O. Morán

Magnetic and electrical properties in Co-doped KNbO3 bulk samples

Multiferroic materials exhibit in the same phase at least two of the ferroic properties: ferroelectricity, ferromagnetism, and ferroelasticity, which may be coupled to each other. In this work, we investigated bulk materials with a nominal composition KNb0.95Co0.05O3 (KN:Co) fabricated by the standard solid-state reaction technique. X-ray diffraction analysis of the polycrystalline sample shows the respective polycrystalline perovskite structure of the KNbO3 phase with only small variation due to the Co doping. No secondary or segregated phases are observed. The values of the extracted lattice parameters are very close to those reported in the literature for KNbO3 with orthorhombic symmetry (a = 5.696 A, b = 3.975 A, and c = 5.721 A) with space group Bmm2. Measurements of the electric polarization as a function of the electric field at different temperatures indicate the presence of ferroelectricity in our samples. Magnetic response of the pellets, detected by high sensitivity measurements of magnetizatio...

Evaluation of the magnetocaloric response of nano-sized La0.7Ca0.3Mn1-xNixO3 manganites synthesized by auto-combustion method

A systematic study of the dependence of the magnetization on the magnetic field around the ferromagnetic–paramagnetic phase transition temperature is carried out on La0.7Ca0.3Mn1-xNixO3 (x=0, 0.02, 0.07, and 1) samples synthesized by auto-combustion method. The successful substitution of Mn3+ ions by Ni2+ ions in the La0.7Ca0.3MnO3 lattice is corroborated by X-ray diffraction technique. Banerjees criteria, Arrott plots, and the scaling hypothesis are used to analyze the experimental data. It is verified that the Ni-doping increases the operating temperature range for magnetocaloric effect through tuning of the magnetic transition temperature. Probably, the replacement of Mn3+ by Ni2+ ions in the La0.7Ca0.3MnO3 lattice weakens the Mn3+-O-Mn4+ double exchange interaction, which leads to a decrease in the transition temperature and magnetic moment in the samples. The Arrott plots suggest that the phase transition from ferromagnetic to paramagnetic in the nano-sized manganite is of second order. The analysis of the magnetization results show that the maximum magnetic entropy changes observed for x=0, 0.02, 0.07, and 0.1 compositions are 0.85, 0.77, 0.63, and 0.59 J/kg K, under a magnetic field of 1.5 T. These values indicate that the magnetic entropy change achieved for La0.7Ca0.3Mn1-xNixO3 manganites synthesized by auto-combustion method is higher than those reported for other manganites with comparable Ni-doping levels but synthesized by standard solid state reaction. It is also observed that the addition of Ni2+ increases the value of the relative cooling power as compared to that of the parent compound. The highest value of this parameter (∼60 J/kg) is found for a Ni-doping level of 2 % around 230 K in a field of 1.5 T.A systematic study of the dependence of the magnetization on the magnetic field around the ferromagnetic–paramagnetic phase transition temperature is carried out on La0.7Ca0.3Mn1-xNixO3 (x=0, 0.02, 0.07, and 1) samples synthesized by auto-combustion method. The successful substitution of Mn3+ ions by Ni2+ ions in the La0.7Ca0.3MnO3 lattice is corroborated by X-ray diffraction technique. Banerjees criteria, Arrott plots, and the scaling hypothesis are used to analyze the experimental data. It is verified that the Ni-doping increases the operating temperature range for magnetocaloric effect through tuning of the magnetic transition temperature. Probably, the replacement of Mn3+ by Ni2+ ions in the La0.7Ca0.3MnO3 lattice weakens the Mn3+-O-Mn4+ double exchange interaction, which leads to a decrease in the transition temperature and magnetic moment in the samples. The Arrott plots suggest that the phase transition from ferromagnetic to paramagnetic in the nano-sized manganite is of second order. The analysis ...

On the magnetic behavior of polycrystalline RBaCo205+δ synthesized by solid state and wet chemical routes

In this paper, polycrystalline RBaCo2O5+δ (R = La, Y, Eu) samples were obtained through solid state reaction and polymeric precursor method. The crystalline quality of the samples was carefully evaluated by means of X-ray diffraction. Depending on the R cation, the main phases were characterized in a tetragonal P4/mmm, orthorhombic Pmmm or trigonal R-3c structure. The oxygen content, being a fundamental parameter in the studied system, was determined by iodometric tritration. While no stoichiometric oxygen content was determined, the value of 5 ended up being close to 0.5 for all the samples studied. VSM magnetization measurements were taken according to the zero field cooling protocol. The M(T) curves clearly shows the characteristic magnetic behavior of the cobaltate with stoichiometry 112. The temperature at which the paramagnetic-ferromagnetic-antiferromagnetic transition occurs varies with the cation R.