Magnetic Susceptibility Curves Research Articles

Transport (Electrical Resistivity/Magnetoresistance) and Specific Heat Measurements of Cu2 LnNbO8Sr2 with Ln = Er, Dy

The magnetic, transport and specific heat measurements of 1212-type compounds crystallized in tetragonal symmetry with starting composition, Cu2.1LnNb0.9O7.9Sr2; Ln = Er, Dy have been investigated. The Cu2.1LnNb0.9O7.9Sr2; Ln = Er, Dy compounds showed non-superconducting properties down to 1.8 K in the magnetic susceptibility measurements. The magnetic parameter (μeff) obtained from the linear region of inverse molar magnetic susceptibility curves agrees with the calculated values for the respective free trivalent Er and Dy ions in Cu2.1LnNb0.9O7.9Sr2; Ln = Er, Dy compounds. Though there is no strong evidence of magnetic ordering seen from magnetic susceptibilities, the hysteresis, M(H) curve obtained at 1.8 K looks like a canted antiferromagnet. The S-shaped (slightly curved) magnetization curve suggests weak ferromagnetic interactions that exist in the Ln = Er compound. A small hysteresis is observed with the coercive field (Hc) of 49 Oe and the remnant magnetization (Mr) of about 0.06 μB/f.u. for Ln = Er. Interestingly, such a hysteresis loop opening is not seen for the Ln = Dy compound. While specific heat anomaly (λ-like transition) was observed for Ln = Dy compound at low temperature (around 6 K), for Ln = Er compound such an anomaly was not seen in the specific heat measurements. The electrical resistivity versus temperature, ρ(T), data showed that the compounds Cu2.1LnNb0.9O7.9Sr2; Ln = Er, Dy are not in metallic state and they are really semiconducting-in-nature. Interestingly, rather large magnetoresistance, MR (∼18%) was observed at low temperature ∼2 K for Er-based niobio-cuprate.

Impact of High Pressure and High Temperature on Annealed Oxygen-deficient CoSrO3−δ Perovskites: Structural and Magnetization Studies

In this brief article, structural, magnetization studies of oxygen deficient perovskite cobalt oxides CoSrO3−δ synthesized in two different ways are reported. The structural refinements (JANA2006) of X-ray powder diffraction data indicate that the sample prepared under ambient pressure (stage-1) shows a hexagonal structure with P63/mmc (194) as a possible space group. The stage-1 sample subsequently sintered at 1450 °C for 1–2 h under high-pressure 6 GPa conditions (stage-2) crystallizes in tetragonal symmetry with I4/mcm (140) space group having a=5.444(7) A and c=7.68(2) A. While the stage-1 sample exhibits a paramagnetic nature in the magnetic susceptibility, M(T), measurements, interestingly the sample annealed under high-pressure conditions shows ferromagnetism in the magnetic susceptibility, M(T) and field dependence magnetization, M(H) measurements. The high-pressure annealed sample shows hysteresis opening with a quite large coercive field of 7.3 kOe at 1.8 K. The temperature dependence of the inverse molar susceptibility curves exhibits linear behavior in the high-temperature regime and could be fitted to the Curie–Weiss expression, χ(T)=C/(T−θW). The experimental values of θW and peff obtained from the linear region of the inverse molar magnetic susceptibility curves are found to be: −210.7(5) K and 2.38(2) μB/Co for stage-1 and 260.2(7) K and 1.87(3) μB/Co for stage-2 samples, respectively. A negative sign of θW indicates rather strong antiferromagnetic correlations in the stage-1 sample. Apart from these results, the structural parameters reported by various groups for the strontium-based perovskite cobalt oxides are also presented in the form of literature collections.

Optical, electrical and magnetic properties of Co 3O 4 nanocrystallites obtained by thermal decomposition of sol–gel derived oxalates

Nanocrystallites of tricobalt tetraoxide (Co 3O 4) have been synthesized by sol–gel process using cobalt acetate tetrahydrate, oxalic acid as precursors and ethanol as a solvent. The process comprises of gel formation, drying at 80 °C for 24 h to obtain cobalt oxalate dihydrate (α-CoC 2O 4·2H 2O) followed by calcination at or above 400 °C for 2 h in air. These results combined with thermal analysis have been used to determine the scheme of oxide formation. The room temperature optical absorption spectra exhibits blue shift in both (i) ligand to metal (p(O 2−) → e g(Co 3+), 3.12 eV), and (ii) metal to metal charge transfer transitions (a) t 2g(Co 3+) → t 2(Co 2+), 1.77 eV, (b) t 2(Co 2+) → e g(Co 3+), 0.95 eV together with the d–d transitions (0.853 and 0.56 eV) within the Co 2+ tetrahedra. The temperature dependent ac electrical and dielectric properties of these nanocrystals have been studied in the frequency range 100 Hz to 15 MHz. There are two regimes distinguishing different temperature dependences of the conductivity (70–100 K and 200–300 K). The ac conductivity in both the temperature regions is explained in terms of nearest neighbor hopping (NNH) mechanism of electrons. The carrier concentration measured from the capacitance ( C)–voltage ( V) measurements is found to be 1.05 × 10 16 m −3. The temperature dependent dc magnetic susceptibility curves under zero field cooled (ZFC) and field cooled (FC) conditions exhibit irreversibilities whose blocking temperature ( T B) is centered at 35 K. The observed Néel temperature ( T N ∼ 25 K) is significantly lower than the bulk Co 3O 4 value ( T N = 40 K) possibly due to the associate finite size effects.

Magnetic properties of the noncollinear phase of a FeBO3:Mg single crystal

The magneto-optical method is used to investigate magnetization and low-frequency magnetic susceptibility curves of the FeBO3 single crystal doped with diamagnetic Mg ions. It is demonstrated that substitution of a fraction of Fe ions by the Mg ions in the structure of this easy-plane weak ferromagnet causes a significant intraplane magnetocrystalline anisotropy at low temperatures as well as different forms of magnetic hysteresis loops and field dependences of the magnetic susceptibility recorded for different orientations of the external magnetic field relative to the basal crystal plane. The established special features of the FeBO3:Mg magnetic properties are explained by the transition of the magnetic crystal from the uniform to spatially modulated state during technical magnetization.

High-pressure study of the magnetic phase transition in MnSi

Measurements of ac magnetic susceptibility and dc resistivity of a high-quality single-crystal MnSi were carried out at high pressure making use of helium as a pressure medium. The form of the ac magnetic susceptibility curves at the magnetic phase transition suddenly changes upon helium solidification. This implies strong sensitivity of magnetic properties of MnSi to nonhydrostatic stresses and suggests that the early claims on the existence of a tricritical point at the phase-transition line are probably a result of misinterpretation of the experimental data. At the same time resistivity behavior at the phase transition does not show such a significant influence of helium solidification. The sharp peak at the temperature derivative of resistivity, signifying the first-order nature of the phase transition in MnSi successfully survived helium crystallization and continued the same way to the highest pressure.

Dust source of the Holocene loess-soil and pedogenic environmental changes in the upper Huaihe River

Based on field surveys, soil samples were collected at the YPC site, Yuzhou City, Henan Province for analysis of contents of major and trace elements and their variations with XRF and comparison with the curves of magnetic susceptibility, pH value distribution, loss on ignition and particle-size distribution. It was concluded that the dust source of loess in the upper reaches of the Huaihe River Basin was different from that in the Loess Plateau. And the Holocene pedogenic environmental changes in the upper reaches of the Huaihe River Basin were revealed.

Geostatistical evaluation of magnetic indicators of forest soil contamination with heavy metals

The goal of the study was the geostatistical evaluation of quantitative magnetic measures, which can be used for effective delineation of the extent of the area polluted with heavy metals. Several parameters of magnetic susceptibility, measured in the soil profile, were proposed as magnetic indicators of soil pollution and analyzed in detail. The following parameters were calculated: maximum magnetic susceptibility, magnetic susceptibility at the depth of 3 cm and 5 cm, and the area under the curve of magnetic susceptibility. Measurements were performed at two forested study areas, located in Upper Silesian Industrial Area (Poland). Analyses were performed using geostatistical methods, and the results were verified using dense chemical measurements.

Can theoretical methods go beyond the experimental data? The case of molecular magnetism

The complexity of polynuclear transition metal complexes with the most appealing magnetic properties makes it impossible to extract the values of exchange interactions between the paramagnetic centers using experimental techniques. Hence, theoretical methods based on density functional theory are used because they allow the accurate estimation of such values. Three Mn(6) complexes were studied and the calculated exchange coupling constants used to plot a magnetic susceptibility curve that can be compared with the experimental ones. We propose a new tool to facilitate the understanding of the magnetic properties in systems of this kind. We employed magnetostructural maps to correlate the calculated exchange coupling constants with structural parameters for the dinuclear or polynuclear manganese complexes that we have studied.

On the existence of temperature induced changes in the magnetic topology of crystals that show no first-order crystallographic phase transitions

The First-Principles Bottom– Up study of the 88 K and 273 K X-ray diffraction structures of the bis-2,3-dimethylpyridinium tetrabromocuprate molecular magnet shows that the analysis of the magnetic properties of a molecule-based magnet, that does not present any first order polymorphic transition in the range of temperature studied, depends on the X-ray structure employed. The reason is the thermal expansion anisotropy when the crystal goes from the low temperature phase to 273 K, which induces changes in the radical–radical J AB interactions. As a consequence, the magnetic topology of the low temperature and 273 K structures change, a fact that induces a change in the macroscopic magnetic susceptibility curve (only the 88 K structure of bis-2,3-dimethylpyridinium tetrabromocuprate reproduces well the two-leg spin ladder experimental properties of this magnet). When anisotropic thermal effects are suspected one should use low temperature structures to study the magnetic properties at low temperature, and high temperature structures for the study of the magnetic properties in that range of temperatures.

Structure and magnetism of the β-Mn–Co solid-solution phase

The crystal structure of the β-Mn 1− t Co t solid-solution phase (0 ≤ t ≤ 0.40) has been studied with powder neutron (10 and 298 K) and single-crystal X-ray (150 K) diffraction methods. The lattice-constant ( a) isotherms at 10, 150, and 298 K go through flat maxima between t = 0.10 and 0.25. Up to t = 0.25 all Co is found to substitute at the T1 ( T1 = Mn and/or Co) site of the β-Mn crystal structure (position 8 c of space group P4 132) whereas for t = 0.40 also the T2 site (position 12 d) is partly occupied by Co (some 0.2 Mn + 0.8 Co occupancy of the T2 site). The variable positional parameters x (for T1) and y (for T2) exhibit remarkably small variations with composition ( t) and temperature. The present low-temperature powder neutron-diffraction data confirm the earlier finding that the β-Mn 1− t Co t phase does not exhibit conventional co-operative magnetic ordering. However, the appearance of diffuse scattering in the low-temperature diffraction patterns is clearly generated by short-range ordering of magnetic moments, which owing to the atomic arrangement of the β-Mn-type structure becomes geometric frustrated. The temperature dependence of the magnetic susceptibility for β-Mn 1− t Co t is re-measured. Neglecting β-Mn itself (which exhibits virtually temperature-independent paramagnetism), our magnetic susceptibility curves above some 80 K for t = 0.15, 0.25, and 0.40 can with good-will be described by the Curie–Weiss relation, indicating antiferromagnetic correlations at low temperatures. However, the thus involved paramagnetic moments and Weiss constants must indeed be stamped as unphysically large.

Magnetic properties of DyNi2B2C studied with a two-ion model for antiferromagnets

In a rare-earth antiferromagnet, two neighboring magnetic ions order spontaneously in opposite directions below the Neel temperature. Especially when it is placed in an external magnetic field, the two magnetic ions react to the field in different ways, so that they usually have different magnitudes and orientations below the magnetic transition temperature. Therefore, to describe the magnetic structure of an antiferromagnet, the single-ion ferromagnetic-like model is inadequate. To solve this problem, a two-ion model for rare-earth antiferromagnets is proposed and used in this work to investigate the magnetic properties of DyNi2B2C. The magnetic susceptibility curves obtained with this model show good agreements with experimental data.

Controllable synthesis of beta-Mn 2V 2O 7 microtubes and hollow microspheres

β-Mn 2V 2O 7 microtubes with the range of 15–25 μm in length, 2.5–3.5 μm in external diameter, and ca 0.4 μm of the wall in thickness, as well as β-Mn 2V 2O 7 hollow microspheres with an average outer diameter of 2 μm were successfully synthesized in a suitable molar ratio of NH 4VO 3 and MnCO 3 powders via a hydrothermal process. XRD and FESEM were used to characterize the products, and the magnetic susceptibility curve was also measured. In the whole process, the concentration of Mn 2+ cations derived from MnCO 3 dissolution plays a crucial role in the formation of β-Mn 2V 2O 7 microtubes and hollow microspheres.

Crystallographic and magnetic structure ofSrCoO2.5brownmillerite: Neutron study coupled with band-structure calculations

A study of the crystallographic and magnetic structure of ${\text{SrCoO}}_{2.5}$ with a brownmillerite-type structure has been carried out from neutron powder-diffraction (NPD) measurements at temperatures ranging from 10 to 623 K, across the N\'eel temperature $({T}_{N}=537\text{ }\text{K})$ of this antiferromagnetic oxide. The study has been complemented with differential scanning calorimeter (DSC), $dc$ susceptibility and magnetization measurements. Although the refinement of the crystal structure from NPD data is possible in the orthorhombic $Pnma$ and $Ima2$ space groups, the support of ab-initio band-structure calculations has allowed us to select, without ambiguity, the $Ima2$ space group as the ground state for ${\text{SrCoO}}_{2.5}$ brownmillerite. In $Ima2$ the crystallographic structure of ${\text{SrCoO}}_{2.5}$ is described as layers of corner-sharing $\text{Co}1{\text{O}}_{6}$ octahedra alternating along the $a$ axis with layers of vertex-sharing $\text{Co}2{\text{O}}_{4}$ tetrahedra, conforming chains running along the [0 0 1] direction. The magnetic structure below ${T}_{N}=537\text{ }\text{K}$ is $G$-type with the magnetic moments directed along the $c$ axis. This magnetic arrangement is stable from ${T}_{N}$ down to 10 K. At $T=10\text{ }\text{K}$, the magnetic moment values for Co1 and Co2 atoms are $3.12(13){\ensuremath{\mu}}_{B}$ and $2.88(14){\ensuremath{\mu}}_{B}$, respectively, compatible with a ${\text{Co}}^{2+}\underset{}{L}$ state, where $\underset{}{L}$ stands for a ligand hole. The magnetic susceptibility curves show, below 200 K, a divergence of zero-field cooling and field cooling curves, displaying broad maxima which are interpreted as due to the presence of ferromagnetic clusters embedded into an antiferromagnetic matrix. These inhomogeneities are inherent to the synthesis process, by quenching microcrystalline samples of ${\text{SrCoO}}_{3\ensuremath{-}x}$ composition from high temperature, where cubic, ferromagnetic perovskites have been identified by diffraction methods.

Controllable synthesis of β-Mn2V2O7 microtubes and hollow microspheres

β-Mn2V2O7 microtubes with a length of 15–25 μm, 2.5–3.5 μm external diameter, and ∼0.4 μm wall thickness, as well as β-Mn2V2O7 hollow microspheres with an average outer diameter of 2 μm, were successfully synthesized in a suitable molar ratio of NH4VO3 and MnCO3 powders via a hydrothermal process. X-ray powder diffraction (XRD) and field emission scanning electron microscopy (FESEM) were used to characterize the products, and the magnetic susceptibility curve was also measured. In the whole process, the concentration of Mn2+ cations derived from MnCO3 dissolution plays a crucial role in the formation of β-Mn2V2O7 microtubes and hollow microspheres.

A first-principles bottom-up study of the magnetic interaction mechanism in the bulk ferromagnet p- O2N- C6F4- CNSSN

The crystals of the p-nitro perfluorophenyl dithiadiazolyl radical have been shown to present bulk ferromagnetism below 1.32 K. Using our first-principles bottom-up methodology, the mechanism of the magnetic interactions in these crystals has been studied to gain a rigorous quantitative understanding of such bulk ferromagnetism. The p- O 2 N- C 6 F 4- CNSSN crystal is found to present only two non-negligible interactions ( J(d1) = 0.83 cm −1 and J(d3) = 0.07 cm −1). The dominant interaction J(d1) generates a three-dimensional (3D) magnetic topology that can be described as a distorted diamond-like arrangement. Using the appropriate minimal magnetic model to describe this topology, the magnetic susceptibility and heat capacity curves were computed. A good agreement is found between the computed and experimental magnetic susceptibility data. Furthermore, the critical temperature obtained from the heat capacity curve (0.6 K) agrees well with the experimental one. A comparison of the magnetic data for p- O 2 N- C 6 F 4- CNSSN and four nitronyl nitroxide bulk ferromagnets indicates that the critical temperature not only depends on the size of the largest J interactions, but also on the corresponding magnetic topology.

Inelastic neutron scattering study of crystalline-electric-field interaction in Ce3Ir4Sn13

The Ce3Ir4Sn13 single crystal was grown using Sn-flux method. Inelastic neutron scattering measurements were performed on the Ce3Ir4Sn13 powder sample at T=5.3 and 200K. Two magnetic origin peaks of ΔE1=4.4 and ΔE2=45.9meV in the inelastic neutron scattering spectra were detected as the crystalline-electric-field excitations for Ce3Ir4Sn13. The results of our neutron data are roughly consistent with the calculation by fitting the magnetic susceptibility curve using a simple point-charge model.

Thermodynamic properties of polyacenes

Carbon nanoribbons have been a subject of great interest lately because of their interesting physical properties, particularly their use as electrodes in lithium-based batteries, in a way to improve the performance of these batteries. By means of a diagrammatic perturbation expansion of the Hubbard model, the thermodynamic properties of a cyclical polyacene have been calculated. The entropy, magnetic susceptibility and specific heat curves present crossing points. The molecular hardness multiplied by the carbon number ( N C) in a polyacene molecule is a relevant parameter to determine its energy storage capability. Our results show that this parameter versus N C, for some cyclical polyacenes, presents a peak in N C=36 and it practically does not change for N C>60. The behavior for N C<30 is very similar to that of the available experimental curve for polyacenes.

Magnetic studies on Mn-doped TiO2 bulk samples

Mn-doped TiO2 (Ti1−xMnxO2) bulk samples with nominal composition x = 0.02, 0.04, 0.08 have been prepared by a solid-state reaction and sintered at different temperatures ranging from 450 °C to 900 °C. For samples with x = 0.02, magnetic investigations show that room temperature ferromagnetism can be obtained and the magnetization of samples decreases monotonically with the increase in the sintering temperature. For the samples sintered at 600 °C with different doping content, the temperature dependence of magnetic susceptibility shows that a magnetic transition appears near room temperature, besides a magnetic transition at 43 K perhaps caused by Mn3O4. From the extrapolation of the inverse magnetic susceptibility curves at high temperatures, a positive Curie–Weiss temperature is obtained and it shifts to a low temperature with Mn doping content, revealing that ferromagnetic coupling decreases monotonically with the increase in Mn doping content. In addition, an exchange bias is clearly observed below 60 K, which also provides strong evidence that Ti1−xMnxO2 is ferromagnetic.

Anisotropy in magnetic properties and electronic structure of single-crystalLiFePO4

crystals. The values of the in-plane nearest- and next-nearest-neighbor spin exchange J1 and J2, interplane spin exchange J, and single-ion anisotropy D, obtained recently from neutron scattering measurements, are used for calculating the Curie temperatures with the formulas derived from the mean-field Hamiltonian. It is found that the calculated Curie temperatures match well with that obtained by fitting the magnetic susceptibility curves to the modified Curie-Weiss law. For the polarized Fe K-edge x-ray absorption spectra of single-crystal LiFePO4, a different feature assignment for the 1s →4p transition features is proposed and the anisotropy in the intensities of the 1s →3d transition features is explained adequately by a one-electron theory calculation of the electric quadrupole transition terms in the absorption coefficient.

Magnetic susceptibility of glass-forming Al-Co-Ce alloys at high temperatures

In this work magnetic susceptibility of Al91-xCo9Cex (1<x<11 at.%) and Al91-xCoxCe7 (1<x<11 at.%) alloys was investigated by Faraday's method in the wide temperature (T=300-2000 K) and field (B=0.6-1.2 T) ranges. The abnormal behavior of susceptibility above melting point of Al2R compound is discovered. The magnetic susceptibility vs concentration curves for quasybinary systems Al-Ce (XCo = 9 at.%) and Al-Co (XCe = 7 at.%) were plotted. It was found that χ=f(Ce) dependences have oscillating form similar both in solid and liquid states; while for χ=f(Co) susceptibility practically does not depend on Co content. Some parameters of electron structure in Al-Co-Ce alloys are calculated from experimental results. The effective magnetic moment per cerium atom was found to be at a level of 1.1 μB and does not depend on alloy composition, while cobalt atoms exist in non-magnetic state in these alloys. The existence of Al2R quasimoleculars is highly probable in these alloys and their destruction starts only near melting point of Al2R compound.