Magnetic Susceptibility Curves Research Articles

X-ray diffraction and magnetic susceptibility measurements forFexNi1−xTa2O6

The trirutile family of the tapiolite-like compoundFexNi1−xTa2O6 was investigated by means of x-ray powder diffraction (XRD) and magnetic susceptibilitymeasurements. From Rietveld refinement it is demonstrated that the family is ahomogeneous solid solution obeying Vegard’s law. Magnetic susceptibility curves exhibittypical signatures of low-dimensional systems, with broadened maxima due to short rangecorrelations immediately above the antiferromagnetic transition temperatureTN.The T versus x phase diagram presents a minimum that suggests bicritical behaviour.

The structural change of Cu-Sn melt

With the high-temperature viscometer and magnetic susceptibility measurement device designed by our group, the viscosity and the magnetic susceptibility of the Cu65Sn35 melt were measured during the cooling process. An anomalous change can be found in the curves of viscosity and magnetic susceptibility at a certain temperature. The structure of the melt was studied by the high-temperature X-ray diffractometer. The anomalous change also can be found in the pair distribution function, correlation radius, and coordination number at the approximate temperature, which shows the microstructural change of the Cu65Sn35 melt. From the results, it was confirmed that the Cu6Sn5 compound occurs in the melt, which leads to the structural change of the melt.

Paleointensities from Tertiary basalts, Inner Mongolia and Hebei Province, northeastern China

Abstract A paleointensity study using the Thellier’s method was made on Tertiary basaltic rocks in Inner Mongolia and Hebei Province, northeastern China. K-Ar ages were previously reported for all the rocks, which range around 6–8 Ma and 28–32 Ma. Sample selection was based on total quality of remanence behavior and rock magnetism. High stability to AF and thermal demagnetization, small difference between the heating and cooling curves of magnetic susceptibility vs. temperature measurements, and PSD to SD characteristics in the Day plot of the hysteresis parameters were required. Experiments in vacuum using Coe’s procedure were applied to 54 specimens from nine flows. Experiments were successful for 34 specimens, giving seven flow mean paleointensities. Excluding two flow means (in one flow, only two specimens from the same sample survived and in the other, the within-site error amounts to 42%) the final success rate was 29 out of 54 (54%), which is not low. The obtained results range from 54 to 65 μT, except for one lava which gave 23 μT. These results indicate that although the paleointensity in the Tertiary was generally smaller than the present-day value, there were large fluctuations in the dipole moment, and paleointensities of the present-day level were often attained.

Synthesis, Properties, and Formation Mechanism of Zinc Ferrite Hollow Spheres

Hollow spheres of zinc ferrite were prepared via a surfactant‐assisted hydrothermal approach. The morphology and composition of the final products were characterized by X‐ray diffraction, transmission electron microscopy, and field emission scanning electron microscopy. It was observed from the microscope images that the final products were composed of spherical nanostructures about 70–100 nm in diameter. Anti‐ferromagnetic transition at the temperature of about 18.06 K was observed from the temperature–magnetic susceptibility curve of the ZnFe2O4 hollow spheres. Possible formation mechanism of the hollow sphere has been discussed. This work may provide us a new synthesis route for the preparation and fabrication of other ferrite nanostructures.

Magnetic properties of Co nanoparticles in zirconia matrix

Granular films composed of nanometric Co particles embedded in an insulating ZrO 2 matrix were prepared by pulsed laser deposition in a wide range of Co volume concentrations (0.06< x v<0.42). High-resolution electron microscopy (HREM) shows very sharp interfaces between the crystalline particles and the amorphous matrix, with no evidence of intermixing. The mean particles size and width of the distribution determined by fitting the low-field magnetic susceptibility and magnetization curves in the paramagnetic regime to a distribution of Langevin functions are in agreement with the parameters extracted from direct TEM observations. Ferromagnetic correlations between Co particles are evident in the field-cooled state when increasing Co concentration. The effective anisotropy constant estimated from magnetic measurements is about two orders of magnitude larger than the bulk value, and decreases as particle size increases.

Magnetic anomalies associated with the Tb3+ level crossing in YBa2Cu3O x (x ≈ 6.0) in strong magnetic fields up to 50 T

Jumps of the magnetic moment of a Tb:YBa2Cu3Ox crystal (x ≈ 6.0) are observed in pulsed magnetic fields of up to 50 T for the field orientations along the [100] and [110] axes. The jumps are caused by the Tb3+ level crossing (crossover) in the layered perovskite structure. Based on the previously determined parameters of the crystalline electric field, the Zeeman effect, magnetization curves, and magnetic susceptibility curves are calculated for the Tb:YBa2Cu3Ox crystal in the tetragonal phase. The results of calculations provide an adequate description of the magnetic anomalies and the critical parameters of the crossover. The relatively large width of the jumps in magnetization curves can indicate the inhomogeneity of the second-order parameter of the crystalline electric field in the dilute crystals.

Curie temperatures of synthetic titanomagnetites in the Fe‐Ti‐O system: Effects of composition, crystal chemistry, and thermomagnetic methods

The present study is aimed at improving the calibration of the compositional dependence of the Curie temperature (TC) of titanomagnetite (Tmt) on the basis of temperature‐dependent magnetic susceptibility (χ‐T) curves measured on synthetic Tmts in the Fe‐Ti‐O system. In order to assess the possible influence of high‐temperature cation vacancies onto the TC values, we have synthesized two types of assemblages in subsolidus conditions at 1 bar, 1100°C and 1300°C, under controlled oxygen fugacity conditions. Tmts synthesized in equilibrium with ilmenite‐hematitess (Ilmss) are expected to have the highest vacancy concentrations, those in equilibrium with wüstite (Wus) the lowest. The composition and homogeneity of the synthetic Tmts were carefully checked with a scanning electron microscope (SEM) and an electron microprobe (EMP). TC was determined from χ‐T curves using a kappabridge and, for comparison, from Ms‐T curves measured with a variable field translation balance. Our data set shows systematically higher TC values for Tmt coexisting with Ilmss than for Tmt coexisting with Wus. Most χ‐T curves are nonreversible, whereby the largest ΔTC (40 K) concern Tmt(+Ilmss) of intermediate compositions synthesized at 1300°C. Nonreversibility is interpreted as reflecting cation reordering in Tmt during the high‐temperature χ‐T measurements. TC values obtained from Ms‐T curves are higher than those obtained from the χ‐T curves, whereby the difference regularly increases (up to 40 K) with increasing Ti content, up to XUsp = 0.6. Our new calibration curves are suitable to retrieve Tmt compositions in basalts that were rapidly cooled and not oxidized by deuteric or hydrothermal fluids.

Structure and magnetic properties of R-P phase Sr3Mn2− xFexO7−δ (0.10 ≤x≤ 0.5)

Double layer R-P (Ruddlesden-Popper) manganate phases were stabilized in an air atmosphere by partial substitution of Mn by Fe. The crystal structures and magnetic structures of the R-P phase Sr 3 Mn 2-x Fe x O 7-δ (x = 0.1, 0.2, and 0.5) have been refined from the room temperature and low temperature neutron diffraction data. All of these samples adopt space group 14/mmm at room temperature. 10 K diffraction patterns showed antiferromagnetic ordering and magnetic superlattice reflection pattern that can be indexed on a 2a 0 x 2a 0 x c 0 supercell for x = 0.1 and x = 0.2 samples. The temperature dependence of the ZFC (zero field cooled) and FC (field cooled) molar magnetic susceptibility curve showed divergence for x = 0.5 samples which implies that this double R-P phase shows spin-glass transition.

Critical behaviours and magnetic properties of three-dimensional bond and anisotropy dilution Blume–Capel model in the presence of an applied field

This paper studies the critical behaviours and magnetic properties of three-dimensional bond and anisotropy dilution Blume–Capel model (BCM) in the presence of an applied field within the effective field theory. The trajectory of tricritical point, reentrant transitions and degenerate patterns of anisotropy are obtained both for the bond and the anisotropy dilutions. The global phase diagrams demonstrate unusually reentrant phenomena. The temperature dependences of magnetization curves undergo remarkable spin glass behaviour at low temperatures, and transform from ferromagnetism to paramagnetism at high temperature in applied fields. Temperature dependence of magnetic susceptibility curve is in qualitative agreement with experimental result.

High field magnetization and multi-frequency ESR in the spin-ladder compound Na2Fe2(C2O4)3(H2O)2

We have performed high field magnetization and multi-frequency electron spin resonance (ESR) measurements on single crystal and powder samples of Na2Fe2(C2O4)3(H2O)2, abbreviated as SIO. The Fe2+ ions in SIO are bridged by oxalate groups to make two-leg ladders. The temperature dependence of magnetic susceptibilities parallel and perpendicular to the leg direction show very different and anisotropic behavior. Experimental results of the isomorphous compound Na2Co2(C2O4)3(H2O)2 (SCO) are well explained by isolated magnetic dimers with an Ising-type anisotropy. Therefore, we analyze the frequency dependence of the ESR resonance fields by the same model with a fictitious spin 1 as in SCO. The agreement between experiment and calculation is satisfactorily good. Magnetic susceptibility and magnetization curves calculated with the same parameters obtained in the ESR analyses, however, do not agree well with the experimental ones. This indicates the presence of the exchange interaction between the dimers, namely the interaction along the leg.

Mössbauer study of chemical transformations in soil samples during thermomagnetic measurements

Mossbauer spectroscopy was used in order to identify iron oxides responsible for soil magnetism and for changes of the shape of the magnetic susceptibility curves obtained in the thermomagnetic measurements. The chemical composition of the soil samples was transformed due to the thermal treatment through dehydration/dehydroxylation and than oxidation/reduction process. The largest content of the magnetite has been observed for samples annealed up to T a = 700°C, which indicates that conversion process occurred under reduction conditions.

A theoretical study of the magnetism of the α- p-cyano-tetrafluorophenyl-dithiadiazolyl radical using a first principles bottom-up procedure

The mechanism of the magnetic interaction in the α phase of the organic radical p-cyano-tetrafluorophenyl-dithiadiazolyl has been studied using a first-principles bottom-up theoretical procedure. Six J AB radical–radical magnetic interactions are computed to be larger than ∣0.05∣ cm −1 (two, with values +10.91 and −10.25 cm −1, dominate over the others, whose absolute values are always smaller than 1.5 cm −1). The connectivity of these non-negligible J AB interactions creates a complex 3D magnetic topology within the crystal. The computed magnetic susceptibility curve, χ, was also calculated by diagonalizing the matrix representation of the Heisenberg Hamiltonian, whose J AB parameters are set to their computed values. This fully reproduces the shape of the experimental curve and is consistent with the bulk antiferromagnetism reported experimentally (reflected in a sharp maximum observed in χ at 10 K). Attempts to model the magnetic susceptibility data using a simple model based only upon the two dominant interactions proved impossible.

Structure and Physical Properties of Ternary Uranium Transition‐Metal Antimonides U3MSb5 (M: Zr, Hf, Nb).

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Nonlinear magnetic susceptibility and the spin glass state in the new nonstoichiometric spinel compounds Cu 1+ xCr 1.5+ ySb 0.5+ zSe 4+ t (where −0.02 ≤ x ≤ 0.01, 0.03 ≤ y ≤ 0.35, −0.2 ≤ z ≤ − 0.02, 0.01 ≤ t ≤ 0.08)

New nonstoichiometric spinel compounds Cu 1+ x Cr 1.5+ y Sb 0.5+ z Se 4+ t (where −0.02 ≤ x ≤ 0.01, 0.03 ≤ y ≤ 0.35, −0.2 ≤ z ≤ −0.02, 0.01 ≤ t ≤ 0.08) have been obtained with the aid of the solid-phase synthesis from the stoichiometric mixtures of the constituent elements. Six samples of these compounds with the different compositions have been chosen to the dc and ac magnetic susceptibility measurements. From the analysis of these measurements spin glass states have been revealed with the spin freezing temperature about 70 K for all the six samples. The magnetization measurements were performed for the same samples with the use of the induction method in the high stationary magnetic fields up to 14 T in the temperature range of 4.2–273 K. No sample under study reaches the saturation magnetization even at 14 T though they display a spontaneous magnetization, the latter existing at least up to 273 K. The temperature dependence of the dc inverse molar magnetic susceptibility reveals two different rectilinear parts which can be interpreted as related to two different Curie–Weiss temperatures: ∼68 and ∼45 K. It seems that these two temperatures correspond to two different types of the magnetically ordered clusters. The average effective magnetic moment is here equal to 2.35 μ B/ion pointing to the high defectiveness of both the crystal and magnetic structures. All the effects observed on both the magnetization and inverse molar magnetic susceptibility curves point to the appearance of the cluster spin glass states in the samples under study. Generally speaking, it is the statistical character of the substitution of the nonmagnetic antimony ions instead of the magnetic chromium ions which leads to the frustration of the orientations of the localized magnetic moments in the samples under study and in the consequence to the appearance of the spin glass states.

Anomalous magnetic nanostructural evolution in annealed CuCo granular thin films

Studying annealed, magnetron sputtered, granular Cu80Co20 thin films revealed an anomalous magnetic particle size distribution in films annealed above 300°C. The measured magnetic susceptibility (χ-T) curves show a distinct double-peak structure, indicating the coexistence of two particle sizes. The emergence of a second peak around 250–300K was accompanied by an overall reduction in magnetization; this peak subsequently grew with annealing temperature coupled with magnetization recovery. These features, observed over a wide range of thicknesses (40–200nm), result from decomposition of Co nanoparticles around 300°C, followed by the growth of larger particles.

Direct versus Mediated Through‐Space Magnetic Interactions: A First Principles, Bottom‐Up Reinvestigation of the Magnetism of the Pyridyl‐Verdazyl:Hydroquinone Molecular Co‐Crystal

The mechanism of the magnetic interaction in the pyridyl-verdazyl radical:hydroquinone (pyvd:hq) molecular co-crystal is important as it has been suggested to originate by a unique "mediated through-space" magnetic interaction. This interaction was proposed to magnetically connect two nonadjacent pyridyl-verdazyl radicals within a pi stack, where adjacent radicals pile up in a head-over-tail orientation. The connection is made through a third radical sitting between the previous two mediated radicals. Given the relevance of this proposal, we decided to reinvestigate the magnetic properties of this co-crystal by using our recently proposed first-principles "bottom-up" procedure. Based on B3LYP/6-31+G(d) and CASSCF(6,6)/6-31+G(d) calculations (the results of which are identical to those provided by CASSCF(10,10)/6-31+G(d) calculations), we have computed the microscopic J(AB) values for all direct through-space magnetic interactions between nearby pyridyl-verdazyl radicals. The magnetic interactions give rise to two dominant values of similar strength: -56 and -54 cm(-1) at the B3LYP level, which are calculated as -38 and -31 cm(-1) at the CASSCF(6,6) and CAS(10,10) levels (all other interactions being smaller than |1| cm(-1)). The dominant interactions correspond to the direct through-space interaction between two adjacent radicals of a pi stack. The crystal also exhibits a radical-mediated through-space interaction of -0.31 cm(-1) between two nonadjacent radicals of a pi stack. The direct through-space magnetic interactions are two orders of magnitude larger than the mediated through-space interaction. Thus, first-principles calculations do not support a mediated through-space mechanism to explain the magnetism of the pyvd:hq co-crystal. The magnetic topology generated by the two dominant antiferromagnetic interactions in the pyvd:hq co-crystal consists of one-dimensional (1D) alternating chains (interacting very weakly along the b and c axes). By using this topology, the computed macroscopic magnetic susceptibility curve reproduces the experimental one properly. This first-principles bottom-up description of the magnetism in the pyvd:hq co-crystal differs in some fundamental aspects from that previously proposed in the literature.

The Mixed-Valent Manganese [3 × 3] Grid [Mn(III)4Mn(II)5(2poap-2H)6](ClO4)10·10H2O, a Mesoscopic Spin-1/2 Cluster

The magnetic susceptibility and low-temperature magnetization curve of the [3 x 3] grid [Mn(III)4Mn(II)5(2poap-2H)6](ClO4)10.10 H2O (1) are analyzed within a spin Hamiltonian approach. The Hilbert space is huge (4,860,000 states), but the consequent use of all symmetries and a two-step fitting procedure nevertheless allows the best-fit determination of the magnetic exchange parameters in this system from complete quantum mechanical calculations. The cluster exhibits a total spin S = 1/2 ground state; the implications are discussed.

Bulk ferromagnetism in nitronyl nitroxide crystals: a first principles bottom-up comparative study of four bulk nitronyl nitroxide ferromagnets (KAXHAS, YOMYII, LICMIT and YUJNEW)

Searching for general trends that could help to design new bulk (3D) ferromagnets, we have carried out a first-principles bottom-up theoretical study of four bulk ferromagnets of the nitronyl nitroxide (NN) family of crystals: β-p-(nitro)phenyl-NN (KAXHAS), α-o-(hydroxy) phenyl-NN (YOMYII), α-2,5-(dihydroxy)phenyl-NN (LICMIT) and p-(methylthio) phenyl-NN (YUJNEW). This first-principles bottom-up theoretical study connects, in a rigorous form, the microscopic magnetic pair interactions (J AB) with the macroscopic magnetic properties (e.g. magnetic susceptibility or heat capacity curves). The microscopic magnetic pair interactions are computed from the crystal structure using DFT methods. The network of non-negligible J AB magnetic pair interactions between AB radicals provides the magnetic topology of the crystal. Using the room-temperature crystal structure (the only experimentally available) for KAXHAS, YOMYII and LICMIT, we found a 3D magnetic topology. However, although the computed magnetic susceptibility χ( T ) curves reproduce, in all three cases, the ferromagnetic experimental χ( T ) data, not all the J AB pair interactions are ferromagnetic. For YUJNEW, there are three sets of crystallographic coordinates (room temperature, 114 and 10K) and its magnetic topology depends on the temperature: at room temperature, there is a 2D magnetic topology but, using the 114 and 10K crystal structures, the magnetic topology becomes 3D. The computed magnetic susceptibility curve only reproduces the experimental data when using the magnetic topology computed at 10K (at 114K, there is only a qualitative agreement). The dependence of the J AB magnetic pair interactions on the geometry of the A–B radical–radical pair is also analysed. Our results show that small changes in the geometry induce changes in the sign of the interaction, a fact that can be only explained by considering that the nature of the interaction is a cooperative effect that depends on all atoms of the radical.

Hybrid-density functional study of magnetism and ligand control in Ni9 complexes

Strong influences of bridging ligands L on the magnetism of two Ni 9 complexes, Ni 9 L 2 (O 2 CMe) 8 {(2-py) 2 CO 2 } 4 (L=OH − 1 and N 3 - 2 ) are demonstrated by magnetic interactions. Effective exchange integrals J for 1 and 2 are determined non-empirically using UB3LYP and UBLYP. The calculated magnetic susceptibility for 1 is wholly consistent with the experimental values. Although the ground spin state of 2 obtained using the calculated J values agrees with the experimental S = 9 state, fitting of the J values to the experimental magnetic susceptibility curve indicates weak antiferromagnetic interactions via the azido ligands.

Magnetic properties of [formula omitted

We report measurements on magnetic properties of Ce 2 CuIn 3 compound. Irreversibility of the ZFC–FC curves of the DC magnetic susceptibility (M/H) at low field, and the shift of the peak with the frequency in the AC susceptibility give evidences for spin glass (SG) behavior at freezing temperature of T f = 2.1 K . In addition, the relative shift per frequency decade, Δ T f / T f Δ log ν = 0.016 , is similar to those reported for other spin glasses. We discuss the results in relation with the other isotypic, Ce 2 TX 3 ( T = Transition metal and X = Si , Ge and In). The interplay of disorder and frustration within hexagonal CaIn 2 type of structure and competition between RKKY interaction and Kondo effect are suggested as the main causes for the arising magnetic ground state.