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The structural and magnetic properties of Bi1-xNdxFe1-xMnxO3 ceramics prepared by the tartaric acid modified sol-gel technique have been studied to understand the effect of structural modification on the magnetic Properties of BiFeO3. The co-substitution of Nd and Mn at Bi and Fe sites respectively in BiFeO3 significantly suppress the impurity phases (Bi25FeO40, Bi2Fe4O9 etc.). The Rietveld analysis of X-ray diffraction (XRD) patterns indicates the existence of compositional driven crystal structure transformation from rhombohederal (R3c space group, higher crystal symmetry) to the orthorhombic (Pbnm space group, lower crystal symmetry) with the increase in substitution concentration due to excess chemical pressure (lattice strain). The quantitative crystallographic phase analysis has been carried out by Rietveld analysis of all the XRD patterns. Magnetic measurements reveal that co-substituted BiFeO3 nanoparticles for x=0.050 have enhanced remnant magnetization about 21 times as compared to pure one. The remnant magnetization reaches a maximum value at the morphological phase boundary (x=0.050) and further increase (x>0.050) in substitution concentration results in the reduction of remnant magnetization due to the appearance of complete antiferromagnetic ordering in the orthorhombic structure because of the significant contribution from the crystallographic phase of Pbnm space group (as obtained from the quantitative crystallographic phase contribution by the Rietveld analysis). [ABSTRACT FROM AUTHOR]

Temperature variation of DC electrical resistivity and magneto-resistivity have been measured on mono-valent, Ag- doped La1−xAgxMnO3 compounds for x=0.05–0.30. All these samples exhibit metal–insulator transitions and the transition temperature increases with applied field. The resistivity data in the metallic region, i.e. below the transition temperature could be fitted to the empirical relation ρ=ρ0+ρ1Tn. The value of exponent n, mostly varies from n=3 for zero field case to n=2 for 50 kOe field. The electrical transport in zero field is controlled by strong spin fluctuations scattering and in the presence of high magnetic field, it is mostly due to electron–electron scattering. The applied magnetic fields are found to suppress the scattering due to spin fluctuations. The resistivity data in the semiconducting region, i.e. above the transition temperature could be fitted to Mott variable range hopping model. The applied magnetic fields tend to delocalize the charge carriers in the semiconducting region and thereby decrease in hopping energy and increase in density of states has been observed. Colossal magneto-resistivity have been observed in all the above samples and the maximum value is found to be 73% for x=0.15 sample for 50 kOe field. [Copyright &y& Elsevier]

We report ferromagnetic behavior in undoped ZnO nanofibers prepared by electrospinning a solution of zinc acetate and poly vinyl alcohol followed by annealing at 550°C for about 90min. X-ray diffraction patterns of the heat treated as-spun composite fibers reveal the formation of ZnO nanowires in wurtzite structure with no noticeable impurity phases. ZnO nanowires annealed between 500°C and 600°C exhibited room temperature ferromagnetism with decreasing magnetization with increasing annealing temperature. Room temperature ferromagnetism was observed in as-spun fibers annealed in air as well as under vacuum. However, vacuum annealed nanofibers show higher magnetization as compared to air annealed fibers, which indicates that oxygen vacancy is a cause for the observed room temperature ferromagnetism in the ZnO nanofibers. [ABSTRACT FROM AUTHOR]

Nanocomposite of NiO and CoFe 2 O 4 (CFO) has been prepared using the high energy planetary ball mill technique. Both crystallographic symmetries correspond to NiO and CFO has been observed from the X-ray diffraction pattern, which indicates no major chemical reaction between the two phases. The fraction of weight percentage for CFO and NiO are obtained from the double phase Rietveld analysis by using the space group F d 3 ¯ m for CFO and F m 3 ¯ m for NiO and, it is found to be as per the expected one. Magnetocrystalline anisotropy has been studied by analyzing magnetic hysteresis loop (obtained in the field range of ±2T) by employing the Law of approach to saturation. The anomaly in the hysteresis loops at symmetric position in the nanocomposite reveals the interaction between antiferromagnetic (NiO) and ferrimagnetic (CFO) phases at the interface. [ABSTRACT FROM AUTHOR]

The magnetic properties of nanocrystalline cobalt ferrite could be tuned with substituting small amount of non-magnetic rare earth cation at Fe site in cobalt ferrite. The variation in magnetic parameter of samples could also be obtained by measuring its anhysteretic magnetization curve without tailoring its chemical composition. The magnetic parameters such as coercivity, remanent magnetization and saturation magnetization critically depend upon different values of external magnetic fields. In the present study, the anhysteretic magnetization curve of the samples CoFe2-xLaxO4 (x=0.025, 0.05, 0.075 and 0.1) has been recorded and response of coercivity to different maximum values of applied field has been investigated. It has been observed that the response of coercivity to different maximum values of applied field shows non-linear behavior. The analysis of the response of coercivity to different values of applied field in low field regime has been carried out with the help of Rayleigh laws. The analysis of the plot yields significant information about magnetic anisotropy. [ABSTRACT FROM AUTHOR]

Raman Characterization of Materials in powder form has always remained challenging because of low signal to noise ratio. We, herein, propose a method to make use of Surface Enhanced Raman Scattering (SERS) technique to improve the usefulness of Raman study of powder samples containing particles of sub wavelength size. As a case study, we have successfully applied the method to barium hexaferrite (BHF) synthesized by the modified citrate sol-gel method. The crystal structure and surface morphology of the prepared BHF powder were characterized by X-ray diffraction (XRD) and scanning electron microscopy. As many as 19 Raman peaks in a single spectrum with unpolarized laser were observed in the present work, against the commonly observed (in literature) 10–12 peaks for BHF. This report, as it is believed, will enable the research community to probe further into the distortions in crystal structure through Raman studies. • The issues associated to Raman characterization of powder sample has addressed for the first time. • The well known SERS technique has been applied to characterize Barium Hexaferrite (BHF) nanoparticles in powder form. • As many as 19 Raman modes could be observed with unpolarized laser against the commonly observed 10–12 peaks for BHF. • This work will help researchers probing further into the distortions in crystal structure of samples in powder form. [ABSTRACT FROM AUTHOR]

Al-substituted strontium hexaferrite (SrFe 12-x Al x O 19) has been synthesized by the sol-gel auto-combustion method, followed by microwave sintering at 1100 °C. The Rietveld refinement of XRD patterns reveals the hexagonal crystal symmetry with P6 3 /mmc space group. Lattice contraction has been observed with the increasing Al3+ concentration in SrFe 12-x Al x O 19. The anisotropy field is found to be ∼25 kOe for SrFe 11·5 Al 0·5 O 19. The (BH) max (maximum energy product) of 1.20 MGOe is obtained for x = 0.0 whereas there is a 63.66% enhancement of coercivity for SrFe 11·5 Al 0·5 O 19 at 300 K. However, the highest (BH) max of 1.84 MGOe has been achieved at 60 K for SrFe 11·5 Al 0·5 O 19. The criterion for a permanent magnet is satisfied by analyzing the hardness parameter. All the samples are found to be magnetically hard with (BH) max in the range (1.00–1.20) MGOe at 300 K. • Lattice contraction in SrFe12-xAlxO19 (0≤x≤0.5) • All the synthesized samples are magnetically hard • Enhancement of anisotropy field up to 25 kOe • Uniform magnetic interaction confirmed by ΔH vs M plot • Highest (BH)max of 1.84 MGOe achieved for SrFe11.5Al0.5O19 at 60 K [ABSTRACT FROM AUTHOR]

The structural and magnetic properties have been investigated in the magnetic composites of hard magnetic Barium hexaferrite (BHF) and soft magnetic Ni–Mn–Sn Heusler alloy. The magnetic composites undergo two distinct ferromagnetic to paramagnetic and ferrimagnetic to paramagnetic phase transitions corresponding to alloy and BHF phases, respectively. Magnetic biasing between the hard and soft magnetic phases has been observed in the composites when both the phases are in the ferromagnetic ordering i.e., a squeezing in the magnetic hysteresis curve is observed around H = 0. The squeezing effect may be used in the magnetic memory device application where an optimum coercivity, high remanent magnetization, and high squareness ratio are required. On the other hand, the composites show high magnetocaloric effect with a constant high value of magnetic entropy changes between the two successive magnetic transitions. This gives an advantage with wide working temperature in the magnetocaloric application. • Magnetic composite of soft magnet Ni 1.8 Mn 1.2 Sn and hard magnetic BaFe 12 O 19. • Magnetic biasing i.e., a squeezing in the M-H curve around H = 0. • Squeezing effect in the magnetic memory device application. • Constant high magnetic entropy changes between the two magnetic transitions. • Potential material for magnetocaloric application with wide working temperature. [ABSTRACT FROM AUTHOR]

Nickel ferrite fiber (NFO–F) was synthesized using the electrospinning technique and annealed at five different temperatures (500, 600, 700, 800, and 900 °C) to study its effect on crystal structure and magnetic properties. The X-Ray diffraction pattern analysis was carried out to explore its crystal structure. The morphology and microstructure of fibers were studied by employing the Field Emission Scanning Electron Microscopy technique. The crystallinity of the material increases with the increase of annealing temperature from 500 to 900 °C. The saturation magnetization of nickel ferrite fiber increases from 31.1 to 54.0 emu/g with the increase in annealing temperature. The anisotropy constant for NFO–F calculated using the Law of Approach to Saturation (LA) and it shows the highest value for 900 °C annealed sample. Hence, the hyperthermia property of NFO–NF annealed at 900 °C has been explored. The Specific Absorption Rate (SAR) of NFO–NF calculated using Linear Response Theory and the Box-Lucas models. • Fabrication of nickel ferrite nanofiber by Electrospinning method. • The study of magnetic properties by M-H and M-T curve analysis. • Nickel ferrite nanofiber annealed at 900° C suitable for Hyperthermia application. • LR theory and B-L model are used for SAR calculation. [ABSTRACT FROM AUTHOR]

The Rietveld refinement of XRD patterns reveals the crystallization of all the materials (BaFe 12-x Zn x O 19 for x = 0.0, 0.2, 0.4, and 0.6) to hexagonal symmetry with space group P6 3 /mmc. The lattice strain created in the crystal due to the ionic size mismatch of Zn and Fe. The Law of Approach (LA) to saturation method is employed to obtain the saturation magnetization (M s) and magnetocrystalline anisotropy constant (K 1) from M − H hysteresis loop. The maximum saturation Magnetization (M s) and minimum coercivity are found to be for BaFe 11·8 Zn 0·2 O 19 (i.e., x = 0.2). The magnetocrystalline anisotropy constant (K 1) reduces with the increase in temperature. The magnetic properties and magnetic crystalline anisotropy in Zn modified barium hexaferrite have been explained by considering the strain in the lattice site and superexchange interaction. [ABSTRACT FROM AUTHOR]

The barium hexaferrite (BaFe 12 O 19) is synthesized by the modified sol-gel method. The nanoparticle BHF with different average particle sizes have been prepared by using the high energy planetary ball mill. The X-ray diffraction (XRD) patterns reveal that all the materials crystallize to hexagonal crystal symmetry with P6 3 /mmc space group. It is observed that the maximum magnetization decreases with the decrease in the average particle size of BHF. However, the maximum dielectric constant is found to be for the BHF with average particle size ~24 nm. [ABSTRACT FROM AUTHOR]

Full Heusler alloy Fe 2 MnSi 0.75 Al 0.25 has been prepared by the arc melting method with proper stoichiometry followed by nitrogen atmosphere annealing. Structural and magnetic characterizations have been carried out. X-ray diffraction data analysis reveals that this alloy crystallizes to L2 1 structure in Fm 3 ‾ m space group. It exhibits ferromagnetic behavior below Curie temperature. Curie temperature is found to be around 290 K. The Kouvel-Fisher plot and the Arrott plot have been employed to understand the nature of para to ferromagnetic transition. Here values obtained for critical exponents (β = 0.5284 , γ = 1.084 , δ = 3.05336 ) are convergent with the mean-field model. Law of Approach (LA) to saturation magnetization has been employed to obtain the saturation magnetization and it is found to be maximum (2.4317 μ B /f.u.) at 50 K. [ABSTRACT FROM AUTHOR]