bond ordering of the organic chains intra plane. In addition, the inter plane in perovskite is stacking via van der Waals force. However, such magnetoelectric coupling properties for this compound have not been reported since it is difficult to characterize the properties in single crystals since most of the hybrid perovskites are usually deliquescent and unstable when exposed to air. To deal with these problems, we synthesized a (CH3NH3)2CuCl4 single crystal by using a simple evaporation technique, and demonstrated ferroelectric, magnetic and magneto-electric properties of (CH3NH3)2CuCl4. The internal hydrogen bonding of easily tunable organic unit combined with 3d transition-metal layers in such hybrid perovskites make (CH3NH3)2CuCl4 a multiferroic crystal with magnetoelectrical coupling and offer an new way to engineer multifunctional multiferroic.

3.
ACS Appl Mater Interfaces ; 12(5): 6082-6089, 2020 Feb 05.
Artigo em Inglês | MEDLINE | ID: mdl-31939651

RESUMO

Advances in smart and wearable devices are driving innovations in multifunctional flexible materials at a tremendous pace. Here, drawing support from the unique flexible fluorophlogopite mica platform, we present a promising all-inorganic bendable Mn-modified 0.65(0.94Na0.5Bi0.5TiO3-0.06BaTiO3)-0.35SrTiO3 (NBBST) film with dual use in electrocaloric (EC) refrigeration and energy storage via a cost-effective transfer-free process. An appreciable room-temperature EC effect with adiabatic temperature change of 12 K and isothermal entropy of 18 J K-1 kg-1 was realized in the NBBST film, which benefits from the large change in dipolar ordering near depolarization temperature. Also, the film exhibits a broad operating temperature span over 25 °C because of its relaxor feature. Most importantly, the film can maintain a high EC performance either under bending deformation at 5 mm radius or after undergoing 104 bending-unbending cycles. Meanwhile, the flexible NBBST film possesses good energy storage property with a recoverable energy density of 56 J cm-3 and an efficiency of 66%. This is the first example of a lead-free all-inorganic multifunctional film capacitor toward the flexible EC refrigeration and energy storage devices. This work shows bright prospects in the emerging flexible e-market.

4.
Nanoscale ; 12(3): 1904-1911, 2020 Jan 23.
Artigo em Inglês | MEDLINE | ID: mdl-31904055

RESUMO

Using dispersed nanostructures to induce an energy filtering effect is an easy and effective mechanism to optimize the performance of bulk thermoelectric materials. Compared with other nanostructures, core-shell nanostructures possess more interfaces and multiple potential barriers, which would lead to a significant impact on the thermal and electrical properties of materials. In this paper, after BiCuSeO alloy doping into SnTe, SnO2 layers were formed at the interfaces and the BiCuSeO nanoparticles were wrapped in the SnO2 shell during the following high temperature solid state reaction. The formation of SnO2 layers could be observed and confirmed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). BiCuSeO@SnO2 core-shell nanostructures can introduce multiple potential barriers to enhance the energy filtering effect. Once the BiCuSeO doping concentration was over 3%, the carrier concentration could decrease to about 10% while the mobility increases to 350% compared to the values of the undoped sample at room temperature. Meanwhile, the Seebeck coefficients were improved to 176.05 µV K-1 at 835 K. Additionally, due to the scattering of core-shell nanostructures for the phonons, a lower thermal conductivity is achieved with a value of 1.04 W m-1 K-1 at 835 K in Sn1.03Te-5% BiCuSeO. Combined with the improvement of thermal and electrical properties by the BiCuSeO@SnO2 core-shell, a high ZT value of ∼1.21 was achieved for Sn1.03Te-5% BiCuSeO at 835 K, which was enhanced by 190% compared to pristine SnTe.

5.
Adv Mater ; 32(2): e1905632, 2020 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-31777986

RESUMO

Topological insulators have spurred worldwide interest, but their advantageous properties have scarcely been explored in terms of electrochemical energy storage, and their high-rate capability and long-term cycling stability still remain a significant challenge to harvest. p-Type topological insulator SnSb2 Te4 nanodots anchoring on few-layered graphene (SnSb2 Te4 /G) are synthesized as a stable anode for high-rate lithium-ion batteries and potassium-ion batteries through a ball-milling method. These SnSb2 Te4 /G composite electrodes show ultralong cycle lifespan (478 mAh g-1 at 1 A g-1 after 1000 cycles) and excellent rate capability (remaining 373 mAh g-1 even at 10 A g-1 ) in Li-ion storage owing to the rapid ion transport accelerated by the PN heterojunction, virtual electron highways provided by the conductive topological surface state, and extraordinary pseudocapacitive contribution, whose excellent phase reversibility is confirmed by synchrotron in situ X-ray powder diffraction. Surprisingly, durable lifespan even at practical levels of mass loading (>10 mg cm-2 ) for Li-ion storage and excellent K-ion storage performance are also observed. This work provides new insights for designing high-rate electrode materials by boosting conductive topological surfaces, atomic doping, and the interface interaction.

6.
IUCrJ ; 6(Pt 6): 990-995, 2019 Nov 01.
Artigo em Inglês | MEDLINE | ID: mdl-31709054

RESUMO

In the past three years, Dirac half-metals (DHMs) have attracted considerable attention and become a high-profile topic in spintronics becuase of their excellent physical properties such as 100% spin polarization and massless Dirac fermions. Two-dimensional DHMs proposed recently have not yet been experimentally synthesized and thus remain theoretical. As a result, their characteristics cannot be experimentally confirmed. In addition, many theoretically predicted Dirac materials have only a single cone, resulting in a nonlinear electromagnetic response with insufficient intensity and inadequate transport carrier efficiency near the Fermi level. Therefore, after several attempts, we have focused on a novel class of DHMs with multiple Dirac crossings to address the above limitations. In particular, we direct our attention to three-dimensional bulk materials. In this study, the discovery via first principles of an experimentally synthesized DHM LaNiO3 with many Dirac cones and complete spin polarization near the Fermi level is reported. It is also shown that the crystal structures of these materials are strongly correlated with their physical properties. The results indicate that many rhombohedral materials with the general formula LnNiO3 (Ln = La, Ce, Nd, Pm, Gd, Tb, Dy, Ho, Er, Lu) in the space group R 3 c are potential DHMs with multiple Dirac cones.

7.
Small ; : e1903663, 2019 Nov 15.
Artigo em Inglês | MEDLINE | ID: mdl-31729163

RESUMO

Bismuth ferrite (BiFeO3 ) has recently become interesting as a room-temperature multiferroic material, and a variety of prototype devices have been designed based on its thin films. A low-cost and simple processing technique for large-area and high-quality BiFeO3 thin films that is compatible with current semiconductor technologies is therefore urgently needed. Development of BiFeO3 thin films is summarized with a specific focus on the chemical solution route. By a systematic analysis of the recent progress in chemical-route-derived BiFeO3 thin films, the challenges of these films are highlighted. An all-solution chemical-solution deposition (AS-CSD) for BiFeO3 thin films with different orientation epitaxial on various oxide bottom electrodes is introduced and a comprehensive study of the growth, structure, and ferroelectric properties of these films is provided. A facile low-cost route to prepare large-area high-quality epitaxial BFO thin films with a comprehensive understanding of the film thickness, stoichiometry, crystal orientation, ferroelectric properties, and bottom electrode effects on evolutions of microstructures is provided. This work paves the way for the fabrication of devices based on BiFeO3 thin films.

8.
Front Chem ; 7: 550, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-31508406

RESUMO

Equiatomic quaternary Heusler compounds (EQHCs) generally have the advantages of high Curie temperature, large spin polarization and long spin diffusion length, and they are regarded as one of the most promising candidates for spintronics devices. Herein, we report a theoretical investigation on an EQHC CoRhMnGe based magnetic tunnel junction (MTJ) with (i) MnGe-terminated interface and (ii) modified pure Mn terminated interface, i.e., MnMn-terminated interface. By employing first principle calculations combined with non-equilibrium Green's function, the local density of states (LDOS), transmission coefficient, spin-polarized current, tunnel magnetoresistance (TMR) ratio and spin injection efficiency (SIE) as a function of bias voltage are studied. It reveals that when the MTJ under equilibrium state, TMR ratio of MnGe-terminated structure is as high as 3,438%. When the MTJ is modified to MnMn-terminated interface, TMR ratio at equilibrium is enhanced to 2 × 105%, and spin filtering effects are also strengthened. When bias voltage is applied to the MTJ, the TMR ratio of the MnGe-terminated structure suffers a dramatic loss. While the modified MnMn-terminated structure could preserve a large TMR value of 1 × 105%, even bias voltage rises up to 0.1 V, showing a robust bias endurance. These excellent spin transport properties make the CoRhMnGe a promising candidate material for spintronics devices.

9.
ACS Appl Mater Interfaces ; 11(40): 36658-36665, 2019 Oct 09.
Artigo em Inglês | MEDLINE | ID: mdl-31483591

RESUMO

The thermoelectric hetero nano region, as a new strategy, can effectively modulate the electrical and thermal transport properties. In this study, the thermoelectric hetero nano region is explored to improve the thermoelectric performance for Bi0.46Sb1.54Te3 material at room temperature, and a high ZT of 1.45 at 325 K has been achieved. We introduce the thermoelectric hetero nano SnTe regions in a Bi0.46Sb1.54Te3 matrix by mechanical alloying and spark plasma sintering technique, which decouples the relation between electrical and thermal transport properties. The improved electrical conductivity can be attributed to the increase in carrier concentration due to the increased point defects and Bi/SbTe antisite defects. Thermoelectric hetero nano regions effectively scatter the acoustic phonon and thus induce the low lattice thermal conductivity of 0.33 W m-1 K-1. Due to the synergistic modulation of electrical and thermal transport by the introduction of the thermoelectric hetero nano region, a high ZT value of 1.45 is realized at 325 K.

10.
ACS Appl Mater Interfaces ; 11(37): 33792-33802, 2019 Sep 18.
Artigo em Inglês | MEDLINE | ID: mdl-31454222

RESUMO

SnTe has attracted more and more attention due to the similar band and crystal structure with high performance thermoelectric materials PbTe. Here, we introduced Pd into SnTe and the valence band convergence was confirmed by first-principles calculation. In the experimental process, we found that Pd-doped SnTe exhibit a reduced thermal conductivity because of softening chemical bonds and grain refining effects. To further improve the thermoelectric performance, Pd-In codoped SnTe samples were prepared, and the abnormal change of thermal conductivity was observed. The results of synchrotron powder diffraction suggest that the local phase transition (local structural distortions) near 400 K results in the first turn on thermal conductivity. Similarly, the second local phase transition in near 600 K observed by neutron powder diffraction lead to a decrease thermal conductivity of the sample. Finally, a peak thermoelectric figure of merit (ZT) ≈ 1.51 has been obtained in Sn0.98Pd0.025In0.025Te at 800 K.

11.
Phys Chem Chem Phys ; 21(27): 14973-14983, 2019 Jul 10.
Artigo em Inglês | MEDLINE | ID: mdl-31237601

RESUMO

SrTiO3-based transition-metal oxide heterostructures with superconducting, ferromagnetic, ferroelectric, and ferroelastic properties exhibit high application potential in the fields of energy storage, energy conversion, and spintronic devices. Meanwhile, high effective (charge)-Seebeck coefficient materials composed of a ferromagnetic layer and SrTiO3 insulator layer have been achieved but we still have blocks to pursuing high spin-Seebeck coefficient materials. Here, we use first-principles calculations combined with spin-resolved Boltzmann transport theory to investigate the spin- and effective-Seebeck coefficients in the LaX(X = Mn and Co)O3/SrTiO3 superlattice. Compared with the LaMnO3/SrTiO3 superlattice, LaCoO3/SrTiO3 with ferromagnetic ordering has high spin polarization, relatively low valence valley degeneracy but high effective mass. Utilizing these characteristics, the maximum spin-Seebeck coefficient of LaMnO3/SrTiO3 is -152 µV K-1 at 450 K along the cross-plane direction, while LaCoO3/SrTiO3 reaches -247 µV K-1 under the same conditions. Interestingly, the spin- and effective-Seebeck coefficients are amazingly consistent with each other below 200 K, which indicates that one spin channel (spin-up or spin-down) dominates the carrier transport, and the other one (spin-down or spin-up) is filtered out. These characteristics are mainly associated with the magnetic MnO2/CoO2 layers with distinct dxy and dz2 orbitals near the Fermi level. Our results clarify the relationship of spin- and effective-Seebeck coefficients and indicate that SrTiO3-based transition metal oxide heterointerfaces are a key candidate for spin caloritronics.

12.
ACS Appl Mater Interfaces ; 11(26): 23372-23381, 2019 Jul 03.
Artigo em Inglês | MEDLINE | ID: mdl-31252505

RESUMO

Very recently, the ferroelectric photovoltaic property of bismuth ferrite (BiFeO3, BFO) has attracted much attention. However, the physical mechanisms for its anomalous photovoltaic effect and switchable photovoltaic effect are still largely unclear. Herein, a novel design was proposed to realize a high photovoltaic output in BiFeO3 films by manipulating its oxygen vacancy concentration through the alteration of the Bi content. Subsequent results and analysis manifested that the highest photovoltaic output was achieved in Bi1.05FeO3 films, differing 1000 times from that of Bi0.95FeO3 films. Simultaneously, the origin of photovoltaic effect in all BiFeO3 films was suggested as the bulk photovoltaic mechanism instead of the Schottky effect. Moreover, oxygen vacancy migration should be the dominant factor determining the switchable photovoltaic effect rather than the ferroelectric polarization. A switchable Schottky-to-Ohmic interfacial contact model was proposed to illustrate the observed switchable photovoltaic or diodelike effect. Therefore, the present work may open a new way to realize the high power output and controllable photovoltaic switching behavior for the photovoltaic applications of BiFeO3 compounds.

13.
Phys Chem Chem Phys ; 21(23): 12301-12309, 2019 Jun 21.
Artigo em Inglês | MEDLINE | ID: mdl-31139776

RESUMO

Magnetism in two-dimensional (2D) materials, that is, a 2D version of the magnetism of three-dimensional bulk materials, and the associated novel physics have recently been the focus of many spintronics researchers. Here we investigate the manipulation of 2D magnetism at the interfaces of ferromagnetic/ferroelectric hematene/BaTiO3(001) heterostructures (HSs) fabricated via a precisely chosen sequence. By introducing four types of interfaces of 2D hematene and three-dimensional BaTiO3 that induce different oxygen environments, the control of magnetism is directly demonstrated from first-principles. An obvious 2D electron gas originates from the Fe-3d and O-2p hybridization; the electron gas is sensitive to the interfacial atomic displacements. Robust control of both the direction and magnitude of the net magnetization has been realized for an Fe/TiO2 terminated bilayer HS. The electron occupancies of the dxy and dxz orbitals and changes to the Fe-O bond play a key role in determining the magnetism of our systems. Our work not only demonstrates the technique's potential for manipulating magnetism in 2D hematene, but also sheds light on the underlying mechanism and the fundamental properties of hematene HSs.

14.
Phys Chem Chem Phys ; 21(32): 17538-17545, 2019 Aug 28.
Artigo em Inglês | MEDLINE | ID: mdl-31134251

RESUMO

Hydrogen solubility and diffusivity are the key features of hydrogen permeable membrane materials. To characterize the hydrogen permeation performance of NbTM (TM = W, Ru) phases, their hydrogen diffusion coefficient and solution coefficient, thermodynamic stability and chemical bonding are studied by a series of first principles calculations. The phonon spectra and elastic constants show that NbTM is dynamically stable. The TM-H chemical bonds have an ionic/covalent mixed character and are stronger than the Nb-H bond. The preferential diffusion paths of H in both Nb16H and Nb15TMH are from a tetrahedral interstitial site (TIS) to another TIS. The TM doping in Nb16H lowers the solubility and energy barrier of H diffusion and enhances the H diffusion coefficient (D), with Nb16RuH exhibiting the highest D value for TIS to TIS diffusion (2.14 × 10-8 m2 s-1) at 600 K. This study shows that alloying and temperature could significantly affect the solubility and diffusivity of hydrogen in Nb. Moreover, TM doping could greatly improve the hydrogen diffusion performance with good control of hydrogen embrittlement.

15.
Nanoscale ; 11(20): 9931-9936, 2019 May 28.
Artigo em Inglês | MEDLINE | ID: mdl-31070212

RESUMO

Exploring two-dimensional (2D) materials with both ferromagnetic and ferroelectric properties is scientifically interesting and of great technical importance to numerous functionalities in nanoscale devices. In this work, we have demonstrated a strong magnetoelectric coupling that appeared in the 2D FeI2/In2Se3 van der Waals heterostructure. FeI2 layers undergo a transition from ferromagnetic to antiferromagnetic by reversing the direction of ferroelectric polarization. First-principles calculation predicts a new magnetoelectronic coupling mechanism which is completely different from the Dzyaloshinskii-Moriya (DM) effect in multiferroic materials. Because of the polarization discontinuity at the interface, the valence states of Fe ions change between +2 and +3 for two different polarization directions, leading to the magnetic interaction variation between the direct exchange and I ion mediated superexchange. Moreover, metallic 2D electron gas (2DEG) transfers from the surface of FeI2 to In2Se3 when the polarization reverses, which induces the spin polarization of the heterostructure varying from 93% to 0%. Our work is the first realization of manipulation magnetism by an electric field in full 2D van der Waals heterostructures.

16.
IUCrJ ; 6(Pt 3): 465-472, 2019 May 01.
Artigo em Inglês | MEDLINE | ID: mdl-31098027

RESUMO

In this work, a series of all-d-metal Heusler alloys, X 2 - x Mn1 + x V (X = Pd, Ni, Pt, Ag, Au, Ir, Co; x; = 1, 0), were predicted by first principles. The series can be roughly divided into two categories: XMn2V (Mn-rich type) and X 2MnV (Mn-poor type). Using optimized structural analysis, it is shown that the ground state of these all-d-metal Heusler alloys does not fully meet the site-preference rule for classic full-Heusler alloys. All the Mn-rich type alloys tend to form the L21 structure, where the two Mn atoms prefer to occupy the A (0, 0, 0) and C (0.5, 0.5, 0.5) Wyckoff sites, whereas for the Mn-poor-type alloys, some are stable with XA structures and some are not. The c/a ratio was also changed while maintaining the volume the same as in the cubic state to investigate the possible tetragonal transformation of these alloys. The Mn-rich Heusler alloys have strong cubic resistance; however, all the Mn-poor alloys prefer to have a tetragonal state instead of a cubic phase through tetragonal transformations. The origin of the tetragonal state and the competition between the cubic and tetragonal phases in Mn-poor alloys are discussed in detail. Results show that broader and shallower density-of-states structures at or in the vicinity of the Fermi level lower the total energy and stabilize the tetragonal phases of X 2MnV (X = Pd, Ni, Pt, Ag, Au, Ir, Co). Furthermore, the lack of virtual frequency in the phonon spectra confirms the stability of the tetragonal states of these Mn-poor all-d-metal Heusler alloys. This work provides relevant experimental guidance in the search for possible martensitic Heusler alloys in all-d-metal materials with less Mn and new spintronic and magnetic intelligent materials among all-d-metal Heusler alloys.

17.
ACS Appl Mater Interfaces ; 11(20): 18825-18832, 2019 May 22.
Artigo em Inglês | MEDLINE | ID: mdl-31007006

RESUMO

Fluorine-doped Fe(Se, Te) has been successfully synthesized using the melting method. A dual-oscillation effect was found in the F-doped sample, which combined both microstructural oscillation and chemical compositional oscillation. The microstructural oscillation could be attributed to alternate growth of tetragonal ß-Fe(Se, Te) and hexagonal δ-Fe(Se, Te), which formed a pearlite-like structure and led to the enhancement of δ l flux pinning due to the alternating distributed nonsuperconducting δ-Fe(Se, Te) phase. The chemical compositional oscillations in ß-Fe(Se, Te) phase were because of the inhomogeneously distributed Se and Te, which changes the pinning mechanism from surface pinning in the undoped sample to Δκ pinning in the 5% F-doped one. As a result, the critical current, upper critical field, and thermally activated flux-flow activation energy of FeSe0.45Te0.5F0.05 were enhanced by 7, 2, and 3 times, respectively. Our work revealed the physical insights into F-doping resulting in high-performance Fe(Se, Te) superconductors and inspired a new approach to optimize superconductivities in iron-based superconductors through phase and element manipulations.

18.
Science ; 364(6437): 264-268, 2019 04 19.
Artigo em Inglês | MEDLINE | ID: mdl-31000659

RESUMO

High-performance piezoelectrics benefit transducers and sensors in a variety of electromechanical applications. The materials with the highest piezoelectric charge coefficients (d 33) are relaxor-PbTiO3 crystals, which were discovered two decades ago. We successfully grew Sm-doped Pb(Mg1/3Nb2/3)O3-PbTiO3 (Sm-PMN-PT) single crystals with even higher d 33 values ranging from 3400 to 4100 picocoulombs per newton, with variation below 20% over the as-grown crystal boule, exhibiting good property uniformity. We characterized the Sm-PMN-PT on the atomic scale with scanning transmission electron microscopy and made first-principles calculations to determine that the giant piezoelectric properties arise from the enhanced local structural heterogeneity introduced by Sm3+ dopants. Rare-earth doping is thus identified as a general strategy for introducing local structural heterogeneity in order to enhance the piezoelectricity of relaxor ferroelectric crystals.

19.
IUCrJ ; 6(Pt 2): 189-196, 2019 Mar 01.
Artigo em Inglês | MEDLINE | ID: mdl-30867916

RESUMO

Robust control of magnetism is both fundamentally and practically meaningful and highly desirable, although it remains a big challenge. In this work, perovskite oxide superstructures LaFeO3/BaTiO3 (LFO/BTO), LaMnO3/BaTiO3 (LMO/BTO) and LaCrO3/BaTiO3 (LCO/BTO) (001) are designed to facilitate tuning of magnetism by the electric field from ferroelectric polarization, and are systemically investigated via first-principles calculations. The results show that the magnetic ordering, conductivity and exchange interactions can be controlled simultaneously or individually by the reorientation of the ferroelectric polarization of BTO in these designed superstructures. Self-consistent calculations within the generalized gradient approximation plus on-site Coulomb correction did not produce distinct rotations of oxygen octahedra, but there were obvious changes in bond length between oxygen and the cations. These changes cause tilting of the oxygen octahedra and lead to spin, orbital and bond reconstruction at the interface, which is the structural basis responsible for the manipulation. With the G-type antiferromagnetic (G-AFM) ordering unchanged for both ±P cases, a metal-insulator transition can be observed in the LFO/BTO superstructure, which is controlled by the LFO thin film. The LMO/BTO system has A-type antiferromagnetic (A-AFM) ordering with metallic behavior in the +P case, while it shifts to a half-metallic ferromagnetic ordering when the direction of the polarization is switched. LCO/BTO exhibits C-type antiferromagnetic (C-AFM) and G-AFM orders in the +P and -P cases, respectively. The three purpose-designed superstructures with robust intrinsic magnetoelectric coupling are a particularly interesting model system that can provide guidance for the development of this field for future applications.

20.
IUCrJ ; 6(Pt 2): 218-225, 2019 Mar 01.
Artigo em Inglês | MEDLINE | ID: mdl-30867919

RESUMO

In this work, two kinds of competition between different Heusler structure types are considered, one is the competition between XA and L21 structures based on the cubic system of full-Heusler alloys, Pd2 YZ (Y = Co, Fe, Mn; Z = B, Al, Ga, In, Tl, Si, Ge, Sn, Pb, P, As, Sb). Most alloys prefer the L21 structure; that is, Pd atoms tend to occupy the a (0, 0, 0) and c (0.5, 0.5, 0.5) Wyckoff sites, the Y atom is generally located at site b (0.25, 0.25, 0.25), and the main group element Z has a preference for site d (0.75, 0.75, 0.75), meeting the well known site-preference rule. The difference between these two cubic structures in terms of their magnetic and electronic properties is illustrated further by their phonon dispersion and density-of-states curves. The second type of competition that was subjected to systematic study was the competitive mechanism between the L21 cubic system and its L10 tetragonal system. A series of potential tetragonal distortions in cubic full-Heusler alloys (Pd2 YZ) have been predicted in this work. The valley-and-peak structure at, or in the vicinity of, the Fermi level in both spin channels is mainly attributed to the tetragonal ground states according to the density-of-states analysis. ΔE M is defined as the difference between the most stable energy values of the cubic and tetragonal states; the larger the value, the easier the occurrence of tetragonal distortion, and the corresponding tetragonal structure is stable. Compared with the ΔE M values of classic Mn2-based tetragonal Heusler alloys, the ΔE M values of most Pd2CoZ alloys in this study indicate that they can overcome the energy barriers between cubic and tetragonal states, and possess possible tetragonal transformations. The uniform strain has also been taken into consideration to further investigate the tetragonal distortion of these alloys in detail. This work aims to provide guidance for researchers to further explore and study new magnetic functional tetragonal materials among the full-Heusler alloys.

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