Low temperature magnetic studies on PbFe0.5Nb 0.5O3 multiferroic

PbFe0.5Nb0.5O3 (PFN), a well-known A(B′1/2B″1/2)O3 type multiferroic, was successfully synthesized in single phase by a single step solid state reaction method. The single phase PFN was characterized through XRD, microstructure through SEM, and magnetic studies were carried out through a temperature dependent vibrating sample magnetometer (VSM) and neutron diffraction (ND) measurements. PFN exhibits a cusp at around 150 K in the temperature dependent magnetic susceptibility corresponding to the Néel temperature (TN1) and another peak around 10 K (TN2) corresponding to spin-glass like transition. In the temperature dependent ND studies, a magnetic Bragg peak appears at Q=1.35 Å−1 (where Q=4πsinθ/λ, is called the scattering vector) below TN (150 K) implying antiferromagnetic (AFM) ordering in the system. On the basis of Rietveld analysis of the ND data at T=2 K, the magnetic structure of PFN could be explained by a G-type antiferromagnetic structure

Low-temperature neutron diffraction and magnetic studies on the magnetoelectric multiferroic Pb(Fe0.534Nb0.4W0.066)O3

We report detailed low-temperature magnetic and neutron diffraction studies on 0.8 Pb(Fe0.5Nb0.5)O3�0.2 Pb(Fe0.67W0.33)O3 which is written as Pb(Fe0.534Nb0.4W0.066)O3 (PFWN) in the general form. Magnetic susceptibility measurement data show that PFN exhibits antiferromagnetic to paramagnetic transition (TN) around 155 K (Matteppanavar et al. in J Mater Sci 50:4980�4993. doi:10.1007/s10853-015-9046-5, 2015). In the present solid solution, the magnetic susceptibility (�) shows Néel temperature enhanced up to around 187 K. Temperature-dependent neutron diffraction studies well support the tuning up of TN from 155 to 187 K. On decreasing the temperature, for T < TN (TN = 187 K), an extra peak grows at scattering vector Q = 1.35 à �1, which indicates the onset of antiferromagnetic ordering. The observed magnetic structure is G-type antiferromagnetic with the propagation vector, k = 0.25, 0.5, 0.5. The refined monoclinic lattice parameters (a, b and c), angle (β), unit cell volume, derivative of unit cell volume, magnetic moments and integrated intensity of magnetic peak (111) show anomaly around the TN, which is a manifestation of spin�lattice coupling. Also, the lattice parameters (a, b and c) and unit cell volume exhibit negative thermal expansion below TN and a large thermal expansion above TN. © 2017, Springer Science+Business Media New York

Composition Dependent Room Temperature Structure, Electric and Magnetic Properties in Magnetoelectric Pb (Fe1/2Nb1/2) O3Pb (Fe2/3W1/3) O3 Solid-Solutions

We report on the studies of room temperature (RT) crystal structure, electric and magnetic properties of (1−x) Pb(Fe1/2Nb1/2)O3 – x Pb(Fe2/3W1/3)O3 (PFN1−x – PFWx) (x = 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0) solid solutions through the measurements of X-ray diffraction, FTIR, scanning electron microscopy (SEM), Neutron diffraction, Raman, Magnetic, Mössbauer and ferroelectric measurements. FTIR spectra showed two main perovskite related transmission bands. The SEM analysis shows an average grain size of 2 μm for all the solid solutions. Rietveld refinement was performed on RT X-ray diffraction (XRD) and neutron diffraction (ND), which reveals, the monoclinic phase for x = 0.0 with space group Cm and Cubic phase for x = 1.0 with space group Pm-3m. In other words, increasing x, the samples exhibit a gradual phase transition from monoclinic to cubic. In addition, the Raman spectroscopy corroborates the change in structural symmetry from monoclinic (Cm) to cubic (Pm-3m) on varying x. The coexistence of both monoclinic and cubic symmetries was observed between x = 0.2–0.8. Magnetic measurements shows that, the magnetic phase transition from paramagnetic to antiferromagnetic (AFM) was observed at or above RT for x = 0.6 and above. The magnetic structure was refined using the propagation vector k = (½, ½, ½) and structure was found to be G-type antiferromagnetic. Magnetic properties (M-H loops) shows, a weak ferromagnetic behaviour with antiferromagnetic ordering at RT. At RT, x = 0.0–0.6 the samples exhibits disordered paramagnetic property but weakly coupled with antiferromagnetic domains. But, x = 0.8 and 1.0 samples show antiferromagnetic and they are weakly coupled with paramagnetic domains. The temperature dependent magnetization (M(T)) confirms, the augmentation of Néel temperature (TN) from 155 K to 350 K on increasing x. Mössbauer spectroscopy confirms superparamagnetic nature with the presence of Fe in 3+ state and on increasing x, the spectra changes from doublet to sextet. The ferroelectric (P-E) study confirms the existence of ferroelectric ordering with leaky behaviour. The reasonable ferroelectric loops with antiferromagnetic properties indicate samples with x = 0.2–0.6 show good magnetoelectric characteristics and may find applications in multiferroics

Structural and magnetic properties of nanocrystalline BaFe12O19 synthesized by microwave-hydrothermal method

Nanocrystalline BaFe12O19 powders were prepared by microwave-hydrothermal method at 200 °C/45 min. The as-synthesized powders were characterized by using X-ray diffraction (XRD), thermogravimetry (TG) and differential thermal analysis (DTA). The present powders were densified at different temperatures, i.e., 750, 850, 900 and 950 °C for 1 h using microwave sintering method. The phase formation and morphology studies were carried out using XRD and field emission scanning electron microscopy (FE-SEM). The average grain sizes of the sintered samples were found to be in the range of 185–490 nm. The magnetic properties such as saturation magnetization and coercive field of sintered samples were calculated based on magnetization curves. A possible relation between the magnetic hysteresis curves and the microstructure of the sintered samples was investigated

Electric field-induced tuning of magnetism in PbFe0.5Nb0.5O3 at room temperature

We study the influence of electrical poling, carried out at room temperature, on the structure and magnetism of Pb(Fe0.5Nb0.5)O-3 by analyzing the differences observed in structural and magnetic properties before and after the electrical poling. The changes observed in magnetization of Pb(Fe0.5Nb0.5)O-3 before and after electrical poling exhibit considerably strong converse magnetoelectric effect at room temperature. In addition, the strengthening of Fe/Nb-O bond due to electrical poling is discussed on the basis of Raman spectral studies and analysis of neutron diffraction patterns. The potential tunability of magnetization with electrical poling can be an ideal tool for realization of application potential of this multiferroic material. (C) 2015 AIP Publishing LLC

Size Control and Magnetic Property Trends in Cobalt Ferrite Nanoparticles Synthesized Using an Aqueous Chemical Route

Cobalt ferrite (CoFe2O4) is an engineering material which is used for applications such as magnetic cores, magnetic switches, hyperthermia based tumor treatment, and as contrast agents for magnetic resonance imaging. Utility of ferrites nanoparticles hinges on its size, dispersibility in solutions, and synthetic control over its coercivity. In this work, we establish correlations between room temperature co-precipitation conditions, and these crucial materials parameters. Furthermore, post-synthesis annealing conditions are correlated with morphology, changes in crystal structure and magnetic properties. We disclose the synthesis and process conditions helpful in obtaining easily sinterable CoFe2O4 nanoparticles with coercive magnetic flux density (H-c) in the range 5.5-31.9 kA/m and M-s in the range 47.9-84.9 A.m(2)Kg(-1). At a grain size of similar to 54 +/- 2 nm (corresponding to 1073 K sintering temperature), multi-domain behavior sets in, which is indicated by a decrease in H-c. In addition, we observe an increase in lattice constant with respect to grain size, which is the inverse of what is expected of in ferrites. Our results suggest that oxygen deficiency plays a crucial role in explaining this inverse trend. We expect the method disclosed here to be a viable and scalable alternative to thermal decomposition based CoFe2O4 synthesis. The magnetic trends reported will aid in the optimization of functional CoFe2O4 nanoparticle

Evidence for Room-Temperature Weak Ferromagnetic and Ferroelectric Ordering in Magnetoelectric Pb(Fe0.634W0.266Nb0.1)O3 Ceramic

We report the evidence of weak ferromagnetic and ferroelectric ordering in polycrystalline Pb(Fe0.634 W0.266Nb0.1)O3 (0.8(PbFe2/3W1/3)O3�0.2Pb(Fe1/2Nb1/2) O3) (PFWN) ceramic at room temperature. The Pb(Fe0.634 W0.266Nb0.1)O3solid solution synthesized through the columbite method. The obtained single-phase Pb(Fe0.634 W0.266Nb0.1)O3ceramic was subjected to X-ray diffraction, neutron diffraction, magnetization, Mössbauer spectroscopy, and ferroelectric measurements. The X-ray diffraction and neutron diffraction pattern confirms the formation of single phase without any traces of pyrochlore phases, having cubic structure with Pm-3m space group. The Rietveld refinements were carried out on both patterns, and ND data confirms the G-type antiferromagnetic structure with propagation vector (k = 1/2, 1/2, and 1/2). However, along with the antiferromagnetic ordering of the Fe spins, we also observed the existence of weak ferromagnetism. This result was confirmed through (i) a clear opening of hysteresis (M � H) loop, (ii) bifurcation of the field-cooled (FC) and zero-field-cooled (ZFC) susceptibilities, (iii) spin-glass behavior, and (iv) Mössbauer spectroscopy. © 2016, Springer Science+Business Media New York

Synthesis and Studies of High-Temperature Electrical Properties of Pb0.8Bi0.2Fe0.734W0.266O3 Solid Solution

The Pb0.8Bi0.2(Fe0.734W0.266)O3 (PBFW) high temperature ceramic has been successfully synthesized by the modified columbite method. The phase purity was confirmed by the room temperature X-ray diffraction measurement and it confirms the formation of cubic structure with Pm-3m space group. The lattice parameters were obtained from the Rietveld refinement technique; with a = b = c = 3.9750 Å. From the Scanning Electron Micrograph; the average grain size were measured about 1 µm and the Gaussian distribution showed uniform distribution of particles with small amount of porous nature. Temperature-dependent ferroelectric (P-E loop) measurement confirms the presence of polar Nanodomains along with leaky behavior owing to the conducting nature of the sample. A detailed study of frequency dependent permittivity and loss tanδ evidenced the Maxwell-Wagner type of polarization. The Non-Debye type of relaxation in the PBFW was confirmed by analyzing the Impedance spectra and fitting the Kohlraush-Williams-Watt function to the electric modulus at few selected temperatures. The impedance spectra reveal that the grain boundaries are more resistive than grains. By fitting the Johnscher's power law to the ac conductivity and from the ‘n' value; we conclude that the system has Correlated Barrier Hopping (CBH) conduction mechanis

Effect of Sm3+ substitution on structural and magnetic investigation of nano sized Mn-​Sm-​Zn ferrites

Nano size Mn0.4Zn0.6SmxFe2-​xO4 (x = 0.00, 0.01, 0.02, 0.03, 0.04, and 0.05) ferrites were prepd. by soln. combustion method. The structural and magnetic properties of samples were characterised by X-​ray diffractometer, Fourier transform IR spectrometer, transmission electron micrographs and magnetic properties at room temp. The X-​ray diffraction patterns and two prominent absorption bands in the frequency range 375-​589 cm-​1 confirmed the single phase with spinel cubic structure. The av. nano crystallite sizes were in best agreements with transmission electron microscope images. Magnetic studies revealed the narrow hysteresis loops of ferrimagnetic nature at room temp. The values of satn. magnetization (Ms)​, remanence magnetization (Mr)​, coercivity (Hc)​, remanence ratio (Mr/Ms)​, magneton no., anisotropy const. and Yaffet-​Kittle angle decreased with the increase in Sm3+ ion concn. was attributed to relative no. of ferric ions on the tetrahedral sites diminished and reduced the Sm-​Fe interaction

Low temperature Mössbauer spectroscopic studies on Sm3+ doped Zn-Mn ferrites

For the first time, we report on the low temperature Mössbauer spectroscopic study of Zn2+ 0.5Mn2+ 0.5Sm3+ xFe3+ 2�xO4 (where x = 0.01�0.05) prepared by the modified solution combustion method using a mixture of urea and glucose as a fuel. The Mössbauer spectroscopy at room and low temperatures was applied to understand the magnetic properties of the samples. The room temperature Mössbauer spectroscopy results suggest that the occupation of the octahedral sites by Sm3+ ions leads to the distortion enhancement of 57Fe nuclei environments, which leads to an increase in quadrupole splitting � values of D2 and D3 doublets. The low temperature Mössbauer spectroscopy results indicate that the presence of Sm3+ ions in the octahedron sites causes the decrease in the number of Fe�O�Fe chains. The transformation of Mössbauer spectra doublets into Zeeman sextets is accompanied by a significant decrease in the magnitude IM of Mössbauer spectra intensity within the 0�1.2 mm/s velocity range normalized to its value at 300 K. This drop in the temperature dependence of IM allows one to obtain the magnetic phase transition temperature TM from the Mössbauer experiment. © 2017 Elsevier B.V