Query: Gd2CoMnO6

title: Synthesis and characterization of rare earth ion based double perovskite: Gd2CoMnO6
abstract: The double perovskite gadolinium cobalt manganate (Gd2CoMnO6) ceramic material was prepared via mixed oxide route. The preliminary X ray structural study reveals that the material was found in monoclinic structure. We have found the small voids with almost uniform distribution of grains from the microstructural analysis. Analysis of the dielectric and electrical data, collected in a wide range of frequency range (1 kHz 1 MHz) and temperature (25 500 degC) has provided many interesting results. We have discussed frequency dependence dielectric parameter by Maxwell Wagner model. We found that the room temperature dielectric constant at 1 kHz frequency is 300 and tangent loss is nearly equal to 2. A dielectric anomaly (ferroelectric paraelectric phase transition) was found in the temperature dependence of dielectric study. The study of diffuse phase transition exhibits the existence of relaxation process in the compound. In the Nyquist plots, both grain and grain boundary effects are observed which is characterized by (RQC) and (RQC)(RC) circuits. As the resistance decreases with increase of temperature, the material shows the semiconductor behavior. The existence of non Debye type of relaxation mechanism in the material is confirmed by the depression angle. The frequency dependence of electric conductivity has been studied using the Jonscher's power law, in which the frequency exponent n 1) signifies the translational motion with involvement of an intuitive hopping of charge carriers. The leakage current and conduction mechanism follow the space charge limited conduction phenomenon. The low leakage current density may be suitable for high temperature applications.

title: Structure, magnetism and dielectric study of nano crystalline Gd2CoMnO6
abstract: Structural, magnetization, phonon behavior, and dielectric response of nano crystalline Gd2CoMnO6 have been presented in this paper. The study shows that the material crystallizes in P21/n phase group of monoclinic crystal structure. XPS measurement shows Co2+ and Mn4+ oxidation states are present in the sample. Magnetization study reveals that sample undergoes a ferromagnetic ordering of Co2+ and Mn4+ magnetic ions around T c 132 K. Raman study shows the presence of spin phonon coupling in Gd2CoMnO6. Dielectric study reveals that the sample shows large dielectric constant and strong dispersion in mid frequency range. The dielectric loss shows there are two relaxation processes present in the material with different relaxation time and which are driven by thermally activated relaxation mechanics. Further, the Nyquist plot and AC conductivity study shows that this sample is non Debye's in nature.

title: Vibrational properties and infrared dielectric features of Gd2CoMnO6 and Y2CoMnO6 double perovskites
abstract: perovskite ceramics were obtained from the polymeric precursors method and investigated by X ray diffraction, X ray photoelectron spectroscopy (XPS) scanning electron microscopy (SEM) Raman and Fourier Transform Infrared (FTIR) spectroscopies. Our results show that these samples present similar structural and vibrational characteristics that are fully compatible with a monoclinic structure belonging to the P21/n space group, with ordered Co2+ and Mn4+ cations. Infrared reflectivity spectroscopy was employed to investigate the polar phonon features and to determine the intrinsic dielectric response of the materials. In particular, the extrapolated dielectric constants at the lower frequency infrared limit showed to be independent on the particle size, and were determined as e intr 17.8 and 16.0, for Gd2CoMnO6 and Y2CoMnO6, respectively. Otherwise, it is shown that for smaller RE radius the FTIR bands become more evidenced, due to a higher octahedral rotation and lower Co O Mn angle into the distorted monoclinic structure.

title: Synthesis and Magnetic Study of Nano Crystalline Gd2CoMnO6
abstract: oxides having great research interest due to their physical properties with some great technological application. Magnetodielectric, magnetocaloric effect, ferroelectric, exotic magnetic phases etc are some properties that double perovskite materials shows, thus received attention of researchers. Magnetic refrigeration is the great cooling technology based on magnetocaloric effect due to high energy efficiency and environmental friendly. Recently, it is found that Gadolinium (Gd) have magnetic refrigerant properties because of large magnatochloric effects at room temperature. In this paper we present the double perovskite Gd2CoMnO6 nano crystalline which was prepared by sol gel method and its magnetic properties studied by vibrating sample magnetometer (VSM) There is a paramagnetic to ferromagnetic phase transition observed in the sample. We found that paramagnetic Curie Weiss temperature of Gd2CoMnO6 is around Tc 131.27 K. Further, temperature dependent inverse magnetic susceptibility (kh 1) shows deviation from curie Weiss behavior around TG 213 K which is depicts that Griffiths phase singularities is present in this material.

title: Amino acid modified combustion synthesis, characterization and investigation of magnetic, optical and photocatalytic properties of Gd2CoMnO6 nanostructures
abstract: were synthesized through a simple combustion method at 800 degC calcination temperature in the presence of the different amino acids, including phenylalanine, beta alanine, leucine, valine and glycine, as combustion, gelling and stabilizing agents. In this work, metal nitrate salts were used as starting materials and the Gd:Co:Mn molar ratio was selected to be 2:1:1. The beta alanine was selected as the optimum amino acid. Effects of type of the amino acid and calcination temperature on the morphology and particle size of the products were investigated. X ray diffraction (XRD) Fourier transform infrared spectroscopy (FTIR) ultra violet diffuse reflectance spectroscopy (UV DRS) scanning electron microscopy (SEM) transmission electron microscopy (TEM) energy dispersive X ray (EDX) and vibrating sample magnetometer (VSM) were used for characterization and investigation of the applications of GCMO NSs. VSM results showed an antiferromagnetic behavior for the GCMO NSs. Optical properties of the NSs were investigated and the optical band gap of them was found to be 3.28 eV. Also photocatalytic properties of the GCMO NSs for the degradation of methyl violet, erythrosine and eriochrome black T were investigated.

title: Pechini synthesis and characteristics of Gd2CoMnO6 nanostructures and its structural, optical and photocatalytic properties.
abstract: GCMO NSs were synthesized by the reaction of metal nitrate salts in the presence of stabilizing agent and PG, by a Pechini method. Citric acid, maleic acid, succinic acid and 1,3,5 benzenetricarboxylic acid were used as stabilizing agents. The structure, morphology, optical, magnetic and photocatalytic properties of the GCMO NSs were investigated using various characterization techniques. Effects of type of stabilizing agent, the molar ratio of stabilizing agent:PG and also calcination temperature on particle size and morphology of the products were investigated. Also the influence of kind of pollutant on photocatalytic behavior of GCMO NSs was evaluated.

title: Role of Gd spin ordering on magnetocaloric effect and ferromagnetism in Sr substituted Gd2CoMnO6 double perovskite
abstract: The phenomenon of magnetocaloric effect occurring around the ordering temperatures for Gd2 xSrxCoMnO6 (x 0 and 0.5) has been investigated in order to disclose the effects of Sr substitution on the individual collinear Gd spin order. It is shown that 25% Sr substitution of Gd ions significantly suppresses the independent spin order, leading to enhancement of ferromagnetism. As a result, magnetic entropy change DSM) increases from +0.9 J kg 1 K 1 to +3.7 J kg 1 K 1 at Curie temperature for a change in magnetic field (DH) 6.9 T. On the other hand, the DSM changes sign at Neel temperature due to the effect of Sr substitution. We have also observed noticeably large DSM +25.84 J kg 1 K 1) and +21.01 J kg 1 K 1) for DH 6.9 T at 4f 4f negative coupling temperature (T 10 K) of x 0 and x 0.5 samples, respectively.The phenomenon of magnetocaloric effect occurring around the ordering temperatures for Gd2 xSrxCoMnO6 (x 0 and 0.5) has been investigated in order to disclose the effects of Sr substitution on the individual collinear Gd spin order. It is shown that 25% Sr substitution of Gd ions significantly suppresses the independent spin order, leading to enhancement of ferromagnetism. As a result, magnetic entropy change DSM) increases from +0.9 J kg 1 K 1 to +3.7 J kg 1 K 1 at Curie temperature for a change in magnetic field (DH) 6.9 T. On the other hand, the DSM changes sign at Neel temperature due to the effect of Sr substitution. We have also observed noticeably large DSM +25.84 J kg 1 K 1) and +21.01 J kg 1 K 1) for DH 6.9 T at 4f 4f negative coupling temperature (T 10 K) of x 0 and x 0.5 samples, respectively.

title: Giant Anisotropic Magnetocaloric Effect in Double perovskite Gd2CoMnO6 Single Crystals
abstract: The magnetocaloric effect (MCE) is described by the change in temperature of a material by magnetic field variation and is a crucial subject in magnetism; it is motivated by the desire to enhance energy efficient magnetic refrigeration for clean technology. Despite the recent discovery of the giant cryogenic MCE in double perovskites, the role of magnetic anisotropy has not yet been clearly discussed, because of the averaging effect of polycrystalline samples. Here, we investigated the anisotropic MCE in the single crystal double perovskite Gd2CoMnO6. In addition to the ferromagnetic order of the Co2+ and Mn4+ moments, the large Gd3+ moments align below TGd 21 K, exhibiting an isotropic nature. Because of the intricate temperature development of magnetically hysteretic behaviour and metamagnetism, the change in magnetic entropy along the c axis appears to be relatively small. On the contrary, the smaller but almost reversible magnetization perpendicular to the c axis leads to a large MCE with a maximum entropy change of 25.4 J/kg*K. The anisotropic MCE generates a giant rotational MCE, estimated as 16.6 J/kg*K. Our results demonstrate the importance of magnetic anisotropy for understanding the MCE and reveal essential clues for exploring suitable magnetic refrigerant compounds aiming at magnetic functional applications.

title: 4f 3d exchange coupling induced exchange bias and field induced Hopkinson peak effects in Gd2CoMnO6
abstract: Double perovskite R 2 CoMnO 6 systems, with magnetically active rare earth (R) elements, have attracted much attention because of their interesting field sensitive magnetic phenomena and remarkable physical properties. The perovskite compound Gd 2 CoMnO 6 exhibits a field induced metamagnetic phase transition from ferrimagnetic to long range ferromagnetic (FM) ordering below a critical temperature of T C ~112 K. It also shows polarization of the Co/Mn magnetic sublattice to the Gd moments resulting in antiferromagnetic (AFM) like behaviour at T N ~47 K. Further, the large change in magnetization at low temperatures of T 3+ excitations. A sharp peak at T C in AC susceptibility measurements reveals that susceptibility is the sum of the true critical maximum and Hopkinson peak contributions. Below T N ~47 K, the 4 f 3 d negative exchange interaction is responsible for the observed antiferromagnetic spin polarizations; consequently the exchange bias (EB) effect originates from the unidirectional anisotropy induced at the antiferromagnetic/ferromagnetic interface.

title: Giant magnetocaloric effect in Gd2NiMnO6 and Gd2CoMnO6 ferromagnetic insulators
abstract: We have investigated magnetocaloric effect in double perovskite Gd2NiMnO6 (GNMO) and Gd2CoMnO6 (GCMO) samples by magnetic and heat capacity measurements. Ferromagnetic ordering is observed at ~130 K ~112 K) in GNMO (GCMO) while the Gd exchange interactions seem to dominate for T 20 K. In GCMO, below 50 K, an antiferromagnetic behaviour due to 3d 4f exchnage interaction is observed. A maximum entropy \Delta}SM) and adiabatic temperature change of ~35.5 J Kg 1 K 1 ~24 J Kg 1 K 1) and 10.5 K (6.5 K) is observed in GNMO (GCMO) for a magnetic field change of 7 T at low temperatures. Absence of magnetic and thermal hysteresis and their insulating nature make them promising for low temperature magnetic refrigeration.