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The insoluble organic material (IOM) in primitive chondritic meteorites is very enriched in D (up to δD ≈ 3500‰ in bulk). Based largely on a series of electron paramagnetic resonance (EPR) studies of IOM from three meteorites (Orgueil, Murchison and Tagish Lake), it has been suggested that these enrichments are the result of exchange with H2D+ in the solar nebula and that exchange with radicals in the IOM was particularly facile so that they are enormously enriched in D (δD ≥ 95000‰). To try to test whether radicals are largely responsible for the D enrichments in IOM, we have used EPR to measure the radical concentrations (spins/g) and g-factors of 18 IOM separates from C1-2 chondrites of varying petrologic type and chemical group that have a much wider range of H isotopic compositions (δD ≈ 600–3500‰) than in previous studies. We confirm the previous studies findings that IOM exhibits non-Curie law behavior and that it does not completely saturate even at microwave excitation powers of 200 mW. We also have obtained similar g-factor values. However, our IOM samples typically exhibit a lower and more limited range of spin concentrations, and smaller deviations from Curie law behavior than in previous studies. Nor do we observe correlations between bulk δD and either spins/g or non-Curie law behavior that would be expected if exchange between H2D+ and radicals, as previously proposed, was the cause of the D-enrichments in IOM. Indeed, in general the radical concentrations and the degree of non-Curie law behavior do not seem to correlate with any of the measured IOM properties, with chondrite group or parent body history (e.g., degree of aqueous alteration). The only exceptions are the IOM in four Tagish Lake lithologies whose spin concentrations increase with increasing degree of thermal processing as indicated by decreasing H/C and δD, and increasing aromaticity.

Bovine spleen has been used as a sample for deep magnetochemical investigation. Temperature dependence of the magnetic susceptibility and field dependence of the magnetization reveal a paramagnetic behaviour that violates the Curie law. The zero-field cooled magnetization and field cooled magnetization experiments show the bifurcation point at ca TC = 20 K and the blocking temperature TB = 10 K confirming a dominating portion of ferritin along with the organic tissue. There is a remnant magnetization at temperature below 20 K and the search for the magnetic hysteresis was positive.

We explain the lambda (λ) transition in the heat capacity in terms of spin freezing on the basis of finite-sized block spin concepts. Thus, the spin-glass phase or the antiferromagnetic/paramagnetic phase near the Neel temperature may be considered as a short-range ordering of the block spins comprised of many random spins with respective majority spin directions. Using the Curie law for the block spins, we obtain the λ-type heat capacity in the lower and the higher temperature approximations of the Brillouin function. The theoretical heat capacity gives a good fit to the experimental data.

The temperature scales of screening of local magnetic and orbital moments are important characteristics of strongly correlated substances. In a recent paper X. Deng et al. using dynamic mean-field theory (DMFT) have identified temperature scales of the onset of screening in orbital and spin channels in some correlated metals from the deviation of temperature dependence of local susceptibility from the Curie law. We argue that the scales obtained this way are in fact much larger, than the corresponding Kondo temperatures, and, therefore, do not characterize the screening process. By reanalyzing the results of this paper we find the characteristic (Kondo) temperatures for screening in the spin channel $T_K\approx 100$ K for V$_2$O$_3$ and $T_K\approx 350$ K for Sr$_2$RuO$_4$, which are almost an order of magnitude smaller than those for the onset of the screening estimated in the paper ($1000$ K and $2300$ K, respectively); for V$_2$O$_3$ the obtained temperature scale $T_K$ is therefore comparable to the temperature of completion of the screening, $T^{\rm comp}\sim 25$ K, which shows that the screening in this material can be described in terms of a single temperature scale., This is a post-peer-review, pre-copyedit version of an article published in Matters Arising section of Nature Communications. The final authenticated version is available online at http://dx.doi.org/10.1038/s41467-021-21641-2

We introduce and study a simplification of the symmetric single-impurity Kondo model. In the Ising-Kondo model, host electrons scatter off a single magnetic impurity at the origin whose spin orientation is dynamically conserved. This reduces the problem to potential scattering of spinless fermions that can be solved exactly using the equation-of-motion technique. The Ising-Kondo model provides an example for static screening. At low temperatures, the thermodynamics at finite magnetic fields resembles that of a free spin-1/2 in a reduced external field. Alternatively, the Curie law can be interpreted in terms of an antiferromagnetically screened effective spin. The spin correlations decay algebraically to zero in the ground state and display commensurate Friedel oscillations. In contrast to the symmetric Kondo model, the impurity spin is not completely screened, i.e., the screening cloud contains less than a spin-1/2 electron. At finite temperatures and weak interactions, the spin correlations decay to zero exponentially with correlation length $\xi(T)=1/(2\pi T)$., Comment: 26 journal pages, 15 figures

In the Kitaev honeycomb model, the quantum spin fractionalizes into itinerant Majorana and gauge flux spontaneously upon cooling, leading to rich experimental ramifications at finite temperature and an upsurge of research interest. In this work, we employ the exponential tensor renormalization group approach to explore the Kitaev model under various perturbations, including the external fields, Heisenberg, and the off-diagonal couplings that are common in the Kitaev materials. Through large-scale manybody calculations, we find a Kitaev fractional liquid at intermediate temperature that is robust against perturbations. The fractional liquid exhibits universal thermodynamic behaviors, including the fractional thermal entropy, metallic specific heat, and an intermediate-temperature Curie law of magnetic susceptibility. The emergent universal susceptibility behavior, with a modified Curie constant, can be ascribed to the strongly fluctuating $\mathbb{Z}_2$ fluxes as well as the extremely short-ranged and bond-directional spin correlations. With this insight, we revisit the susceptibility measurements of Na$_2$IrO$_3$ and $\alpha$-RuCl$_3$, and find evident signatures of finite-temperature fractionalization and ferromagnetic Kitaev couplings. Moreover, the peculiar spin correlation in the fractional liquid corresponds to a stripy structure factor which rotates in the extended Brillouin zone as the spin component changes. Therefore, our findings encourage future experimental exploration of fractional liquid in the Kitaev materials by thermodynamic measurements and spin-resolved structure factor probes., Comment: 16 pages, 16 figures

An in situ electrochemical electron paramagnetic resonance (EPR) spectroscopic study of N-doped reduced graphene oxide (N-rGO) is reported with the aim of understanding the properties of this material when employed as an electrical double-layer capacitor. N-rGO shows a capacitance of 100 F g−1 in 6 M KOH, which is twice that found for reduced graphene oxide (rGO). The temperature dependence of the rGO EPR signal revealed two different components: a narrow component, following the Curie law, was related to defects; and a broad curve with a stronger Pauli law component was attributed to the spin interaction between mobile electrons and localised π electrons trapped at a more extended aromatic structure. The N-rGO sample presented broader EPR signals, indicative of additional contributions to the resonance width. In situ EPR electrochemical spectroscopy was applied to both samples to relate changes in unpaired electron density to the enhanced capacitance. The narrow and broad components increased and diminished reversibly with potential. The potential-dependent narrow feature was related to the generated radical species from corresponding functional groups: e.g. O- and N-centred radicals. Improved capacitance seen for the N-modified basal graphene planes can be accordingly suggested to underlie the enhanced capacitance of N-rGO in basic electrolytes.

The Cryogenic Sapphire Oscillator is today recognized for its unprecedented frequency stability, mainly coming from the exceptional physical properties of its resonator made in a high quality sapphire crystal. With these instruments, the fractional frequency measurement resolution, currently of the order of 1e-16, is such that it is possible to detect very small phenomena like residual resonator environmental sensitivities. Thus, we highlighted an unexpected magnetic sensitivity of the Cryogenic Sapphire Oscillator (CSO) at low magnetic field. The fractional frequency sensitivity has been preliminary evaluated to 1e-13/Gauss, making this phenomenon a potential cause of frequency stability limitation. In this paper we report the experimental data related to the magnetic sensitivity of the quasi-transverse magnetic Whispering Gallery (WGH) modes excited in sapphire crystals differing from their paramagnetic contaminants concentration. The magnetic behavior of the WGH modes does not follow the expected theory combining the Curie law and the Zeeman effect affecting the Electron Spin Resonance of the paramagnetic ions present in the crystal., 7 pages,10 figures, to be submitted to PRB

First-principles calculations have been performed to study elastic, electronic, thermodynamic, transport and superconducting properties of recently reported osmium based two superconductors, XOsSi (X = Nb, Ta). We have calculated elastic constants and elastic moduli of XOsSi compounds for the first time. The calculated values of bulk, Young's, shear moduli are slightly larger than the average value obtained from the rule of mixtures of the constituents. NbOsSi and TaOsSi both compounds are found to be relatively hard material, elastically stable and ductile in nature. The obtained directional bulk modulus and shear anisotropic factors indicate that both compounds have high elastic anisotropy. The shear anisotropic factors show higher elastic anisotropy than the percentage anisotropy in these compounds. The Debye temperature and bulk modulus increases with pressure but decreases with temperature as usual for metals. The magnetic susceptibility (χ) of TaOsSi follows the Curie law but NaOsSi does not follow due to its delocalized magnetic moment and electronic specific heat (c) slightly deviates from the linear relationship with temperature. The calculated band structures of XOsSi compounds exhibit metallic nature. In both cases, d-orbitals have the dominating contribution to the total density of states. The smaller electron-phonon coupling constant implies that XOsSi (X = Nb, Ta) are weakly coupled superconductors.

We report structural, magnetic and temperature dependent dielectric properties of diluted magnetic semiconductor Zn0.90Ni0.05Mn0.05O prepared by solid state reaction technique. X-ray diffraction analysis revealed formation of single phase hexagonal wurtzite structure. Scanning electron microscopy and atomic force microscopy images indicated increase in grain size and roughness respectively with increasing sintering temperature. Field dependent DC magnetization at low temperature exhibited ferromagnetic ordering with coercivity ~ 6 × 104 A/m and remanence ~ 17 A/m. Complex initial permeability values were found to be positive for the measurement frequency range (1 kHz–120 MHz) with a relaxation at lower frequency. Temperature dependent DC magnetization and AC susceptibility followed curie law with curie temperature below 65 K. Temperature dependent dielectric constants ($$\varepsilon ^{\prime}\,\& \,\varepsilon ^{\prime\prime}$$) and loss tangents ($$tan\delta$$) measured for selected frequencies were found to be an increasing function of temperature and decreasing function of frequency. AC conductivity ($${\sigma }_{ac}$$) values were found to be an increasing function of frequency and temperature. Clear signatures of relaxations were observed in $$\varepsilon ^{\prime},\,\varepsilon ^{\prime\prime},$$ $$tan\delta$$ and $${\sigma }_{ac}$$ for temperatures above 200 °C.

In this paper, we study the effect of the signal-to-noise ratio of magnetization measurements on the determination of the Curie temperature from the analysis of the magnetocaloric response. The procedure has been compared with the method of the inflection point of the magnetization versus temperature curves. Magnetization data have been simulated using the Arrott–Noakes equation of state, with the addition of different noise levels (either 1% of the measured signal or 0.3% of the measurement range). It is shown that the obtained values of the Curie temperature are more accurate in the case of the magnetocaloric procedure, although this method requires more data analysis than the inflection point method. Moreover, the field independence of the Curie temperature obtained from the magnetocaloric procedure allows us to perform a statistical analysis of the obtained values, reducing the associated error in the Curie temperature determination.

Using full-potential local-orbital minimum-basis along with spin-polarized relativistic Korringa-Kohn-Rostoker methods, we study the electronic, Fermi surface, Curie temperature and optical properties of Zr2CoAl alloy. The alloy with Li2AgSb and Cu2MnAl structures are compared in terms of magnetic properties, and the electronic structures in two structures are also discussed. According to the calculated electronic states, it finds that the Zr2CoAl with Li2AgSb structure is half-metallic ferromagnet with an integral magnetic moment of 2.00 μ B , meanwhile we also notice the d-d and p-d hybridizations are responsible for the formation of minority-spin gap, furthermore, the fat-bands are applied to discuss the mixture between d and p electrons in the vicinity of the Fermi level. The Fermi surfaces related to the valence bands are constructed, and it is found that the spin-up valence bands 26, 27 and 28 across the Fermi energy dominate the nature of electrons. By mapping the system onto a Heisenberg Hamiltonian, we obtain the exchange coupling parameters, and observe that the Zr(A)-Co(C) and Zr(A)-Zr(B) interactions provide a major contribution for exchange interactions. Based on the calculated exchange coupling parameters, the Curie temperature is estimated to be 287.86 K at equilibrium, and also the dependence of Curie temperature on lattice constant related to the tunable Curie temperature in Zr2CoAl alloy is studied. Finally, we report the optical properties of Zr2CoAl alloy, and present the photon energy dependence of the absorption, the optical conductivity and the loss function.

Using the spin-polarized relativistic Korringa-Kohn-Rostoker method, we study the exchange interactions and Curie temperatures of Fe 2 Ni Z ( Z = Al, Ga, Si, Ge) with the Hg 2 CuTi structure. The Heisenberg exchange coupling parameters and Curie temperatures are obtained by calculating the exchange interactions between the constituents. It is found the nearest neighbor exchanges play a leading role in interactions, the calculated Curie temperatures, which are higher than the room temperature, decrease when changing Z from III to IV group. In addition, we study the influence of lattice constant on magnetic moments and Curie temperatures. It is found the Fe magnetic moments become more larger due to the reduction of atomic orbital overlap as the expansion of lattice parameters. Only small changes are observed for the moment of Ni atom, while for the Z atom, the magnetic moment is nearly constant. Finally, the Curie temperatures of Fe 2 Ni Z compounds under different lattice constants are acquired by using the mean-field approximation.

The magnetization of noninteracting metallic nanoparticles is investigated by comparing the particle-size and temperature dependences of the magnetization for several mechanisms. The nanoparticle magnetization deviates from that of the underlying bulk materials due to zero-temperature and thermal effects, and on a mean-field level, the corresponding surface-core interaction is described by a Landau–Ginzburg approach. A major factor is the reduced atomic coordination at the surface, which has often, but not always, opposite effects on the zero-temperature magnetization and Curie temperatures. The coordination effect is particularly pronounced for very weak itinerant ferromagnets and for strongly exchange-enhanced Pauli paramagnets. With regard to external magnetic fields, the nanoparticle magnetization involves several “superparamagnetic” phenomena, namely, Neel relaxation, Brownian relaxation, and Langevin macrospin paramagnetism.

We report Raman-scattering results of YbRu$_2$Ge$_2$ single crystals to explore the phononic and crystal-field (CF) excitations. This heavy-fermion metal is suggested to enter a ferroquadrupolar (FQ) phase below T$_0$=10 K. The tetragonal CF potential splits the Yb$^{3+}$ $^2F_{7/2}$ ground multiplet into two $\Gamma_6$ and two $\Gamma_7$ Kramers doublets. We establish the following CF level scheme of the ground multiplet: a $\Gamma_6$ ground state, with the two $\Gamma_7$ states at 2 cm$^{-1}$, 95 cm$^{-1}$ and the other $\Gamma_6$ state at 239 cm$^{-1}$. The $\sim$2 cm$^{-1}$ separation between the CF ground and first excited states is in agreement with the previously proposed quasi-quartet CF ground state. The intensity of the lowest-energy CF transition remarkably increases on cooling, indicating a coupling of this CF excitation to the quadrupolar fluctuations above T$_0$. From symmetry analysis, we suggest that the FQ order has B$_{1g}$ symmetry. Moreover, temperature-dependent study of four Raman-active phonon modes shows that the intensities of the A$_{1g}$ and one E$_{g}$ modes increase significantly on cooling, which is explained by a near-resonant coupling between these two phonon modes and CF transitions.

Electron paramagnetic resonance (EPR) spectroscopy is used to address the remarkable persistence of the native Arrhenius dependence of the 2-aminopropanol substrate radical rearrangement reaction in B(12)-dependent ethanolamine ammonia-lyase (EAL) from Salmonella typhimurium from physiological to cryogenic (220 K) temperatures. Two-component TEMPOL spin probe mobility in the presence of 10 mM (0.08% v/v) 2-aminopropanol over 200–265 K demonstrates characteristic concentric aqueous-cosolvent mesodomain and protein-associated domain (PAD, hydration layer) solvent phases around EAL in the frozen solution. The mesodomain formed by the relatively small amount of 2-aminopropanol is highly confined, as shown by an elevated temperature for the order–disorder transition (ODT) in the PAD (230–235 K) and large activation energy for TEMPOL rotation. Addition of 2% v/v dimethylsulfoxide expands the mesodomain, partially relieves PAD confinement, and leads to an ODT at 205–210 K. The ODT is also manifested as a deviation of the temperature-dependence of the EPR amplitude of cob(II)alamin and the substrate radical, bound in the enzyme active site, from Curie law behavior. This is attributed to an increase in sample dielectric permittivity above the ODT at the microwave frequency of 9.5 GHz. The relatively high frequency dielectric response indicates an origin in coupled protein surface group–water fluctuations of the Johari–Goldstein β type that span spatial scales of ∼0.1–10 Å on temporal scales of 10(−10)–10(−7) s. The orthogonal EPR spin probe rotational mobility and solvent dielectric measurements characterize features of EAL protein–solvent dynamical coupling and reveal that excess substrate acts as a fluidizing cryosolvent to enable native enzyme reactivity at cryogenic temperatures.

En el presente trabajo se utilizó el código Wien2k, en el marco de la teoría del funcional de la densidad de Kohn-Sham, aplicando el método de ondas planas aumentadas y linealizadas (full-potential linearized augmented plane wave, FP- LAPW) y adoptando la aproximación de gradiente generalizado (GGA) de Perdew, Burke y Ernzerhof para la energía de intercambio y correlación, así como la aproximación de densidad local (local density approximation, LDA) para el cálculo de la densidad de estados y la estructura de bandas de la perovskita doble Sr2HoNbO6. Para los cálculos se consideró el grupo Fmm (#225), experimentalmente obtenido a partir de mediciones de difracción de rayos X y del método de refinamiento de Rietveld. El parámetro de red experimental fue de 8.018 Å, el cual concuerda en un 99,2 % con las predicciones teóricas efectuadas a partir de la minimización de la energía mediante la ecuación de estado de Murnaghan. A partir de mediciones de susceptibilidad magnética en función de la temperatura y del ajuste con la ley de Curie, se obtuvo el valor del momento magnético efectivo 10,01 μB. Este valor es muy cercano del esperado teóricamente a partir de las reglas de Hund (10,60 μB). La brecha de energía determinada entre las bandas de valencia y de conducción fue de 3,3 eV, lo que revela el carácter aislante de la perovskita compleja Sr2HoNbO6 para la configuración de espín hacia arriba, en tanto que se observó el carácter semiconductor para la polarización de espín hacia abajo, con una brecha de energía de 0,77 eV. Las propiedades termodinámicas se calcularon a partir de la ecuación de estado usando el modelo cuasi-armónico de Debye. Un comportamiento del calor específico, con CV≈CP, se encontró a temperaturas inferiores a T = 500 K, con valores del límite de Dulong-Petit que doblaban los que se han reportado para materiales del tipo de la perovskita. In this work we used the Wien2k code, within the framework of the Kohn-Sham Density Functional Theory (DFT), applying the Full-Potential Linearized Augmented Plane Wave method (FP-LAPW) and adopting the Generalized Gradient approximation (GGA) for the exchange-correlation energy due to Perdew, Burke, and Ernzerhof, as well as the Local Density approximation (LDA) for the calculation of the Density of States and band structure of the Sr2HoNbO6 double perovskite. For calculations, we considered the Fmm (#225) space group, which was experimentally obtained from X-ray diffraction measurements and Rietveld refinement. The experimental lattice parameter was 8.018 Å, which is 99.2% in agreement with the theoretical prediction from the minimization of energy through the Murnaghan state equation. From the measurements of magnetic susceptibility as a function of temperature and the adjustment with the Curie law, we obtained a value for the effective magnetic moment of 10.01 μB, which is close to the theoretical expected from Hund’s Rule (10.60 μB). An energy gap of 3.3 eV between the valence band and the conduction band revealed the insulator character of the Sr2HoNbO6 complex perovskite for the spin up configuration, but a semiconductor feature was observed for the spin down polarization, with an energy gap of 0.77 eV. The thermodynamic properties were calculated from the state equation by using the Debye quasiharmonic model. A specific heat behavior of CV≈CP was found at temperatures below T = 500 K, with Dulong-Petit limit values doubling those reported for perovskite materials.

The ε-Fe2O3 nanoparticles in borate glasses co-doped with low concentrations of Fe2O3 and Gd2O3 were investigated with two experimental techniques – visible magnetic circular dichroism (MCD) and electron spin resonance (ESR). The most prominent features of the MCD spectra are: non-linear dependence of the spectral maxima intensities on the Gd concentration and strong increase with the temperature decrease. The ESR spectra of these glasses exhibit two features with g = 4.3 due to the diluted Fe3+ ions and 2.0 associated both with Fe3+ ions and with nanoparticles. The integrated spectra intensities do not follow the T-1 Curie law suggesting a considerable contribution from the magnetically ordered nanoparticles to ESR. Analysis of the MCD and ESR concentration dependences allow suggestion on the Gd ions incorporation into nanoparticles.

International audience; The new compound K2CoV2O7 has been synthesized by a solid state reaction route. Its crystal structure has been determined using powder X-ray diffraction data (PXRD). The compound K2CoV2O7 crystallizes with the melilite-type structure with the tetragonal unit cell parameters a = 8.4574(1), c = 5.5729(1) Å and the space group View the MathML sourceP4−21m. The structure consists of [CoV2O7]2− layers perpendicular to the c axis separated by K+ layers. The [CoV2O7]2− layers consist of corner-sharing CoO4 tetrahedra and V2O7 pyrovanadate units, the linkage of these tetrahedra forming five-membered rings. The K+ cations occupy distorted square antiprisms of oxygen atoms. The magnetic susceptibility of K2CoV2O7 follows the Curie law χT = C with an effective magnetic moment μeff = 4.71 μB.

Two-temperature electron paramagnetic resonance (EPR) measurements, applied to determine the relative contributions of paramagnetic centers – fulfilling and not-fulfilling the Curie law, were carried out. The measurements were made on the macerals – exinite and vitrinite, separated from clarain of the Polish medium-rank coal (85.6 wt% C). The two-temperature EPR measurements, presented in this work, were performed respectively, at temperatures: T 1 = 293 K and T 2 = 173 K for exinite, and T 1 = 293 K and T 2 = 153 K for vitrinite. The relative contributions X of spins not-fulfilling the Curie law present in the studied macerals were calculated. A comparison of different methods of calculating the relative contributions of paramagnetic centers – fulfilling and not-fulfilling the Curie law, present in exinite and vitrinite studied by EPR was made.

We report experimental and theoretical results of crystal structure, morphology, magnetic and electric features, and electronic structure for the Sr2DyNbO6 ceramic compound. Samples were produced by the solid-state reaction recipe. X-ray diffraction experiments show that the material crystallizes in a monoclinic structure, P21/n space group. SEM images exhibit a granular submicrometric surface. Temperature curves of magnetic susceptibility reveal a paramagnetic response. Curie law fitting permitted to obtain a magnetic moment 10.28 μB. Polarization as a function of electric fields shows a hysteretic feature with 264.28 relative dielectric constant at 300 K. DFT calculations of electronic structure suggest the semiconductor character of this material, energy gap 3.21 eV for the spin-up polarization and 0.26 eV for spin-down. The calculated effective magnetic moment was 10.0 μB, which is strongly in accordance with the measured value. The theoretical cell parameters obtained from the Murnaghan state-equation are 98.5% in agreement with the experimental result. Se reportan resultados experimentales y teóricos de estructura cristalina, morfología, carácter magnético y eléctrico, y estructura electrónica para el material cerámico Sr2DyNbO6. Las muestras fueron producidas mediante reacción sólida. Resultados de difracción de rayos X muestran que el material cristaliza en una estructura monoclínica, grupo espacial P21/n. Imágenes de MEB muestran superficies granulares submicrométricas. La susceptibilidad en función de la temperatura revela una respuesta paramagnética con momento magnético 10.28μB. La histéresis de polarización en función del campo eléctrico a 300K permitió obtener una constante dieléctrica de 264.28. Cálculos de estructura electrónica por DFT sugieren que el material es semiconductor con brecha de energía 3.21 eV para la orientación espín arriba y 0.26 eV para espín abajo. El momento magnético calculado es 10.0μB, muy próximo del valor medido. Los parámetros de red obtenidos mediante la ecuación de Murnaghan están de acuerdo con los resultados experimentales en un 98.5%.

Magnetic properties of copper dimolybdate trihydrate CuMo2O7·3H2O have been studied from room temperature down to 2 K with the use of ac and dc magnetometry. There was no sign of long range order; however, the compound deviates from the classical Curie law for paramagnetic systems. This situation is due to exchange interactions between Cu ions forming dimers, whereas Mo ions do not possess magnetic moments. The estimated value of Jex is −2.74(1) K from fitting the dc susceptibility and −3.01(1) K from the fit of magnetization versus magnetic field. The antiferromagnetic coupling is confirmed by the value of θ=−4.0(3) K from the Curie–Weiss analysis. The dynamic properties measured by ac susceptibility as a function of applied dc field indicate three regions of different magnetic relaxation behaviors.

The magnetic properties of two metal formate systems with formula M[(H2O)(2)(HCOO)(2)], which are isostructural, are described (M = Co, Cu). These compounds contain two different crystallographic metal centers (M2+), in octahedral coordination, which are connected through (HCOO) bridges, leading to the formation of two types of infinite chains: M(1) - HCOO - M(2) and M(1) - HCOO - M(1). The packing of these chains, along with hydrogen bonds, generates a 3-D framework. Cu-sample presents an usual paramagnetic behavior, following Curie law. On the contrary, Co-sample has an order-disorder magnetic transition, further analyzed by means of magnetization and specific heat. These data lead us to conclude an anisotropic environment for Co ions, as expected for an octahedral neighborhood. Critical exponents of these thermodynamic quantities around the thermal transition are in accordance with 3-D model. This is a very important remark, since a previous work had shown that the magnetic phase transition is 2-D.

The structure and magnetic properties of the off-stoichiometric GdNi2Mnx (0 ⩽ x ⩽ 0.6) alloys have been studied. The alloys with 0

This paper introduces the historical development of the symmetries for describing magnetic structures culminating in the derivation of the black and white and colored space groups. Beginning from the Langevin model of the Curie law, it aims to show the challenges that magnetic ordering presented and how different symmetry frameworks were developed to meet them. As well as explaining core ideas, later papers will show how the different schemes are connected. With these goals in mind, the maths related is kept to the minimum required for clarity., 10 figures

SrTiO3 plays a central role in oxide electronics. It is the substrate of choice for functional oxide heterostructures based on perovskite-structure thin-film stacks, and its surface or interface with a polar oxide such as LaAlO3 can become a two-dimensional conductor because of electronic reconstruction or the presence of oxygen defects. Inconsistent reports of magnetic order in SrTiO3 abound in the literature. Here we report a systematic experimental study aimed at establishing how and when SrTiO3 can develop a magnetic moment at room temperature. Polished 100, 110 or 111 crystal slices from four different suppliers are characterized before and after vacuum annealing at 750 {\deg}C, both in single-crystal and powdered form. Impurity content is analysed at the surface and in the bulk. Besides the underlying intrinsic diamagnetism of SrTiO3, magnetic signals are of three types-a Curie law susceptibility due to dilute magnetic impurities at the ppm level, a hysteretic, temperature-dependent ferromagnetic impurity contribution, and a practically-anhysteretic, defect-related temperature-independent component that saturates in about 200 mT. The latter component is intrinsic. It is often the largest, reaching 10 Bohr magnetons per nm2 of surface area or more and dominating the magnetic response in low fields at room temperature. It is associated with defects near the surface, and can be destroyed by treatment with Tiron (C6H4Na2O8S2), an electron donor molecule that forms a strong complex with titanium at the surface. The origin of this unusual high-temperature ferromagnetic-like response is discussed.

A new method is proposed for determining the Curie temperature from magnetocaloric measurements. It is based on the field dependence of the magnetic entropy change close to the Curie temperature. The main advantages over other methods are that the obtained temperature is field independent, and the process is noniterative and does not require a fitting procedure nor prior knowledge of the critical exponents of the transition. The reliability of the method is demonstrated using both simulated and experimental data for pure Ni and an Fe-based amorphous alloy.

We investigate the magnetic properties of ultra-pure type-IIa diamond following irradiation with proton beams of ≈1-2 MeV energy. SQUID magnetometry indicate the formation of Curie type paramagnetism according to the Curie law. Raman and Photoluminescence spectroscopy measurements show that the primary structural features created by proton irradiation are the centers: GR1, ND1, TR12 and 3H. The Stopping and Range of Ions in Matter (SRIM) Monte Carlo simulations together with SQUID observations show a strong correlation between vacancy production, proton fluence and the paramagnetic factor. At an average surface vacancy spacing of ≈1-1.6 nm and bulk (peak) vacancy spacing of ≈0.3-0.5 nm Curie paramagnetism is induced by formation of ND1 centres with an effective magnetic moment μ∼(0.1-0.2)μ. No evidence of long range magnetic ordering is observed in the temperature range 4.2-300 K., This work was supported by the University of the Witwatersrand, Johannesburg and the Center of Excellence in Strong Materials.

We study the response of classical impurities in quantum Ising chains. The Z 2 degeneracy they entail renders the existence of two decoupled Majorana modes at zero energy, an exact property of a finite system at arbitrary values of its bulk parameters. We trace the evolution of these modes across the transition from the disordered phase to the ordered one and analyze the concomitant qualitative changes of local magnetic properties of an isolated impurity. In the disordered phase, the two ground states differ only close to the impurity, and they are related by the action of an explicitly constructed quasi-local operator. In this phase the local transverse spin susceptibility follows a Curie law. The critical response of a boundary impurity is logarithmically divergent and maps to the two-channel Kondo problem, while it saturates for critical bulk impurities, as well as in the ordered phase. The results for the Ising chain translate to the related problem of a resonant level coupled to a 1d p-wave superconductor or a Peierls chain, whereby the magnetic order is mapped to topological order. We find that the topological phase always exhibits a continuous impurity response to local fields as a result of the level repulsion of local levels from the boundary Majorana zero mode. In contrast, the disordered phase generically features a discontinuous magnetization or charging response. This difference constitutes a general thermodynamic fingerprint of topological order in phases with a bulk gap.

We present a detailed magnetic critical behavior study of Fe 2CrAl Heusler alloy, for the first time, with rigorous analysis of high precision magnetization data obtained over the critical temperature region. Our studies confirm that B2 type site-disordered in Fe 2CrAl alloy exhibits long-range ferromagnetic order below a well defined Curie temperature (T=208 K). Though the nature of this transition is found to be of second order, the estimated critical exponents ?=0.42, ?=1.356 and ?=4.25, are in between the theoretically predicted values for three-dimensional Heisenberg and mean-field interaction models. However, it is noteworthy that the scaling relations are obeyed indicating renormalization of interactions around the Curie temperature (T C), where magnetization data collapse into two separate branches, above and below T C. This conclusively shows that calculated critical exponents as well as critical temperature are unambiguous and intrinsic to the system. However, magnetization vs temperature data shows another magnetic transition (at T=313 K) above the Curie temperature. It is shown that the short range magnetic correlation exist even beyond T C with cluster moment ?10 2 ? B. This is attributed to a site disorder which results in formation of Cr clusters with short range ferromagnetic order. � 2011 Elsevier B.V. All rights reserved.

The experimental charge-density distribution of the dinuclear cobalt(II) complex [Co2(sym-hmp)2](BPh4)2·2H2O·2C3H6O was determined at 100 K. When decreasing the temperature, the magnetic susceptibility of this complex deviates from Curie law because of anti-ferromagnetic exchange interactions, but the susceptibility increases sharply at low temperature (< 20 K). To explain this magnetic behaviour a tilt angle between the Co-atom environments was previously theoretically predicted. The structure and experimental charge density determined in this study show a tilt angle. The calculated value, based on the 100 K experimental d-orbital model, is in agreement with the theoretical one.

La 0.7 Ca 0.3 MnO 3 (LCMO) nanoparticles with average diameter of 16–73 nm were prepared by reactive milling and thermal processing methods. Interaction and size effects on the magnetic properties of the LCMO nanoparticle samples were investigated. Phenomena related to the interparticle interaction, such as an un-overlapping of the M ( H ext , T )/ M S vs. H ext / T scaling plots and a Curie–Weiss rather than Curie law behavior of the dc susceptibility at high temperatures were analyzed. The magnetization curves of interacting nanoparticles were well described by using the mean-field approximation. The dependence of the blocking temperature T B on the strength of the interactions, magnetic anisotropy, as well as the thermal dependence of magnetization deviates from the expected Bloch law was also estimated.

This study investigated the magnetism and anomalous transport properties of the melt-spun ribbon Fe2MnAl alloy. It is found that the alloy exhibits ferromagnetic order with the Curie temperature of ∼150 K, followed by another magnetic transition at TR ∼ 51 K. It is suggested there is antiferromagnetism pinning effect on the ferromagnetic matrix at the temperature below TR. A steep rise of the resistance below TR has been observed, which can be understood in terms of antiferromagnetic scattering. An appearance of the resistance maximum near the Curie temperature and the negative temperature dependence of the resistance above Curie temperature are associated with the magnetic phase transition from ferromagnetism to paramagnetism. A negative magnetoresistance at low temperature arising from inhomogeneous magnetic scattering is reported.

Paramagnetic susceptibility of alloys Ni3AlxMn1 − x in the field of the transition between the ferromagnets described in the band theory (Ni3Al) and in the spin-localized (Ni3Mn) model of magnetic moments has been investigated. The concentration dependences of the paramagnetic Curie temperature, effective magnetic moment, and temperature-independent component of magnetic susceptibility have been determined.

Fe3GeTe2 was synthesized by solid state reaction and chemical transport methods. Our magnetic measurements show that it is a ferromagnet with the Curie temperature of 226 K. The Rhodes-Wohlfarth ratio Pc/Ps∼6.6 indicates that it is an itinerant ferromagnet. On the other hand, we found the single crystal sample with the Curie temperature of 146 K shows the large anisotropy in the temperature dependence of magnetic susceptibilities and the magnetization curves when the external magnetic fields are applied along the c axis and within the ab plane.

Results of investigation of the temperature dependence of magnetization of Ni2.08Mn0.96Ga0.96 alloy in the magnetic fields of various intensities are reported. An abrupt change in magnetization at transformation of low temperature phase to the high temperature one is observed. Magnetization increases during the phase transition in the magnetic field having intensity below 500 kA/m and decreases at higher intensities. The explanation is based on zigzag configuration of domains in twinned structure. In the Curie temperature region the ferromagnetic ? paramagnetic phase transition occurs sharply at low field strength, while at higher field strength the transition is smooth. It is concluded that the increase in flatness of the curve σ = f (T) and the increase of ferromagnetic state destruction temperature with increase of the intensity of the magnetic field is indicative of the main role of Mn in magnetization of the alloy.

Possible dust alignment in dense regions due to paramagnetic anisotropy ΔχPARA is discussed based on the results of a laboratory experiment on ortho-pyroxene grains containing a small amount of Fe2+ ions (1.8 mol%). Ortho-pyroxene has been detected in circum-stellar regions by infrared emission spectroscopy. Our experiment was performed at room temperature using He gas as the dispersing medium. Although the grains do not contain strong magnetic moments, alignment was achieved at low field strength ( 1 mol%; this increasing ΔχPARA is the cause of the above-mentioned alignment obtained at the low field strength. Based on our observations, we infer the field intensity needed to obtain partial dust alignment of sufficient size to explain the observed polarization in astrophysical environments. Due to temperature dependences caused by a Curie Law and a rotational Brownian motion, the field intensity required to cause the alignment is expected to decrease considerably at low-temperature conditions assumed for a proto-planetary disk. The results of our experiment performed at room temperature provide a technical basis to reproduce grain alignment under such temperature conditions.

Mn0.5Zn0.5Fe2O4 ferrite nanoparticles with tunable Curie temperature and saturation magnetization are synthesized using hydrothermal co-precipitation method. Particle size is controlled in the range of 54 to 135 A by pH and incubation time of the reaction. All the particles exhibit super-paramagnetic behaviour at room temperature. Langevin’s theory incorporating the interparticle interaction was used to fit the virgin curve of particle magnetization. The low-temperature magnetization follows Bloch spin wave theory. Curie temperature derived from magnetic thermogravimetric analysis shows that Curie temperature increases with increasing particle size. Using these particles magnetic fluid is synthesized and magnetic characterization is reported. The monolayer coating of surfactant on particle surface is confirmed using thermogravimetric measurement. The same technique can be extended to study the magnetic phase transition. The Curie temperature derived using this measurement complies with the low-temperature magnetic measurement. The room-temperature and high-temperature magnetization measurements are also studied for magnetic fluid systems. The magnetic parameters derived for fluid are in good agreement with those obtained for the particle system.

We have investigated the effective synthesis of Pyrococcus furious virus like particle (PfV) and the integration of Ni2+ ions with PfV. Application of Isopropyl-β-D-1-thiogalactopyranoside (IPTG) during incubation of P. furious causes the marked improvement of yield of P. furious. Using the synthesized P. furious, the spherical structure of PfV is successfully obtained. Concerning magnetism, the native PfV shows the diamagnetic properties. On the contrary, after the integration with Ni2+ ions, the paramagnetic behavior appears, namely the non-saturated M-H curve with zero remanence and coercivity, and Curie law like M-T curve. The obvious changes in the magnetic properties indicate that the Ni2+ ions are successfully integrated with PfVs.

Concentrational dependences of the lattice parameters, spontaneous magnetic moment, and magnetic ordering temperature of nonstoichiometric Mn1.9 − x Co x Ge (0.8 < x < 1.65) compounds with a hexagonal crystal structure of the Ni2In type have been studied. As the Co content (x) increases from 1.1 to 1.2, the Curie temperature and magnetic moment were found to increase abruptly. The magnetization curves measured for oriented single crystals indicate the presence of a concentrational spin-reorientation transition in this system. The experimental data obtained are discussed taking into account the results of energy-band electronic-structure calculations.

We present the renormalization group (RG) flow diagram of a spin-half antiferromagnetic chain with magnetic impurity and one altered link. In this two parameters (competing interactions) model, one can find the complex phase diagram with many interesting fixed points. There is no evidence of intermediate stable fixed point in weak coupling phase. It may arise at the strong coupling phase. Depending on the strength of couplings the phases correspond either to a decoupled spin with Curie law behavior or a logarithmically diverging impurity susceptibility as in the two channel Kondo problem., Comment: 4 figures

The influence of applied magnetic field on the Curie temperature, Gibbs free energy and α (bcc)/γ (fcc) phase transition in Fe-based alloys was studied. The calculated results indicate that with the increasing of external magnetic field strength, the magnetization and Curie temperature increase, however, the magnetic free energy of the α phase decreases, which results in that the α phase becomes more stable in pure Fe and Fe–X systems.

The magnetic order of La0.7Sr0.3MnO3 nanoparticles (NPs) fabricated in a SPEX D8000 mill was systematically studied. The La0.7Sr0.3MnO3 nanocrystals grow from the milled constituent oxides during the milling processes. The magnetization data obtained by using a SQUID magnetometer show the NPs as a superparamagnet in terms of anhysteretic curves near room temperature. Unoverlaping of the scaled M(H-ext, T)/M-s vs. H-ext, T plots and the dc susceptibility obeying the Curie-Weiss behavior rather than the Curie law at high temperatures provide evidence that the NPs are interacting superparamagnetic ensembles. A mean-field correction to the Langevin function L ([H-ext + alpha M]/k(B)T) worked well for the magnetic ordering of the NPs. By means of the Langevin fitting, the diameter of the NP was estimated to be lower than 15 nm, depending oil the milling time. The saturation magnetization of NPs varied from 48.5 em/g to 19 emu/g, with the higher value corresponding to a larger particle size. A core-shell structure of the NP was adopted, with the NP having the core-shell magnetically-effective mass density. This is applicable to the variation of the saturation magnetization with particle size., 10 pages, 5 figures

SUMMARY Progressive thermal demagnetization of natural samples to above 300 °C may cause significant alterations of magnetic mineral phases. Such changes are commonly monitored by magnetic susceptibility (MS) determinations at every demagnetization step. In an attempt to characterize in more detail alteration products created during thermal demagnetization of some Chinese loess/palaeosols (L1/S1), MS was measured at both room temperature (MS293K) and at liquid Nitrogen temperature (MS77K) between each demagnetization step. We have used the difference between MS77K and MS293K (temperature dependent susceptibility, kTD= MS293K− MS77K) to monitor production of superparamagnetic (SP) magnetic grains. kTD is a function of; (1) paramagnetic susceptibility according to the Curie law (k∼ 1/T) that predicts a theoretical 3.83 times increase in MS at 77K. (2) SP grains at 293 K that passes into the single-domain (SD) state on cooling to 77 K causing a dramatic reduction in MS77K. (3) magnetite grains exhibiting magnetic changes when passing through the Verwey transition at 120 K will also reduce MS77K. We observe a linear relationship between frequency-dependent MS (kFD) and temperature dependent susceptibility (kTD) indicating that SP-SD blocking of magnetite may be the dominant factor of MS change during cooling. High values of kTD indicates high SP concentrations, and an increase of kTD with increasing demagnetization temperature is mainly attributed to the production of SP grains since the amount of magnetite exhibiting changes in MS at the Verwey-transition is unlikely to increase during heating of loess/palaeosol to 600 °C in air. This interpretation is also based on results from Zero Field Heating IRM77K(1T), Zero Field Cooling of IRM77K(1T) and short-time (100 s) viscous decay of IRM500mT. Our findings suggest that SP-grains are produced continuously in both loess and palaeosol with thermal treatment, and that SP-production in palaeosol apparently commence at the ‘surprisingly’ low temperature of around 200 °C.

Multi-shell fullerene-like nanoparticles of glassy carbon were synthesized by a low-temperature pyrolysis of sucrose. These samples were studied by magnetic resonance spectroscopy. 13 C NMR spectrum of glassy carbon shows a complicated line the most intensive component of which originated from sp 2 carbons. Measured values of nuclear spin-lattice relaxation times are discussed with a model of system containing intrinsic paramagnetic centers, as it is supported by EPR. EPR reveals extrinsic and intrinsic magnetism in the samples. The former is probably due to para- and ferromagnetic impurities entrapped during the synthesis. The latter is attributed to the carbon system (e.g., dangling bonds). The carbon-originated EPR signal has Lorentzian lineshape and g-factor of 2.0030±0.0001. Its line width as well as electron spin-lattice relaxation time was found to be extremely sensitive to partial oxygen pressure and humidity. The intrinsic magnetism obeys the Curie law at 130–400 K. The total amount of carbon-originated paramagnetic defects exceeds 2×10 19 spin/g. They are suggested to exist in all layers of imperfect fullerene

We explored the magnetic behavior of a common two-phase nanomagnetic system by Monte Carlo computer simulation of a modified Heisenberg model on a 3D complex lattice with single- and cluster-spins. The effect of exchange coupling between two component magnetic phases was studied on the enhancement in Curie temperature (ECT) of the intergranular amorphous region of a common duplex-phase alloy system, with numerous nano-crystallites embedded in amorphous matrix. The dependences of ECT were investigated systematically upon the nanocrystallite size, the volume fraction and the interspace among crystallites. It was observed that large crystallized volume fraction, small grain size and thin inter-phase thickness lead to the obvious ECT of intergranular amorphous region whereas the Curie temperature of nanocrystallites declines slightly. There is a simulative empirical formula which relates the reduced ECT to microstructure parameter and conforms to its experimental counterpart within an order of magnitude. In addition, we also simulated the demagnetization of a hard-soft nanocomposite system. We estimated the influence of exchange coupling between two component phases on the cooperativity of two-phase magnetizations and the coherent reversal of magnetizations as well as coercivity and energy product., 18 pages, 14 figures

The method of calculation of average and local magnetic characteristics of transition metals at finite temperatures developed by the author and Grebennikov in previous works and based on the employment of a real band structure and spin fluctuations has been applied to a disordered invar alloy Fe0.65Ni0.35. The magnetization, Curie temperature, local magnetic moment, and uniform and local susceptibilities have been calculated for both ferromagnetic and paramagnetic states. The results are in agreement with experimental data in a wide temperature range. It has been shown that the effect of disorder in the filling of sites with Fe and Ni atoms on the magnetic properties of the Fe-Ni invar is insignificant.

The lattice parameters, magnetic phase transition, Curie temperature and magnetocaloric properties for the (Gd 1− x Tb x ) 5 Si 1.72 Ge 2.28 compounds with x = 0, 0.02, 0.04, 0.06, 0.08 and 0.10 have been investigated by X-ray powder diffraction and magnetization measurement. A small amount of the Tb substitution in Gd 5 Si 1.72 Ge 2.28 compound can remain its first order magnetic-crystallographic transition and enhance its magnetic entropy change significantly, although have the negative influence on the compound Curie temperature T c . The influence of the applied magnetic field on transition temperature also was discussed. The maximum magnetic entropy changes in the low magnetic field change of 2.0 T for the (Gd 0.94 Tb 0.06 ) 5 Si 1.72 Ge 2.28 sample reaches 25.13 J kg −1 K −1 , much lager than that of pure Gd 5 Si 1.72 Ge 2.28 compound (13.73 J kg −1 K −1 at 247 K) in this work.