Field-dependent Magnetization Curves Research Articles

Influence of Ce addition on the structural, magnetic, and magnetocaloric properties in La0.7−xCexSr0.3MnO3 (0≤x≤0.3) ceramic compound

We report improvement in the magnetocaloric properties of Ce-doped lanthanum manganites. Polycrystalline La0.7−xCexSr0.30MnO3 (0≤x≥0.3) samples were prepared using the conventional solid-state reaction method with phase purity and structure confirmed using X-ray diffraction. Temperature dependent magnetization measurements and Arrott analysis reveal second order ferromagnetic transition in parent sample and as well as in doped sample with Curie temperature decreasing progressively with increasing Ce-concentration from ~370K for x=0.0 to 310K for x=0.30. Magnetic entropy change (ΔSM) was calculated by applying the thermodynamic Maxwell equation to a series of isothermal field dependent magnetization curves. A large ΔSM associated with the ferromagnetic–paramagnetic transition in La0.7−xCexSr0.30MnO3 samples has been observed. The value of ΔSM was found to increase with Ce-doping up to x=0.15 and the highest value of 2.12Jkg−1K−1 (at ΔH=2T) was observed for La0.55Ce0.15Sr0.30MnO3 sample near the Curie temperature of 356K. Also, improved relative cooling power of ~122Jkg−1 was observed for the same sample. Due to the large magnetic entropy change and high Curie temperature, the La0.55Ce0.15Sr0.30MnO3 sample is suggested to be used as potential magnetic refrigerants for magnetic refrigeration technology above room temperature.

Study of magnetic and magnetocaloric properties of La0.6Pr0.1Ba0.3MnO3 and La0.6Pr0.1Ba0.3Mn0.9Fe0.1O3 perovskite-type manganese oxides

The compositional dependence of the magnetic and magnetocaloric properties of La0.6Pr0.1Ba0.3MnO3 (LPBMO) and La0.6Pr0.1Ba0.3Mn0.9Fe0.1O3 (LPBMFO) were investigated. Polycrystalline samples were prepared by the standard solid-state reaction method. Temperature-dependent magnetization measurements and Arrott analysis reveal second-order ferromagnetic transitions in both samples with Curie temperature increasing with doping iron from 94 K for LPBMO to 277 K for LPBMFO. Magnetic entropy change $$ | {\Delta S_{\text{M}} } | $$ was calculated by applying the thermodynamic Maxwell equation to a series of isothermal field-dependent magnetization curves. However, the analysis of the magnetocaloric effect (MCE) using Landau theory of phase transition shows that the contributions to the free energy from the presence of ferromagnetic clusters are strongly influencing the MCE by coupling with the order parameter around the Curie temperature.

Anomalous magnetic behavior in nanocomposite materials of reduced graphene oxide-Ni/NiFe2O4

Magnetic Reduced Graphene Oxide-Nickel/NiFe2O4 (RGO-Ni/NF) nanocomposite has been synthesized by one pot solvothermal method. Respective phase formations and their purities in the composite are confirmed by High Resolution Transmission Electron Microscope and X Ray Diffraction, respectively. For the RGO-Ni/NF composite material finite-size effects lead to the anomalous magnetic behavior, which is corroborated in temperature and field dependent magnetization curves. Here, we are reporting the behavior of higher magnetization values for Zero Field Cooled condition to that of Field Cooled for the RGO-Ni/NF nanocomposite. Also, the observed negative and positive moments in Hysteresis loops at relatively smaller applied fields (100 Oe and 200 Oe) are explained on the basis of surface spin disorder.

Ferrimagnetism and magnetization reversal in Pr1−x Gd x MnO3

Temperature dependent magnetic properties of Pr1−x Gd x MnO3 (x = 0.3, 0.5, 0.7) have been reported. All the samples belong to the family of orthorhombic perovskites structure with Pbnm space group. Below the Neel temperature T N (~92 K), a magnetization reversal is observed in DC magnetization measurements (at 50 Oe), in all the samples. This may be due to the competition between two magnetic sublattices (Pr + Gd and Mn) coupled with a negative exchange interaction. In the temperature dependent magnetization data, the bifurcation between the zero field cooled and field cooled magnetization is attributed to the canted antiferromagnetism. Ferrimagnetic characteristic is observed in the field dependent magnetization curve below T N .

Field-induced spin-flop-like metamagnetism in α-CoB4O7

We successfully obtained pure α-CoB4O7 powder sample by a two-step synthesis method. First, a new cobalt polyborate with unknown crystal structure was synthesized by boric acid flux method in a sealed system. Subsequently, α-CoB4O7 powder was obtained by the thermal decomposition of this new phase at 800 °C. The purity was carefully checked by Le Bail fitting of its powder XRD with good convergence. The magnetic susceptibilities in paramagnetic region agree well with Curie–Weiss law with θ = −17.7 K, C = 3.13 cm3 K mol−1. Ac magnetic measurements confirm its long-range AFM ordering at ∼5 K. The field-dependent magnetization curve at 1.85 K indicates a spin-flop-like phase transition, with Hc = 35 kOe. Considering the relatively weak magnetic super-exchange, we believe this transition is due to the large magnetic anisotropy of Co2+.

Biodegradation of magnetic nanoparticles evaluated from Mössbauer and magnetization measurements

In order to extract a quantitative information about characteristics of the magnetic nanoparticles injected into a living organism it is necessary to define a model of the magnetic dynamics for fitting self-consistently the whole set of the experimental data, specifically, the evolution of Mossbauer spectral shape with temperature and external magnetic field as well as the magnetization curves. We have developed such a model and performed such an analysis of the temperature- and magnetic field-dependent spectra and magnetization curves of nanoparticles injected into mice. This allowed us to reliably evaluate changes in the characteristics of the residual particles and their chemical transformation to paramagnetic ferritin-like forms in different mouse organs as a function of time. Actually, the approach makes it possible to quantitatively characterize biodegradation and biotransformation of magnetic nanoparticles delivered in a body.

Biodegradation of Nanoparticles in a Body from Mössbauer and Magnetization Measurements

In order to extract a quantitative information about characteristics of the magnetic nanoparticles injected into a living organism one has to define a model of the magnetic dynamics in order to fit self-consistently the whole set of the experimental data, particularly, the evolution of Mössbauer spectral shape with temperature and external magnetic field as well as the magnetization curves. We have developed such a model and performed such an analysis of the temperature-and magnetic field-dependent spectra and magnetization curves of nanoparticles injected into a mice. This allowed us to reliably evaluate changes in the residual nanoparticles characteristics and their chemical transformation to paramagnetic ferritin-like forms in different mouses organs as a function of time after injection of nanoparticles. Actually, the approach allows one to quantitatively characterize biodegradation and biotransformation of magnetic nanoparticles injected into a body.

How cellular processing of superparamagnetic nanoparticles affects their magnetic behavior and NMR relaxivity

Cellular processing of nanomaterials may affect their physical properties at the root of various biomedical applications. When nanoparticles interact with living cells, their spatial distribution is progressively modified by cellular activity, which tends to concentrate them into intracellular compartments, changing in turn their responsivity to physical stimuli. In this paper, we investigate the consequences of cellular uptake on the related magnetic properties and NMR relaxivity of iron oxide nanoparticles. The superparamagnetic behavior (field-dependent and temperature-dependent magnetization curves investigated by SQUID (Superconducting Quantum Interference Device) measurements) and nuclear magnetic relaxation dispersion (NMRD) R(1) profiles of citrate-coated maghemite nanoparticles (mean diameter 8 nm) were characterized in colloidal suspension and after being uptaken by several types of cells (tumor cells, stem cells and macrophages). The temperature-dependent magnetization as well as the NMRD profile were changed following cellular uptake depending on the stage of endocytosis process while the field-dependent magnetization at room temperature remained unchanged. Magnetic coupling between nanoparticles confined in cell lysosomes accounts for the modification in magnetic behavior, thereby reflecting the local organization of nanoparticles. NMR longitudinal relaxivity was directly sensitive to the intracellular distribution of nanoparticles, in line with Transmission Electron Microscopy TEM observations. This study is the first attempt to link up magnetic properties and NMR characterization of iron oxide nanoparticles before and after their cell processing.

Tunable magnetocaloric effect near room temperature in La0.7-xPrxSr0.3MnO3 (0.02 ≤ x ≤ 0.30) manganites

We have systematically investigated the compositional dependence of the magnetic and magnetocaloric properties of La0.7-xPrxSr0.3MnO3 (LPSMO). Polycrystalline samples of LPSMO with 0.02 ≤ x ≤ 0.30 were prepared by a standard solid-state reaction method with phase purity and structure confirmed using x-ray diffraction. Temperature dependent magnetization measurements and Arrott analysis reveal second order ferromagnetic transitions in each sample with Curie temperature decreasing progressively with increasing Pr content from ∼350 K for x = 0.02 to ∼295 K for x = 0.30. Magnetic entropy change (ΔSM) was calculated by applying the thermodynamic Maxwell equation to a series of isothermal field dependent magnetization curves. In the sample with x = 0.30, the maximum value of −ΔSM reaches ∼2.08 J/kg K at 295 K for a field change of 1.5 T. Reduced Pr content corresponds to larger values of entropy change, reaching −ΔSM ∼2.79 J/kg K for the x = 0.02 doping. The refrigeration capacity for each composition reached sizable values of 33–48 J/kg for a small applied field of 1.5 T.

Crystal growth and magnetic properties of spinel (Co,Mn)3O4

Single crystals of cubic and tetragonal spinel Co3−xMnxO4 (x=1.0 and 1.5) were successfully grown using a solvent evaporation method with PbF2 flux. Single crystals in octahedral shape with a size of about 4mm on edge were obtained from 100cm3 Pt crucibles. Ferrimagnetic transitions were detected at 170K and 160K from the measurements of temperature dependent magnetization and specific heat of Co2MnO4 and Co1.5Mn1.5O4, respectively. Low temperature field-dependent magnetization curves give a strong indication of the non-collinear spin structure, offering an insulating Co3−xMnxO4 system as a possible candidate for examining the multiferroicity.

Interparticle interaction effects on magnetic behaviors of hematite (α-Fe2O3) nanoparticles

The interparticle magnetic interactions of hematite (α-Fe2O3) nanoparticles were investigated by temperature and magnetic field dependent magnetization curves. The synthesis were done in two steps; milling metallic iron (Fe) powders in pure water (H2O), known as mechanical milling technique, and annealing at 600°C. The crystal and molecular structure of prepared samples were determined by X-ray powder diffraction (XRD) spectra and Fourier transform infrared (FTIR) spectra results. The average particle sizes and the size distributions were figured out using transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The magnetic behaviors of α-Fe2O3 nanoparticles were analyzed with a vibrating sample magnetometer (VSM). As a result of the analysis, it was observed that the prepared α-Fe2O3 nanoparticles did not perform a sharp Morin transition (the characteristic transition of α-Fe2O3) due to lack of unique particle size distribution. However, the transition can be observed in the wide temperature range as “a continuously transition”. Additionally, the effect of interparticle interaction on magnetic behavior was determined from the magnetization versus applied field (σ(M)) curves for 26±2nm particles, dispersed in sodium oxalate matrix under ratios of 200:1, 300:1, 500:1 and 1000:1. The interparticle interaction fields, recorded at 5K to avoid the thermal interactions, were found as ∼1082Oe for 26±2nm particles.

Molecule-based magnetic materials based on dinuclear ruthenium carboxylate and octacyanotungstate

Two structurally different polymeric complexes consisting of ruthenium(II,III) pivalate ([Ru2(piv)]4+) (Hpiv = pivalic acid) and octacyanotungstate(V) ([W(CN)8]3−) ions, [{Ru2(piv)4}3W(CN)8(H2O)] (1) and (PPh4)2[Ru2(piv)4W(CN)8]·0.5H2O (2), were synthesized. The infrared spectra as well as diffused reflectance spectra confirmed the existence of the ruthenium(II,III) pivalate dimer in 1 and 2. The X-ray crystal structure analysis of 2 showed an alternating arrangement of [Ru2(piv)]4+ and [W(CN)8]3− ions in a one-dimensional chain. The temperature-dependent magnetic susceptibility of 2 showed a ferrimagnetic-like behavior. However, the field dependent magnetization curve at 2 K indicates that this complex has an S = 0 ground state. The X-ray crystal structure analysis of 1 showed a two-dimensional layered structure made up of windmill-shaped 28 membered-rings of alternating arrangement of [Ru2(piv)]4+ and [W(CN)8]3−. The magnetic susceptibility and zero-field-cooled and field-cooled magnetization data of 1 showed that this complex is ferrimagnetic with Tc = 44 K. The field dependence of magnetization exhibited a hysteresis with a coercive field of 5600 Oe at 5 K.

Substrate Dependent Structural and Magnetic Properties of Pulsed Laser Deposited Fe<SUB>3</SUB>O<SUB>4</SUB> Thin Films

Nanocrystalline iron oxide thin films have been deposited on various substrates such as quartz, MgO(100), and Si(100) by pulsed laser deposition technique using excimer KrF laser (248 nm). The orientations, crystallite size and lattice parameters were studied using X-ray diffraction. The XRD results show that the films deposited on MgO and Si substrates are highly oriented and show only (400) and (311) reflections respectively. On the other hand, the orientation of the films deposited on quarts substrate changed from (311) to (400) with an increase in the substrate temperature from 400 degrees C to 600 degrees C, indicating thereby that the film growth direction is highly affected with nature of substrate and substrate temperature. The surface morphology of the deposited films was studied using Atomic Force Microscopy (AFM) and spherical ball like regular features of nanometer size grains were obtained. The magnetic properties were studied by Superconducting Quantum Interference Device (SQUID) magnetometer in the magnetic field +/- 6 Tesla. The magnetic field dependent magnetization (M-H) curves of all the Fe3O4 thin films measured at 5 K and 300 K show the ferrimagnetic nature. The electrochemical sensing of dopamine studied for these films shows that the film deposited on MgO substrate can be used as a sensing electrode.

Magneto-electric coupling in multiferroic La 0.8Bi 0.2Fe 0.7Mn 0.3O 3 ceramic

We present here the structural, electrical, magnetic and magneto-electric properties of La 0.8Bi 0.2Fe 0.7Mn 0.3O 3 multiferroic sample synthesized by conventional solid state reaction route. X-ray diffraction (XRD) data show single phase character of the sample. Temperature (150–475 K) variation of dielectric constant exhibits step like escalation which consists of two transitions corresponding to the respective peaks in temperature vs. loss tangent curve. Slight shift in peak positions to higher temperatures with the increase of frequency indicates the presence of relaxor behavior. Magnetic field dependent magnetization (M–H) curve at 300 K demonstrates weak ferromagnetic conduct. Coupling between the electric and magnetic orders has been explored by means of magneto-capacitance measurement. Presence of magneto-electric (ME) coupling ascertains the candidature of this material for device application.

Mössbauer spectra and magnetization curves of nanoparticles in a weak magnetic field

Magnetic relaxation effects revealed in Mössbauer spectra and magnetization measurements of nanoparticles are discussed in the framework of specific models for magnetic dynamics of an ensemble of single-domain particles, which allow one to treat both the temperature and magnetic field-dependent magnetization curves and Mössbauer spectra in a self-consistent way within the same set of physical parameters inherent to the system studied. Based on the stochastic approaches, a simplified three-level stochastic model taking into account the magnetic anisotropy, precession and diffusion of uniform magnetization of single-domain particles is developed in order to describe the Mössbauer absorption spectra of nanoparticles in a weak magnetic field.

High-Field Magnetization of the Distorted Spin Frustration System Ni5(TeO3)4Br2

We performed high-field magnetization measurements, M(H), on the Ni-5(TeO3)(4)Br-2 by using a pulse magnet. The Ni2+ ions (S = 1) of this compound form a two dimensional distorted spin frustrated system (distorted kagome lattice), and undergo a Neel transition at T (N) similar to 29 K, due to the anisotropy. Below T (N) , a complex spin arrangement which contains ten spin sub-lattices was suggested by neutron scattering and electron spin resonance studies. We observed a step-like transition at H (c) similar to 11 T when T T (N) , the field-dependent magnetization curves behaved like a straight line. The H (c) is close to those obtained by previous spin resonance studies of Ni-5(TeO3)(4)Br-2 and Ni-5(TeO3)(4)Cl-2 in which a spin-flop-like transition was proposed to explain the field-dependent resonance spectra. Interestingly, the observed change in magnetization (Delta M) at H (c) corresponds to nearly one-half of the magnetic moment of Ni2+ ion, suggesting that the observed step-like behavior possibly corresponds to a spin-flip-like transition (i.e. from antiferromagnetic state to ferrimagnetic state). In addition, in the high-field region (H > H (c) ), the M(H) curves did not show plateau behavior, but exhibited the straight lines having finite slopes without any sign of saturation up to 55 T.

Paramagnetic Mn-implanted amorphous Si

Different fluences of Mn ions have been implanted into 200 nm thick, n-type conducting amorphous Si films on a cold stage cooled by liquid N 2 with a Mn concentration in Mn x Si 1− x ranging from x = 0.0006 to 0.088. Magnetic measurements reveal paramagnetism in all the films at temperatures down to 2 K. The field dependent magnetization curves were well fitted by Brillouin functions, indicating that the magnetically active Mn ions are on Mn I 2 + interstitial sites with J = 5/2. Only a small percentage of the implanted Mn ions contributes to the magnetization, indicating that the magnetic moments are quenched for most of the Mn ions, which was attributed to the nonuniform distribution of Mn ions in amorphous Si. Positive magnetoresistance due to ordinary magnetoresistance was observed at 5 K in the highest fluence Mn-implanted amorphous Si film, indicating the lack of magnetic scattering of the conducting electrons by the implanted Mn 2+ ions.

Compensation-dependent in-plane magnetization reversal processes inGa1−xMnxP1−ySy

We report the effect of dilute alloying of the anion sublattice with S on the in-plane uniaxial magnetic anisotropy and magnetization reversal process in ${\text{Ga}}_{1\ensuremath{-}x}{\text{Mn}}_{x}\text{P}$ as measured by both ferromagnetic resonance (FMR) spectroscopy and superconducting quantum interference device (SQUID) magnetometry. At $T=5\text{ }\text{K}$, raising the S concentration increases the uniaxial magnetic anisotropy between in-plane $⟨011⟩$ directions while decreasing the magnitude of the (negative) cubic anisotropy field. Simulation of the SQUID magnetometry indicates that the energy required for the nucleation and growth of domain walls decreases with increasing $y$. These combined effects have a marked influence on the shape of the field-dependent magnetization curves; while the $[0\overline{1}1]$ direction remains the easy axis in the plane of the film, the field dependence of the magnetization develops double hysteresis loops in the [011] direction as the S concentration increases, similar to those observed for perpendicular magnetization reversal in lightly doped ${\text{Ga}}_{1\ensuremath{-}x}{\text{Mn}}_{x}\text{As}$. The incidence of double hysteresis loops is explained with a simple model whereby magnetization reversal occurs by a combination of coherent spin rotation and noncoherent spin switching, which is consistent with both FMR and magnetometry experiments. The evolution of magnetic properties with S concentration is attributed to compensation of Mn acceptors by S donors, which results in a lowering of the concentration of holes that mediate ferromagnetism.

Equilibrium magnetic properties of dipolar interacting ferromagnetic nanoparticles

We use Monte Carlo simulations to study the influence of dipolar interaction on the equilibrium magnetic properties of monodisperse single-domain ferromagnetic nanoparticles. Low field magnetizations simulated in zero field cooling (ZFC)/field cooling (FC) procedures and field-dependent magnetization curves above the blocking temperatures show strong dependence on the concentration and the spatial arrangement (cubic or random) of the magnetic particles. The field-dependent magnetizations can not be simply described by the T * model at relative low temperatures due to the interplay between anisotropy and dipolar interactions, as well as the spatial arrangement effect.

Optically transparent magnetic nanocomposites based on encapsulatedFe3O4 nanoparticles in a sol–gel silica network

Composite Fe3O4–SiO2 materials were prepared by the sol–gel method with tetraethoxysilane and aqueous-basedFe3O4 ferrofluids as precursors. The monoliths obtained were crack free and showed bothoptical and magnetic properties. The structural properties were determined byinfrared spectroscopy, x-ray diffractometry and transmission electron microscopy.Fe3O4 particles of 20 nm size lie within the pores of the matrix without any strong Si–O–Febonding. The well established silica network provides effective confinement to thesenanoparticles. The composites were transparent in the 600–800 nm regime and the fielddependent magnetization curves suggest that the composite exhibits superparamagneticcharacteristics.