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We report a study on the competition between soft ferromagnetism (FM) and enhanced Pauli paramagnetism (PM) in Ce(Fe 1− x Ni x ) 2 ( x =0.0, 0.5, 0.8) compounds under doping. We provide convincing experimental evidence for the occurrence of a ferromagnetic (FM) phase and a paramagnetic (PM) phase at different concentrations. The quality of the samples was established by X-ray diffraction and X-ray photoelectron spectroscopy. Quantification of f - d hybridization was made from high-resolution X-ray photoelectron spectroscopy. A proportionality was found between ‘ x ' dependencies of fall of f - d hybridization strength and magnetic order. A prediction that a quantum critical point may exist at a nickel concentration x close to 0.69 can be made from the extrapolation of x dependent Curie temperature (T c ) plot. [ABSTRACT FROM AUTHOR]

The site preference of Cu does not follow the usual valence electrons rule in Ni 2 -based Heusler alloys Ni 2 CuSn and Ni 2 CuSb. The phase stabilities of three possible structures, namely L2 1 , XA and L2 1 B, have been compared. Among them L2 1 has the lowest total energy and is preferable, while L2 1 B has the highest energy. The energy differences between L2 1 and the other two structures are quite large. The high phase stability of the L2 1 structure is mainly related to the strong hybridization between the d states of Cu, Ni and the low N(E F ). Single phase, highly-ordered Ni 2 CuSn and Ni 2 CuSb samples have been prepared experimentally. The XRD patterns suggest that Ni 2 CuSn and Ni 2 CuSb do crystallize in the L2 1 structure, agreeing with the theoretical prediction. Finally, both of them have a paramagnetic ground state. [ABSTRACT FROM AUTHOR]

The acoustic spin pumping (ASP) stands for the generation of a spin voltage from sound waves in a ferromagnet/paramagnet junction. In this letter, we propose and demonstrate a method for pure detection of the ASP, which enables the separation of sound-wave-driven spin currents from the spin Seebeck effect due to the heating of a sample caused by a sound-wave injection. Our demonstration using a Pt/YIG/PZT sample shows that the ASP signal in this structure measured by a conventional method is considerably offset by the heating signal and that the pure ASP signal is one order of magnitude greater than that reported in the previous study. [ABSTRACT FROM AUTHOR]

A consistently diamagnetic persistent current (PC) of period halving ( Φ 0 /2-current) observed in mesoscopic rings is in apparent contradiction with the theoretical prediction of barely exclusively paramagnetism . By developing a super-cell method, we analytically and numerically study the magnetic response mechanics of non-interacting mesoscopic rings in both the absence and presence of random disorder. A maximal paramagnetic and/or diamagnetic PC is obtained in primary Φ 0 - and/or Φ 0 /2-period, exhibiting a remarkable quantum size effect. It is shown that for lower free energy, an electron circling the ring accumulates an additional phase on each inter-channel transition induced by magnetic flux, leading to the period halving and the paramagnetic–diamagnetic transition. Our results can well mediate the disputes between the experiments and theory. [ABSTRACT FROM AUTHOR]

The characteristics of the local environment around the paramagnetic centers formed by the Nd3+ ions doped into three tungstate crystals (CaWO4, SrWO4 and PbWO4) are investigated by using superposition model analysis. The inter-relation between the electronic and molecular structures of Nd3+ ion in a tetragonal (S 4 symmetry) ligand field has been established by a complete diagonalization (of energy matrix) method. The local lattice distortions in the vicinity of the impurity ion Nd3+ have been derived and the local distortion angles Δθ=−1.69°, −1.13°, and −1.48° are obtained for Nd3+ in CaWO4, SrWO4 and PbWO4, respectively. The calculated EPR parameters are in good agreement with the experimental values. On the basis of this, the links between EPR g-factors and the local structure as well as crystal field parameters are studied. [ABSTRACT FROM AUTHOR]

Abstract: Quantum Confined Stark Effect in hybrid of CdTe quantum dot with superparamagnetic iron oxide nanoparticles in both nonporous and mesoporous silica matrix has been realized. The observed QCSE is due to the local electric field induced by charge dispersion at SiO2/polar solvent interface. Enhanced Stark shift of 89.5meV is observed in case of mesoporous hybrid structure and the corresponding local electric field has been evaluated as 4.38×104 V/cm. The enhancement is assumed to be caused by greater density of charge in the mesoporous hybrid. The conjugation of superparamagnetic nanoparticles in this tailored hybrid microstructure has not imparted any alteration to the Stark shift, but has added multifunctional attribute. The present study on the local electric field induced enhanced QCSE with wavelength modulation towards red end paves the way of developing magneto-fluorescent hybrid systems for biomedical imaging application. [Copyright &y& Elsevier]

Abstract: We used Banerjee's criteria, modified Arrott plots, and the scaling hypothesis to analyze magnetic-field dependences of magnetization near the ferromagnetic–paramagnetic (FM–PM) phase-transition temperature (T C) of perovskite-type manganites La0.7Ca0.3Mn1−x Ni x O3 (x=0.09, 0.12 and 0.15). In the FM region, experimental results for the critical exponent β (=0.171 and 0.262 for x=0.09 and 0.12, respectively) reveal two first samples exhibiting tricriticality associated with the crossover of first- and second-order phase transitions. Increasing Ni-doping content leads to the shift of the β value (=0.320 for x=0.15) towards that expected for the 3D Ising model (β=0.325). This is due to the fact that the substitution of Ni ions into the Mn site changes structural parameters and dilutes the FM phase, which act as fluctuations and influence the FM-interaction strength of double-exchange Mn3+–Mn4+ pairs, and the phase-transition type. For the critical exponent γ (=0.976–0.990), the stability in its value demonstrates the PM behavior above T C of the samples. Particularly, around T C of La0.7Ca0.3Mn1−x Ni x O3 compounds, magnetic-field dependences of the maximum magnetic-entropy change can be described by a power law of |ΔS max|∝H n , where values n=0.55–0.77 are quite far from those (n=0.33–0.48) calculated from the theoretical relation n=1+(β−1)/(β+γ). This difference is related to the use of the mean-field theory for the samples exhibiting the magnetic inhomogeneity. [Copyright &y& Elsevier]

Abstract: The electrical conductivity and magnetoresistance property of the bulk sample has been reported, between the magnetic fields 0 and 5T and in temperature range 10–300K. Ferromagnetic metallic resistivity is observed well below the metal insulator (MI) transition temperature . Above the metal insulator transition the electrical conductivity is dominated by the Shklovskii–Efros variable-range hopping mechanism (SE-VRH), giving . Based on the scenario that the doped manganites consists of phase separated ferromagnetic metallic and paramagnetic insulating regions, a good fit of ρ(T) is well described by combining the contribution of and by the single expression between the temperature region 33 and 300K. Above the ρ(T) also gives satisfactory fit and is well described using the small polaronic model (SPC) and Mott''s VRH. At , a critical behavior of ρ(T) obeys the scaling law . Investigations of magnetoresistance (MR) using magnetic field up to 5T shows two kinds of contribution: one is intrinsic MR and the other is extrinsic MR, which has been accounted fairly well by a phenomenological model based on spin polarized tunneling. [Copyright &y& Elsevier]

Abstract: We have investigated, using effective mass approach (EMA), magnetic properties of a one-dimensional electron gas in graphene armchair ribbons when the electrons occupy only the lowest conduction subband. We find that magnetic properties of the one-dimensional electron gas may depend sensitively on the width of the ribbon. For ribbon widths , a critical point separates ferromagnetic and paramagnetic states while for paramagnetic state is stable (M is an integer and a 0 is the length of the unit cell). These width-dependent properties are a consequence of eigenstates that have a subtle width-dependent mixture of and states, and can be understood by examining the wavefunction overlap that appears in the expression for the many-body exchange self-energy. Ferromagnetic and paramagnetic states may be used for spintronic purposes. [Copyright &y& Elsevier]

Abstract: We have studied the magnetic properties of three phenalenyl based organic neutral radicals. The first one is a Heisenberg chain antiferromagnet with one unpaired spin per molecule; second one is a diamagnetic, exhibiting a diamagnetic to paramagnetic phase transition at high temperature; the third one comprises of free neutral radicals and shows paramagnetic behaviour. Temperature dependent magnetic susceptibility measurements and isothermal magnetization measurements (as a function of magnetic field) were performed on all the three systems. In the case of the antiferromagnetic system, temperature dependent susceptibility and magnetization isotherms were fitted to the Bonner Fisher model. In the case of second system the diamagnetic to paramagnetic phase transition is investigated by performing isothermal magnetization measurements in the two different phases. The diamagnetic to paramagnetic phase transition seems to be of first order in nature. [Copyright &y& Elsevier]

Abstract: The current–voltage characteristics of several manganite systems like , and show non-Ohmic behaviour at different temperatures. The onset voltage at which conductance starts deviating from its zero-bias value scales as with x T being the onset exponent. A detailed scaling analysis with these manganite systems reveal that the onset exponents x T are different in the paramagnetic insulating and ferromagnetic metallic phases. Besides, the magnitudes of x T are different in different manganite systems. Non-Ohmic conduction and the onset exponent are described with the help of inelastic multi-step tunneling model and scaling concepts. [Copyright &y& Elsevier]

Abstract: Magnetic properties and magnetocaloric effects (MCEs) of the intermetallic Ho3Al2 compound are investigated by magnetization and heat capacity measurements. Two successive magnetic transitions, a spin-reorientation (SR) transition at T SR =31K followed by a ferromagnetic (FM) to paramagnetic (PM) transition at T C =40K, are observed. Both magnetic transitions contribute to the MCE and result in a large magnetic entropy change (ΔS M ) in a wide temperature range. The maximum values of −ΔS M and adiabatic temperature change (ΔT ad ) reach 18.7J/kgK and 4.8K for the field changes of 0–5T, respectively. In particular, a giant value of refrigerant capacity (RC) is estimated to be 704J/kg for a field change of 5T, which is much higher than those of many potential refrigerant materials with similar transition temperatures. [Copyright &y& Elsevier]

Abstract: Magnetization of NiO nanoparticles, at different temperatures, is measured and analyzed taking into account a distribution in particle magnetic moment. We find that disregarding this distribution in the analysis is the reason for the many anomalous observations reported on this system in the literature. [Copyright &y& Elsevier]

Abstract: We report detailed studies of the non-equilibrium magnetic behavior of antiferromagnetic Co3O4 nanoparticles. The temperature and field dependence of magnetization, wait time dependence of magnetic relaxation (aging), memory effects, and temperature dependence of specific heat have been investigated to understand the magnetic behavior of these particles. We find that the system shows some features that are characteristic of nanoparticle magnetism such as bifurcation of field-cooled (FC) and zero-field-cooled (ZFC) susceptibilities and a slow relaxation of magnetization. However, strangely, the temperature at which the ZFC magnetization peaks coincides with the bifurcation temperature and does not shift on application of magnetic fields up to 1 kOe, unlike most other nanoparticle systems. Aging effects in these particles are negligible in both FC and ZFC protocols, and memory effects are present only in the FC protocol. We show that Co3O4 nanoparticles constitute a unique antiferromagnetic system which enters into a blocked state above the average Néel temperature. [Copyright &y& Elsevier]

Abstract: The origin of the singular diamagnetic susceptibility at the Dirac point is probed through the study of effects of band-gap opening and spatially varying magnetic field. In the presence of a band gap, the susceptibility is nonzero only inside the band gap and exhibits a discrete jump at the band edges down to zero in the conduction and valence bands. The jump height is understood in terms of the pseudo-spin paramagnetism arising from valley degree of freedom. In spatially varying magnetic field with wave vector , the susceptibility becomes nonzero only in a finite energy region containing the Dirac point, determined by . This behavior is understood in terms of electronic states numerically calculated in periodic magnetic field. [Copyright &y& Elsevier]

Abstract: Critical behavior in La0.7Pb0.05Na0.25MnO3 has been investigated by dc magnetization measurements. Magnetic data indicate that the compound exhibits a continuous (second-order) paramagnetic (PM) to ferromagnetic (FM) phase transition. Estimates of critical exponents yield , and (consistent with both the predictions for the three-dimensional-Heisenberg model and with those reported for materials when the FM transition is ascribed to the double exchange (DE) mechanism as a major origin) with . The critical exponent is slightly inferior than predicted from the 3D Heisenberg model. Such a difference may be due, within the context of the quenched disorder, to the presence of some alterations of short-range magnetic order of FM clusters in the PM phase. The temperature variation in the effective exponent () is similar to those for disordered ferromagnets. [ABSTRACT FROM AUTHOR]

Abstract: Room temperature ferromagnetic and paramagnetic Zn0.98Mn0.02O samples have been synthesized by the solid state reaction method and by selecting the final annealing temperature. Employing positron annihilation techniques, defects for both samples have been characterized. The results indicate that the presence of cation vacancy type defects is relatively less in the ferromagnetic Zn0.98Mn0.02O sample than in the paramagnetic Zn0.98Mn0.02O sample. [ABSTRACT FROM AUTHOR]

Abstract: The reflection and absorption spectra and the resistivity data for La0.93Sr0.07MnO3, La0.9Sr0.1MnO3, La0.85Sr0.15MnO3, La0.92Ca0.08MnO3 and La0.85Ba0.15MnO3 single crystals have been collected and analyzed by using small lattice polaron theory. The activation energies of the polaron hop are determined. The lattice polarons are found to be dominated in the electronic transport and optical properties in the paramagnetic state in La0.93Sr0.07MnO3, La0.92Ca0.08MnO3 and La0.85Ba0.15MnO3 crystals. It is shown that lattice polaron involves more than one Mn site. [Copyright &y& Elsevier]

Abstract: We report the structural and magnetic properties of Ni1−x Mn x O ( to 0.05) prepared by chemical method. Within the XRD resolution, no impurity phases could be detected up to 5 at.% Mn doping in NiO. The fcc structure and the lattice parameter of host NiO matrix is not altered on Mn doping. The average crystallite size was found to remain almost constant (28 nm) up to 3 at.% Mn doping, beyond which it decreases to 21 nm for 5 at.% Mn doping in NiO. The magnetic properties on the other hand showed a drastic change with Mn doping. While 0 and 1 at.% Mn doped NiO showed antiferromagnetic behaviour down to 10 K, 3 and 5 at.% Mn doped NiO were superparamagnetic at 300 K with a blocking temperature of 186 and 171 K respectively. Clear hysteresis loops were thus observed for these samples at 10 K. The distribution of blocking temperature of the Mn doped NiO particles matches well with the distribution of particle size as obtained from TEM. The observed antiferro to superparamagnetic transition on Mn doping in NiO is understood on the basis of Mn occupying Ni site and breaking the translational symmetry of the parent antiferromagnetic correlation. [Copyright &y& Elsevier]

Abstract: The concentration of the Mn(NO3)2 solution has significant influence on the morphologies and the phases of the MnO2 products. A large number of - MnO2 nanowires were prepared via a simple pyrolysis under lower reaction concentration. The nanowires have lengths up to tens of micrometers and diameters in the range of 20–100 nm. The - MnO2 nanobundles and nanoflowers were prepared by increasing the concentration of Mn(NO3)2 solution. The superparamagnetism of - MnO2 nanowires and paramagnetism of - MnO2 nanoflowers indicate their potential applications in magnetic materials. [Copyright &y& Elsevier]

Abstract: -band electron spin resonance (ESR) technique was employed to study films of regioregular poly(3-hexylthiophene) (P3HT) and P3HT/PCBM ([6,6]-phenyl- C61-butyric acid methyl ester) blends to estimate their structural macroscopic anisotropy. As for nematic liquids (or liquid crystals) our consideration was based on the approach that the free energy of self-organised polymer molecules of P3HT is a function of molecular orientation and therefore chains in polymer films exhibit some degree of orientational order. The lamellar molecular orientation of the films was confirmed by angular-dependent ESR spectroscopy of polarons, which were considered as a localised paramagnetic centre with an unpaired carbon -electron of the thiophene ring. The additional ESR signal initiated by the UV/visible CW Xe-lamp illumination of the films at air atmosphere was attributed to the negative polaron (trapped photo-electron) on the polymer chain, as well as to the radical due to chain degradation. [Copyright &y& Elsevier]

Abstract: The effect of calcium doping upon the magnetic and transport properties of the smaller size lanthanide cobaltites of the type Ln1−x Ca x BaCo2O5.50+δ (Ln=Dy and Ho) has been investigated for . The substitution of Ln by calcium induces a large deterioration of the long-range magnetic ordering in the system finally leading to a paramagnetic state. Such instability in the magnetic ordering could be related to strong bending of the Co–O–Co bond, the local lattice distortion and the random vacancies in oxygen sublattice. The present results suggest that not only the cobalt valence but also the size of the lanthanide and the local lattice distortion play a crucial role in determining the physical properties of this layered cobaltite. [Copyright &y& Elsevier]

Abstract: Nickel ferrite nanoparticles have been prepared through a gentle chemistry route, starting from iron nitrate, nickel nitrate and stearic acid. The nickel ferrite crystalline phase, the particle size and shape, and the homogeneity of the resulting nanoparticles were studied by X-ray diffraction and transmission electron microscopy. Fourier transform infrared techniques were used to study the composition characteristics of the as-prepared sample. Magnetization studies at room temperature showed superparamagnetic behavior for the nanoparticles. Magneto-optic rotation studies at different wavelengths of He–Ne lasers reveal non-linear behavior. [Copyright &y& Elsevier]

Abstract: We report enhancement of magnetization below the antiferromagnetic ordering temperature in nanoparticles of two antiferromagnets, viz CoRh2O4 and Cr2O3. The enhancement of magnetization below is systematic, being larger for sample with smaller particle size. Scaling analysis showed that such enhancement of magnetization in CoRh2O4 nanoparticles is due to the superparamagnetic type contribution of surface (shell) spins. The present work shows that similar analysis can also be applied in Cr2O3 nanoparticles. [Copyright &y& Elsevier]

Abstract: Fe-based cadmium sulfide alloy thin films have been grown on -plane sapphire substrates by a low-pressure metalorganic chemical vapor deposition technique at different growth temperatures. From X-ray diffraction and absorption spectra of the samples, the evolutions with growth temperature show an inflexion at the growth temperature of 300 ∘C. This was attributed to the phase transformation from zinc-blende to wurtzite. With increasing growth temperature from 270 ∘C to 360 ∘C, Fe concentration in the films increases monotonously. The electronic states of Cd1−x Fe x S were investigated by X-ray photoelectron spectroscopy. Magnetic measurement shows Van Vleck paramagnetism of the Cd1−x Fe x S thin film in the temperature region below 7 K. [Copyright &y& Elsevier]

Abstract: Photoinduced effects in a single crystal of bilayered manganites, La2-2xSr1+2xMn2O7 (x=0.38), were investigated in a wide range of temperatures by pump-probe measurement at a photon energy of 1.6eV. In a ferromagnetic metallic state, significant enhancement of positive rise in differential reflectivity with a slow relaxing time of 100ps was observed just below TC=127K, indicating that the reflectivity change with the slow relaxation time constant is induced by laser heating. We have also observed an unconventional fast relaxing component that has a time constant of the order of 10ps. This fast relaxing component, whose absolute value has an asymmetric peak at TC, is presumably due to short-range correlation of Jahn–Teller distortion. [Copyright &y& Elsevier]

The crystal structure and magnetic properties of CeMn2-xFexGe2 (0≤x≤1.0) were studied by X-ray powder diffraction and DC magnetization measurements. All the compounds crystallize in ThCr2Si2-type structure. Substitution of Fe for Mn led to a decrease in the unit cell parameters and the unit-cell volume, whereas c/a exhibits parabolic variations. For the samples with x=0.625 and 0.65, the SmMn2Ge2-like magnetic behavior was observed. The results of earlier neutron and Mössbauer studies in CeMn2Ge2 were also used for interpreting the magnetization data and to give an account of the competing effects between various magnetic structures in the Mn sublattice. The results are summarized in a preliminary magnetic phase diagram. [Copyright &y& Elsevier]

We report on the structural, frequency dependent ac susceptibility, dc magnetization and magnetoresistance (MR) measurements on polycrystalline samples of La0.9Ca0.1Mn1-yCryO3 (y=0, 0.1 and 0.2) prepared by sol–gel technique. For y=0, a paramagnetic to ferromagnetic transition is observed at Tc=136K. Both for y=0.1 and 0.2, Tc increases from 136 to 180K. For y=0, the imaginary part of the ac susceptibility shows a broad transition at Tf

We report the optical and magnetic properties of laser-deposited Zn1-xCoxO (x=0.06–0.3) thin films with no intentional electrical carrier doping. The analysis of the high-temperature magnetization data provides an unambiguous evidence that antiferromagnetic superexchange interaction is the dominant mechanism of the exchange coupling between Co ions in Zn1-xCoxO alloy, yielding the value of the effective exchange integral J1/kB to be about -27K. The low-temperature magnetization data reveals a spin glass transition in Zn1-xCoxO alloy for the Co content x>0.15, giving the value of the spin freezing temperature Tf to be ∼8 and ∼12K for x=0.2 and 0.25, respectively. Optical spectra analysis shows a linear increase of the band gap Eg with the increase of the Co content following Eg=3.231+1.144x eV. [Copyright &y& Elsevier]

A series of samples consisting of spinel Fe3O4 nanoparticles with controlled particle sizes and increasing concentration has been obtained through ‘mild’ ball milling (BM) experiments by using an organic carrier liquid. We have succeeded in producing quite narrow particle size distributions with mean values 〈d〉∼7–10 nm by an appropriate choice of the milling time for each concentration. The method proved to be practical to tailor the final particle size without formation of undesirable phases. All samples showed superparamagnetic behavior at room temperature, with transition to a blocked state at TB∼10–20 K. The mean value and distribution width of the size distributions for the three samples studied were obtained from M(H) cycles recorded at T>TB showing good agreement with X-ray diffraction and electron microscopy results. The effect of increasing interparticle interactions was to shift TB upwards, as inferred from magnetization measurements. Mössbauer spectra at low temperatures showed no evidence of enhanced spin disorder. [Copyright &y& Elsevier]