Showing papers by "S. M. Yusuf published in 2013"
TL;DR: In this article, polycrystalline M-type barium hexaferrite (BaFe12O19) samples have been synthesized by solution combustion route at different pH and calcination conditions in order to reduce the coercivity for microwave applications in low-temperature co-fired ceramic (LTCC) substrates.
Abstract: Polycrystalline M-type barium hexaferrite (BaFe12O19) samples have been synthesized by solution combustion route at different pH and calcination conditions in order to reduce the coercivity for microwave applications in low-temperature cofired ceramic (LTCC) substrates. Structural, morphological, and magnetic properties of BaFe12O19 were studied by x-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), Raman spectroscopy, vibrating sample magnetometry (VSM), and Mossbauer spectroscopy. The formation of a single-phase hexagonal structure was confirmed by XRD. The Raman spectra reveal all characteristic peaks of BaFe12O19, illustrating the phase purity and crystal lattice symmetry of the synthesized material. Mossbauer spectra illustrate the existence of Fe3+ cations at all five crystallographic lattice sites. The microstructural features observed by FESEM disclose the growth of nanoregime particles into hexagonal platelet particles after calcination at temperatures from 800°C to 1200°C. The VSM results show a lower coercivity (1350 Oe to 3500 Oe) together with reasonably high saturation magnetization (55 emu/g to 60 emu/g) and a high bulk resistivity (>109 Ω-cm) at room temperature. The dependence of magnetic and electrical properties on the preparation and processing conditions is also discussed.
60 citations
TL;DR: In this paper, the authors carried out magnetization measurements on BiFeO3 core/NiFe2O4 shell nanoparticles, and searched for the exchange bias phenomenon in this system.
Abstract: We have carried out magnetization measurements on BiFeO3 core/NiFe2O4 shell nanoparticles, and searched for the exchange bias phenomenon in this system. The core-shell nature of these nanoparticles has been established from the transmission electron microscopy images. The neutron diffraction study establishes that the core is G-type antiferromagnetic, while the shell is ferrimagnetic in nature. The search for an exchange bias phenomenon in the core-shell system shows a shift of the field-cooled (FC) hysteresis loops, at 5 K, along the magnetic field axis. The present investigation shows an unusual shift of the zero field-cooled (ZFC) hysteresis loop along the magnetic field axis as well. An enhancement of the remanent magnetization along with a decrease in the coercivity is also observed in the FC case, as compared to the corresponding values in the ZFC case, which is not found commonly in any conventional exchange-biased system. All these features indicate the presence of an interface exchange coupling between core and shell of the studied nanoparticles.
40 citations
TL;DR: In this article, the effect of Ni substitution on the magnetic properties of polycrystalline Ni2+xMn1−xSn (x = 0, 0.05, and 0.1) Heusler alloys using the magnetization and neutron diffraction measurement techniques.
Abstract: We report the effect of Ni substitution on the magnetic properties of polycrystalline Ni2+xMn1−xSn (x = 0, 0.05, and 0.1) Heusler alloys using the magnetization and neutron diffraction measurement techniques. The paramagnetic to ferromagnetic transition temperature (Curie temperature, TC) has been tuned with the substitution of Ni at the Mn sites (TC≈ 349, 337, and 317 K for x = 0, 0.05, and 0.1 samples, respectively) without a significant reduction in the magnetic entropy change −ΔSM. For a magnetic field change from 0 to 5 T, −ΔSM of 2.9, 2.5, and 2.2 J kg−1 K−1 have been observed for x = 0, 0.05, and 0.1 samples, respectively. From the neutron diffraction study, it has been found that with increasing x, the Mn site ordered moment decreases. −ΔSM as a function of changing magnetic field and Curie temperature follows the molecular mean field model. The studied Ni2+xMn1−xSn alloys, with their nontoxic constituent elements and low-cost, can be used for magnetic cooling over a wide temperature range of 278–...
19 citations
18 citations
16 citations
TL;DR: In this paper, a single-phase formation of the compounds in the monoclinic structure with a space group P21 has been confirmed using the Rietveld refinement of the powder X-ray and neutron diffraction patterns at room temperature.
Abstract: Oxalate (ox) and phenanthroline (phen) ligands based one dimensional spin chain molecular magnets, [{Fe(Δ)Fe(Λ)}1−x{Cr(Δ)Cr(Λ)}x(ox)2(phen)2]n (x = 0, 0.1, and 0.5) have been designed, and synthesized using a hydrothermal synthesis method. The Rietveld refinement of the powder X-ray and neutron diffraction patterns at room temperature confirms the single-phase formation of the compounds in the monoclinic structure with a space group P21. The compounds consist of two ligands, the oxalate (C2O42−) as a coordination acceptor building block and the neutral phen (C12H8N2) as a coordination donor building block. Both ligands are connected to Fe ions of different symmetry {Fe(Δ) and Fe(Λ)}, thus forming an alternating zigzag chain like crystal structure having the repeating unit of [phen-Fe(Δ)-C2O4-Fe(Λ)-phen]n. The chain is infinite in length and lies in the crystallographic ac plane. The interchain is well separated with an intermetallic distance of ∼8.8 A and the absence of an interchain π–π overlap between the organic ligands, resulting in a magnetic isolation between the interchains. The Mossbauer spectroscopy reveals the presence of high spin states of the Fe2+ ions of the compound for x = 0 whereas, both high-spin Fe2+ (t2g4eg2, S = 2) as well as low spin Fe2+ (t2g6eg0, S = 0) states are present for the compounds x = 0.1 and 0.5. The dc magnetization measurements show that the compounds exhibit spontaneous magnetization below ∼9 K. The transition temperature is found to be ∼8.7, 8.2 and 4.0 K for x = 0, 0.1 and 0.5 compounds, respectively. Moreover, a short range antiferromagnetic spin–spin correlation around 18–45 K has been observed for the compounds x = 0 and 0.1. An application of the Ising chain model to the dc magnetization data reveals the presence of a one-dimensional magnetic nature of all compounds with alternately spaced magnetic Fe sites. It is observed that the different Lande g factors (3.4 and 2.8) and exchange coupling constant values (−86 and −54 K) for x = 0 at two alternating Fe sites give rise to a ferrimagnetic-like behavior of the chains. The ferrimagnetic chain like structure transforms toward antiferromagnetic with Cr doping i.e. for x = 0.1 and 0.5. A hysteresis loop with a giant coercivity (3.2 T for x = 0) has been observed at 1.6 K, indicating a hard magnet-type behavior. The frequency dependence of the peak temperature in ac susceptibility vs. temperature curves for the x = 0 compound has been fitted and analyzed using the Arrhenius law as well as the power law, which exclude the possibility of a spin glass behavior. The fitted parameters (Δ/kB = 208 K and τ0 = 2.9 × 10−14 s obtained from the Arrhenius law, and τ0 = 6.1 × 10−8 s, and zν = 2.6 from the power law) show that the compound obeys the Glauber dynamics and is a real ferrimagnetic one-dimensional single chain magnet. In addition, the high pressure magnetization measurements for the x = 0 compound show an enhancement in the transition temperature from ∼8.7 to 10.7 K with increasing pressure. The observation of both a one-dimensional spin chain nature and giant coercivity (3.2 Tesla) in such compounds opens up new opportunities to design and develop low dimensional molecular chain magnets through the appropriate choice of ligands using the hydrothermal synthesis method, because the observation of magnetic hysteresis of molecular origin in single-molecule magnets is considered one of the most relevant achievements in molecular magnetism.
15 citations
TL;DR: In this article, a quasi-one-dimensional dispersive magnetic excitation was observed in the frustrated triangular-lattice spin-2 chain oxide Ca${}{3}$Co${}_{2}$O ${}_{6}$
Abstract: Using inelastic neutron scattering, we have observed a quasi-one-dimensional dispersive magnetic excitation in the frustrated triangular-lattice spin-2 chain oxide Ca${}_{3}$Co${}_{2}$O${}_{6}$. At the lowest temperature ($T=1.5$ K), this magnon is characterized by a large zone-center spin gap of $\ensuremath{\sim}$27 meV, which we attribute to the large single-ion anisotropy, and disperses along the chain direction with a bandwidth of $\ensuremath{\sim}$3.5 meV. In the directions orthogonal to the chains, no measurable dispersion was found. With increasing temperature, the magnon dispersion shifts towards lower energies, yet persists up to at least 150 K, indicating that the ferromagnetic intrachain correlations survive up to six times higher temperatures than the long-range interchain antiferromagnetic order. The magnon dispersion can be well described within the predictions of linear spin-wave theory for a system of weakly coupled ferromagnetic chains with large single-ion anisotropy, enabling the direct quantitative determination of the magnetic exchange and anisotropy parameters.
15 citations
TL;DR: In this paper, the influence of gold particle addition on structural and magnetic ordering of iron oxide in a glass matrix was studied, where the silica-phosphate glasses containing iron oxide and Au were prepared by the melt quench technique.
13 citations
06 Feb 2013
TL;DR: In this article, the particle size increases with increasing the heat treatment (HT) temperature and Ni ion concentration, and hyperfine sextets appear and become predominant in nanoparticles with 800 °C HT.
Abstract: NixZn1−xFe2O4(x = 05,06,07) nanoparticles were prepared using coprecipitation method and were heat treated at 200, 500 and 800 °C Structure and hyperfine interactions were studied by X-ray diffraction and Mossbauer spectroscopic techniques, respectively The particle size increases with increasing the heat treatment (HT) temperature and Ni ion concentration Only a quadrupole doublet was observed for Ni05Zn05Fe2O4 ferrite, heat treated at 200 °C For higher heat treatment temperatures, hyperfine sextets appear and become predominant in nanoparticles with 800 °C HT However, the quadrupole doublet remains with reduced intensity The results interpreted in terms of an existence of size distribution of nanoparticles
6 citations
TL;DR: In this paper, the structural and magnetic properties of Prussian blue-based molecular magnets are investigated using atomic force microscopy (AFM), X-ray diffraction (XRD), infrared (IR) spectroscopy, and dc magnetization measurements.
Abstract: Crystalline films (thickness ∼1 μm) of Prussian blue-based molecular magnets, synthesized using electrochemical method at two different reduction potentials −0.5 and −0.9 V, result into K0.1CrII1.45[CrIII(CN)6] · mH2O (film 1) and K0.8CrII1.1[CrIII(CN)6] · mH2O (film 2), respectively. The structural and magnetic properties of such films are investigated using atomic force microscopy (AFM), X-ray diffraction (XRD), infrared (IR) spectroscopy, and dc magnetization measurements. The film morphology, examined using AFM, shows uniformly distributed triangular crystallites over the substrate surface. The presence of CrIII–C≡N–CrII sequence, in the range of 1,900 to 2,300 cm−1 in IR spectra, confirms formation of Prussian blue analogues. The XRD results reveal information about the crystalline nature of the films and the relative intensities of the Bragg peaks change with the K+ ions. The exchange interaction between Cr ions through C≡N ligand confirms that the electron transfer from C≡N molecule to Cr ions is ferrimagnetic in nature. The high Curie temperatures (TC) are found to be ∼195 and ∼215 K for film 1 and film 2, respectively. The higher value of TC is attributed to the inclusion of more K+ ions for film 2, resulting decreases in the CrIII(C≡N)6 vacancies and increases in the number of nearest neighbors of CrII ions. The branching in the zero field-cooled and field-cooled magnetization data below Curie temperature is explained in terms of kinetic behavior of magnetic domains with different cooling conditions and the presence of water molecule vacancies in the lattice.
6 citations
TL;DR: The field-induced evolution of the magnetic ordering in (CuBr)Sr{}_{2}$Nb${}{3}$O${}_{10}$ with a $⅓$ magnetization plateau has been investigated by neutron diffraction under magnetic fields up to 10 T.
Abstract: The field-induced evolution of the magnetic ordering in (CuBr)Sr${}_{2}$Nb${}_{3}$O${}_{10}$ with a $⅓$ magnetization plateau has been investigated by neutron diffraction under magnetic fields up to 10 T. With an increasing magnetic field, the zero-field helical antiferromagnetic (AFM) phase, AF1, with \ensuremath{\kappa} $=$ [0 $⅜$ $\textonehalf{}$] is replaced by a simple ferromagnetic phase with \ensuremath{\kappa} $=$ [0 0 0], the formation of which is, however, retarded by the appearance of a second AFM, AF2, with \ensuremath{\kappa} $=$ [0 $⅓\ensuremath{\sim}0.46$]. Upon further increasing of the magnetic field, the AF2 phase disappears and only the ferromagnetic phase persists. The results clearly show that the magnetization plateau, induced by the competition between field-induced ferromagnetic, F, and AF2 phases, is coincidentally situated at $M$ $=$ $⅓$ ${M}_{S}$ of the dc magnetization curve. The AF1 and AF2 phases have strongly differing magnetic propagation vectors and are therefore not directly related.
06 Feb 2013
TL;DR: In this article, a molecular magnet based on Prussian blue analogues, K0.3Mn2.85[Cr(CN)6]2⋅nH2O, has been synthesized using co-precipitation method, and its structural and magnetic properties are investigated using X-ray diffraction (XRD), infra red spectroscopy (IR) and dc magnetization measurement techniques.
Abstract: Molecular magnet based on Prussian blue analogues, K0.3Mn2.85[Cr(CN)6]2⋅nH2O, has been synthesized using co-precipitation method, and its structural and magnetic properties are investigated using X-ray diffraction (XRD), infra red spectroscopy (IR) and dc magnetization measurement techniques. The XRD study confirms the crystalline nature of the compound with a face centered cubic (fcc) structure (space group Fm3m). The positions of the absorption bands in the IR spectrum (∼1900-2300 cm−1), confirm the formation of Prussian blue analogue. The magnetization measurement shows a soft ferrimagnetic nature of the compound with negligible coercive field. The Curie temperature (TC) and magnetization at 5 K are found to be ∼60 K and ∼ 8.2 μB/f.u. respectively.
TL;DR: Neutron powder diffraction experiments have been performed to investigate the nature of magnetic ordering, as a function of temperature and magnetic field, in the compound Ca3Co1.8Fe0.2O6, and found magnetic short-range ordering (SRO) coexists with the SDW long-rangeordering (LRO) at all temperatures below TN.
Abstract: Neutron powder diffraction experiments have been performed to investigate the nature of magnetic ordering, as a function of temperature (1.5?100?K) and magnetic field (0, 2 and 4?T), in the compound Ca3Co1.8Fe0.2O6. In zero applied field, the compound orders magnetically in the incommensurate spin density wave (SDW) structure (TN???20?K). Under an applied field of ?2?T, an incommensurate-to-commensurate magnetic phase transition has been observed. With a further increase in the magnetic field (?4?T), the commensurate magnetic structure transforms into a ferrimagnetic structure. In zero applied field, magnetic short-range ordering (SRO) coexists with the SDW long-range ordering (LRO) at all temperatures below TN. In an applied magnetic field (2 and 4?T), SRO is converted into LRO only over the temperature range 12?20?K; however, below ?12?K, an increase in the volume fraction of the SRO has been observed. The correlation length for the SRO (below ?12?K) also gets affected by the application of a field.
TL;DR: In this article, the magnetocaloric properties of Ni2+xMn1−xSn (x = 0, 0.05 and 0.1) Heusler alloys were investigated by using the dc-magnetization measurement technique.
Abstract: We have investigated the magnetocaloric properties of Ni2+xMn1−xSn (x = 0, 0.05 and 0.1) Heusler alloys by using the dc-magnetization measurement technique. A reduction in the paramagnetic to ferromagnetic transition temperature (Curie temperature, TC) has been observed with a substitution of Ni at the Mn site (from TC ∼ 349 K for x = 0 to ∼ 317 K for x = 0.1 sample). With an increase in x, a very small reduction in the value of the magnetic entropy change −ΔSM has been observed. The −ΔSM values have been found to be ∼ 2.1, 1.8 and 1.5 J kg−1 K−1 for x = 0, 0.05 and 0.1 samples, respectively, for a magnetic field change from 0 to 30 kOe. The hysteresis loss has also been found to be very small for all the compositions. Moreover, a non-toxic as well as a cost effective nature of the studied Ni2+xMn1−xSn alloys can make them promising candidates for magnetic refrigeration near room temperature.
TL;DR: In this article, a detailed temperature dependent (5 −250 K) neutron diffraction study was conducted to understand the emergence of low temperature glassy phase in widely known itinerant ferromagnet SrRuO3 is remotely understood.
Abstract: The emergence of low temperature glassy phase in widely known itinerant ferromagnet SrRuO3 is remotely understood. In order to understand this aspect, we have undertaken a detailed temperature dependent (5–250 K) neutron diffraction study. We observe a freezing of the octahedral tilt near the ferromagnetic transition and an unusual deviation in the octahedral tilt near the onset of low temperature spin glass like phase. A reduction of the ordered magnetic moment and a decline in the total integrated magnetic intensity is observed around the temperature where the glassy behaviour starts to appear. The magnetotransport study also reveals the possibility for an additional magnetic ordering by demonstrating a peak in magnetoresistance at the low temperature side as well. The neutron diffraction study presented here provides useful information to understand the observed unusual low temperature magnetic phenomena in SrRuO3.