Keywords : magnetic properties

Magnetic and dielectric properties of divalent Ca2+ and Ba2+ ions co-doped BiFeO3 nanoparticles

N. Manjula; S. Ramu; K. Sunil Kumar; R. P. Vijayalakshmi

Advanced Materials Letters, 2018, Volume 9, Issue 3, Pages 175-181
DOI: 10.5185/amlett.2018.1411

Pristine BiFeO3 (BFO) and Ca doped BiFeO3: Ba nanoparticles (NPs) were synthesized in aqueous solution by sol-gel method with Tartaric Acid as a chelating agent. EDAX measurements confirmed the presence of Ca, Ba in the BiFeO3 host lattice. X-ray diffraction analysis showed that the average grain size of the prepared samples was in the range of 09–28 nm. The lattice structure of the nanoparticles transformed from rhombohedral to tetragonal phase with Ca 2+ ions substitution increased. TEM images indicated that sphere and square shape of nanoparticles through a size ranging from 10 to 15 nm. Diffusion reflectance spectra of BiFeO3 NPs showed a substantial blue shift of ~100 nm (630 nm -> 530 nm) on Ca, Ba co-doping which corresponds to increase in band gap by 0.47 eV. Dielectric constant (ε’) and dielectric loss (ε’’) were measured in the frequency range 1 Hz to 1 MHz at room temperature. Dielectric constant and loss are increased with Ca concentration except for Ca (4 at. %). The bulk conductivity (σ) increases from 3.07 x 10 -6 S/m to 1.64 x 10 -5 S/m as the Ca concentration increased from 0.00 to 0.03. Magnetic measurements revealed the ferromagnetic character of Pristine BFO and Ca doped BiFeO3: Ba samples. It is observed that by increasing the Ca concentration the value of Mr and magnetization are varied irregularly upto Ca (4 at. %). But for x = 0.01 Mr and magnetization are highest. The values of magnetization and Mr for 1% Ca doped BiFeO3: Ba NPs are 2.99 emu/g, 1.54 emu/g, respectively, which are quite significant at room temperature. These materials have potential applications in data storage, switching devices, spintronics, sensors and microelectronic. 

Hydrothermal synthesis and electrochemical properties of MnFe2O4 nanoplates

Hanfeng Liang; Xun Xu; Jinqing Hong; Zhoucheng Wang

Advanced Materials Letters, 2017, Volume 8, Issue 11, Pages 1052-1056
DOI: 10.5185/amlett.2017.1543

MnFe2O4 nanoplates have been synthesized by a simple hydrothermal method. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), and selected area electron diffraction (SAED) have been employed to characterize the structure and morphology of the as-prepared sample. The results show that the products are plate-like morphology with 100-500 nm in length and 100-200 nm in thickness. Contrast experiments indicate that the formation of the plate-like nanostructure could be ascribed to the effect of citrate complexation. Magnetic measurements at 300 K gave the saturation magnetization and the coercive field of nanoplates 39.2 emu g -1 and 91.5 Oe, respectively. The electrochemical performance as anode material for lithium-ion batteries was further evaluated by cyclic voltammetry (CV), electrochemical impedance and charge-discharge measurements. It was demonstrated that the material could provide an initial reversible capacity of 1067 mAh g -1 at a current density of 0.1 mA cm -2 over the voltage range from 0.5 to 3.0 V. 

Effect of heat treatment on the structure and magnetic properties of Sm-Fe alloys obtained by mechanical alloying

Nikolay G. Razumov; Aleksandr S. Verevkin; Anatoly A. Popovich

Advanced Materials Letters, 2017, Volume 8, Issue 5, Pages 673-677
DOI: 10.5185/amlett.2017.7071

The effect of heat treatment on the structure and magnetic properties of Sm-Fe alloys obtained by mechanical alloying was investigated. The crystallization temperature of Sm2Fe17, an amorphous alloy obtained by mechanical alloying, was determined using differential scanning calorimetry. Based on these results, various samples were annealed at different isothermal holding temperatures, and those with the best magnetic properties were found. Experimental studies show that decreasing the isothermal holding temperature from 750 °C to 630 °C increases magnetic characteristics nearly four times. The saturation magnetization, romance and coercivity of the Sm2Fe17 powder were 121 emu/g, 28.5 emu/g and 800 Oe, respectively. 

Effect Of Grain Size On The Structural And Magnetic Properties Of Nanocrystalline Al3Fe5O12 By Aqueous Coprecipitation Method

S.E.Naina Vinodini

Advanced Materials Letters, 2015, Volume 6, Issue 8, Pages 717-725
DOI: 10.5185/amlett.2015.5874

Al3Fe5O12 (AIG) nanopowders were synthesized at different pH using aqueous co-precipitation method. The effect of pH on the phase formation of AIG is characterized using XRD, TEM, FTIR and TG/DTA. From the Scherer formula, the particle sizes of the powders were found to be 15, 21, 25 and 30 nm for pH= 9, 10, 11 and 12, respectively. It is found that as the pH of the solution increase the particle size also increases. It is clear from the TG/DTA curves that as the pH is increasing the weight losses were found to be small. The nanopowders were sintered at 900°C/4hrs using conventional sintering method. The phase formation is completed at 800°C/4h which is correlated with TG/DTA. The average grain size of the samples is found to be ~55 nm. As the pH increases the magnetization values are also increasing. The saturation magnetization was found to be 4 emu/g, 6 emu/g, 7 emu/g and 9 emu/g corresponding to pH= 9, 10, 11 and 12, respectively which clearly shows that the magnetization values are dependent on pH. Room temperature magnetization measurements established these compounds to be soft magnetic.  The dielectric and magnetic properties (εʹ, εʺ, µÊ¹ and µÊº) of AIG was studied over a wide range of frequency (1GHz-50GHz). With increase of pH both εʹ and µÊ¹ increased. This finding provides a new route for AIG materials that can be used in the gigahertz range.

A Comprative Study Of Sol-gel And Solid-state Prepared La3+ Doped Multiferroic BiFeO3

Pittala Suresh; S. Srinath

Advanced Materials Letters, 2014, Volume 5, Issue 3, Pages 127-130
DOI: 10.5185/amlett.2013.fdm.34

LaxBi1-xFeO3 (LBFO) samples were prepared by sol-gel route using citric acid as chelating agent for x = 0.0 - 0.4. The structure, dielectric and magnetic properties of the LBFO compounds were studied and compared with the corresponding properties of the materials prepared by a conventional solid state reaction. The use of the sol–gel method in preparation lowered the reaction threshold temperature by 200 °C. Effects of the preparation routes and conditions on the phase and microstructures of the materials were investigated in this study using XRD and SEM. The pure BFO without bismuth loss, which cannot be prepared by the solid state reaction, was obtained by the sol–gel method. Sol-gel synthesis could yield a pure phase material at relatively lower temperatures while the solid state method yielded powder with a small amount of the secondary Bi25FeO40 phase. Single phase LBFO prepared by sol-gel method (SG) revealed huge value of dielectric constant than same obtained by the solid state reaction method (SS). Maxwell-Wagner type dielectric dispersion is observed in sol-gel method. Dielectric constant and loss tangent are found to be higher for SG as compared to SS. Huge coercivity (HC) of the order of ~ 15 kOe is observed in both SG and SS samples due to the high anisotropy in these samples. The increase in the magnetization is observed due to the destruction of spin cycloid structure. The enhanced properties made LBFO a promising candidate for the applications in novel memory devices and spintronics.

Study Of Strontium Doping On The Structural And Magnetic Properties Of YMnO3 ceramics

Radheshyam Rai; M. A.Valente;Andrei L. Kholkin; Indrani Coondoo

Advanced Materials Letters, 2013, Volume 4, Issue 5, Pages 354-358
DOI: 10.5185/amlett.2012.9428

AnchorStructural and Magnetic properties are investigated for the Sr doped YMnO3 samples with different composition synthesized by a solid state reaction method. Sr doped YMnO3 is the most distorted perovskite of the RMnO3 series (R=rare earths); the observed sinusoidal magnetic structure is in contrast with those exhibited by the less-distorted members, which are commensurate-type antiferromagnetic structures. A typical anti ferromagnetic (AFM) to paramagnetic (PM) phase transition is observed for the sample with concentration x = 0.12 and the Néel temperature (TN) is about 160 K. With decreasing temperature, the sample with x = 0.12 exhibit a magnetic transition from a paramagnetic (PM) to a ferromagnetic (FM) state.

Template-free Synthesis and Characterization of Leaf-like Fe-Ni Microstructures

Yang Cao; Shi Gang Ai; Jinglin Zhang; Ning Gu; Shuangqi Hu

Advanced Materials Letters, 2013, Volume 4, Issue 2, Pages 160-163
DOI: 10.5185/amlett.2012.6366

Leaf-like Fe-Ni alloy have been synthesized via a facile hydrothermal approach without any soft and hard template. The structure of the leaf-like Fe-Ni alloy was characterized by Scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray energy-dispersive spectroscopy (EDX). The dendrite trunks lengths of the leaf-like Fe-Ni alloy were about 2.0μm-8.5 μm, and those of the branch trunk ranged from 850.0 nm to 4.0 μm. Furthermore, it was founded that the formation of leaf-like Fe-Ni alloy strongly depended on the reaction temperature. Moreover, the magnetic and microwave absorption properties of products with various morphologies were also compared, and the result showed that the leaf-like Fe-Ni alloy had higher ferromagnetic and microwave absorption properties compared with spherical Fe-Ni alloy.

Microwave-hydrothermal Synthesis Of CoFe2O4-TiO2 Nanocomposites

P. Raju;S. R. Murthy

Advanced Materials Letters, 2013, Volume 4, Issue 1, Pages 99-105
DOI: 10.5185/amlett.2013.icnano.130

The nanocomposites of x TiO2+(1-x)CoF2O4 (≤x≤1) powders were synthesized using microwave-hydrothermal method at a low temperature of 165°C/45min. The synthesized powder was characterized by using XRD, TEM, FTIR and DSC. The particle size was obtained from TEM study varies from 18nm to 34nm for all the nanopwders. DSC curve of composites shows no anatase to rutile phase transformation. As synthesized powder was densified using a microwave sintering method at 500°C/30min. In the XRD patterns of sintered composite samples, no peaks other than TiO2 and CoFe2O4 were observed. The grain sizes of the composites have been estimated from SEM pictures and they are in between 54 to 78nm. The dielectric properties were measured in the frequency range of 100 Hz to 1 MHz. The frequency variation of dielectric properties is understood with the help of Maxwell–Wagner type of interfacial polarization, which is in agreement with Koop’sphenomenological theory. The thermal variation of dielectric constant and loss studies were also undertaken at a constant frequency of 1kHz. Magnetic properties were also measured on all the composite samples at room temperature. The saturation magnetization (Ms) of the samples decreases with an increase of TiO2 content in CoFe2O4.

Co And Fe Doped SnO2 nanorods By Ce Co-doping And Their Electrical And Magnetic Properties

Jasneet Kaur; Jaspreet Kaur; R. K. Kotnala; Vinay Gupta; Kuldeep Chand Verma

Advanced Materials Letters, 2012, Volume 3, Issue 6, Pages 511-514
DOI: 10.5185/amlett.2012.icnano.142

In the present work, the self-assembly of Co 2+ and Fe 3+ doped SnO2 nanoparticles (Co and Fe = 5 mol% each) into nanorods by co-doping of Ce 3+ (4 mol%) ions is studied. The nanorods are prepared by a chemical route using polyvinyl alcohol as surfactant with the composition Sn0.91Co0.05Ce0.04O2 (SCC54) and Sn0.91Fe0.05Ce0.04O2 (SFC54). The X-ray diffraction (XRD), transmission electron microscopy (TEM), magnetic and electrical measurements are used to characterize these nanorods. The XRD pattern show the tetragonal rutile and polycrystalline nature of SnO2 nanorods which is also confirmed by TEM. The TEM images exhibit that the diameter of SCC54 nanorods lie in the range of 15-20 nm, length~100-200 nm whereas for SFC54 specimen, diameter ~5-15 nm and length ~50-100 nm. In our previous work, we fabricated Co and Fe (3 and 5 mol% each) doped SnO2 nanoparticles which exhibited high ferromagnetism. It is observed that on Ce 3+ co-doping, nanoparticles assembled themselves into rod like structures and the values of saturation magnetization and dielectric properties have further enhanced. Thus the nature and the concentration of dopants are found to play crucial role in tuning the morphology, magnetic and electrical properties of nanostructures. The values of saturated magnetization (Ms) are 1.14 and 0.14 emu/g and coercive field are 112 and 42 Oe, in SCC54 and SFC54 specimen, respectively, at room temperature. The variation in dielectric behavior is attributed due to the interface polarization. However, in lower frequency regime, the decreasing trend of dielectric permittivity with increasing frequency is explained by the Maxwell-Wagner theory and Koops’ model, whereas, in higher frequency region, the resonant behavior is observed due to nano size effect.

Study on synthesis of magnetic nanocomposite (Ni-Teflon) by swift heavy ion beam mixing

Jai Prakash; A. Tripathi; J.C. Pivin; Jalaj Tripathi; A.K. Chawla; Ramesh Chandra; S.S. Kim; K. Asokan; D.K. Avasthi

Advanced Materials Letters, 2011, Volume 2, Issue 1, Pages 71-75
DOI: 10.5185/amlett.2010.12187

The present work envisages synthesis of magnetic nanocomposites by ion beam mixing technique using swift heavy ion irradiation of Ni-Teflon bilayer system and its magnetic characterizations. The nanocomposite is characterized by Rutherford backscattering spectrometry (RBS), transmission electron microscopy (TEM), scanning probe microscopy (SPM) and superconducting quantum interference device (SQUID) magnetometer. Cross-sectional TEM and magnetic force microscopy (MFM) results confirm the formation of nanocomposite. Magnetic characterizations reveal that nanocomposite exhibits ferromagnetic behavior with an increase in the coercivity, which is attributed to the formation of Ni nanoparticles. The coercivity of the nanocomposite is found to be 112 Oe at room temperature which is two orders of magnitude larger than that of the bulk Ni (0.87 Oe).