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In this work, a novel combustion synthesis of nanocrystalline MgFeO materials using hexamethylenetetramine as a fuel is reported. The properties and features of as-prepared MgFeO materials were evaluated by X-ray diffraction, thermogravimetric analysis, vibrating sample magnetometer, UV-vis and Fourier transform infrared spectroscopic techniques, and field emission scanning electron microscope. The as-prepared MgFeO materials crystallized in cubic spinel phase with an average crystalline of 26.34 and 21.54 nm for the samples obtained at pH = 1 and 10, respectively. It is evident from the room temperature (300 K) field (±15 kOe) dependence magnetization measurements that the saturation magnetization of the MgFeO materials is 25.86 emu/g and 9.98 emu/g for pH = 1 and 10, respectively. For the as-prepared MgFeO materials, the agglomeration of fine particles is seen through a micro-image under higher magnification. The FT-IR spectra reveal a typical metal-oxygen absorption band at ∼568 cm for the as-prepared MgFeO materials which suggest the intrinsic stretching vibration of the metal (Fe-O) at the tetrahedral site. [ABSTRACT FROM AUTHOR]

The nanocrystalline SrFe O materials were prepared by a sol-gel auto-combustion method using different fuels such as citric acid, dextrose, aniline, and hexamine. The combustion product obtained from all the fuels except from that of aniline show a single phase of SrFe O materials upon annealing at 1000 C/2 h. The combustion product obtained from aniline as fuel shows SrFe O as the main phase with α-Fe O as impurity. No notable change in lattice parameters is observed due to variation in fuels for SrFe O materials. With a little change in the NIR relative reflectance (72-85 %) on fuels, the different SrFe O materials display high NIR reflectance in the wavelength range, 1500-2500 nm. The photoluminescence emission spectra of SrFe O materials reveal a broad emission peak at ∼350 nm which is reminiscent to the Ba-based hexaferrite, BaFe O . The FESEM images expose quite dissimilar morphology for the various fuels used in the synthesis of SrFe O materials. Hysteresis loops for all the nanocrystalline SrFe O materials observed under the applied field of ±1.5 T at room temperature exhibit hard ferromagnetic property. The SrFe O materials produced from glycine and aniline as fuels exhibit highest and lowest M values of 61.3 and 50.5 emu/g, respectively. [ABSTRACT FROM AUTHOR]

This paper reports the eco-friendly synthesized BaFeO phase materials by a molten salt flux approach and their experimental findings. The reaction mixture (BaCO and Fe O ) annealed with the mixture of salt (NaCl:KCl) flux yielded good quality nanocrystalline hexagonal ferrite BaFeO phase materials. The plate-like hexagonal-shaped BaFeO phase morphology with random particle sizes of ∼370 to 940 nm is seen for the good quality flux-annealed sample. The room-temperature magnetic hysteresis loop of the BaFeO sample exhibits hard ferromagnetic saturation magnetization ( M ) of 50.23 emu/g at 15 kOe, and coercive field ( H ) is 3500 Oe. The determined energy bandgap ( E ) is found to be 3.58 eV for the BaFeO phase material. The Fourier transform infrared (FT-IR) spectral features confirm the presence of Fe-O and Ba-O bonds in the flux-synthesized BaFeO materials. The photoluminescence (PL) emission peak (∼360 nm) intensity of BaFeO materials varies regardless of annealing temperatures. The different salt flux-synthesized BaFeO materials appear as brown- and dark gray-colored powders that can be applied as a ceramic color pigment due to its high NIR reflectivity. [ABSTRACT FROM AUTHOR]

We report here a simple solution combustion synthesis of nickel oxide (NiO) nanoparticles by using urea as a fuel and nickel nitrate as an oxidizer. The structural, morphological, optical, and magnetic properties of NiO nanoparticles were investigated by X-ray diffraction (XRD); highresolution scanning electron microscopy (HRSEM); Fourier transform infrared (FT-IR), nearinfrared (NIR), and UV-vis spectroscopic techniques; and vibrating sample magnetometer. The combustion-synthesized NiO nanoparticles have a cubic structure with an average crystalline size of ∼8 nm without any impurity. The agglomeration of fine particles with particle sizes in the range of 19.5 ∼22.4 nm is seen by HRSEM images. The FT-IR spectrum of NiO nanoparticles reveals that an absorption band at ∼493 cm is due to the bending vibration of NiO phase. The NIR spectrum exhibits poor NIR reflectivity of the combustion product, NiO. The as-prepared combustion product was black in color in contrast to the usual light green color. The room-temperature magnetization of the as-prepared NiO nanoparticles reveals an antiferromagnetic behavior. [ABSTRACT FROM AUTHOR]

The physical properties of high-pressure synthesized polycrystalline Cu(ReMoCa)SrO samples are reported in this article to attract the scientific community. The present system undergoes a structural phase transition from cubic symmetry (for x=0, 0.1) to tetragonal for 0.2≤ x≤0.4 and again cubic perovskite structure for x=0.5 and 0.6. The pristine compound ( x=0) undergoes a ferromagnetic (ferrimagnetic) transition with high T∼460 K. Neither the Curie temperature nor the effective magnetic moment is enhanced upon Mo substitution. The mechanism of the suppression of ferromagnetism in the present system is discussed assuming a localized electron system which is reminiscent of W substitution (Balamurugan et al. in J. Appl. Phys. 101:09N501, ). The temperature dependence of electrical resistivity, ρ decreases with x=0-0.4 and then increases for x=0.5 and 0.6. Though the suppression of ferromagnetism in the present system is similar to W-substitution, interestingly the former one (Mo) shows different results on structural and transport electrical properties which urge for further studies. The interesting aspect of the present work is for x=0.6, the specific heat data shows significant electronic contribution, whereas the resistivity measurement reveals insulating behavior. [ABSTRACT FROM AUTHOR]

In order to check the solubility of Zn in the (SrZn)CoO perovskite structure and their research findings, several polycrystalline samples have been prepared under wide extreme synthesis conditions at 6 GPa/1300-1650 °C. While 0.05≤ x≤0.3 compositions revealed single phased cubic structure materials, x>0.3 showed multi-phased materials for (SrZn)CoO system. Like other substituted perovskite cobalt oxide systems (Ca, Y, Ho and Ce), the transport properties of the present materials show rather sizable changes with respect to ' x', although there are insignificant variations in lattice parameter and in Curie temperature, T. All the present samples show soft ferromagnetism with T in the range of 272-285 K for 0.05≤ x≤0.3. The effective paramagnetic moment, P determined from the paramagnetic region decreases upon the substitution of Zn for Sr-site. These P (3.3-2.8 μ/Co) values for 0.05≤ x≤0.3 compositions seem to suggest that the Co lie in intermediate spin (IS) state for the present (SrZn)CoO series, although they are slightly smaller than those expected for IS-Co; P=3.87 μ/Co. The electrical resistivity is found to increase with increase of ' x' for the investigated samples. The temperature and field dependence of both positive and negative magnetoresistance (MR) are noted for the Zn substituted samples. About 5% of -MR is observed for x=0.05 sample around the transition temperature (280 K) under the field strength difference, Δ H=90 kOe. The present research findings are compared with our previous results on different perovskite cobalt oxides. [ABSTRACT FROM AUTHOR]

In this present investigation, both YBaRuCuO and SrReCaCuO perovskite compounds were prepared through high pressure/high temperature (HPHT) synthetic route. The as-prepared samples were structurally characterized by powder X-ray diffraction technique and their magnetic properties were measured. Both compounds crystallized in cubic symmetry with a different space group. The refined lattice parameter for the YBaRuCuO and SrReCaCuO compounds are found to be a=8.332(2) Å with space group, Fm-3m (225) and a=7.967(4) Å space group Pm-3m (221), respectively. The cuprate ordered perovskite compound shows ferromagnetism with high Curie temperature, T at ∼450 K whereas the YBaRuCuO compound reveals mixed magnetic natures below ∼170 K which is complicated by the presence of magnetic order in the Ru and Cu sublattices. Below 170 K, the compound shows two antiferromagnetic-like transitions (in ZFC mode) at ∼135 K and ∼60 K. With a further decrease of temperature (below 60 K), the susceptibility crosses negative (diamagnetic) signal at ∼35 K and shows maximum negative susceptibility at ∼11 K. By decreasing the temperature below 11 K, the negative susceptibility decreases and shows positive magnetic susceptibility at 2 K. In the fc mode curve, the sample shows broad antiferromagnetic like transition at ∼55 K. At low temperature (below 30 K), an increase in susceptibility signal is seen in the fc magnetic susceptibility curve. The magnetic parameters, such as Weiss temperature, θ and the effective paramagnetic moment, p obtained from the linear region of χ( T) plots are found to be −307.25 K and 3.74 μ/Ru, respectively, for the YBaRuCuO compound. The negative sign of θ reveals the antiferromagnetic correlations of the compound. While these studied compounds are already known to the literature, the synthesis method (HPHT) employed for the present YBaRuCuO compound is a new approach and quite different from the routine conventional solid state synthesis approach. [ABSTRACT FROM AUTHOR]

The impact of slightly tuning molar ratio in the starting materials on the physical properties of 1212-type rutheno-cuprate, YSrRuCuO (nominal) samples prepared under four synthesis approaches are reported. Interestingly, all samples clearly show the differences in the physical properties of the samples prepared under different synthetic protocols. However, neither XRD nor EDX reveal any notable differences in the crystal structure or sample composition. All the samples exhibit magneto-superconducting properties ( H=5 Oe) which are slightly varied with synthetic approaches. The high field ( H=10 kOe) temperature dependence of magnetization data shows a sharp ferromagnetic transition around 150 K and all the samples obey Curie-Weiss linear behavior above 180 K. The experimental effective paramagnetic moment for the various samples is in the range of 2.5 and 2.7 μ/Ru which are in line with the literature report. The magnetization, M( H) isotherm curves measured at 5 K and −10 kOe≤ H≤10 kOe conditions reveal weak ferromagnetic-like hysteresis loops for all samples with returning moment ( M) and coercive field ( H), whereas the high field M( H) loops indicate soft ferromagnetic behaviors with magnetic saturation. The saturation moment of the samples is slightly varied with the synthesis approaches. None of the samples showed bulk superconductivity ( $T_{\mathrm{c}}^{R = 0})$ down to 2 K, while all samples show onset transitions ( $T_{\mathrm{c}}^{\mathrm{onset}}$) except the sample prepared by approach-3. The latter approach sample shows semiconducting behavior down to 2 K. The $T_{\mathrm{c}}^{\mathrm{onset}}$ noticed at 34 K, 12 K, and 6 K for the sample prepared by approach-1, 2, and 4, respectively. The nearly linear dependence suggests that hopping conduction is dominant in certain temperature range for all samples. The magneto-transport features of these samples exhibit maximum magnetoresistance (MR) at low temperatures. Remarkably, the sample prepared by approach-1 shows largest −MR about 77% at low temperature 2 K and H=90 kOe which stimulates for further investigations. Among the four synthesis approaches employed in the present study, we can probably suggest that the approach-1 (0.5YO+0.5SrO+1.5SrCuO+0.9RuO+0.6CuO) is the preferable method to achieve the best sample ( in terms of magneto-transport features). [ABSTRACT FROM AUTHOR]

The optimized nominal composition, (RuCu) SrYCuO sample, has been prepared through high-pressure and high-temperature solid-state densification method. The obtained material has been studied by X-ray (laboratory) diffraction powder technique, magnetization and detailed magneto-transport measurements. The title compound indicates bulk magneto-superconducting properties under field strengths of H=10, 100, 500 and 1000 Oe. It shows diamagnetic transition at T=54, 38, 20 and 8 K for H=10, 100, 500 and 1000 Oe, respectively, in the zero-field-cooled susceptibility measurements. The high-field ( H=5 and 10 kOe) molar susceptibility measurements show sharp ferromagnetic transition at ∼150 K with reduced molar susceptibility values. The various field dependence of magnetization, M( H), isotherm curves recorded at constant temperatures (5, 10, 25, 50, 100 and 150 K) indicate ferromagnetic saturation, whereas the MH curves measured at 200 and 300 K conditions reveal the paramagnetic state of the compound. Though the sample showed onset transition temperature, $T_{\mathrm{c}}^{\mathrm{onset}}$, at ∼34 K under different field strengths ( H=0, 10, 30, 50, 70 and 90 kOe), no $T_{\mathrm{c}}^{R=0}$ is seen down to 2 K. Even under relatively low applied field (Δ H=10 kOe) the title compound shows large negative magnetoresistance ( MR) of about 68% at 2 K and increases with increasing the field strength up to Δ H=90 kOe ( MR=77% at 2 K). This value is amazing and probably higher than other 1212 type ruthenocuprates. The title compound which shows little negative MR (about 1%) in the high temperature regions (125-300 K) is not affected much by different field strengths. Among the different fixed temperature MR( H) isotherms, the MR( H) curve measured at 5 K shows maximum negative MR of about 47% at 90 kOe compared to other four ( T=50, 100, 200 and 300 K) MR( H) curves. [ABSTRACT FROM AUTHOR]

In this article, the magneto-transport features of 57Fe isotope (1%) doped SrCoO3 (referred to as SrCo0.99 57Fe0.01O3) perovskite compound have been investigated. The compound crystallized in cubic symmetry undergoes ferromagnetic transition around ∼270 K. The isothermal magnetization data collected at low temperature (1.8 K) indicates a characteristic of soft ferromagnet with saturation moment, Ms∼1.81 μB/Co. Interestingly, the electrical resistivity, ρ( T), measurements indicate semiconducting properties while metallic nature is seen for the pristine compound. The SrCo0.99 57Fe0.01O3 sample shows temperature and field dependence of magnetoresistance, MR, around 1.5%, which is rather smaller than of the pristine perovskite. The second part of the present work reports the attempt to dope Cd on Sr-site in the perovskite structure, Sr1− xCd xCoO3, under extreme conditions. A minimum amount of about x=0.05, 0.1 is tested for solid solution in the Sr1− xCd xCoO3 structure. However, the structural data indicate that Cd is not fully doped in the matrix for x=0.05, 0.1 samples; some of the CdO is intact as an impurity and it did not show major impact on the physical properties of the samples. The ρ( T) data reveal metallic nature for both x=0.05 and 0.1 samples with relatively low resistivity at low temperature regions, and they exhibit − MR ∼4% around ∼250 K. For x=0.05 the molar magnetic susceptibility of the sample shows ferromagnetic transition at Tc=244 K, whereas x=0.1 sample exhibits ferromagnetism at Tc=264 K. The effective Bohr magnetron parameter, peff, determined for x=0.05 and 0.1 samples is found to be 3.10 μB/Co and 3.25 μB/Co, respectively, and these data suggest intermediate spin state for Co4+ ion for both the samples. The M( H) data for both the samples reveal soft ferromagnetism. The Ms of x=0.05 reaches 1.9 μB/Co and of x=0.1 reaches 1.86 μB/Co at 1.8 K and 70 kOe conditions. [ABSTRACT FROM AUTHOR]

The magnetic, transport and specific heat measurements of 1212-type compounds crystallized in tetragonal symmetry with starting composition, Cu2.1 LnNb0.9O7.9Sr2; Ln = Er, Dy have been investigated. The Cu2.1 LnNb0.9O7.9Sr2; Ln = Er, Dy compounds showed non-superconducting properties down to 1.8 K in the magnetic susceptibility measurements. The magnetic parameter ( μeff) obtained from the linear region of inverse molar magnetic susceptibility curves agrees with the calculated values for the respective free trivalent Er and Dy ions in Cu2.1 LnNb0.9O7.9Sr2; Ln = Er, Dy compounds. Though there is no strong evidence of magnetic ordering seen from magnetic susceptibilities, the hysteresis, M( H) curve obtained at 1.8 K looks like a canted antiferromagnet. The S-shaped (slightly curved) magnetization curve suggests weak ferromagnetic interactions that exist in the Ln = Er compound. A small hysteresis is observed with the coercive field ( Hc) of 49 Oe and the remnant magnetization ( Mr) of about 0.06 μB/f.u. for Ln = Er. Interestingly, such a hysteresis loop opening is not seen for the Ln = Dy compound. While specific heat anomaly ( λ-like transition) was observed for Ln = Dy compound at low temperature (around 6 K), for Ln = Er compound such an anomaly was not seen in the specific heat measurements. The electrical resistivity versus temperature, ρ( T), data showed that the compounds Cu2.1 LnNb0.9O7.9Sr2; Ln = Er, Dy are not in metallic state and they are really semiconducting-in-nature. Interestingly, rather large magnetoresistance, MR (∼18%) was observed at low temperature ∼2 K for Er-based niobio-cuprate. [ABSTRACT FROM AUTHOR]

In this brief article, structural, magnetization studies of oxygen deficient perovskite cobalt oxides CoSrO3− δ synthesized in two different ways are reported. The structural refinements (JANA2006) of X-ray powder diffraction data indicate that the sample prepared under ambient pressure ( stage-1) shows a hexagonal structure with P63/ mmc (194) as a possible space group. The stage-1 sample subsequently sintered at 1450 °C for 1–2 h under high-pressure 6 GPa conditions ( stage-2) crystallizes in tetragonal symmetry with I4/ mcm (140) space group having a=5.444(7) Å and c=7.68(2) Å. While the stage-1 sample exhibits a paramagnetic nature in the magnetic susceptibility, M( T), measurements, interestingly the sample annealed under high-pressure conditions shows ferromagnetism in the magnetic susceptibility, M( T) and field dependence magnetization, M( H) measurements. The high-pressure annealed sample shows hysteresis opening with a quite large coercive field of 7.3 kOe at 1.8 K. The temperature dependence of the inverse molar susceptibility curves exhibits linear behavior in the high-temperature regime and could be fitted to the Curie–Weiss expression, χ( T)= C/( T− θW). The experimental values of θW and peff obtained from the linear region of the inverse molar magnetic susceptibility curves are found to be: −210.7(5) K and 2.38(2) μB/Co for stage-1 and 260.2(7) K and 1.87(3) μB/Co for stage-2 samples, respectively. A negative sign of θW indicates rather strong antiferromagnetic correlations in the stage-1 sample. Apart from these results, the structural parameters reported by various groups for the strontium-based perovskite cobalt oxides are also presented in the form of literature collections. [ABSTRACT FROM AUTHOR]

We have successfully synthesized a new 1222-type Y-based niobio-cuprate for the first time with the chemical composition, NbSr2(Y1.5Ce0.5)Cu2O10 by a high-pressure and high-temperature (HPHT) technique under different synthesis conditions. Good quality (nearly single-phase) Nb1222Y polycrystalline sample was synthesized at 1,450 ○C and 6 GPa for 2 h. It crystallizes in a tetragonal symmetry of space group I4/ mmm with lattice parameters a= b=3.863(2) Å and c=28.687(5) Å, which is isostructural with the corresponding Ru1222Y (RuSr2(Y1.5Ce0.5)Cu2O10) phase. The dc-magnetic susceptibility measurements show a mixed magnetic state at ∼29 K, which is apparently associated with magneto-superconductivity. The magnetic moment ( M) versus field ( H) curve of Nb1222Y sample measured at 1.8 K looks like a hybrid and it normally ensembles for both superconducting and a ferromagnetic curve. As the field increases, a low field diamagnetic signal emerges. However, temperature dependence of electrical resistivity of Nb1222Y did not show superconductivity, but semiconducting nature with a relatively large magnetoresistance (∼6% at almost entire region). No specific heat anomaly was observed at the vicinity of the transition temperature. [ABSTRACT FROM AUTHOR]

We have successfully synthesized a new 1222-type Y-based niobio-cuprate for the first time with the chemical composition, NbSr2(Y1.5Ce0.5)Cu2O10 by a high-pressure and high-temperature (HPHT) technique under different synthesis conditions. Good quality (nearly single-phase) Nb1222Y polycrystalline sample was synthesized at 1,450 ○C and 6 GPa for 2 h. It crystallizes in a tetragonal symmetry of space group I4/ mmm with lattice parameters a= b=3.863(2) Å and c=28.687(5) Å, which is isostructural with the corresponding Ru1222Y (RuSr2(Y1.5Ce0.5)Cu2O10) phase. The dc-magnetic susceptibility measurements show a mixed magnetic state at ∼29 K, which is apparently associated with magneto-superconductivity. The magnetic moment ( M) versus field ( H) curve of Nb1222Y sample measured at 1.8 K looks like a hybrid and it normally ensembles for both superconducting and a ferromagnetic curve. As the field increases, a low field diamagnetic signal emerges. However, temperature dependence of electrical resistivity of Nb1222Y did not show superconductivity, but semiconducting nature with a relatively large magnetoresistance (∼6% at almost entire region). No specific heat anomaly was observed at the vicinity of the transition temperature. [ABSTRACT FROM AUTHOR]

Nano particle of Fe3O4 ( nFe3O4) up to 6 at% were doped in the superconducting MgB2 samples. Despite the strong ferromagnetic nature of Fe3O4, both the ac susceptibility and the resistivity measurements show that up to 4 at% of Fe3O4, T c =38 K is not changed, whereas for 6% T c decreases by 6 K. This indicates that a low concentration of Fe does not substitute either the Mg or B sites and probably occupies the intergrain spaces. For 0.5% doped Fe3O4, an increase in J c with respect to the pure MgB2 samples is observed in the lower field and temperature regions ( H<2 T and 20 K) indicating an enhanced flux pinning and the magnetic activation, i.e., the interaction between the magnetic dipole of Fe ion and the vortices is weak in comparison to the effective pinning potential. Whereas, at H>2 T, J c of the doped samples is always less than that of MgB2, and the activation is dominant in comparison with the effective pinning potential provided by the doping. Flux jumps are observed in lower T and H regions for the samples doped up to 1% nFe3O4 only. Magnetization plots of higher Fe content samples exhibited clear paramagnetic background. Mossbauer measurements for the higher (4, 6 at%) nFe3O4 doped MgB2 samples show that at RT, the hyperfine field for both samples is ∼100 kOe and ∼120 kOe at 90 K. This means that the nFe3O4 particles decompose and form possibly an intermetallic Fe-B phase in the matrix. [ABSTRACT FROM AUTHOR]