Weak Ferromagnetic Component Research Articles

Mechanism Behind the Enhanced Ferromagnetic Contributions Upon Ru Substitution in Ca3Mn2O7 from X-Ray Absorption Spectroscopies.

We have studied the local structure and electronic and magnetic properties of hybrid improper ferroelectric Ca3Mn2O7 upon Ru substitution at the Mn site by a combination of atomic-selective X-ray absorption spectroscopies in the soft and hard X-ray energy regimes. Ru substitution enhances the macroscopic ferromagnetic contributions, whose origin is here elucidated. In particular, soft X-ray magnetic circular dichroism (XMCD) data indicate that the spin moments of Mn and Ru are aligned in opposite directions, with the effective magnetic moments of Ru being about 1 order of magnitude smaller than for Mn. The XMCD results also demonstrate the presence of an intrinsic ferromagnetic component in the Mn sublattice for Ru contents x ≥ 0.3, although the values of the net Mn magnetic moment are much smaller than expected for a fully saturated Mn4+ magnetic sublattice. Soft and hard X-ray absorption spectroscopy measurements show that Mn keeps a +4 valence state independently of the Ru content, whereas Ru is in an intermediate valence state, ranging between +4.7 (x ≤ 0.1) and +4.4 (x ≥ 0.7). Analysis of the extended X-ray absorption fine structure (EXAFS) signals at the Mn and Ru K-edges suggests the lack of a complete solid solution in the local structure across the entire range of compositions. These findings disclose the existence of charge transfer between Mn and Ru atoms, so the weak ferromagnetic component is attributed to a canting of the antiferromagnetically ordered Mn4+ spins caused by the oxygen-mediated hybridization between localized Mn4+ 3d and itinerant intermediate valence Ru 4d bands, in analogy to the mechanism proposed for ferromagnetism in ordered doubled perovskites with 3d and 4d/5d transition-metal ions. In the present case, disorder prevents the formation of long-range ferromagnetism.

Magnetic structure of the noncentrosymmetric magnet Sr2MnSi2O7 through irreducible representation and magnetic space group analyses.

Magnetic structures of the noncentrosymmetric magnet Sr2MnSi2O7 were examined through neutron diffraction for powder and single-crystalline samples, as well as magnetometry measurements. All allowed magnetic structures for space group P421m with the magnetic wavevector qm = (0, 0, ½) were refined via irreducible representation and magnetic space group analyses. The compound was refined to have in-plane magnetic moments within the magnetic space group Cmc21.1'c (No. 36.177) under zero field, which can be altered to P212121.1'c (No.19.28) above μ0H = 0.067 (5) T to align induced weak-ferromagnetic components within one layer on the ab plane. All refined parameters are provided following the recent framework based upon the magnetic space group, which better conveys when exchanging crystallographic information for commensurate magnetic structures.

Observation of Thermally Induced Piezomagnetic Switching in Cu2OSeO3 Polymorph Synthesized under High‐Pressure

AbstractA polymorph of Cu2OSeO3 with the distorted kagome lattice is successfully obtained using the high‐pressure synthesis technique (Cu2OSeO3‐HP). The structural analysis using X‐ray and neutron powder diffraction suggests that the tetrahedral Cu2+ clusters [similar to those in Cu2OSeO3 ambient‐pressure phase (Cu2OSeO3‐AP)] exist in Cu2OSeO3‐HP but with three symmetry inequivalent sites. No structural change is observed between 1.5 K and the room temperature. The complex magnetic H‐T phase diagram is established based on the temperature‐ and field‐dependent magnetization data, indicating two distinct antiferromagnetic phases at low and intermediate temperatures, in addition to the higher‐temperature spin‐glass‐like phase. The low temperature phase is identified by neutron powder diffraction refinements as a canted noncollinear antiferromagnetic order with a weak ferromagnetic component along the b‐axis. Size of the refined ordered moment is ≈1.00(4) µB in Cu2OSeO3‐HP, indicating a large enhancement compared to that of Cu2OSeO3‐AP (≈0.61 µB). By applying a uniaxial stress, finite enhancement of weak ferromagnetic component in the noncollinear antiferromagnetic phase in Cu2OSeO3‐HP is observed, which is the clear evidence of the piezomagnetic effect. Interestingly, the sign of the induced magnetization changes on heating from the low‐temperature to the intermediate‐temperature phases, indicating a novel piezomagnetic switching effect in this compound.

In Situ Local Imaging of Ferromagnetism and Superconductivity in RbEuFe4As4.

The coexistence of superconductivity and ferromagnetism is an intrinsically interesting research focus in condensed matter physics, but the study is limited by low superconducting (Tc) and magnetic (Tm) transition temperatures in related materials. Here, we used a scanning superconducting quantum interference device to image the in situ diamagnetic and ferromagnetic responses of RbEuFe4As4 with high Tc and Tm. We observed significant suppression of the superfluid density in the vicinity of the magnetic phase transition, signifying fluctuation-enhanced magnetic scatterings between Eu spins and Fe 3d conduction electrons. Intriguingly, we observed multiple ferromagnetic domains that should be absent in an ideal magnetic helical phase. The formation of these domains demonstrates a weak c-axis ferromagnetic component probably arising from the Eu spin-canting effect, indicative of possible superconductivity-driven domain Meissner and domain vortex-antivortex phases, as revealed in EuFe2(As0.79P0.21)2. Our observations highlight that RbEuFe4As4 is a unique system that includes multiple interplay channels between superconductivity and ferromagnetism.

Evaluation of the optical and magnetic properties of novel Nd0.9Zn0.1FeO3 perovskite nanoparticles and their adsorption of Pb2+ ions from water

Nd0.9Zn0.1FeO3 was prepared in a single-phase with an average crystallite size of 25.82 nm using a citrate combustion technique. The energy dispersive X-ray assures the chemical formula of the sample. The elemental mapping of Zn-doped NdFeO3 illustrates the good homogeneous distribution of the elements in the sample. Nd0.9Zn0.1FeO3 has antiferromagnetic properties with weak ferromagnetic components and has good UV absorbance. The values of the band gap for the direct and indirect transitions are 1.473 eV and 1.250 eV, respectively. The adsorption of nickel(II), cobalt(II), chrome(VI), cadmium(II), and lead(II) ions has been studied at pH 7. The highest removal efficiency (η = 73.72%) was observed for the lead ions from water. The current study has examined the kinetics, recoveries, and mechanisms of utilizing Nd0.90Zn0.10FeO3 to remove Pb2+ ions from water. The optimum conditions for the absorbing Pb2+ are pH 7 and a contact time of 60 min. The Freundlich isotherm model is the best model for the absorption of Pb2+ ions. While, the pseudo-second-order kinetic model describes the kinetic adsorption data. The sample has a good efficiency for removing Pb2+ ions from water several times.

Magnetic hyperfine interactions of probe 57Fe atoms within the hexagonal manganite ScMnO3

Here we present the Mössbauer study of the combined magnetic and electrical hyperfine interactions of the probe 57Fe nuclei localized in the hexagonal manganite ScMnO3. The hyperfine interactions were measured in the temperature range where ScMnO3 demonstrates spin ordering: 15 K <T <TN (∼ 130 K). By analyzing the hyperfine parameters of 57Fe nuclei, we evaluated the oxidation state of the iron ions, their local crystal environment, and the orientation of the magnetic moments μFe in the structure of ScMn0.99657Fe0.004O3 at T <<TN. The temperature-dependent evolution of Zeeman structures in Mössbauer spectra was analyzed using the stochastic relaxation model, and indicates the presence of frustration of the superexchange interactions Fe3+−O−Mn3+. The temperature dependence of the hyperfine magnetic field Bhf(T) was described using critical indices, whose values reflect the reduced dimensionality of the magnetic system under study. It was shown that the observed sharp temperature-dependent change of the quadrupole shift of the Zeeman structure components may be attributed to the spin reorientation process, resulting in antiferromagnetism with a weak ferromagnetic component.

Investigating the magnetic properties of rGO, and rGO-ZnO nanocomposite

In the present work, magnetic properties of the graphene oxide (GO), reduced graphene oxide (rGO), rGO-ZnO hybrid (RGZ) nanocomposite and ZnO nanorods have been investigated. A simple hydrolysis method is used to synthesize (RGZ) nanocomposite and ZnO nanorods. The structural and the morphological studies are performed using XRD, TEM, FTIR, TGA and FESEM. Magnetic properties of the samples have been investigated through SQUID magnetometer. The as synthesized GO, rGO samples show diamagnetic behavior with weak ferromagnetic component at room temperature (RT) while at low temperatures (10 K) these samples exhibit paramagnetic behavior with small ferromagnetic signature. As synthesized ZnO nanorods exhibit weak ferromagnetism at RT. The RGZ nanocomposite exhibits weak ferromagnetic behavior at RT and the magnetization value is found greater than that of ZnO. Moreover, RGZ nanocomposite shows higher value of magnetization than GO, rGO and pure ZnO samples at low temperatures. Further, we have investigated the temperature dependent magnetization (M−T) in zero field cooled (ZFC) and field cooled (FC) conditions for ZnO nanorods, GO, rGO and rGO-ZnO samples at 100 Oe applied magnetic field. The possible mechanisms for magnetic behavior of rGO-ZnO composite are discussed and described in this manuscript.

Synthesis and Functional Properties of La2FeCrO6 Based Nanostructures

Ordered double perovskite La2FeCrO6 nanoparticles (NPs) were synthesized via the citrate auto-combustion technique. The prepared sample was characterized by X-ray diffraction (XRD), energy dispersive X-ray analysis (EDAX), and Raman spectroscopy, which confirmed the double perovskite structure of the studied sample. XRD illustrated that the investigated sample has an orthorhombic structure with an average crystallite size of 25.3 nm. La2FeCrO6 NPs exhibit a porous structure and spongy morphology, as determined through analyses using Brunauer–Emmett–Teller (BET) specific surface area and field emission scanning electron microscopy (FESEM). The studied sample exhibits anti-ferromagnetic (AFM) behavior with weak ferromagnetic (FM) components, as an example of d5(Fe3+)–d3(Cr3+) systems. The AFM behavior is caused by the super-exchange interaction between [Fe3+(d5)–O–Cr3+(d3)], according to the Kanamori–Goodenough (KG) rule. This behavior is induced by the pdπ hybridization between the eg orbital of the transition metal and the pσ orbital of the oxygen, while the one induced by the pdσ hybridization is FM. The number of excited-state configurations mediated by the pdπ hybridization in the Fe–Cr pair is greater than that mediated by pdσ hybridization. Pb(II) heavy metal ions are used in adsorption studies. The electrostatic nature of the bonding between Pb(II) and the La2FeCrO6 nano ferrite sample is thought to be the main cause of the observed high sorption of La2FeCrO6 to a Pb(II) ion. La2FeCrO6 has a favorable morphology, which bodes well for its prospective applications in Li-ion batteries, water purification, and gas sensors.

Synthesis, crystal structures, thermal and magnetic properties of Mn(NCS)2 coordination compounds with 3-cyanopyridine

The reaction of Mn(NCS)2 and 3-cyanopyridine in different solvents leads to the formation of pure Mn(NCS)2(3-cyanopyridine)4 (1), Mn(NCS)2(3-cyanopyridine)2(H2O)2-bis(3-cyanopyridine) solvate (2) and Mn(NCS)2(3-cyanopyridine)(H2O) (4). In further investigations single crystals of Mn(NCS)2(3-cyanopyridine)2(H2O)2 (3) were accidentally obtained, but this compound cannot be prepared pure. Compounds 1-3 consist of discrete complexes with octahedrally coordinated Mn cations, whereas in compound 4 the Mn cations are linked by single µ-1,3-bridging thiocyanate anions into chains, that are further connected into layers by the 3-cyanopyridine coligands. Thermogravimetric measurements reveal that upon heating compound 1 loses some of the 3-cyanopyridine ligands and transforms into [(Mn(NCS)2)3(3-cyanopyridine)4]n (5), which is isotypic to the corresponding Cd compound reported in the literature. In this structure, the Mn cations are linked by pairs of thiocyanate anions into chains that are further connected into layers by every second 3-cyanopyridine coligand. When compound 2 is heated, a transformation into the complex 1 is observed, that upon further heating transforms into 5. Magnetic measurements for compound 4 show that the Mn-NCS-Mn exchange is dominant and antiferromagnetic, and susceptibility dependence in the paramagnetic phase is well described by the Heisenberg spin chain model. Below 2.77 K, the Mn(II) spins in 4 are ordered with a weak ferromagnetic component due to the Dzyaloshinskii-Moriya interaction.

Preparation, characterization and magnetic properties of Sm0.95Ho0.05FeO3 nanoparticles and their application in the purification of water

Sm0.95Ho0.05FeO3 was successfully prepared in a single phase using the citrate combustion method. The investigated sample was characterized using X-ray diffraction (XRD), a high-resolution transmission electron microscope (HRTEM) and X-ray photoemission spectroscopy (XPS). XRD confirmed that the sample was synthesized in an orthorhombic phase with an average crystallite size of 12 nm. HRTEM indicated that the sample was prepared in the nanoscale with an average particle size of 18 nm. XPS was used to identify the chemical bonds, binding energies and core levels of Sm0.95Ho0.05FeO3. The magnetic properties were studied using a vibrating sample magnetometer and DC magnetic susceptibility using Faraday’s method. The sample has an antiferromagnetic behavior with weak ferromagnetic components. The presence of magnetic Ho3+ ions in the SmFeO3 sample causes the magnetic exchange interaction between the 2p orbital of Fe3+ and the 4d sub-shell of Ho3+ ions. The dependence of pH value on the removal efficiency of Pb2+ from water was studied. The maximum Pb2+ removal efficiency of the Ho-doped SmFeO3 nano perovskite is 26% at pH = 5 and 99% at pH = 8. The Freundlich, Langmuir and Temkin isotherms were studied to understand the adsorption mechanism. The Temkin adsorption isotherm best fitted with the experimental data.

Structural and magnetic properties of LaVO3 - Absence of anomalous diamagnetism

The novel magnetic and structural properties of LaVO3 have been studied in a comprehensive manner using X-ray and neutron powder diffraction, thermogravimetric analysis, X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, electrical transport, and dc magnetization. The lattice parameters have been found to be larger than previously reported, indicating the possibility of a novel phase. For vanadium ions, the valence state is found to be in accordance with the expected value (+3), the effect of larger lattice parameters is also present in the X-ray absorption spectroscopy measurement. Magnetic transition due to the antiferromagnetic ordering of the vanadium sublattice is observed at 142 K (TN). It undergoes a transition to a monoclinic crystal structure below 140 K (Tt). Negative magnetization (anomalous diamagnetism), which has been reported in earlier studies on the magnetic properties of LaVO3, is not observed in the present study. In the M − H isotherms, the ferromagnetic component of vanadium spins is absent. Below TN, the estimated magnetic structure of vanadium sublattice from powder neutron diffraction measurements is C-type antiferromagnetic, which persists in the entire low temperature region. The observed novel structural phase gives rise to pure C-type antiferromagnetic arrangement without weak ferromagnetic component. Theoretical calculations have been carried out to understand the nature of the magnetic ground state.

An electrochemical sensor based on multiferroic NdFeO3 particles modified electrode for the detection of H2O2

The high dielectric constant and lower dielectric loss make NdFeO 3 materials ideal for potential use in many several applications. Specifically, NdFeO 3 is a promising candidate for electrochemical sensing applications owing to its high thermal stability, and non-toxicity. In this present study, multiferroic NdFeO 3 particles are synthesized using a solid-state reaction at a higher temperature. Structural studies confirm that NdFeO 3 crystallizes in an orthorhombic symmetry. Elemental color mapping of the NdFeO 3 sample reveals there is no impurity, and that the sample comprises Nd, Fe, and O elements. In addition, the Nyquist plot suggests the contribution of grain and grain boundary effect towards the resistive and capacitive characteristics of NdFeO 3 . Magnetic measurements at room temperature indicated an antiferromagnetic nature of the sample with a weak ferromagnetic component arising due to the canted nature of Fe 3+ . The non-collinear magnetic structure of NdFeO 3 promotes the ferroelectric loop. Single-phase room temperature NdFeO 3 multiferroics were coated upon the glassy carbon electrode with the aim of sensing hydrogen peroxide (H 2 O 2 ) using a three-electrode electrochemical setup. The cyclic voltammetry technique showed an increase in the peak current with an upsurge in the concentration of H 2 O 2 between 1 mM and 10 mM. The limit of detection, the limit of quantification, and sensitivity was calculated to be 0.87 µM, 2.92 µM, and 52.6 µA mM −1 cm −2 respectively. The correlation coefficient R 2 was found to be 0.9792. The value of linearity with regression coefficient was calculated to be R 2 = 0.9922 from the effect of scan rate. NdFeO 3 showed an excellent selectivity towards H 2 O 2 in the presence of H 2 SO 4 , KCl, HCl, and NaOH, and good sensitivity for monitoring H 2 O 2 in a real milk sample. The sensitivity of modified Glassy carbon electrode (GCE) in milk was calculated to be 46.58 µA mM −1 cm −2 . • Solid state reaction of single phase multiferroic particles NdFeO 3 . • Extensive studies of electrical, impedance, X-ray photoelectron spectroscopy. • Weak ferroelectric and antiferromagnetic with weak ferromagnetic behavior are observed. • Electrochemical sensing of the hydrogen peroxide in real milk samples.

Antiferromagnetic order in Yb4Ru7As6 with the cubic U4Re7Si6-type structure

We investigated the electronic properties of Yb4Ru7As6 using single crystalline samples grown by the Bi-flux method. Yb4Ru7As6 crystallizes in the cubic U4Re7Si6-type structure. From the electrical resistivity, magnetic susceptibility, and specific heat measurements, we have found that Yb4Ru7As6 orders antiferromagnetically below the Néel temperature of 2.5 K with the moderately enhanced electronic specific heat coefficient of 120 mJ/(Yb-mol⋅K2). A rapid increment in magnetization of about 0.25 μB/Yb has been detected at low magnetic field below 4 K, implying a weak ferromagnetic component.

Ultrasmall Superparamagnetic Iron Oxide Nanoparticles Synthesized by Micellar Approach as a Potential Dual-Mode T1-T2 Contrast Agent

Purpose: A micellar approach is used to synthesize Ultrasmall Superparamagnetic Iron Oxide Nanoparticles (USPIONs) with an average diameter of 3.4±0.5 nm, suitable for dual-mode T1-T2 contrast agents. Methods: Micelles with 3.8 nm, measured by dynamic light scattering, were obtained by self-organizing the surfactant iron(III) dodecyl sulfate (IDS) in 1-octanol. IDS was prepared by replac-ing Na+ cation in sodium dodecyl sulfate molecule, and its critical micelle concentration (CMC) was measured by electrical conductivity. The USPIONs were synthesized in a biphasic system: IDS in octanol (55% above the CMC) and water containing NaBH4. Results: A yellow precipitate is immediately formed at the water/alcohol interface, rapidly changes to a black one, and transfers to the aqueous phase. The magnetite phase was confirmed by X-ray diffraction and Mössbauer spectroscopy. The magnetic behavior shows a major paramagnetic char-acter with a weak ferromagnetic component at 5 K, the latter attributed to the interparticle couplings below its blocking temperature (TB = 35 K). The particles were coated with carboxymethyl dextran, showing an isoelectric point of 2.7 with electrokinetic potential around -30 mV in the physiological pH range. Magnetic relaxation measurements showed relaxivity values r1 = 0.17 mM-1 s-1 and r2 = 1.73 mM-1 s-1 (r2/r1 = 10) in a 3T field. These values infer that the ultrasmall size affects the interac-tions with the protons of the nearby water molecules. The r2 value decreases because the core mag-netization decreases with size; r1 intensifies due to the high surface. Conclusion: The results show a system with high colloidal stability, non-cytotoxic, and potential application as T1-T2 dual-mode contrast agents.

Structural, magnetic and dielectric properties of Ni doped LiInCr4O8 breathing pyrochlore

Herein, polycrystalline compounds of breathing pyrochlore LiInCr4-xNixO8 (x = 0, 0.1, 0.2, 0.4) were synthesized by the solid state method. Structure, magnetism, and dielectric properties have been investigated with x-ray diffraction, Raman spectroscopy, magnetic susceptibility, isothermal magnetization, AC impedance, and heat capacity measurements. The mean particle size of the Ni substituted samples decreased from 1.95 μm to 1.22 μm, which is larger than the size determined by the Scherrer formula and the Williamson-Hall method. Raman scattering revealed slightly red-shifted modes Eg, F2g(2), F2g(3), and A1g, which were caused by higher effective atomic mass and increased bond strength. At low temperatures, field cooled and zero field cooled susceptibility measurements, as well as frequency dependent χac data, show a spin-glass type freezing. The resulting Mydosh parameter p of x = 0.4 is 0.01, suggesting the spin glass state. Magnetic measurements exhibit a large negative CW temperature (|θCW| > 290 K), initially decreasing and then increasing at high Ni concentration, in support of the relationship between magnetic interactions and the structural parameters of Cr–Cr spins. Despite the large negative θCW in substituted samples, long-range magnetic order was suppressed at high Ni contents. With increasing nickel concentration, the spin gap gradually vanished, indicating a significant reduction in breathing distortion. The isothermal magnetization at 2 K confirms antiferromagnetic characteristics and weak ferromagnetic components in the substituted samples. When the frequency is increased at room temperature, the dielectric data shows a drop in dielectric constant as well as lower dielectric loss. At low frequencies, interfacial polarization mechanisms play a crucial role. In contrast, at high frequencies, the dielectric constant becomes frequency independent up to ∼ 105 Hz, due to reverse electron motion. The low temperature specific heat behavior implies the good insulator characteristic of LiInCr3.6Ni0.4O8 and a residual entropy feature related to spin-glass type freezing.

Modulation of dielectric and magnetic ordering of DyFeO3 system with Fe-site doping

In this attempt, dysprosium orthoferrite (DyFeO3) system is explored to investigate dielectric and magnetic ordering by modulating ferrites structure using Ni and Co-dopants in place of Fe. X-ray diffraction (XRD) study confirms the formation of single-phase materials; dopants effect on modifications of atomic-scale structural parameters like lattice parameters, Fe–O bond angles, and O–Fe–O bridging angles are extracted from Rietveld refinement. Microstructural features of sintered pellet of DFO system exhibits compacted sample having grain size around 100 nm. Frequency and temperature- dependent dielectric studies depict systematic decrease of dielectric constant and loss with temperature for almost all systems. Moreover, it is found that dielectric constant and loss increases by doping; for Co and Co-Ni co-dopants the effect is maximum. Temperature profile of dielectric constant of DFO system is found to exhibit relaxor behavior. A real part of impedance as a function of frequency indicates the values of Z′ coincides with high frequency, indicates reduction of barrier potentials at high frequency due to increase in AC-conductivity. Low-frequency resistance of doped systems is lower than DFO, except Co-doped DFO. Impedance loss spectra reveal relaxation behavior of the system, which is influenced by dopants. Relaxation frequency of Ni-doped and Ni-Co codoped DFO is found shifting toward higher frequency side than DFO and DCFO systems; indicate charge relaxation is faster in DNFO and DNCFO than DFO and DCFO systems. However, activation energy of charge relaxation is found lowest for DCFO system. Same trends are revealed from Modulus spectra. Conductivity mechanisms are revealed from a combined plot of M′′(f) and –Z′′(f) as a function of frequency and corresponding relaxation process. The results conclude that conductivity in DFO and Ni-doped DFO system is dominated by delocalized motion of charge carriers, while DCFO and DNCFO systems are due long-range motion. Magnetic hysteresis (M-H) curve shows the presence of a canted antiferromagnetic ordering matrix within weak Ferromagnetic components. Coercivity of doped DFO is greated than pure DFO.

Noncollinear spin structure with weak ferromagnetism in NbMnP

NbMnP is a metallic material, which consists of the zigzag chains of Mn moments along the $b$ axis. The magnetic susceptibility as well as the resistivity shows an anomaly at 233 K, which indicates an antiferromagnetic phase transition. Our neutron powder diffraction experiment reveals that the magnetic structure is a $Q=0$ structure and noncollinear with an easy plane anisotropy perpendicular to the $b$ axis, and the $a$- and $c$-axis magnetic components align antiferromagnetically and ferromagnetically along the zigzag chain direction, respectively. The ordered moment is $1.2{\ensuremath{\mu}}_{\mathrm{B}}$, which is reduced probably due to the itineracy of the Mn moments. A localized picture model suggests that the $Q=0$ magnetic structure is formed by the frustration among several exchange couplings. A weak ferromagnetic component is also present in the antiferromagnetic phase, which is considered to be caused by a Dzyaloshinskii-Moriya interaction.

Large magnetic anisotropy and field-induced spin-flop transition in Fe2(TeO3)2(SO4)·3H2O single crystals

Single crystals of Fe2(TeO3)2(SO4)·3H2O with an alternating spin-chain structure are successfully grown by a hydrothermal method. Magnetic and heat capacity measurements show that this compound possesses a short-range antiferromagetic order at ~55 K and a long-range antiferromagetic order at 32.5 K. A large magnetic anisotropy with magnetization easy c-axis is observed, in which a weak ferromagnetic component is observed along the a- and b-axes, while a spin flop transition is observed at applied field along the c-axis. Also, the magnetic anisotropy energy at 2 K is estimated to be 4.78(3) × 108 ergs/cm3. Such magnetic anisotropy may be due to a strong nonsymmetric distortion in the FeO6 octahedra.

Topological Hall effect in the antiferromagnetic Dirac semimetal EuAgAs

The nontrivial magnetic texture in real space gives rise to the intriguing phenomenon of the topological Hall effect (THE), which is relatively less explored in topological semimetals. Here, we report a large THE in the antiferromagnetic (AFM) state in single crystals of EuAgAs, an AFM Dirac semimetal. EuAgAs hosts an AFM ground state below ${T}_{N}=12$ K with a weak ferromagnetic component. The in-plane isothermal magnetization below ${T}_{N}$ exhibits a weak metamagnetic transition. We also observe chiral anomaly induced positive longitudinal magnetoconductivity, which indicates a Weyl fermion state under an applied magnetic field. The first-principles calculations reveal that EuAgAs is an AFM Dirac semimetal with a pair of Dirac cones, and therefore a Weyl semimetallic state can be realized under time-reversal symmetry breaking via an applied magnetic field. Our study establishes that EuAgAs is a system for exploiting the interplay of band topology and the topology of the magnetic texture.

Evolution from sinusoidal to collinear A-type antiferromagnetic spin-ordered magnetic phase transition in Tb1−x Pr x MnO3 solid solution

The present study reports on the structural and magnetic phase transitions in Pr-doped polycrystalline Tb0.6Pr0.4MnO3, using high-resolution neutron powder diffraction (NPD) collected at SINQ spallation source, to emphasize the suppression of the sinusoidal magnetic structure of pure TbMnO3 and the evolution to a collinear A-type antiferromagnetic ordering. The phase purity, Jahn–Teller distortion, and one-electron bandwidth for eg orbital of Mn3+ cation have been calculated for polycrystalline Tb0.6Pr0.4MnO3, in comparison to the parent materials TbMnO3 and PrMnO3, through the Rietveld refinement study from x-ray diffraction data at room temperature, which reveals the GdFeO3 type orthorhombic structure of Tb0.6Pr0.4MnO3 having Pnma space group symmetry. The temperature-dependent zero field-cooled and field-cooled dc magnetization study at low temperature down to 5 K reveals a variation in the magnetic phase transition due to the effect of Pr3+ substitution at the Tb3+ site, which gives the signature of the antiferromagnetic nature of the sample, with a weak ferromagnetic component at low temperature-induced by an external magnetic field. The field-dependent magnetization study at low temperatures gives the weak coercivity having the order of 2 kOe, which is expected due to the canted-spin arrangement or ferromagnetic nature of Terbium ordering. The NPD data for Tb0.6Pr0.4MnO3 confirms that the nuclear structure of the synthesized sample maintains its orthorhombic symmetry down to 1.5 K. Also, the magnetic structures have been solved at 50 K, 25 K, and 1.5 K through the NPD study, which shows an A-type antiferromagnetic spin arrangement having the magnetic space group Pn′ma′.