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A high degree of spin polarization in half-metallic double perovskites is a prerequisite for several applications in spintronics, which depends crucially on the cationic order of the systems. This paper reports a study on tailoring the structure and morphology of nano-sized Sr2Fe1-xZnxMoO6 (x = 0.05, 0.1, 0.15) materials to improve their spin polarization. The combined analysis of synchrotron X-ray diffraction and magnetization data shows that Zn replaces Fe in the B sites. Although the majority of particles have lateral dimensions in the range 30–60 nm as observed by scanning electron microscope, the samples with x = 0.1 and 0.15 show finite-size effects with superparamagnetism below room temperature and a reduced Curie temperature (from 410 K for x = 0.05–390 K for x = 0.15). The results are due to the formation of networks of insulating Mo–O–Zn–O–Mo linkages and anti-phase boundaries, which divide the particles into smaller domains with a mean diameter of ∼11 nm as determined via a Langevin fit. The almost perfectly ordered structure in the nanodomains is responsible for a high magnetoresistance ratio. A value of -42% at 5 K in 50 kOe is recorded for the sample x = 0.15. Via fitting the magnetoresistance curve using the Inoue-Mekagawa theory, the spin polarization of 99% is determined.

In this paper, we report the H2S sensing properties of partially inverse copper ferrite (CuFe2O4) nanoparticles with sizes ranging from 16 nm to few hundreds of nanometers prepared through hydrothermal method. Effects of annealing temperature on the particle size, microstructure and gas-sensing properties of spinel ferrite were studied through scanning electron microscopy, synchrotron X-ray powder diffraction and resistance measurement. Electrical conduction mechanism is discussed based on the cation distribution in the lattice and resistance contribution from the grain boundaries. Gas sensing ability of the samples was recognized for H2S concentrations from 5 down to 0.5 ppm and in working temperature range from 50 to 250 °C.

Sn-substituted yttrium iron garnet samples, Y3Fe5-xSnxO12 (x = 0–0.1, step 0.02) were prepared using a citrate sol–gel method and followed by a sintering process. Synchrotron X-ray diffraction (SXRD), X-ray absorption near edge structure (XANES), scanning electron microscope (SEM) and Fourier infrared spectroscopy (FTIR) measurements were used to investigate the structure parameters, valence state of Fe, oxygen vacancies and lattice distortion in the samples. The magnetic properties of the samples were measured with the SQUID and VSM equipments. The Sn substitution and oxygen vacancies cause the transformation of Fe3+ to Fe2+ which leads to the decrease of Curie temperature and slight increase of saturation magnetization. Temperature dependence of the resistivity in the range of 300–573 K was investigated to elucidate the conduction mechanism in the samples. The resistivity of the sol-gel derived samples was found to be nine orders of magnitudes lower than the value for the bulk sample prepared by flux-grown method. The effects of Fe2+ centers, lattice dislocation, porosity and grain boundary on the resistivity are discussed. This study indicates that Sn-substituted yttrium iron garnets are good candidates for sensor elements which operate based on electrical signals.

Indium-substituted yttrium iron garnet samples, Y3Fe5−xInxO12 (x = 0–0.7, step 0.1), were prepared using a citrate solgel method. Synchrotron X-ray diffraction (SXRD) measurements combined with the Rietveld refinement technique were used to investigate the crystallization, structure parameters and lattice distortion in the samples. Magnetization and Curie temperature of the samples were measured with the SQUID and VSM equipments. The non-magnetic indium ions were found to reside at the octahedral sites, leading to an increase of the total magnetization and a decrease in the Curie temperature. Molecular field coefficients Naa, Ndd and Nad were determined by fitting the experimental thermomagnetization curves in the framework of a two-sublattice ferrimagnetic model. The stiffness constant of the spin waves, D, in these samples was calculated based on the exchange interaction constants, Jij, and its temperature dependence was derived for the sublattice magetizations. The calculated results for D(T) are in good agreement with the experimentally measured data and are significantly large around room temperature.

Co-substituted Y3-2xCa2xFe5-xVxO12 samples (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 0.95 and 1) were prepared by using citrate sol-gel method. Synchrotron X-ray diffraction (SXRD) measurements combined with Rietveld refinement technique were used to investigate the crystallization, structural parameters and lattice distortion in the samples. Magnetization and Curie temperature were studied by means of a vibrating sample magnetometer (VSM). Molecular-field coefficients Naa, Ndd and Nad of the samples were determined by fitting the experimental thermomagnetization curves in the framework of two-sublattice ferrimagnetic model. The information of local structure change was employed to analyze the influence of the substitution effects in the magnetic interactions.

In this paper, we report the H₂S sensing properties of partially inverse copper ferrite (CuFe₂O₄) nanoparticles with sizes ranging from 16 nm to few hundreds of nanometers prepared through hydrothermal method. Effects of annealing temperature on the particle size, microstructure and gas-sensing properties of spinel ferrite were studied through scanning electron microscopy, synchrotron X-ray powder diffraction and resistance measurement. Electrical conduction mechanism is discussed based on the cation distribution in the lattice and resistance contribution from the grain boundaries. Gas sensing ability of the samples was recognized for H₂S concentrations from 5 down to 0.5 ppm and in working temperature range from 50 to 250 °C.

This study examines the effect of substituted concentration on the structure and magnetic properties of Y3Fe5-xInxO12 (x = 0.1 ÷ 0.7) powder samples prepared using the sol-gel method. The morphological properties of the samples were analysed using XRD, SEM. The single phase of garnet was obtained in x = 0.1 ÷ 0.6 samples. The lattice parameters of the samples exhibit a linear increase with the increasing In3+ content, which can be explained by a substitution of In3+ ions for Fe3+ ions, considering the larger ionic radius of In3+ compared with that of Fe3+. Crystallite sizes were determined via the XRD data which are of 38 – 49 nm while the particle sizes were estimated from SEM images to be in range of 50 - 100 nm. Magnetization and Curie temperature of the single phase samples were studied by magnetization curves in fields up to 10 kOe and in the temperature range from 80 K to 560K. With the increase of In3+, the magnetization gradually increases while the Curie temperature decreases due to the occupation of In atoms at the a sites and the reduction of intersublattice interaction, respectively. Keywords: Yttrium iron garnet, Indium substitution, cation distribution, magnetization, Curie temperature. References[1] R. L. Streever, Anisotropic exchange in ErIG, Journal of Magnetism and Magnetic Materials 278 (1-2) (2014) 223-230.[2] N.I. Tsidaeva, The magnetic and magnetooptical properties of Y-substituted erbium iron garnet single crystals, Journal of Alloys and Compounds 374 (1-2) (2004) 160-164.[3] Y.Nakata, T. Okada, M. Maeda, S. Higuchi and K. Ueda, Effect of oxidation dynamics on the film characteristics of Ce:YIG thin films deposited by pulsed laser deposition, Optics and Lasers in Engineering 44 (2) 2006, 147-154.[4] M. Laulajainen, P. Paturi, J. Raittila, H. Huhtinen, A.B. Abrahamsen, N.H. Andersen and R. 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Jadhav, Magnetic properties of In Substituted ytrium iron garnet (YIG), Rev. Res. 1(10) (2012) 1-4.[10] G. Cuijing, Z. Wei, J. Rongjin, Z. Yanwei, Effect of In3+ substitution on the structure and magnetic properties of multi-doped YIG ferrites with low saturation magnetizations, Journal of Magnetism and Magnetic Materials 323, (2011) 611-615.[11] Vu Thi Hoai Huong, Dao Thi Thuy Nguyet, To Thanh Loan, Luong Ngoc Anh, Nguyen Phuc Duong, Than Duc Hien, Structural and magnetic properties of Y3-2xCa2xFe5-xVxO12 nanoparticles prepared by sol-gel method, Proceeding of the 3rd International Conference on Advanced Materials and Nanotechnology (2016) 219-223.[12] Imaddin A. Al-Omari, Ralph Skomski, David J. 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Results of crystal analysis. –III, Philosophical magazine Series 6, 32: 191, 505 – 518.[17] Ronald W. Armstrong, Crystal dislocations, Crystals 6, 1 (2016) 9.[18] Gerald F. Dionne, Molecular field coefficients of substituted yttrium iron garnets, Journal of Applied Physics. 41 (1970) 4874.[19] M.A. Gilleo, Ferromagnetic insulators: Garnets, in: E.P. Wohlfarth (Ed.), Handbook of Magnetic Materials, Volume 2, North-Holland Publishing Company, 1980, 1-54.[20] Z. Azadi Motlagh, M. Mozaffari, J. Smighian, Preparation of nano-sized Al-substituted yttrium iron garnets by the mechanochemical method and investigation of their magnetic properties, Journal of Magnetism and Magnetic Materials 321 (2009) 1980-1984.[21] P. Belov and I.S. Lyubutin, Effective magnetic fields at tin nuclei in substituted iron garnets CaxY3-x SnxFe5-x O12, Soviet Physics JETP 22 (3) (1966) 518 – 520.

X-ray diffraction, scanning electron microscopy, and vibrating sample magnetometry were used to investigate the structural, morphological, and magnetic properties of Ni1-xZnxFe2O4 nanosubmicron powders (x = 0–0.8). The samples were prepared by a coprecipitation method at temperatures between 600 and 1100 degree Celsius for five hours. The lattice constant, average size of coherent scattering regions, and cation distribution were analyzed by Rietveld refinement of the X-ray diffraction measurements. Scanning electron micrographs showed that the particle size increased from the nano- to the submicron scale as the zinc content increased from x = 0 to x = 0.8. The magnetization as functions of temperature and applied magnetic field were measured on the single-phase samples obtained at an annealing temperature of 1100 degrees Celsius. The derived saturation magnetization and Curie temperature were compared to those of the bulk counterparts reported previously and discussed based on finite-size effects and poss...

Structural and magnetic properties of NiCr x Fe2− x O4( \(x=0.7\) and 0.9) spinel ferrites prepared by sol-gel route have been investigated using synchrotron X-ray powder diffraction (SXPD) and magnetization measurements. The gel products after annealing at 1000°C for 2 h are found to crystallize in cubic phase. Rietveld refinements of X-ray diffraction and SXPD patterns revealed that the compounds are almost perfect inverse spinel with only few percents of nickel atoms located at the tetrahedral sites. Transmission electron microscopy (TEM) images showed that the samples are composed of nanoparticles with mean diameter in agreement with crystallite size determined by the Rietveld analysis. The spontaneous magnetization \(M_{s}\) as a function of temperature was determined via magnetization curves measured using vibrating sample magnetometer in a temperature range from 88 K to above Curie temperature in applied fields up to 10 kOe. The sample \(x=0.9\) shows a cancelation of sublattice magnetizations at 400 K. The temperature dependence of saturation magnetization \(M_{s}\) of the samples can be described in terms of molecular-field model for collinear spins with the derived cation distributions.

Gadolinium iron garnet (GdIG) nanoparticles with mean particle size of about 37 nm have been synthesized by citrate precursor gel formation followed by annealing at 800 °C for 2 hours. Magnetic behavior of clustered GdIG nanoparticles was studied in temperature range from 5 K to above Curie temperature. The sample shows a magnetization compensation temperature T comp ∼286.5 K and a Curie temperature T C ∼560 K. In comparison with the bulk saturation magnetization, the sample exhibits lower spontaneous magnetization in the temperature region from 5 K to T comp whereas higher spontaneous magnetization is observed at higher temperatures up to near the Curie point. The magnetization curves show a differential susceptibility in high fields which increases sharply below 50 K. At very low temperatures, irreversibility was observed in the magnetization loops, enduring in the fields up to ∼12.5 kOe. The spontaneous magnetization, high - field susceptibility and low - temperature irreversible effect were discussed based on a model for the interacting particles consisting of ferrimagnetically aligned core spins and disordered spins in surface layer which become frozen at low temperatures. We proposed a mechanism for the enhancement of the spontaneous magnetization above T comp in which the Gd and Fe spins in the surface layer are largely decoupled at high temperatures and the surface Fe spins realign to the magnetic moment of the core. The magnetic coercivity H c at low temperatures is governed by the effective anisotropy whereas in the vicinity of the compensation point a peak in the coercive force shows up as a result of the so - called paraprocess with the maximum value of 1.2 kOe at T comp and by further increasing temperature the coercivity decreases and eventually vanishes at about 500 K. The interparticle interactions were found to play an important role in the hysteresis behavior of the sample.

Yttrium iron garnet (YIG) nanoparticles have been synthesized by citrate precursor gel formation with subsequent heat treatment. The single phase sample of standard garnet cubic structure was obtained after sintering the gel at 800 °C for 2 h. The lattice constant a is comparable to the value of the bulk material. The mean crystallite size determined from the broadening of X-ray diffraction (XRD) peak is 35 nm. Transmission electron microscope (TEM) analysis shows that the particles form clusters with the particle size in the range of 22–55 nm. The Curie temperature T C of 560 K was determined via the temperature dependence of the saturation magnetization. The hysteresis loop M ( H ) were measured at temperatures between 5 and 560 K and in applied magnetic fields up to 20 kOe. The coercive force H c was found to decrease monotonously with increasing temperature and above room temperature the hysteresis loops manifest the superparamagnetic character which obey Langevin theory. The blocking temperature T B and the interparticle interaction parameter T o were also determined and based on that an effective anisotropy constant K eff was found to be 2.0 × 10 4 erg/cm 3 for the particles of 35 nm in diameter. The thermal variation of the saturation magnetization ratio M s ( T )/ M s (5 K) is in good agreement with that reported earlier for bulk samples and thus can be very well described by the mean–field approximation for the two Fe 3+ sublattices.

NiFe2O4 nanoparticles have been synthesized by citrate precursor gel formation with subsequent heat treatment. Differential thermal and thermogravimetric (DTA/TG) analyses show that the metal citrates decomposed around 230 ◦C followed by crystallization of the ferrite. X-ray diffraction (XRD) patterns reveal the formation of the cubic spinel phase in the samples after sintering the gel at 350 ◦ C, 500 ◦ C and 700 ◦C. For the samples annealed at 350 ◦C and 500 ◦C a small amount of ˛-Fe2O3 was detected whereas single phase was obtained for the sample annealed at 700 ◦ C. The lattice constant a for all the samples is comparable to the value of the bulk material. The mean crystallite size DXRD of the samples determined from XRD line broadening is 26.2–28.5 nm. Transmission electron microscope (TEM) analysis shows that the single-phase particles form clusters with the particle size in the range of 21–82.5 nm and the most probable value DTEM of 55.4 nm. Magnetic measurements show that its Curie temperature TC is close to the bulk value while the spontaneous magnetization Ms at 5 K is lower than that of the bulk. The thermal variation of Ms in the temperature range from 5 to 300 K can be best fitted to a modified Bloch T˛ law with the exponent value ˛ ≈ 2. The magnetization data are explained with reference to the disordered surface spins and the finite size effects. In this investigated temperature range, the coercive force Hc decreases linearly with increasing temperature. The coercivity mechanism in the nanoparticle sample with broad particle size distribution is expected to be complex and different factors which affect the Hc value were proposed.