FC Curves Research Articles

Low temperature study of micrometric powder of melted Fe50Mn10Al40 alloy

Melted Fe50Mn10Al40 alloy powder with particle size less than 40μm was characterized at room temperature by XRD, SEM and XPS; and at low temperatures by Mössbauer spectrometry, ac susceptibility, and magnetization analysis. The results show that the sample is BCC ferromagnetic but with a big contribution of paramagnetic sites, and presents super-paramagnetic and re-entrant spin-glass phases with critical temperatures of 265 and 35K, respectively. The presence of the different phases detected is due to the disordered character of the sample and the competitive magnetic interactions. The obtained values of the saturation magnetization and the coercive field as a function of temperature present a behavior which indicates a ferromagnetic phase. However, the behavior of the FC curve and that of the coercive field as a function of temperature suggest that the dipolar magnetic interaction between particles contributes to the internal magnetic field in the same way as was reported for nanoparticulate powders.

Double anomalies in heat capacity and dc and ac magnetization in a superconducting Pb-porous glass nanocomposite

Studies of ac and dc magnetization and heat capacity in a superconducting lead-porous glass nanocomposite were carried out. Double anomalies were found on their temperature dependences at different magnetic field. The positions of anomalies of heat capacity and ac and dc magnetization correlated with each other. The additional, low-temperature anomalies shifted remarkably with increasing magnetic field. The FC and FCW curves observed upon cooling and warming, respectively, showed thermal hysteresis at the second step. The peak effect on magnetization loops was seen above 6K. The low-temperature anomalies in the ac and dc magnetization were treated as a manifestation of transformation in the vortex system which is triggered by superconductivity in confined lead islands.

Study of magnetic inhomogeneity in β-Cu3Fe4V6O24

The temperature dependence of dc magnetization and electron paramagnetic resonance (EPR) spectra of the β-Cu3Fe4V6O24 multicomponent vanadate were investigated. Dc magnetic measurements showed the presence of strong antiferromagnetic interactions (Curie-Weiss temperature, Θ ∼ 80 K) at high temperatures, while zero-field-cooled (ZFC) magnetization revealed a cusp-like maximum in low fields at T f1 = 4.4 K, which coincides with the splitting of the ZFC and FC curves. Another maximum was registered at T f2 = 3.0 K. These two temperatures (T f1 and T f2) could be regarded as freezing temperatures in the spin glass state of two magnetic sublattices of Fe1 and Fe2 ions. The EPR spectrum of β-Cu3Fe4V6O24 is dominated by a nearly symmetrical, very intense and broad resonance line centered at g eff ∼ 2.0 that could be attributed to iron ions. Below 10 K, an additional EPR spectrum with g 1 = 2.018(1) and g 2 = 2.175(1) appears, as well as a very weak line at geff = 1.99(1). The former spectrum is probably is due to divalent copper ions, and the latter line due to vanadium V4+ complexes. The temperature dependence of EPR parameters (g-factor, linewidth, integrated intensity) was determined in the range of 3–300 K. Two low-temperature maxima in the temperature dependence of the integrated intensity (at 40 and 6 K) were fitted with a function suitable for pairs of exchange-coupled Fe3+ ions. A comparison of dc magnetic susceptibility and EPR integrated intensity indicates the presence of spin clusters, which play an important role in determining the low-temperature magnetic response of β-Cu3Fe4V6O24.

Physical properties ofAxFe2−yS2(A=K, Rb, and Cs) single crystals

We successfully synthesized two new compounds Rb$_x$Fe$_{2-y}$S$_2$ and Cs$_x$Fe$_{2-y}$S$_2$ which were isostructural with K$_x$Fe$_{2-y}$Se$_2$ superconductor. We systematically investigated the resistivity, magnetism and thermoelectric power of $A_x$Fe$_{2-y}$S$_2$ ($A$=K, Rb and Cs) single crystals. High temperature resistivity and magnetic measurements show anomalies above 500 K depending on $A$ which are similar to $A_x$Fe$_{2-y}$Se$_2$. Discrepancy between ZFC and FC curves was observed in K$_x$Fe$_{2-y}$S$_2$ and Rb$_x$Fe$_{2-y}$S$_2$, while it disappears in Cs$_x$Fe$_{2-y}$S$_2$. Our results indicate the similar magnetism between $A_x$Fe$_{2-y}$S$_2$ and $A_x$Fe$_{2-y}$Se$_2$ at high temperature.

Magnetic and magnetoelectric properties of nickel ferrite–lead iron niobate relaxor composites

Abstract Magnetoelectric effect in bulk ceramic and multilayer (laminated) structures consisting of 6 nickel ferrite and 7 lead iron niobate relaxor (PFN) layers was investigated. This paper describes the synthesis and tape-casting process for ferrimagnetic Ni 0.3 Zn 0.62 Cu 0.08 Fe 2 O 4 ferrite and multiferroic relaxor Pb(Fe 0.5 Nb 0.5 )O 3 . X-ray analysis and studies of the electrical and magnetic properties were performed for bulk and layered composites. Complex impedance and dielectric permittivity of bulk and layered composites were studied in a temperature range from −40 to 300 °C and a frequency range of 10 Hz to 2 MHz. Magnetic hysteresis, ZFC–FC curves and dependencies of magnetization versus temperature for nickel ferrite, PFN relaxor and magnetoelectric composites were measured with a vibrating sample magnetometer (VSM) in an applied magnetic field up to 85 kOe at −269 °C. Magnetoelectric effect at room temperature was investigated as a function of static magnetic field (0.3–6.5 kOe).

Magnetic Characterization of Co Doped Cu$_{2}$O Layers

In this work we have studied the magnetic properties of room temperature electrodeposited Cu2O layers doped with Co. These layers showed anhysteretic ferromagnetic behavior with Curie temperature of 550 K. Structural characterization indicated the incorporation of Co+2 ions to the Cu2O lattice. No evidences for the existence of superparamagnetic particles and contaminations were observed, respectively, from (zero field cooling) ZFC and (field cooling) FC curves and (electron paramagnetic resonance) EPR measurements.

Low temperature properties of multiferroic [formula omitted] compound

Single-phase BiFe 0.9Cr 0.1O 3 compound with a grain size of ∼ 63 nm was prepared by the sol–gel technique. A well-defined nonlinearity in the field dependences of magnetization as a result of the collapse of the space-modulated spin structure and the strong coupling between Fe 3+ and Cr 3+ superexchange interaction indicated a weak ferromagnetic character, and the observed significant deviation between the ZFC and FC curves suggested a spin-glass-like behavior at low temperatures. The low temperature dielectric constant showed two subtle anomalies at 50 and 230 K, which are related to the spin-glass behavior and magnetoelectric coupling. Moreover, the magnetoelectric coupling was estimated by determining the variation of the dielectric constant with applied magnetic field.

Magnetic‐field influence on magnetization dependence of temperature in Cu56Ga27Mn17 annealed microwires

AbstractGlass‐coated Cu56Ga27Mn17 magnetic microwires, resulting from thermal annealing at 523 K for 1 h, have been structural and magnetically characterized. The crystalline structure shows the coexistence of four crystalline phases: a hexagonal phase with a = b = 0.4536 nm and c = 0.8386 nm lattice parameters, a cubic B2 one having a lattice parameter a = 0.29208 nm, a second fcc Cu‐rich minority phase with a = 0.3592 nm, and a monoclinic CuO appearing at the sample surface. ZFC–FC–FH thermomagnetic curves performed at different applied magnetic fields in the CuGaMn microwires annealed at 523 K, show a clear coexistence of two ferromagnetic phases with a Curie temperature around 150 K for the major phase while that corresponding to the second one is above room temperature. The field effect on ZFC–FC–FH magnetization behavior displays that the increase in the applied field modifies and shifts two peaks observed in the ZFC curve, also reducing the thermal hysteresis between FC and FH curves existent in the applied field range of 50–500 Oe. The magnetization behavior exhibited by the CuGaMn annealed microwires depending on the temperature range and magnetic field value will be discussed on the basis of the coexistence of antiferromagnetic and ferromagnetic interactions.

Magnetic susceptibility curves of a nanoparticle assembly, I: Theoretical model and analytical expressions for a single magnetic anisotropy energy

We study a model system made of non-interacting monodomain ferromagnetic nanoparticles, considered as macrospins, with a randomly oriented uniaxial magnetic anisotropy. We derive a simple differential equation governing the magnetic moment evolution in an experimental magnetic susceptibility measurement, at low field and as a function of temperature, following the well-known Zero-Field Cooled/Field Cooled (ZFC/FC) protocol. Exact and approximate analytical solutions are obtained, together for the ZFC curve and the FC curve. The notion of blocking temperature is discussed and the influence of various parameters on the curves is investigated. A crossover temperature is defined and a comparison is made between our progressive crossover model (PCM) and the crude “two states” or abrupt transition model (ATM), where the particles are assumed to be either fully blocked or purely superparamagnetic. We consider here the case of a single magnetic anisotropy energy (MAE), which is a prerequisite before considering the more realistic and experimentally relevant case of an assembly of particles with a MAE distribution (cf. part II that follows).

Magnetic susceptibility curves of a nanoparticle assembly II. Simulation and analysis of ZFC/FC curves in the case of a magnetic anisotropy energy distribution

Starting from the theoretical results established in Tournus and Bonet (2010 [1]) to describe ZFC/FC (zero-field cooled/field cooled) susceptibility curves, we examine the limitations of the widely used two states model (or abrupt transition model) where the magnetic particles are supposed to be either fully blocked or fully superparamagnetic. This crude model appears to be an excellent approximation in most practical cases, i.e. for particle assembly with broad enough size distributions. We improve the usual model by taking into account the temperature sweep existing in experimental measurements. We also discuss a common error made in the use of the two states model. We then investigate the relation between the ZFC peak temperature and the particle anisotropy constant, and underline the strong impact of the size dispersion. Other useful properties of ZFC/FC curves are discussed, such as invariance properties, the reversibility of the FC curve and the link between the susceptibility curves and the magnetic anisotropy distribution. All these considerations lay solid bases for an accurate analysis of experimental magnetic measurements.

Effect of Nickel Doping on the Magnetotransport Properties of Sm0.55Sr0.45MnO3 Manganites

We studied the effects of nickel (Ni) doping on the magneto-transport properties of Sm0.55Sr0.45MnO3 manganites near the metal-insulator transition. Various concentrations of Ni-doped Sm0.55Sr0.45MnO3 samples up to 10% were prepared (Ni was partially substituted at the Mn-site). The temperature dependence of resistivity and magnetoresistance were measured as a function of Ni concentrations at various applied magnetic fields. We observed a nonlinear reduction of the metal-insulator transition temperature (MIT) with increasing concentration of Ni, 5% of Ni was sufficient to completely suppress the insulator-metal transition. Moreover, we observed dramatic increases of the resistance of the doped material with an increasing Ni-doping (5% of Ni increases R by more than 1000 times). The resistivity peaks at various magnetic fields collapses on themselves at the high temperature ends above the MIT. We also performed magnetization versus temperature measurements on both Ni-free the Ni-doped samples for FC and ZFC states. The FC and ZFC curves rapidly decrease to paramagnetic state at 175 K and 130 K for ZFC and FC states, respectively. For other Ni-doped samples, we observed a reduction in the paramagnetic transition temperature with increasing Ni concentration.

Origin of Magnetic Anomalies below the Néel Temperature in Nanocrystalline LuMnO3

Rare earth manganites crystallize in distorted orthorhombic perovskite or hexagonal structures and exhibit quite interesting optical and magnetic properties dictated by the size of the rare earth ion. Many of these materials might exhibit both ferroelectric and magnetic ordering as well as magnetoelectric coupling. However, their physical properties at reduced particle sizes remain underexplored due to the challenges associated with their synthesis with a proper control over the crystalline phase. Here, we report the wet-chemical synthesis of the hexagonal phase of nanocrystalline LuMnO3 with an average crystallite size of ∼32 nm. The room-temperature Raman spectroscopy data are consistent with the calculated values of isomorphous hexagonal RMnO3 (R = rare earth atom) compounds with P63cm symmetry. The UV−vis-NIR spectra recorded in the diffused reflectance mode at room temperature show electronic transitions at 1.7 eV (729 nm), 2.3 eV (539 nm), and 5 eV (258 nm). The magnetization measurements show that the Néel temperature for the LuMnO3 is situated at around 89 K, which is in close proximity to the reported value of the bulk phase. We also observed two unique and field-dependent magnetic anomalies that were predicted earlier but never reported experimentally. The first anomaly is observed as a sharp bifurcation in the ZFC−FC curves below 44 K at a 100 Oe applied field, which is accompanied with a sudden rise in the coercivity and magnetization. A second transition is observed at 12 K as a sharp peak in the ZFC curves, which is accompanied with a dip in coercivity. We attribute the transition at 44 K to the reorientation of the Mn3+ ions due to the Dzyaloshinskii−Moriya interaction, and the transition at 12 K is explained by weak antiferromagnetic coupling between Mn−O−Mn in the ab plane, which becomes dominant at lower temperatures.

Irreversibility Line and Flux Relaxation in Bi:2223/Ag Tape Prepared by CTFF Technique: H//c axis

We have studied flux dynamics in Bi:2223/Ag tape prepared by the CTFF technique in the orientation of H//c axis. Irreversibility line (IL) of a Bi:2223/Ag tape has been determined from AC susceptibility and the DC magnetization technique based on FC and ZFC curves. We have observed that the irreversibility temperature determined from the AC susceptibility method locates at a higher temperature than that was determined from the DC magnetization method. This shift could be attributed to the viscous dissipation generated by the oscillation of flux lines. FC magnetization at 20 K and 30 K for the field range from 500 to 2500 Oe are the same and show a plateau implying the same amount of reversible magnetization due to the Meissner current. Remanent magnetization versus temperature curves, which give us information on the flux pinning mechanism of the vortices, are also presented.

Structural and magnetic properties of single-crystalline spinel systems ZnCr 2− x In xSe 4

The single crystals of In 3+-doped zinc chromium selenide spinel ZnCr 2Se 4 were prepared by a chemical transport method and characterized by X-ray diffraction, magnetic measurements and ESR spectroscopy in order to examine an effect of nonmagnetic indium on the structural and magnetic properties of the system. The X-ray diffraction analysis has shown that only small amount of In entered the octahedral sites in the cubic spinel structure with space group F d 3 ¯ m . As compared with parent ZnCr 2Se 4, the unit cell dimensions increased slightly with increasing In content, however at the In concentration of about 10%, the structures exhibited a certain amount of octahedral vacancies. For examined compounds the Neel temperature is very similar to that of the parent spinel ZnCr 2Se 4, whereas the paramagnetic Curie temperature is much lower (of about 59 K) than that for matrix. It means that the frustration introduced into systems by B-sublattice indium dilution reflects the change of ferromagnetic interactions in the magnetic exchange. The temperature dependence of the ESR linewidth over region ( T/ T N)>8 is interpreted by an occurrence of spin–phonon interaction. The interesting feature of the low-field magnetization is that the magnetic irreversibility observed in the separation of the FC and ZFC curves below T N is consistent with a new, weak resonance-like features.

Effect of hole doping and antiferromagnetic coupling on the itinerant ferromagnetism of [formula omitted] through Cu substitution at Ru site

Systematic studies on the structural, transport and magnetic properties of SrRu 1− x Cu x O 3 ( x = 0.0 – 0.2 ) compounds have been performed. SrRu 0.8Cu 0.2O 3 shows a tetragonal structure unlike the other compositions which exhibit a pseudo-cubic structure. Low temperature powder X-ray diffraction data of SrRu 0.8Cu 0.2O 3 collected at a synchrotron beam line reveals that the tetragonal structure is stable down to 8 K. Ferromagnetic transition temperatures ( T c ) are significantly reduced from 160 to 34 K with Cu doping. All the compositions exhibit irreversibilities in M ZFC( T) and M FC( T) curves ascribable to the presence of domain structures. Magnetic susceptibility measurements show that the copper ions are anti-ferromagnetically coupled for concentrations higher than x = 0.16 . The antiparallel arrangement of Ru 5+ ions with its neighboring cations also contributes to the large reduction in the observed magnetic moment. X-ray photoemission spectroscopy measurements show evidence for both tetravalent and pentavalent Ru ions while copper is in a divalent state. We conclude from our resistivity data that Cu 2+ substitution promotes a polaronic type of conductivity.

Effects of Ca substitution on the magnetic properties in La1-xCaxMn0.90Cu0.10O3 (x=0.05–0.30) manganites

Systematic AC and DC magnetic measurements were carried out to investigate the magnetic properties of La1-xCaxMn0.90Cu0.10O3 (x=0.05–0.30) system. A striking paramagnetism (PM) to ferromagnetism (FM) transition is observed at the FM ordering temperature TC. Below TC, the samples with x≤.0.20 show a visible unexpected drop in zero-field cooled (ZFC) DC magnetization curves near 100 K, which is believed to be associated with the domain wall pinning effects. As for the sample with x=0.30, there is no anomalous behavior near 100 K, while another different magnetic phase transition is shown up below 50 K in both FC and ZFC curves. Detailed experimental results show that the phenomenon is resulted from the phase competition rather than solely magnetic interactions.

Magnetic and structural characterization of silver-iron oxide nanoparticles obtained by the microemulsion technique

In the present paper we report the magnetic characterization of silver-iron oxide nanocomposite obtained by the chemical microemulsion method. TEM images and X-ray diffractograms show that the nanocomposite consists of Ag nanoparticles of ∼ 7 nm surrounded by a quasiamorphous matrix. The ZFC–FC curves and Mössbauer spectra obtained at different temperatures show a typical evolution of a system composed of weakly interacting nanoparticles with a blocking temperature (Tb) of ∼50 K. The analysis of the magnetic data reveals that the matrix is formed by γ-Fe2O3 phase with a structural range order of ∼2 nm.

Phase transition and magnetic properties of Mg-doped hexagonal close-packed Ni nanoparticles

Mg-doped Ni nanoparticles with the hexagonal close-packed (hcp) and face-centered cubic (fcc) structure have been synthesized by sol–gel method sintered at different temperatures in argon atmosphere. The sintering temperature played an important role in the control of the crystalline phase and the particle size. The pure hcp Mg-doped Ni nanoparticles with average particle size of 6.0 nm were obtained at 320 °C. The results indicated that the transition from the hcp to the fcc phase occurred in the temperature range between 320 °C and 450 °C. Moreover, the VSM results showed that the hcp Mg-doped Ni nanoparticles had unique ferromagnetic and superparamagnetic behavior. The unsaturation even at 5000 Oe is one of the superparamagnetic characteristics due to the small particle size. From the ZFC and FC curves, the blocking temperature T B of the hcp sample (6.0 nm) was estimated to be 10 K. The blocking temperature was related to the size of the magnetic particles and the magnetocrystalline anisotropy constant. By theoretical calculation, the deduced particle size was 6.59 nm for hcp Mg-doped Ni nanoparticles which was in agreement with the results of XRD and TEM.

Magnetic properties of a high energy ball-milled amorphous Gd 5Si 1.8Ge 1.8Sn 0.4 alloy

Amorphous Gd 5Si 1.8Ge 1.8Sn 0.4 has been obtained with the help of a high-energy ball milling technique. XRD and DSC measurements confirm the amorphous nature of the milled alloy. The separation of FC and ZFC curves below the ferromagnetic transition temperature indicates a spin glass-like state in the amorphous alloy. Thermal hysteresis has been significantly reduced in the high energy ball-milled alloy compared with that of a crystalline one. For the amorphous Gd 5Si 1.8Ge 1.8Sn 0.4, magnetic phase transition takes place in a wide temperature span and the RC value reaches around 495 J kg −1.

Magnetic study of single domain ɛ-Fe 3N nanoparticles synthesized by precursor technique

Nanostructured single domain ɛ-Fe 3N particles have been prepared by chemical route. Magnetic dipolar interaction among particles has been observed. The FC and ZFC magnetization curves show the superparamagnetic blocking temperature around 125 K, at low applied field of 0.005 T. At higher applied field, these ZFC and FC magnetization curves merge because of increase in magnetization energy that overcomes the magnetic anisotropy and dipolar interaction energies. Mössbauer spectroscopy further corroborates the superparamagnetic nature at 300 K.