Weak Antiferromagnetic Order Research Articles

Nontrivial Topological Features and Griffith’s-Phase Behavior in CrFeVGa Probed by Experiment and Theory

We report a combined theoretical and experimental study of the topological semimetal CrFeVGa with an emphasis on the role of atomic disorder on the magnetoelectronic properties. CrFeVGa belongs to the quaternary Heusler alloy family and crystallizes in the cubic structure with B2 disorder. It is found that the disorder plays a crucial role in quenching the magnetization (net moment $\ensuremath{\sim}5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}2}\phantom{\rule{0.2em}{0ex}}{\ensuremath{\mu}}_{B}$ per formula unit) and other anomalies. Ac and dc magnetization data reveal the occurrence of Griffith's-phase-like behavior in the presence of small magnetic clusters with a weak antiferromagnetic or ferrimagnetic ordering. A nonsaturating, linear positive magnetoresistance is observed even at 70 kOe, in a wide temperature range, which is attributed to the quantum linear magnetoresistance arising due to the zero- or small-gap band structure. Hall measurements show some anomalous behavior (including an anomalous Hall conductivity ${\ensuremath{\sigma}}_{xy0}=270\phantom{\rule{0.2em}{0ex}}\mathrm{S}\phantom{\rule{0.2em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ and an anomalous Hall angle of 0.07 at 2 K) with a significant contribution from the semimetallic bands. Hall data analysis also reveals the presence of some non-negligible topological Hall contribution, which is significant at low temperatures. Ab initio calculations confirm the topological Weyl behavior of CrFeVGa, which originates from a unique combination of broken time-reversal symmetry and noncentrosymmetry. The nontrivial band topology stems from the $p$ and $d$ states of vanadium, which overlap near the Fermi level. The presence of multi-Weyl points (24 pairs) near the Fermi level causes a large Berry curvature and hence reasonably high anomalous Hall conductivity. The coexistence of so many emerging features in a single material is rather rare and thus opens up new avenues for future topological and spintronics-based research.

Triangular Magnet Emergent from Noncentrosymmetric Sr0.94Mn0.86Te1.14O6 Single Crystals.

We report the successful growth of high-quality single crystals of Sr0.94Mn0.86Te1.14O6 (SMTO) using a self-flux method. The structural, electronic, and magnetic properties of SMTO are investigated by neutron powder diffraction (NPD), single-crystal X-ray diffraction (SCXRD), thermodynamic, and nuclear magnetic resonance techniques in conjunction with density functional theory calculations. NPD unambiguously determined octahedral (trigonal antiprismatic) coordination for all cations with the chiral space group P312 (no. 149), which is further confirmed by SCXRD data. The Mn and Te elements occupy distinct Wyckoff sites, and minor anti-site defects were observed in both sites. X-ray photoelectron spectroscopy reveals the existence of mixed valence states of Mn in SMTO. The magnetic susceptibility and specific heat data evidence a weak antiferromagnetic order at TN = 6.6 K. The estimated Curie-Weiss temperature θCW = -21 K indicates antiferromagnetic interaction between Mn ions. Furthermore, both the magnetic entropy and the 125Te nuclear spin-lattice relaxation rate showcase that short-range spin correlations persist well above the Néel temperature. Our work demonstrates that Sr0.94(2)Mn0.86(3)Te1.14(3)O6 single crystals realize a noncentrosymmetric triangular antiferromagnet.

Manipulating Exchange Bias in a Van der Waals Ferromagnet.

Spintronics applications of thin-film magnets require control and design of specific magnetic properties. Exchange bias, originating from the pinning of spins in a ferromagnet by these of an antiferromagnet, is a part of the highly important elements for spintronics applications. Here, an exchange bias of ≈90 mT in a van der Waals ferromagnet encapsulated by two antiferromagnets at 5 K, the value of which is highly tunable by the field coolings, is reported. The non-antisymmetric dependence of exchange bias on field cooling is explained through considering an uncompensated interfacial magnetic layer of an antiferromagnet with a noncollinear spin texture, and a weak antiferromagnetic order in the oxidized layer, at two ferromagnet/antiferromagnet interfaces. This work opens up new routes toward designing and controlling 2D spintronic devices made of atomically thin van der Waals magnets.

Two-Dimensional Copper Coordination Polymer Assembled with Fumarate and 5,5’-Dimethyl-2,2’-bipyridine: Synthesis, Crystal Structure and Magnetic Properties

[[Cu(fum)(dmb)]·H2O]n (1) (fum = fumarate; dmb = 5,5’-dimethyl-2,2’-bipyridine) was obtained by a self-assembly solution reaction, at ambient conditions, and characterized by elemental analysis, IR spectroscopy and X-ray single crystal diffraction. Crystallographic studies show that 1 crystallizes in a triclinic system with a P-1 space group, with a = 8.2308(2) A, b = 9.7563(2) A, c = 10.3990(2) A; α = 80.3444(4)°, β = 77.9517(4)°, γ = 82.0440(5)°; V = 800.45(3) A3. The Cu(II) centers are five-coordinated with a distorted square pyramidal configuration. The formation of a two-dimensional (2D) array in 1 can be explained by the presence of two different coordination modes in the fumarate ligand: μ-η1:η0 and μ2-η2:η0, both in a bridging monodentate manner, the latter generating distinctive rhombic-dinuclear units. The thermal stability of 1 has also been analyzed. Magnetic measurements revealed that this polymer exhibits weak antiferromagnetic ordering. [[Cu(fum)(dmb)]·H2O]n, exhibiting weak antiferromagnetic interactions, displays a two-dimensional array comprised of rhombic dinuclear units, where the carboxylate moieties of fumarate bridging ligand displays monodentate and oxo-bridging coordination modes connecting two Cu centers.

Arsenic(III)-Capped 12-Tungsto-2-Arsenates(III) [M2(AsIIIW6O25)2(AsIIIOH)x]n- (M = CrIII, FeIII, ScIII, InIII, TiIV, MnII) and Their Magnetic Properties.

Six arsenic(III)-capped 12-tungsto-2-arsenates(III) of the type [M2(AsIIIW6O25)2(AsIIIOH)x]n- (M = CrIII, 1; FeIII, 2; ScIII, 3; InIII, 4; TiIV, 5; MnII, 6) have been synthesized in aqueous medium by direct reaction of the elements using a one-pot strategy and structurally characterized by FT-IR spectroscopy, single-crystal XRD, and elemental analysis. Polyanions 1-6 are comprised of two octahedrally coordinated guest metal ions M sandwiched between two {AsW6} units, resulting in a structure with C2h point-group symmetry. Polyanions 1-5 contain tri- and tetravalent metal ion guests M (M = CrIII, FeIII, ScIII, InIII, and TiIV, respectively), and they have one {AsIIIOH} group grafted on each {AsW6} unit, whereas the divalent MnII-containing derivative 6 has two such {AsIIIOH} groups grafted on each {AsW6} unit. Magnetic studies on polyanions 3-5 over the temperature range 1.8-295 K and magnetic fields of 0-7 T confirmed that they are diamagnetic. On the other hand, polyanions 1, 2, and 6 are strongly magnetic and follow the Curie-Weiss law above 30 K. The susceptibility plots of 1 and 6 exhibit broad peaks suggesting short-range antiferromagnetic ordering, while the very weak antiferromagnetic ordering of 2 is overshadowed by traces of a paramagnetic impurity. The magnetization data of 1, 2, and 6 at 1.8 K over 0-7 T were analyzed by using the Heisenberg exchange procedure. Small (negative) values of the obtained J values help in understanding the absence of long-range antiferromagnetic ordering.

Low temperature ferromagnetism in CaCu3Ti4O12 * *Project supported by the National Natural Science Foundation of China (Grant Nos. 11504227 and 51971128), the Program of Shanghai Academic/Technology Research Leader, China (Grant No. 20XD1401800), and the Project of the Science and Technology Commission of Shanghai Municipality, China (Grant No. 19020501000).

The low-temperature magnetic order behaviors of perovskite oxide CaCu3Ti4O12 (CCTO) ceramics prepared by different methods are discussed. X-ray diffraction, scanning electron microscope, x-ray photoelectron spectroscopy, and direct current (DC) magnetization are used to characterize the structures, microscopic morphologies, valence states, and magnetic properties of the samples. The results show that the magnetic behaviors of CCTO ceramics are very sensitive to the preparation process. The quenched CCTO ceramic and CCTO powders grown in a molten salt crystal, which contain much more oxygen vacancies and Ti3+, show the coexistence of weak ferromagnetic order and antiferromagnetic order below the Neel temperature. It suggests that the bound magnetopolaron formed by oxygen vacancies and Ti3+ ion composite defects are responsible for the weak ferromagnetic order at low temperature.

Interplay of mass imbalance and frustration in correlated band insulators

We report the emergence or broadening of exotic magnetic metallic phases upon explicit breaking of $SU(2)$ symmetry by introduction of mass imbalance in a variant of Hubbard model, known as the ionic Hubbard model in the presence of frustration at half-filling on a square lattice. The ionic Hubbard model has in addition to hopping($\sim t$) and onsite coulomb repulsion ($\sim U$), a staggered ionic potential ($\sim \Delta$) which breaks translational symmetry of the underlying lattice. In the low to intermediate ranges of $U$ and $\Delta$, we use unrestricted Hartree-Fock theory to construct the phase diagram in the $U-\Delta$ plane for a fixed mass imbalance($\sim\eta$). Where as in the limit where both $U,\Delta$ are comparable and much larger than the first $(\sim t_{\sigma})$ and second $(\sim t_{\sigma}')$ neighbor hopping amplitudes , we employ the technique of generalized Gutzwiller approximation and subsequently use renormalized mean field theory to construct the phase diagram for varying values of hopping asymmetry. In both cases, starting from a correlated band insulator with weak antiferromagnetic spin density wave order, if we tune $U/\Delta$, we observe the opening of novel magnetically ordered metallic phases such as spin imbalanced ferromagnetic metal, ferrimagnetic metal and antiferromagnetic half metal. We also study singlet superconductivity in the d-wave and extended s-wave channels in the strong coupling limit of this model in the presence of mass imbalance.

Tunable polarization with enhanced multiferroic response of W/Co co-doped Bi4LaFeTi3O15 Aurivillius ceramics

A comprehensive investigation on structural, microstructural, optical, electrical, magnetic, and magnetoelectric (ME) properties of the single phase Bi4LaFeTi3−2x(WyCo2y)xO15 (0.00 ≤ x ≤ 0.15, y = 1.0) Aurivillius ceramics has been presented here. The preliminary x-ray diffraction and Raman spectroscopic studies reveal that a layered-structure perovskite Aurivillius phase of orthorhombic space group A21am. Furthermore, the surface morphology study provides a plate-like to spherical-like granules with increasing the dopant concentrations. The ferroelectric response prevails a slim P–E loop for pristine sample, whereas it provides the highest polarization (Ps) values of 7.21 and 13.25 μC/cm2 for x = 0.10 and 0.15 concentrations, respectively. At low temperature, magnetic measurements provide a weak antiferromagnetic ordering of pristine sample, whereas a strong FM (ferromagnetic) ordering of doped ceramics is attained. The observed strong FM behavior of the Aurivillius phase is attributed to either double exchange interactions between neighboring Fe3+–O–Fe3+, Co3+–O–Co3+, and Fe3+–O–Co3+ ions or antisymmetric Dzyaloshinskii–Moriya interactions for spin canting of adjacent sub-lattices via Co3+/2+–O–Co3+/2+, Fe3+–O–Fe3+, and Co3+/2+–O–Fe3+ ions. The temperature dependent dielectric broad-band spectroscopic study enlightened a dielectric relaxation. This is due to cationic disordering through the generation of oxygen vacancies, which yields a conduction mechanism at high temperature regions. Furthermore, a complex modulus spectroscopic technique is also adopted to investigate the dielectric relaxation at high temperature regimes. The observed magnetic ferroelectric polarization responses and magnitudes of ME coupling coefficients provided that this material could be useful for future magnetoelectric sensors.

Correlations and incipient antiferromagnetic order within the linear Mn chains of metallic Ti4MnBi2.

We report measurements on Ti4MnBi2, where a crystal structure involving linear chains of Mn ions suggests one-dimensional magnetic character. The electrical resistivity is metallic, consistent with the results of electronic-structure calculations that find a robust Fermi surface albeit with moderate electronic correlations. A Curie-Weiss fit to the magnetic susceptibility suggests that the Mn moments are in the low-spin S = 1/2 configuration. Neutron diffraction measurements detect weak antiferromagnetic order within the Mn chains, with further evidence for the small staggered moment coming from the entropy associated with the ordering peak in the specific heat as well as from the results of spin-polarized electronic-structure calculations. The antiferromagnetic moments are apparently associated with the and d xy orbitals of Mn while the remaining Mn orbitals are delocalized and nonmagnetic. Strong quantum fluctuations, possibly related to an electronic instability that forms the Mn moment or to the one-dimensional character of Ti4MnBi2, nearly overcome magnetic order.

Trends in Synthesis, Crystal Structure, and Thermal and Magnetic Properties of Rare-Earth Metal Borohydrides.

Synthesis, crystal structures, and thermal and magnetic properties of the complete series of halide-free rare-earth (RE) metal borohydrides are presented. A new synthesis method provides high yield and high purity products. Fifteen new metal borohydride structures are reported. The trends in crystal structures, thermal behavior, and magnetic properties for the entire series of RE(BH4) x are compared and discussed. The RE(BH4) x possess a very rich crystal chemistry, dependent on the oxidation state and the ionic size of the rare-earth ion. Due to the lanthanide contraction, there is a significant decrease in the volume of the RE3+-ion with increasing atomic number, which correlates linearly with the unit cell volume of the α- and β-RE(BH4)3 polymorphs and the solvated complexes α-RE(BH4)3·S(CH3)2. The thermal analysis reveals a one-step decomposition pathway in the temperature range from 247 to 277 °C for all RE(BH4)3 except Lu(BH4)3, which follows a three-step decomposition pathway. In contrast, the RE(BH4)2 decompose at higher temperatures in the range 306 to 390 °C due to lower charge density on the rare-earth ion. The RE(BH4)3 show increasing stability with increasing Pauling electronegativity, which contradicts other main group and transition metal borohydrides. The majority of the compounds follow Curie-Weiss paramagnetic behavior down to 3 K with weak antiferromagnetic interactions and magnetic moments in accord with those of isolated 4f ions. Some of the RE(BH4) x display varying degrees of temperature-dependent magnetic moments due to low-lying excited stated induced by crystal field effects. Additionally, a weak antiferromagnetic ordering is observed in Gd(BH4)3, indicating superexchange through a borohydride group.

Griffiths-like phase and charge-spin glass state in La1.5Sr0.5CoO4

Hole-doped antiferromagnetic La2CoO4 has been known to possess intriguing electronic and magnetic phases due to the complex temperature and magnetic field dependent behavior of Co3+ ions. Here, we report on magnetic and dielectric observations in the half hole-doped La1.5Sr0.5CoO4. A Griffiths-like phase has been observed in the high temperature region below TG (∼244 K). At low temperature (∼55 K), a metamagnetic phase has been observed where antiferromagnetic correlations appear. On further cooling, a static weak antiferromagnetic ordering appears at ∼30 K, and a charge-spin glass state has been realized at ∼14 K.

The melilite-type compound [formula omitted] (A = K, La) being a room temperature ferromagnetic semiconductor

The seeking of room temperature ferromagnetic semiconductors, which take advantages of both the charge and spin degrees of freedom of electrons to realize a variety of functionalities in devices integrated with electronic, optical, and magnetic storage properties, has been a long-term goal of scientists and engineers. Here, by using the spin-polarized density functional theory calculations, we predict a new series of high temperature ferromagnetic semiconductors based on the melilite-type oxysulfide Sr2MnGe2S6O through hole (K) and electron (La) doping. Due to the lack of strong antiferromagnetic superexchange between Mn ions, the weak antiferromagnetic order in the parent compound Sr2MnGe2S6O can be suppressed easily by charge doping with either p-type or n-type carriers, giving rise to the expected ferromagnetic order. At a doping concentration of 25%, both the hole-doped and electron-doped compounds can achieve a Curie temperature (Tc) above 300 K. The underlying mechanism is analyzed. Our study provides an effective approach for exploring new types of high temperature ferromagnetic semiconductors.

Temperature and polarization dependence of low-energy magnetic fluctuations in nearly optimally doped NaFe0.9785Co0.0215As

We use unpolarized and polarized neutron scattering to study the temperature and polarization dependence of low-energy magnetic fluctuations in nearly-optimal-doped NaFe$_{0.9785}$Co$_{0.0215}$As, with coexisting superconductivity ($T_{\rm c}\approx19$ K) and weak antiferromagnetic order ($T_{\rm N}\approx30$ K, ordered moment $\approx0.02$ $\mu_{\rm B}$/Fe). A single spin resonance mode with intensity tracking the superconducting order parameter is observed, although energy of the mode only softens slightly on approaching $T_{\rm c}$. Polarized neutron scattering reveals that the single resonance is mostly isotropic in spin space, similar to overdoped NaFe$_{0.935}$Co$_{0.045}$As but different from optimal electron-, hole-, and isovalent-doped BaFe$_2$As$_2$ compounds, all featuring an additional prominent anisotropic component. Spin anisotropy in NaFe$_{0.9785}$Co$_{0.0215}$As is instead present at energies below the resonance, which becomes partially gapped below $T_{\rm c}$, similar to the situation in optimal-doped YBa$_2$Cu$_3$O$_{6.9}$. Our results indicate that anisotropic spin fluctuations in NaFe$_{1-x}$Co$_x$As appear in the form of a resonance in the underdoped regime, become partially gapped below $T_{\rm c}$ near optimal doping and disappear in overdoped compounds.

Synthesis, luminescent and magnetic properties of new tetranuclear lanthanide complexes with 4-hydroxy-2,1,3-benzothiadiazolate and dibenzoylmethanide ligands

Four new tetranuclear complexes, [Ln4(dbm)4(O-btd)6(OH)2] 1a (Ln=Yb), 1b (Ln=Dy) and [Ln4(dbm)6(O-btd)4(OH)2] 2a (Ln=Yb), 2b (Ln=Dy) (O-btd=4-hydroxo-2,1,3-benzothiadiazolate and dbm=dibenzoylmethanide), and their solvates with toluene and tetrahydrofuran were synthesized. The magnetic properties of the complexes 1a, 1b, 2a and 2b have been studied, revealing different magnetic susceptibility patterns for the Yb(III) and Dy(III) complexes in the temperature range 80–300K. Upon lowering the temperature, a weak antiferromagnetic ordering is observed for both Yb compounds, while the Dy derivatives are assumed to show weak ferromagnetic interactions. The Yb complexes 1a and 2a demonstrate strong NIR luminescence at ∼1000nm in CH2Cl2 solution upon excitation of the (O-btd)− ligand. This observation suggests the (O-btd)− ligand to be an efficient antenna ligand for lanthanide-based NIR luminescence.

Investigation on structural, Mössbauer and ferroelectric properties of (1−x)PbFe0.5Nb0.5O3–(x)BiFeO3 solid solution

In this study, (1−x)PbFe0.5Nb0.5O3(PFN)–(x)BiFeO3(BFO) multiferroic solid solutions with x=0.0, 0.1, 0.2, 0.3 and 0.4 were synthesized through single step solid state reaction method and characterized thoroughly through X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Fourier Transform Infra-Red (FTIR), Raman, Mössbauer spectroscopy and ferroelectric studies. The room temperature (RT) XRD studies confirmed the formation of single phase with negligible amount of secondary phases (x=0.2 and 0.4). The zoomed XRD patterns of (1−x)PFN–(x)BFO solid solutions showed the clear structural phase transition from monoclinic (Cm) to rhombohedral (R3c) at x=0.4. The Raman spectra of the (1−x)PFN–(x)BFO solid solutions showed the composition dependent phase transition from monoclinic (Cm) to rhombohedral (R3c). With increasing x in PFN, the modes related monoclinic symmetry changes to those of rhombohedral symmetry. The RT Mössbauer spectroscopy results evidenced the existence of composition dependent phase transition from paramagnetic to weak antiferromagnetic ordering and weak antiferromagnetic to antiferromagnetic ordering. The Mössbauer spectroscopy showed paramagnetic behavior with a doublet for x=0.0, 0.1 and 0.2 are shows the weak antiferromagnetic with paramagnetic ordering. For x=0.3 and 0.4 shows the sextet pattern and it is a clear evidence of antiferromagnetism. The ferroelectric (P–E) loops at RT indicate the presence of small polarization, as the x concentration increases in PFN, the remnant polarization and coercive field were decreased, which may due to the increase in the conductivity and leaky behavior of the samples.

Effects of antiferro-ferromagnetic phase coexistence and spin fluctuations on the magnetic and related properties of NdCuSi

We report the magnetic, thermal, magnetocaloric and transport properties of polycrystalline NdCuSi. The compound shows a weak antiferromagnetic ordering, as confirmed by different measurements. Arrott plots indicate that the magnetic phase transition is found to be second order in nature. The isothermal magnetic entropy change calculated using the magnetization data gives a value of 11.1 J/kg K for a field change of 50 kOe. The follows h2/3 dependence (h is the reduced field) with a negative intercept, which is predicted by mean field theory for second order phase transitions. Landau theory of phase transition was applied to calculate change in entropy, which was found to be in good agreement with that calculated directly from the magnetization data. Temperature dependence of electrical resistivity shows a pronounced anomaly at the ordering temperature, which is attributed to the spin fluctuations.

Solid phases of spatially nanoconfined oxygen: A neutron scattering study

We present a comprehensive neutron scattering study on solid oxygen spatially confined in 12 nm wide alumina nanochannels. Elastic scattering experiments reveal a structural phase sequence known from bulk oxygen. With decreasing temperature cubic γ-, orthorhombic β- and monoclinic α-phases are unambiguously identified in confinement. Weak antiferromagnetic ordering is observed in the confined monoclinic α-phase. Rocking scans reveal that oxygen nanocrystals inside the tubular channels do not form an isotropic powder. Rather, they exhibit preferred orientations depending on thermal history and the very mechanisms, which guide the structural transitions.

Thermal and electrical transport across a magnetic quantum critical point

A quantum critical point (QCP) arises when a continuous transition between competing phases occurs at zero temperature. Collective excitations at magnetic QCPs give rise to metallic properties that strongly deviate from the expectations of Landau's Fermi-liquid description, which is the standard theory of electron correlations in metals. Central to this theory is the notion of quasiparticles, electronic excitations that possess the quantum numbers of the non-interacting electrons. Here we report measurements of thermal and electrical transport across the field-induced magnetic QCP in the heavy-fermion compound YbRh(2)Si(2) (refs 2, 3). We show that the ratio of the thermal to electrical conductivities at the zero-temperature limit obeys the Wiedemann-Franz law for magnetic fields above the critical field at which the QCP is attained. This is also expected for magnetic fields below the critical field, where weak antiferromagnetic order and a Fermi-liquid phase form below 0.07 K (at zero field). At the critical field, however, the low-temperature electrical conductivity exceeds the thermal conductivity by about 10 per cent, suggestive of a non-Fermi-liquid ground state. This apparent violation of the Wiedemann-Franz law provides evidence for an unconventional type of QCP at which the fundamental concept of Landau quasiparticles no longer holds. These results imply that Landau quasiparticles break up, and that the origin of this disintegration is inelastic scattering associated with electronic quantum critical fluctuations--these insights could be relevant to understanding other deviations from Fermi-liquid behaviour frequently observed in various classes of correlated materials.

The dependence of magnetic properties on temperature for rare earth ErCrO 3 chromites

Multiferroic ErCrO 3 was synthesized and the detailed magnetic as well as ferroelectric properties were investigated. The dc magnetization shows that ErCrO 3 undergoes a antiferromagnetic ordering at T N = 133 K due to the Cr 3+–Cr 3+ followed by weak ferromagnetic ordering. Around T SR ≈ 22 K, ErCrO 3 exhibits a spin reorientation from Γ 4 to Γ 1. And the stability of the ferromagnetic Γ 4 phase increases with the applied magnetic field increasing. Furthermore, at lower temperature, it shows weak antiferromagnetic ordering of Er 3+. We also present the low temperature polarization data for ErCrO 3 and find a remarkable decreasing of polarization around T N = 133 K on increasing temperature, this effect might be due to the coupling between magnetic and ferroelectric order parameters, and the magnetic field suppresses the polarization which demonstrates convincingly the strong magnetoelectric (ME) coupling in ErCrO 3.

BiFeO<sub>3</sub>微晶的水热制备工艺及其磁性研究<br>Study on the Preparation Method of BiFeO<sub>3</sub> by Hydrothermal Method and Its Magnetism

采用Bi(NO3)3·5H2O和Fe(C5H7O2)3为原料，乙醇胺为碱性沉淀剂，用改进的水热法制备了BiFeO3微晶。研究了前驱体沉淀的量，矿化剂浓度以及反应温度对产物形貌，尺度以及结构的影响。采用0.005 M的前驱物溶液在180℃的反应温度下能够制备得到均匀的球形纳米颗粒。BiFeO3的尺度随反应前驱物的量增加而减小，随反应温度增加而增加。XRD研究表明在200℃的反应温度下，当前驱物的浓度低于0.005 M时都能够获得纯的BiFeO3。而TEM结构分析表明BiFeO3纳米颗粒具有完整的单畴结构；磁性分析表明纳米的BiFeO3颗粒具有弱的铁磁有序。 An improved hydrothermal method was adopted to prepare BiFeO3 using Bi(NO3)3·5H2O, Fe(C5H7O2)3 as raw materials and 2-Aminoethanol as alkaline precipitant. The effects of the quantity of pre-cursor precipitate, the concentration of mineralizer, and the reaction temperature on the morphology of prod-ucts, size and structure were studied. The results showed that the size decreases with quantity of precursor precipitate, and increases with reaction temperature. XRD results indicated that pure BiFeO3 can be obtained by the precursor with a concentration lower that 0.005 M reacting under 200°C. TEM results indicated that the BiFeO3 nanoparticles present prefect mono-domain structure. Analyzing on magnetism showed that the BiFeO3 nanoparticles present weak antiferromagnetic order.