Zero-field-cooled Magnetization Research Articles

Temperature dependent magnetic and electrical transport properties of lanthanum and samarium substituted nanocrystalline nickel ferrite and their hyperthermia applications

Structural, optical, temperature dependent magnetic and electrical properties have been investigated for the nanocrystalline NiFe1.97RE0.03O4 (RE = La3+ and Sm3+) compound. Without any signs of a secondary REFeO3 phase, the Rietveld refinement reveals a single-phase spinel structure possessing cubic symmetry for current samples. The decrease in lattice constant has been observed as a result of RE ions substitution. The TEM micrographs reveal nanosized particles with an average size of 35 ± 3 nm and 32 ± 3 nm for La3+ and Sm3+ substituted samples. EDX spectra of both samples show good compositional homogeneity. HRTEM micrographs of both samples show well resolved lattice fringes and their inter-planar spacing matches with that obtained from the Rietveld analysis of the XRD patterns. The concentration of Fe2+ and Fe3+ ions has been estimated from the XPS spectra analysis and it is found to be ∼ 22% and 78% for NiFe1.97La0.03O4 and, 20% and 80% for NiFe1.97Sm0.03O4 compound. The optical energy band gap for rare earth substituted samples is found to be more than that of pure nickel ferrite. The value of saturation magnetization (Ms) and magneto-crystalline anisotropy constant (K1) estimated from the “Law of Approach to Saturation” equation for rare earth substituted samples are found to be less than that of pure nickel ferrite. However, an enhanced value of coercivity has been observed with RE substitution. ZFC (zero field cooling) and FC (field cooling) DC magnetization curves measured at 100 Oe in the temperature range of 60–400 K reveal a combination of weak and intermediate forms of magnetic interaction between the particles for both samples. Temperature dependent analysis of saturation magnetization and coercivity employing modified Bloch’s law and Kneller’s relation supports the nanomagnetic behavior of both samples. Under an AC magnetic field of 14.92 kA/m and frequency 337 kHz, the SAR and ILP values have been found to be ∼ 331 W/g and 4.22 nHm2/kg for NiFe1.97La0.03O4 and, ∼ 241 W/g and 3.21 nHm2/kg for NiFe1.97Sm0.03O4. The dielectric relaxation data have been analyzed at various temperatures ranging from 40 to 300 0C over the frequency range 100 Hz-1 MHz using electrical impedance spectroscopy. The dielectric constant for rare earth substituted samples is found to be more and their AC conductivity is observed to be less than that of pure nickel ferrite. The analysis of temperature dependent AC conductivity employing Jonscher’s power law suggests that the charge carrier’s conduction mechanism of both samples follows the small polaron hopping mechanism below 200 0C, thereafter; it follows the correlated barrier hopping mechanism. The activation energy estimated by imaginary impedance spectra is found to be 0.411 eV and 0.398 eV for NiFe1.97La0.03O4 and NiFe1.97Sm0.03O4 which is more than that of pure nickel ferrite. The Cole-Cole plots at different temperatures suggest the presence of non-Debye-type relaxation. The modeling of Cole-Cole plots with equivalent circuits for both samples confirms the contribution of both grain and grain boundary in electrical conduction. The estimated stretching exponential factor by fitting the modified KWW (Kohlrausch-Williams-Watts) equation to the imaginary modulus curve reveals relatively more dipole-dipole interaction in NiFe1.97Sm0.03O4 than that of the La3+ substituted sample.

Structural and magnetic properties of Dy doped SrFe12O19 ferrites

Hexagonal Sr1−xDyxFe12O19 (x = 0.0–0.1) have been prepared by high-energy ball milling technique. The effect of Dy doping on the structural and magnetic properties is studied. Crystal structure, morphology and magnetic properties are investigated. Single polycrystalline phase of SrFe12O19 is obtained and proved by X-ray diffraction (XRD) analysis. All Sr1−xDyxFe12O19 samples displayed single polycrystalline phase whatever the amount of Dy is. Magnetic properties, as a function of magnetic field and of temperature, were examined before and after Dy doping. Significant improvement of saturation magnetization (Ms) and intrinsic coercivity (Hc) at room temperature were achieved as a result of the Dy substitution. High coercivity were observed for all samples, suggesting the materials are good candidates for high frequency applications. Remnant magnetization (Mr) is obtained from the hysteresis loop and found at 13.5 emu/g for the non-doped sample. The value showed significant increase, reaching 34.2 emu/g, with increasing the dopant (Dy) amount. Magnetic interactions were explored via temperature dependent zero field cooling (ZFC) and field cooling (FC) magnetization measurements. FC magnetization increased slowly with temperature reduction for the samples x = 0, 0.02 and 0.04, indicating the weakly coupled magnetic system. But for highly doped samples (x = 0.06 and 0.08) the FC magnetization decreased with decreasing of temperature, indicating the strong coupling interactions. The ZFC and FC magnetization data indicates that the blocking temperature (TB) is well above the room temperature.

Non-equilibrium magnetic response in concentrated spin-glass Au0.89Fe0.11 alloy

We report a detailed study of dc magnetization and ac susceptibility performed on the zero field cooled (ZFC) and field cooled (FC) state of polycrystalline Au0.89Fe0.11 alloy. The temperature variation of ZFC and FC dc magnetization at low fields shows a distinct peak around Tf = 33 K, which indicates the cooperative freezing of the finite size spin clusters. A weak thermomagnetic irreversibility between ZFC and FC magnetization appears at a temperature Tir, which is slightly below Tf. Further down the temperature at Tsh<Tir, the ZFC and FC magnetization curves exhibit strong thermomagnetic irreversibility. The ac susceptibility recorded after cooling in presence of field shows significant dispersion below Tf, and also, the FC state of Au0.89Fe0.11 alloy exhibits a pronounced memory effect in the dc magnetization which clearly underline that the FC state is not an equilibrium state. In contrast to the general perception obtained through the mean-field theories of thermodynamic phase transition in spin-glass envisaging the FC state to be an equilibrium state, the present experimental results clearly indicate that the energy landscape of the FC state of Au0.89Fe0.11 alloy is a nontrivial one.

Intrinsic magnetic-optical features of Dy3+ ion substituted NiCuZn nanospinel ferrites via sonochemical approach

Ni0·4Cu0·2Zn0.4DyxFe2-xO4 (x ≤ 0.10) (NCZDy) nanospinel ferrites (NSFs) were prepared by an ultrasonication approach assisted sol-gel synthesis methodology. The cubic spinel structures of products were verified by XRD (X-ray powder diffraction) study. Intrinsic vibrational absorption bands of nanoparticles for their octahedral band (υ2) at 417 cm−1 and tetrahedral (υ1) band at 563-580 cm−1 were detected by FT-IR (Fourier-transform infrared) analysis. Magnetic studies by VSM (Vibrating sample magnetometry) confirmed the soft ferromagnetic nature of all products at 15 K and 300 K temperatures. As the amount of Dy3+ rises, saturation and remanent magnetization (Ms and Mr) values first increase for x = 0.02 composition; then they start to decrease with further rising the Dy3+ content. FC (Field-cooled) and ZFC (zero field-cooled) magnetization studies reveal that the irreversible temperature is above 300 K and the samples display spin glass behavior. Mössbauer spectra (MOS) were acquired to calculate hyperfine parameters by room-temperature (RT) spectra fitting and results indicated Dy3+ ions occupy octahedral sites. The optical investigation showed NCZDy (x ≤ 0.10) NSFs carry out a direct band character, and band gap values lay between 1.69 and 2.33 eV. All samples absorb the light within the visible region which is evident from the % Diffuse Reflectance Spectroscopy (DRS) results.

Eff ects of Cr Doping on Physical Properties of CuBO2 Delafossite Oxide

In this research work, CuB1−xCrxO2 (x = 0.00, 0.01, 0.03, 0.05, and 0.07) were synthesized by using a conventional solid-state reaction method. The effects of Cr concentration on its microstructure, optical, magnetic, and dielectric properties were investigated. X-ray diffraction (XRD) results revealed the crystal structure of all samples belongs to the R-3m delafossite structure. Besides, a second phase CuCrO2 appeared in a high Cr content sample. Scanning electron microscope (SEM) indicated that particle size of samples was about 300 nm and slightly increased with increasing the Cr content. The optical properties measured by UV-visible spectroscopy showed the absorbance peak at ~250 nm. The corresponding direct optical band gap was about 2.90 eV. The magnetic hysteresis curve measurements of all samples revealed the paramagnetic behavior at room temperature. Noticeably, the Cr-doped samples (x = 0.01−0.07) exhibited as a ferromagnetic behavior at 50 K. Furthermore, the zero-fi eld-cooling magnetization of the Cr-doped samples shows a ferromagnetic transition temperature at ~130K. Finally, the dielectric measurement of all samples shows the colossal dielectric permittivity.

Structural, chemical and low-temperature magnetic properties of lead-Free 0.6NiFe2O4-0.4Na0.5Bi0.5TiO3 magnetoelectric composite

We report on structural, chemical and low-temperature magnetic properties of lead-free 0.6NiFe2O4-0.4Na0.5Bi0.5TiO3 composite. NiFe2O4 (NFO) and Na0.5Bi0.5TiO3 (NBTO) are seen to crystallize in inverse spinel and perovskite structure, respectively. 0.6NiFe2 O4-0.4Na0.5Bi0.5TiO3 composite exhibits both NFO and NBTO phases in appropriate composition. Zero field-cooled (ZFC) and field-cooled (FC) magnetization measurements carried out from 15 to 300 K shows a large bifurcation at room temperature. ZFC and FC magnetization measurement exhibit a hump at Tm \(\sim\)259.5 K, indicates the possible existence of competing magnetic interactions in 0.6NiFe2 O4-0.4Na0.5Bi0.5TiO3 composite. Saturation magnetization, remnant magnetization and coercivity values are observed to increase with decreasing the temperature. Temperature-dependent saturation magnetization is fit to the Bloch’s law. Magnetocrystalline anisotropy (K1) value at various temperatures are estimated and is seen to increase from 0.23 × 104 erg/cc (at 300 K) to 0.34 × 104 erg/cc (at 15 K).

Doping tuned spin reorientation and spin switching in praseodymium–samarium orthoferrite single crystals

We investigate the detailed analysis of the magnetic properties in a series of Pr1–x Sm x FeO3 single crystals from x = 0 to 1 with an interval of 0.1. Doping controlled spin reorientation transition temperature T SR Γ4 (G x , A y , F z ) to Γ2 (F x , C y , G z ) covers a wide temperature range including room temperature. A ‘butterfly’-shape type-I spin switching with 180° magnetization reversal occurs below and above the magnetization compensation points in x = 0.4 to 0.8 compounds. Interestingly, in Pr0.6Sm0.4FeO3 single crystal, we find an inadequate spin reorientation transition accompanied by uncompleted type-I spin switching in the temperature region from 138 to 174 K. Furthermore, a type-II spin switching appears at 23 K, as evidenced from the magnetization curve in field-cooled-cooling (FCC) mode initially bifurcate from zero-field-cooled (ZFC) magnetization curve at 40 K and finally drops back to coincide the ZFC magnetization value at 23 K. Our current research reveals a strong and complex competition between Pr3+–Fe3+ and Sm3+–Fe3+ exchange interactions and more importantly renders a window to design spintronic device materials for future potential applications.

A novel approach to determine blocking temperature in bulk materials

Blocking temperature (θB) holds utmost significance in magnetic devices. A novel approach to ascertain the θB for bulk materials has been propounded. The θB has been correlated with the magnetic entropy change (ΔS) during zero-field cooled (ZFC) and field cooled (FC) magnetization. The values of ΔS have been calculated in µB/f.u.K. The θB has been investigated for two distinct cases – (I) with ZFC magnetization reversal and (II) without ZFC magnetisation reversal. Based on the reported experimental approach, a novel definition of θB has been propounded for bulk materials. The combined analysis of ZFC and FC magnetization behaviour provides a better approximation of θB for bulk materials.

Grain size influence upon magnetic behavior at nanoscale. A computational approach

In this work, a study of magnetic properties of nanogranular films constructed with different grain sizes is presented. The total energy of the system is proposed by mean a Hamiltonian with four contributions, which was solved using the Monte Carlo Method. The proposed terms include: (i) The exchange interactions, which consider the stress at grain boundaries. (ii) Three anisotropy contributions: cubic magnetocrystallinity in the grain cores, the Neel’s approximation in the film surface and the cubic magnetoelastic distortion at the grain boundaries. (iii) The dipolar interactions with a cutoff radius of five replicas and (iv) the energy contribution from the external magnetic field. Hysteresis loops and the temperature dependence of the magnetization under the zero-field-cooled (ZFC) and field-cooled (FC) conditions were computed. The used parameters, such as grain size, grain polydispersity, exchange values among others were chosen considering typical values reported from experimental works. The ZFC magnetization curve shows a broader maximum of which determines the blocking temperature. This maximum moves towards higher temperatures as the grain volume increases, fact related to greater stability of the ferromagnetic (FM) coupling on those grains with larger sizes, being a direct consequence of the decrease in the number of atoms located at the boundaries and of the reduction in the surface disorder. The hysteresis loops features, as well as the trend of some parameters (e.g., coercive field and remanence magnetization) as function of grain size, are in acceptable agreement with the experimental data tendencies. Local anisotropy in boundaries observed around coercive field explains grain size dependence of coercive field at nanoscale.

Type-II superconductivity below 4K in Sn0.4Sb0.6

In this article, we report the occurrence of superconductivity in Sn0.4Sb0.6 single crystal at below 4K. Rietveld refined Powder XRD data confirms the phase purity of as grown crystal, crystallizing in rhombohedral R-3m space group with an elongated (2xc) unit cell in c-direction. Scanning Electron Microscope (SEM) image and EDAX measurement confirm the laminar growth and elemental composition to be near to desired stoichiometry ratio. Raman Spectroscopy data shows the vibrational modes of Sn–Sb and Sb–Sb modes at 110 and 135 cm−1. ZFC (Zero-Field-Cooled) magnetization measurements done at 10Oe showed sharp superconducting transitions at 4K along with a minor step at 3.5K. On the other hand, Paramagnetic Meissner Effect (PME) is observed in FC measurements. Magnetization vs applied field (M − H) plots at 2, 2.2, 2.5, 2.7, 3, 3.2, 3.5, and 3.7K show typical Type-II nature of observed superconductivity with lower and upper critical fields (Hc1 and Hc2) at 69.42Oe and 630Oe respectively at 2K. Type-II superconductivity is also confirmed by calculated Ginzburg-Landau Kappa parameter value of 3.55. Characteristics length viz. coherence length and penetration depth are also calculated. Weak granular coupling is observed from ρ-T plot, in which resistance is not dropping to zero down to 2K.

Synthesis and magnetic properties of Ba2Fe14O22 Y-type hexaferrite

Using the solid state reaction method, Y-type hexaferrite Ba2Fe2+2Fe3+12O22 (Fe2Y) polycrystalline ceramics were fabricated by calcining and sintering in a nitrogen atmosphere, and their magnetic properties were systematically investigated. The kink occurs at around 130 K in the zero-field-cooled (ZFC) and field-cooled (FC) magnetization curves is independent of measuring frequencies, which is probably derived by the temperature-induced spin reorientation transitions of Fe2Y phase. While the kink at 50 K in the ZFC magnetization and the irreversibility between ZFC and FC curves were observed and ascribed to the spin-glass-like transition in the low temperature region. Both ac susceptibility and thermoremanent magnetization (TRM) measurements confirmed this assumption.

Synthesis and characterizations of magnesium and titanium doped M-type barium calcium hexaferrites by a solid state reaction method

Magnesium and titanium co-substituted M-type barium calcium hexaferrites Ba0.5Ca0.5Fe12-2xMgxTixO19 (0.0 ≤ x ≤ 0.5) have been synthesized by a solid state reaction method and characterized by XRD, XPS, FTIR, SEM, SQUID. XRD patterns confirm single phase M-type hexaferrite and various parameters such as lattice constants, cell volume, average grain size, X-ray density and profile parameters have been calculated from XRD data. XPS survey and FTIR spectra confirm that hexagonal crystal structure is completely formed, which are correlate closely with the results of Reitveld refined XRD patterns. SEM images of the magnetic powders confirm the hexagonal platelet-like shape. The apparent irreversibility between the zero-field-cooling (ZFC) and field-cooling (FC) curves is observed below 390 K, and the ZFC magnetization curves display a broad peak at a temperature TM. The results are discussed within the framework of random particle assembly model and associated with the magnetic domain wall motion. The saturation magnetization Ms slightly increases with increasing x up to 0.2 at 300 K, and then decreases for x > 0.2. The first anisotropy constant (K1), magnetic anisotropy field (Ha) and coercivity (Hc) decrease with increasing x. These results are discussed in light of the cationic distributions based on the results of the structural refinements.

Trapped field characteristics of an HTS magnet with two holes using four magnetization methods

High temperature superconducting (HTS) magnets have widespread applications in a strong and steady magnetic field at low temperature. However, they can not be operated in persistent current mode (PCM) due to their immature joint technique without resistance. In order to realize the PCM, an HTS magnet stacked by double-hole rectangular HTS plates was proposed and fabricated. The trapped field of the HTS magnet was measured and simulated under four kinds of magnetization methods, field cooling (FC), zero field cooling (ZFC) and inner magnetization (a solenoid is placed at right/left hole of double-hole rectangular HTS magnet to magnetize HTS magnet) as well as combination of both methods. Meanwhile, the H-formulation is applied to the 3D model to analyze the electromagnetic behaviour. It was found that the trapped field of double-hole rectangular HTS magnet magnetized by FC with inner magnetization or ZFC with inner magnetization is higher than pure FC or ZFC magnetization. In inner magnetization, the trapped field of one hole in HTS magnet has no effect on the other one. In addition, the experiment results are in good agreement with numerical analysis, which can provide significant references for the magnetization method.

Magnetic properties of hematite (α − Fe2O3) nanoparticles synthesized by sol-gel synthesis method: The influence of particle size and particle size distribution

Abstract Using the sol-gel method we synthesized hematite (α − Fe2O3) nanoparticles in a silica matrix with 60 wt % of hematite. X-ray diffraction (XRD) patterns and Fourier transform infrared (FTIR) spectra of the sample demonstrate the formation of the α − Fe2O3 phase and amorphous silica. A transmission electron microscopy (TEM) measurements show that the sample consists of two particle size distributions of the hematite nanoparticles with average sizes around 10 nm and 20 nm, respectively. Magnetic properties of hematite nanoparticles were measured using a superconducting quantum interference device (SQUID). Investigation of the magnetic properties of hematite nanoparticles showed a divergence between field-cooled (FC) and zero-field-cooled (ZFC) magnetization curves and two maxima. The ZFC magnetization curves displayed a maximum at around T B = 50 K (blocking temperature) and at T M = 83 K (the Morin transition). The hysteresis loop measured at 5 K was symmetric around the origin, with the values of coercivity, remanent and mass saturation magnetization H C10K ≈ 646 A/cm, (810 Oe), M r10K = 1.34 emu/g and M S10K = 6.1 emu/g respectively. The absence of both coercivity (HC300K = 0) and remanent magnetization (Mr300K = 0) in M(H) curve at 300 K reveals super-paramagnetic behavior, which is desirable for application in biomedicine. The bimodal particle size distributions were used to describe observed magnetic properties of hematite nanoparticles. The size distribution directly influences the magnetic properties of the sample.

Dielectric, magnetic and magneto-dielectric properties of (La, Co) co-doped BiFeO3

BLFCO [Bi1−xLaxFe1−xCoxO3 (x = 0.00, 0.01, 0.03, 0.05, 0.10)] ceramics were synthesized using sol-gel technique. The effect of Lanthanum (La) and Cobalt (Co) co-doping in BiFeO3 (BFO) on structural, electrical, magnetic and magneto-dielectric (MD) properties are systematically investigated. The phase purity and crystal structures were studied using x-ray diffraction technique. The dielectric properties [dielectric constant (ε) and tangent loss (tanδ)] were studied as a function of frequency and temperature for pure and co-doped BFO samples. The magnetization study reveals that the ferromagnetic (FM) properties in La and Co co-doped samples enhance with an increasing dopant concentration. The coercive field is found to increase with the doping concentration suggest a competition between the antiferromagnetic and FM ordering. The zero-field-cooled (ZFC) and field-cooled (FC) magnetization measurements of these samples also confirm the change in the magnetic behaviour of BLFCO as doping concentration increases. ZFC and FC magnetization curves split at low temperature with sharp cusps suggest a spin-glass like behaviour of BLFCO. The pure and co-doped samples exhibit a MD coupling effect. Furthermore, the anomaly near the magnetic phase transition (around the Neel temperature of BFO) implies the MD coupling in BLFCO samples.

Effect of α-Fe₂O₃ Phase on the Magnetic Interactions in Nickel Ferrite (NiFe₂O₄) Nanoparticles.

We report on the effect of α-Fe₂O₃ phase in the magnetic properties and magnetic interactions in nickel ferrite (NiFe₂O₄-NFO) nanoparticles synthesized by co-precipitation method. Structural analysis confirms the formation of the cubic inverse spinel phase without any impurities for the NFO sample annealed in air at 650 °C. When the annealing temperature is increased to 750 °C and 850 °C, α-Fe₂O₃ impurity phase is formed along with the parent NFO phase. Raman spectra recorded at room temperature (RT) confirm the presence of pure NFO phase for the sample annealed at 650 °C, and presence of α-Fe₂O₃ phase is observed in the samples annealed at 750 °C and 850 °C. Saturation magnetization values at RT for the NFO samples annealed at 650 °C, 750 °C and 850 °C are 34 emu/g, 19 emu/g and 28 emu/g respectively. Zero Field Cooled (ZFC) and Field Cooled (FC) measurement reveals the super-paramagnetic behavior along with competing magnetic interactions in all the samples. For the NFO sample annealed at 750 °C and 850 °C, a drop in ZFC magnetization and a small kink in FC magnetization observed around 245 K indicate the presence of a Morin transition (TM) from the α-Fe₂O₃ phase. Anisotropy constants were calculated for all the samples using the law of approach to saturation (LAS) method. The magnetocrystalline anisotropy energy distribution function for the NFO samples annealed at 750 °C and 850 °C exhibit broad peak due to the random distribution of spins associated with different particle size.

Competing magnetic interactions, low and high temperature magnetic properties of 0.3NiFe2O4–0.7Na0.5Bi0.5TiO3 nanocomposites

Abstract We report on temperature dependent magnetization and anisotropy properties, magnetic interactions at low temperatures, high temperature magnetic properties and frequency dependent dielectric properties of 0.3NiFe2O4–0.7Na0.5Bi0.5TiO3 nanocomposites. X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) techniques are employed to study the crystal structure, morphology and the chemical state of the NiFe2O4 (NFO) nanoparticles, Na0.5Bi0.5TiO3 (NBTO) nanorods and nanocomposites. XRD and Raman spectroscopy studies indicate the formation of NFO, NBTO and the nanocomposites in pure phase. SEM and TEM images indicates the presence of both nanoparticles (from NFO) and nanorods (from NBTO) in the 0.3NiFe2O4–0.7Na0.5Bi0.5TiO3 nanocomposites and the lattice planes with respect to both the phases are confirmed from the selected area diffraction pattern. Magnetization measurements at various temperatures (300 K, 40 K, 10 K and 2 K), field cooled (FC) and zero field cooled (ZFC) magnetization from 300 K to 2 K are measured for the nanocomposites. Saturation magnetization value at 300 K and 2 K for the nanocomposites is seen to be 14.62 emu/g and 16.80 emu/g respectively. Existence of spin glass behavior and competing magnetic interactions in the 0.3NiFe2O4–0.7Na0.5Bi0.5TiO3 nanocomposites is confirmed from the ZFC and FC magnetization studies. Curie temperature value for 0.3NiFe2O4–0.7Na0.5Bi0.5TiO3 nanocomposites is observed to be 900 K. Frequency dependent dielectric studies shows the relaxation behavior of the nanocomposites with two relaxation times of 5.803 × 10−2 s and 2.770 × 10−4 s arising from NFO and NBTO phases.

Tracking of the electronic re-ordering in Fe3O4/OA nanoparticles using magnetometry

Abstract We performed structural and magnetic investigation of Fe3O4/OA nanoparticles prepared by solvothermal method. Based on XRD, TEM and FTIR examination, investigated sample contained monodisperse, 5 nm-sized spherical magnetite nanoparticles coated with oleic acid. Magnetic measurement of the hysteretic curves at 5 K in zero-field cooled (ZFC) and field-cooled (FC) regime confirmed presence of exchange bias effect. ZFC/FC measurements were performed in applied magnetic fields: 10 Oe, 100 Oe, 200 Oe, 500 Oe and 1000 Oe. Zero-field cooled magnetization curves recorded in 10 Oe and 100 Oe exhibited behavior characteristic for low coercivity Nanomaterials. Same sample exposed to the ZFC/FC measurement protocol in 200 Oe, 500 Oe and 1000 Oe showed increase in ZFC magnetization in the certain temperature range. The observed feature is attributed to the local changes in the magnetite electronic structure, occurred through the spin reorientation process.

Magnetic resonance and magnetization studies of Fe implanted TlInS2 and TlGaSe2 crystals

In this article, the results of investigations of the structure and magnetization of iron implanted TlInS2 and TlGaSe2 layered ferroelectric—semiconductor crystals have been reported. SEM studies revealed that a high—fluency implantation with Fe ions brings to metal nanoparticle formation in the near-surface irradiated region of both samples. Ferromagnetic Resonance (FMR) investigations exhibited an out-of-plane uniaxial magnetic anisotropy of Fe-implanted surface layer of the crystals. A soft ferromagnetic state in the Fe-implanted surface layer of the crystals has been observed from the magnetization measurements in a wide temperature interval. An unexpected magnetization versus temperature behaviour has been revealed by field-cooled (FC) and zero-field-cooled (ZFC) magnetization measurements. It has been found that the temperature dependencies of the ZFC magnetization of both samples are dominated on FC—curve in the temperature region of ∼145–393 K and ∼58–370 K for Fe—implanted TlGaSe2 and TlInS2, respectively. The observed phenomenon has been discussed taking into account various interaction mechanisms between magnetic nanoparticles, including attractive magnetic dipole-dipole interaction and repulsive electrostatic and interparticle exchange coupling interactions.

Spin glass freezing, magnetocapacitance and dielectric anomalies in 0.3NiFe2O4-0.7BiFeO3 nanocomposite

Abstract We report on magnetocapacitance, spin dynamics through AC succeptability measurements and dielectric anomalies in 0.3NiFe2O4 – 0.7BiFeO3 nanocomposite. Structural studies (purity and phase) and surface morphology of the 0.3NiFe2O4 – 0.7BiFeO3 nanocomposite were examined by X-ray diffraction (XRD), Raman Spectra, transmission electron microscopy (TEM) and scanning electron microscopy (SEM). TEM and SEM images indicate the uniform distribution of nanoparticles in parent pahase as well as in the composite. Energy dispersive X-ray (EDX) analysis indicates the presence of Ni, Fe, O and Bi elements in 0.3NiFe2O4 – 0.7BiFeO3 nanocomposite. Magnetization measurements were performed at 300 K, 50 K and at 2 K and the Field Cooled (FC) and Zero Field Cooled (ZFC) measurements were carried out from 350 K to 2 K. ZFC and FC magnetization curves exhibit a hump around 30 K indicating the existence of competing magnetic interactions and possible spin galss behaviour. AC succeptibility measurements at various frequencies confirm the spin glass freezing behaviour of 0.3NiFe2O4 – 0.7BiFeO3 nanocomposite around 25 K with the relaxation time and activation energy in the order of 10−7 s and 0.938 meV respectively. The dielectric constant and dielectric loss at various frequencies and temperatures indicate the dielectric relaxation behaviour of 0.3NiFe2O4 – 0.7BiFeO3 nanocomposite. A rapid increase in the dielectric constant near the antiferromagnetic transition temperature (TN ∼ 643 K) of BiFeO3 indicates the existence of magneto-electric coupling in this composite. Magnetocapacitance (MC) of 0.3NiFe2O4 – 0.7BiFeO3 composite was measured at room temperature and the MC values of 13.5% and 7.8% (at 5000 Oe) are observed when the pellet is perpendicular and parallel to the magneticfield direction respectively. The presented magnetic and dielectric studies reveal the existence of magnetoelectric coupling and spin glass frezing of 0.3NiFe2O4 – 0.7BiFeO3 nanocomposite.