Paramagnetic Peak Research Articles

Crafting defective ZnO nanoparticles: A green synthesis for enhanced photocatalytic degradation of organic pollutants

Surface defect engineering is a promising strategy for enhancing the number of surface-active sites to facilitate efficient redox reactions that occur on the surface of a photocatalyst. A green approach was employed to prepare urea- and choline-chloride-based deep eutectic solvent (DES) for the synthesis of ZnO/Zn(OH)2 supported by a DES complex (Zn precursor). Surface defects on ZnO nanoparticles (NPs) were tailored by decomposing the Zn precursor in air. In addition, calcination improved the crystallinity and surface-active sites of the defective ZnO by creating surface oxygen vacancies (Vo). The appearance of an Electron paramagnetic resonance peak at a g value of 1.96 confirms the formation of single-charged Vo defects on the surface of ZnO. The photocatalyst prepared at a reaction bath temperature of 75 °C (Vo-ZnO-75) showed the highest photocatalytic activity. The observed green emission in the photoluminescence spectrum and X-ray photoelectron spectroscopy analysis suggests the formation of defects on the ZnO surface. Consequently, Vo-ZnO-75 enhanced surface donor density (14.4×1020 cm−3) and lower charge transfer resistance (88.89 × 103 Ω). The optimized photocatalyst of Vo-ZnO-75 has 94% removal efficiency for rhodamine B degradation within 60 min. This study sheds new light on the development of an efficient and eco-friendly approach for preparing defective ZnO NPs for photocatalytic applications.

Paramagnetic Singularities of the Orbital Magnetism in Graphene with a Moiré Potential.

The recent detection of the singular diamagnetism of Dirac electrons in a single graphene layer paved a new way of probing 2D quantum materials through the measurement of equilibrium orbital currents which cannot be accessed in usual transport experiments. Among the theoretical predictions is an intriguing orbital paramagnetism at saddle points of the dispersion relation. Here we present magnetization measurements in graphene monolayers aligned on hexagonal boron nitride crystals. Besides the sharp diamagnetic McClure response at the Dirac point, we detect extra diamagnetic singularities at the satellite Dirac points of the moiré lattice. Surrounding these diamagnetic satellite peaks, we also observe paramagnetic peaks located at the chemical potential of the saddle points of the graphene moiré band structure and relate them to the presence of vanHove logarithmic singularities in the density of states. These findings reveal the long ago predicted anomalous paramagnetic orbital response in 2D systems when the Fermi energy is tuned to the vicinity of saddle points.

The temperature-independent paramagnetic susceptibility peak at zero magnetic field in non-topological WSe2 single crystal

The temperature-independent paramagnetic susceptibility peaks were observed in the non-topological WSe2 single crystal. This is contrary to the proposed explanation that the temperature-independent paramagnetic peak in topological materials originates from the spin texture of the topological surface state. Weak ferromagnetic characteristic was observed from magnetization measurement from 300 to 5 K. The high resolution transmission electron microscope images combined with no detectable magnetic impurity was found in our sample indicate that the ferromagnetism originates from lattice dislocations at different layer planes and axes. The temperature-independent paramagnetism susceptibility peak should originate from the ferromagnetism induced by lattice dislocation.

A singular paramagnetic susceptibility peak in a WSe2/MoSe2 chemical bonding structure

The magnetic characteristics of 1:1 WSe2 and MoSe2 mixed single crystal powder with and without thermal annealing process were studied. Scanning electron microscopy images and Raman spectroscopy support that the WSe2 and MoSe2 are chemically bound at the WSe2 and MoSe2 boundary after the thermal annealing process. Our sample also exhibits the hysteresis loop and splitting of magnetic moment at zero field cooling and field cooling precesses in the chemically bound system. In contrast, all these characteristics are not detected in the unannealed mixed WSe2 and MoSe2 crystal powder. Temperature independent singular paramagnetic peaks are only detected in the WSe2 and MoSe2 mixed single crystal powder with thermal annealing. These results support that the temperature independent singular paramagnetic susceptibility peaks should originate from the intrinsic lattice mismatch induced ferromagnetism.

Infrared Emissivity of La<sub>0.8</sub>Sr<sub>0.2</sub>MnO<sub>3</sub> under 0.76-2.5 μm and 2.5-500 μm Radiation Fields

La0.8Sr0.2MnO3 was prepared to investigate the infrared emissivity of the sample under 0.76-2.5 μm and 2.5-500 μm infrared fields. The sample exhibited characteristic peaks of rhombohedral perovskite structure at 298-318 K, and split of the main peak weakened with increasing temperature. Intensity of the ferromagnetic resonance peak enhanced with increasing temperature, and the peak was shifted toward high magnetic field. A weak paramagnetic resonance peak appeared at 318 K, indicating that ferromagnetic-paramagnetic transition was occurring. The temperature of the sample under 2.5-500 μm field was higher than that under 0.76-2.5 μm. The emissivity of the sample increased with radiation time under 2.5-500 μm, but it had no obvious changes at about 0.665 under 0.76-2.5 μm. The emissivities at the same temperature fields were higher than those under 0.76-2.5 μm and 2.5-500 μm fields, respectively. It suggested that 0.76-2.5 μm and 2.5-500 μm radiations had inhibition effect on emissivity of La0.8Sr0.2MnO3.

Magnetic properties in three electrons under Rashba spin‐orbit interaction and magnetic field

AbstractIn this work, we study three‐electron magnetic susceptibility in quantum dots under Rashba spin‐orbit interaction (SOI) and magnetic field by an analytical methodology. The Hamiltonian of the system is separated to center of mass and relative terms using the Jacobi transformations and the hyperspherical coordinates. By solving Schrodinger equation, energy levels and thereby the susceptibility are calculated using canonical ensemble. At zero temperature, the magnetization reduces with increasing magnetic field with and without Rashba SOI in three‐electron‐quantum dot without electron‐electron (e‐e) interaction. Also, SOI slightly changes the magnetization for three‐electron‐quantum dot without e‐e interaction. At nonzero temperature, the magnetization shows a paramagnetic peak when the magnetic field increases. This peak position changes under the SOI. In the presence of e‐e interaction, the susceptibility enhances with raising magnetic field and it shows a maximum. The susceptibility at low magnetic field is negative and then it becomes positive. The susceptibility with e‐e interaction and without SOI is always diamagnetic and its magnitude reduces with enhancing magnetic field. The susceptibility shows a transition between diamagnetic and paramagnetic with e‐e interaction and SOI.

Entropy jump at the first-order vortex phase transition in Bi2Sr2CaCu2O8+δ with columnar defects

Abstract We study the entropy jump associated with the first-order vortex melting transition (FOT) in Bi2Sr2CaCu2O8+δ crystals by means of Hall probe magnetometry. The samples present a diluted distribution of columnar defects (CD) introduced by irradiation with Xe ions. The FOT is detected in ac transmittivity measurements as a paramagnetic peak, the height of which is proportional to the enthalpy difference entailed by the transition. By applying the Clausius-Clapeyron relation, we quantify the evolution of the entropy jump Δs as a function of the FOT temperature, TFOT, in both pristine crystals and crystals with CD. On increasing the density of CD, Δs decreases monotonically with respect to values found in pristine samples. The Δs versus TFOT dependence in the case of pristine samples follows reasonably well the theoretical prediction of dominant electromagnetic coupling for a model neglecting the effect of disorder. The data for samples with a diluted distribution of CD are not properly described by such a theoretical model.

Electron spin resonance for the detection of long-range spin nematic order

In this paper we propose that electron spin resonance (ESR) measurements enable us to detect the long-range spin nematic order. We show that the frequency of the paramagnetic resonance peak in the ESR spectrum is shifted by the ferroquadrupolar order parameter together with other quantities. The ferroquadrupolar order parameter is extractable from the angular dependence of the frequency shift. In contrast, the antiferroquadrupolar order parameter is usually invisible in the frequency shift. Instead, the long-range antiferroquadrupolar order yields a characteristic resonance peak in the ESR spectrum, which we call a magnon-pair resonance peak. This resonance corresponds to the excitation of the bound magnon pair at the wave vector $\bm k={\bm 0}$. Reflecting the condensation of bound magnon pairs, the field dependence of the magnon-pair resonance frequency shows a singular upturn at the saturation field. Moreover, the intensity of the magnon-pair resonance peak shows a characteristic angular dependence and it vanishes when the magnetic field is parallel to one of the axes that diagonalize the weak anisotropic interactions. We confirm these general properties of the magnon-pair resonance peak in the spin nematic phase by studying an $S=1$ bilinear-biquadratic model on the square lattice in the linear flavor-wave approximation. In addition, we argue applications to the $S=1/2$ frustrated ferromagnets and also the $S=1/2$ orthogonal dimer spin system SrCu$_2$(BO$_3$)$_2$, both of which are candidate materials of spin nematics. Our theory for the antiferroquadrupolar ordered phase is consistent with many features of the magnon-pair resonance peak experimentally observed in the low-magnetization regime of SrCu$_2$(BO$_3$)$_2$.

Structural relaxation and electrical conductivity of molybdovanadate glass

57Fe Mossbauer spectrum of conductive barium iron vanadate glass with a composition of 20BaO·10Fe2O3·70V2O5 (in mol%) showed paramagnetic doublet peak due to distorted FeIIIO4 tetrahedra with isomer shift (δ) value of 0.37 (± 0.01) mm s−1. Mossbauer spectra of 20BaO·10Fe2O3·xMoO3·(70 − x)V2O5 glasses (x = 20–50) showed paramagnetic doublet peaks due to distorted FeIIIO6 octahedra with δ’s of 0.40–0.41 (± 0.01) mm s−1. These results evidently show a composition-dependent change of the 3D-skeleton structure from “vanadate glass” phase, composed of distorted VO4 tetrahedra and VO5 pyramids, to “molybdate glass” composed of distorted MoO6 octahedra. After isothermal annealing at 500 °C for 60 min, Mossbauer spectra also showed a marked decrease in the quadrupole splitting (Δ) of FeIII from 0.70 to 0.77 to 0.58–0.62 (± 0.02) mm s−1, which proved “structural relaxation” of distorted VO4 tetrahedra which were randomly connected to FeO4, VO5, MoO6, FeO6 and MoO4 units by sharing corner oxygen atoms or edges. DC-conductivity (σ) of barium iron vanadate glass (x = 0) measured at room temperature was 3.2 × 10−6 S cm−1, which increased to 3.4 × 10−1 S cm−1 after the annealing at 500 °C for 60 min. The σ’s of as-cast molybdovanadate glasses with x’s of 20–50 were ca. 1.1 × 10−7 or 1.2 × 10−7S cm−1, which increased to 2.1 × 10−2 (x = 20), 6.7 × 10−3 (x = 35) and 1.9 × 10−4 S cm−1 (x = 50) after the annealing at 500 °C for 60 min. It was concluded that the structural relaxation of distorted VO4 tetrahedra was directly related to the marked increase in the σ, as generally observed in several vanadate glasses.

Robust 2D Room-Temperature Dilute Ferrimagnetism Enhancement in Freestanding Ammoniated Atom-Thin [0001] h-BN Nanoplates.

The author reports an anthracene vapor-assisted transport growth (∼4.8% in yield) of freestanding atomically thin pristine two-dimensional (2D) hexagonal boron nitride (h-BN) nanoplates directly from bulk powders. A room-temperature dilute magnetism was first observed in the pyrolytic 2D [0001] h-BN nanoplates, which is attributed to the missing N atom numbers (NN) or existence of a nitrogen-vacancy (Nv) with volume fraction ∼1.46%. Upon the postannealing in ammonia, the unsupported ammoniated 2D h-BN nanoplates showed an enhanced robust ferrimagnetism with the effective magnetic moment as high as 0.024 μB/per N, and Néel temperature at 174.9 K. At 295 K, a symmetric electron paramagnetic resonance peak signal was experimentally measured at g ∼ 2.1267, revealing the presence of an unpaired electron trapped at a B atom site in B-rich h-BN. As a promising 2D dilute magnetic semiconductor candidate, our finding favors the ammoniated atom-thin h-BN nanoplate for realization of spintronic nanodevices operating at room temperature.

Prominent metallic surface conduction and the singular magnetic response of topological Dirac fermion in three-dimensional topological insulator Bi1.5Sb0.5Te1.7Se1.3

We report semiconductor to metal-like crossover in the temperature dependence of resistivity (ρ) due to the switching of charge transport from bulk to surface channel in three-dimensional topological insulator Bi1.5Sb0.5Te1.7Se1.3. Unlike earlier studies, a much sharper drop in ρ(T) is observed below the crossover temperature due to the dominant surface conduction. Remarkably, the resistivity of the conducting surface channel follows a rarely observable T2 dependence at low temperature, as predicted theoretically for a two-dimensional Fermi liquid system. The field dependence of magnetization shows a cusp-like paramagnetic peak in the susceptibility (χ) at zero field over the diamagnetic background. The peak is found to be robust against temperature and χ decays linearly with the field from its zero-field value. This unique behavior of the χ is associated with the spin-momentum locked topological surface state in Bi1.5Sb0.5Te1.7Se1.3. The reconstruction of the surface state with time is clearly reflected through the reduction of the peak height with the age of the sample.

Angular dependence of electron spin resonance for detecting the quadrupolar liquid state of frustrated spin chains

Spin nematic phase is a phase of frustrated quantum magnets with a quadrupolar order of electron spins. Since the spin nematic order is usually masked in experimentally accessible quantities, it is important to develop a methodology for detecting the spin nematic order experimentally. In this paper we propose a convenient method for detecting quasi-long-range spin nematic correlations of a quadrupolar Tomonaga-Luttinger liquid state of $S=1/2$ frustrated ferromagnetic spin chain compounds, using electron spin resonance (ESR). We focus on linewidth of a so-called paramagnetic resonance peak in ESR absorption spectrum. We show that a characteristic angular dependence of the linewidth on the direction of magnetic field arises in the spin nematic phase. Measurments of the angular dependence give a signature of the quadrupolar Tomonaga-Luttinger liquid state. In our method we change only the direction of the magnetic field, keeping the magnitude of the magnetic field and the temperature. Therefore, our method is advantageous for investigating the one-dimensional quadrupolar liquid phase that usually occupies only a narrow region of the phase diagram.

Magnetization and susceptibility of a parabolic InAs quantum dot with electron–electron and spin–orbit interactions in the presence of a magnetic field at finite temperature

The magnetization and susceptibility of a two-electron parabolic quantum dot are studied in the presence of electron–electron and spin–orbit interactions as a function of magnetic field and temperature. The spin–orbit interactions are treated by a unitary transformation and an exactly soluble parabolic interaction model is considered to mimic the electron–electron interaction. The theory is finally applied to an InAs quantum dot. Magnetization and susceptibility are calculated using canonical ensemble approach. Our results show that Temperature has no effect on magnetization and susceptibility in the diamagnetic regime whereas electron–electron interaction reduces them. The temperature however reduces the height of the paramagnetic peak. The Rashba spin–orbit interaction is shown to shift the paramagnetic peak towards higher magnetic fields whereas the Dresselhaus spin–orbit interaction shifts it to the lower magnetic field side. Spin–orbit interaction has no effect on magnetization and susceptibility at larger temperatures.

Tunable orbital susceptibility in α-T3 tight-binding models

We study the importance of interband effects on the orbital susceptibility of three bands α-T3 tight-binding models. The particularity of these models is that the coupling between the three energy bands (which is encoded in the wavefunctions properties) can be tuned (by a parameter α) without any modification of the energy spectrum. Using the gauge-invariant perturbative formalism that we have recently developped[1], we obtain a generic formula of the orbital susceptibility of α-T3 tight-binding models. Considering then three characteristic examples that exhibit either Dirac, semi-Dirac or quadratic band touching, we show that by varying the parameter a and thus the wavefunctions interband couplings, it is possible to drive a transition from a diamagnetic to a paramagnetic peak of the orbital susceptibility at the band touching. In the presence of a gap separating the dispersive bands, we show that the susceptibility inside the gap exhibits a similar dia to paramagnetic transition.

Magnetism and Microstructure Characterization of Phase Transitions in a Steel

We present phase transitions in a low carbon steel according to existing phases and their magnetism. Scanning electron microscope employed research to clarify and evaluate the microstructural details. Additionally, we utilized from Mössbauer spectroscopy for magnetic characteristics of different existed phases. Scanning electron microscope examinations showed that the pure state of the steel was fully in the ferrite phase with equiaxed grains. Moreover, subsequent heat treatments on the studied steel also ensured the first austenite and then pearlite phase formation. Mössbauer spectroscopy of these phases appeared as a paramagnetic single-line absorption peak for the austenite phase and ferromagnetic six-line spectra for both ferrite and pearlite phases. From Mössbauer data, we determined that the internal magnetic fields of ferrite and pearlite phases were as 32.2 Tesla and 31.3 Tesla, respectively.

Material laws and related uncommon phenomena in the electromagnetic response of type-IIsuperconductors in longitudinal geometry

Relying on our theoretical approach for the superconducting critical state problem in 3Dmagnetic field configurations, we present an exhaustive analysis of the electrodynamicresponse for the so-called longitudinal transport problem in the slab geometry. A wide setof experimental conditions have been considered, including modulation of the appliedmagnetic field either perpendicular or parallel (longitudinal) to the transport currentdensity. The main objective of our work was to characterize the role of the macroscopicmaterial law that should properly account for the underlying mechanisms of flux cuttingand depinning. The intriguing occurrence of negative current patterns and theenhancement of the transport current flow along the center of the superconducting sampleare reproduced as a straightforward consequence of the magnetically induced internalanisotropy. Moreover, we show that, related to a maximal projection of the currentdensity vector onto the local magnetic field, a maximal transport current densityoccurs somewhere within the sample. The elusive measurement of the flux cuttingthreshold (critical value of such parallel component ) is suggested on the basis of local measurements of the transport current density. Finally,we show that a high correlation exists between the evolution of the transport currentdensity and the appearance of paramagnetic peak structures in terms of the appliedlongitudinal magnetic field.

ChemInform Abstract: Local Structure, Tg, and IR Transparency of Potassium Titanate Glasses and the Local Structure of Calcium Titanate Ceramics.

The Mossbauer spectrum of xK2O·(95−x)TiO2·5Fe2O3 glasses (x=35–60), consisting of a paramagnetic doublet peak due to tetrahedral Fe3+, suggests that the Fe3+ is substituted for the tetrahedral Ti4+. The isomer shift (δ=0.20–0.23 mm s−1) and the quadrupole splitting (Δ=0.72–0.81 mm s−1) decrease linearly with the increasing K2O content. The glass transition temperature (Tg) decreases similarly as the Δ does, supporting the “Tg−Δ rule” discovered by Nishida et al., i.e., the Tg of oxide glasses is expressed by Tg=aΔ+b. (The slope “a” is 680 °C mm−1 s.) The IR absorption spectra show two peaks at 880 and 640 cm−1 corresponding to the Ti(Fe)O4 and TiO6 units, respectively. The relative absorption intensity of the Ti(Fe)O4 units becomes higher when the K2O content increases. The potassium titanate glasses (plate) show IR transparency, having the transmission edge of 5.4 μm. The Mossbauer spectrum of xCaO·(95−x)TiO2·5Fe2O3 ceramics (x=5–50) consists of two doublet peaks due to Fe3+ and Fe2+. Both the δ and Δ of...

Edged topological disordered quantum ring in the presence of magnetic flux

The effects of edged topological disorder on persistent current and magnetic susceptibility are investigated in a two-dimensional quantum ring enclosed within a magnetic flux in tight binding model. In an ordered quantum ring, persistent current shows kink-like variation, while in an edged topological disordered quantum ring, disorder-averaged current gets continuous variation due to appearance of energy gaps in energy spectra. Magnetic susceptibility has delta-like paramagnetic peaks in an ordered quantum ring, while in the edged topological disordered one; the delta-like peaks become wider and begin to overlap. In addition magnetic susceptibility versus magnetic flux shows a sign reversal, which depends on the disordered configuration. In the ordered quantum ring, the temperature-averaged current decreases when the temperature increases, while in the edged topological disordered one, at first temperature-averaged current raises somewhat and then reduces in a general thermal behavior manner. At absolute zero temperature, in strong regime; the disorder-averaged current versus magnetic flux is periodic with the period of Φ 0 / 2 ; whereas, this period is Φ 0 in weak regime or in an ordered one ( Φ 0 is magnetic flux quantum). Within higher temperatures, the period of Φ 0 is achieved only in the ordered ring and Φ 0 / 2 in either weak or strong regime, wide or narrow ring.

Characterization of nanocrystalline FeSiCr powders prepared by ball milling

FeSi 10Cr 10 powder was mechanically alloyed by high energy planetary ball milling, starting from elemental powders. The microstructural and magnetic properties of the milled powders were characterized by scanning electron microscopy, X-ray diffraction, 57Fe Mössbauer spectrometry and a vibratory sample magnetometer. After 3 h of milling, the formation of two bcc solid solutions α-Fe 1 (Si, Cr) and α-Fe 2 (Si, Cr) is observed. Their grain sizes decrease with increase in milling time attaining, at 15 h of milling, 23 and 11 nm, respectively. Mössbauer spectra of the milled powder show the presence of two components. One is a ferromagnetic type with a broad sextuplet. Its distribution of hyperfine field is characterized by high and low hyperfine field’s peaks and a mean value of 26.5 T. The other is a single paramagnetic peak. Its low concentration increases to ∼4% at 15 h of milling. These results can be explained by different atomic environments affected by Si or/and Cr elements, as well as the increased disordered grain boundaries. Magnetic measurements of the milled FeSi 10Cr 10 alloy powder exhibit a soft ferromagnetic character with a decrease of both magnetization at saturation (Ms) and coercive force (Hc) with milling time attaining values of Ms=151 emu/g and Hc=2500 A/m at 30 h of milling time.

Mössbauer study on indium tin oxides (ITO) doped with Fe

InSnFe mixed oxides were prepared by a sol–gel method, and were investigated by Mossbauer spectrometry and magnetization measurements. The magnetic relaxation peaks in addition to paramagnetic peaks were observed in Mossbauer spectra. Most of Fe3 + species (D1) occupy 24d site of bixbyite structure, and the other Fe3 + species (D2) occupy 8b site. The area intensity ratio of two doublets for sample with x = 0.06 and y = 0.06 was most perfectly consistent with the ratio of d/b site occupations (24/8); this sample showed the highest magnetization among these samples. Fired ash of In oxide (5%Fe), which showed ferromagnetism, consisted of γ Fe2O3 segregated oxides.