Influence of divalent metal ion (Zn2+) on Magnetic properties, Curie temperature and DC Electrical properties in Ce3+ Substituted Ni-Zn Ferrites.

Nanoparticles of Ni1-xZnxCe0.1Fe1.9O4 ferrite substituted with Zn2+ ion concentrations (0.0, 0.2, 0.4, 0.6, 0.8 & 1.0) have been synthesised via aqueous citrate precursor auto combustion method. The obtained Powder X-ray diffraction data suggests a good crystalline phase; the crystallite size exists in the range of 14~38 nm. The lattice constant of samples increases with Zn2+ concentration. It validates Vegard's law and the decreasing trends in porosity of the samples are identified. The inhomogeneity in the grains was confirmed from FE-SEM. The EDS spectrogram attributes the good stoichiometry in the product. The Thermogravimetric analysis reveals that the crystallization occurred within the temperature 800˚C. The high-temperature DC conductivity of the samples shows that NTC behaviour. The Curie temperature and activation energy are estimated and the activation energy of carriers are found to be more at the paramagnetic region. The magnetic saturation ('Ms*') has maximum for Zn2+ = 0.2 (57.7 emu/g) and coercive field (Hc) related with a radius of occupancy of Zn2+ ion validates the relation Hc∝1/r and also, the value of the remanence ratio suggests that isotropic magnetization took place in the heterogeneous material.

Diamagnetism versus paramagnetism of charged ideal spin-1/2 fermions in a harmonic trap under a uniform magnetic field

Magnetic properties of harmonically trapped charged ideal spin-1/2 fermions in a uniform magnetic field are studied. It is shown that the magnetism of charged spin-1/2 fermions can be explained by a competition between the diamagnetic and paramagnetic effects, where a variable spin factor is introduced to describe the strength of paramagnetic effect. As the spin factor increases, a crossover from diamagnetic region to paramagnetic region appears. Moreover, the critical values of spin factor are obtained at low-temperature and under weak magnetic field, respectively. Spin-1/2 fermions display distinct magnetic behaviors from spinless case.

Магнитные свойства и природа магнитного состояния интеркалированных соединений Cr-=SUB=-x-=/SUB=-MoSe-=SUB=-2-=/SUB=-

This is a pioneering work on the synthesis of molybdenum diselenides intercalated by chromium atoms. Their magnetic properties are studied at various intercalant concentrations, temperatures, and magnetic fields. The temperature dependences of effective magnetic moments and positive paramagnetic Curie temperatures in the paramagnetic region evidence the feasible ferromagnetic interactions between intercalated atoms. The existence of low-temperature ferromagnetic state in Cr_ x МоSe_2 is confirmed by hysteresis phenomena in temperature and field dependences of magnetization and magnetic susceptibility.

Смена знака магнитоемкости в парамагнитной области в катион-замещенном селениде марганца

The capacity and the dielectric loss tangent of a Gd_ x Mn_1– x Se ( x ≤ 0.2) solid solution have been measured in the frequency range 1–300 kHz without a magnetic field and in a magnetic field of 8 kOe in the temperature range 100–450 K, and the magnetic moment of the solid solution has been measured in a field of 8.6 kOe. The magnetocapacity effect and the change in the magnetocapacity sign have been observed in room temperature in the paramagnetic region. A correlation of the changes in the dielectric permittivity and the magnetic susceptibility with temperature has been revealed. The magnetocapacity is described using the model with orbital electron ordering and the Maxwell–Wagner model.

Magneto-Electronic Phase Separation in La0.7Sr0.3MnO3 with Metallic Behavior in Paramagnetic Region

The data on transport and magnetic properties (ac linear and nonlinear (second and third orders) susceptibilities) are presented for La0.7Sr0.3MnO3 single crystal with metallic behavior in paramagnetic (PM) region and ferromagnetic (FM) metallic ground state. The FM clusters originate in the PM matrix of the compound below some temperature T* > 425 K, their nonlinear response being weakly T-dependent down to 367 K. This was attributed to clusters arising in the preferable sites formed by chemical inhomogeneities introduced by doping. On cooling below T# ≈ 366 K > TC ≈ 363.3 K, a fast growth of cluster response without the change of its parameters is observed that was attributed to the development of homogeneous nucleation of the FM clusters. The latter stage continues below TC and is accompanied by a crossover to the steeper decreasing of resistivity with cooling that suggests metallic properties of the clusters. The cluster nonlinear response masks completely that of matrix at T = 360.3 K < TC, where it is well described by the model of ensemble of magnetic single-domain nanoparticles in superparamagnetic regime based on the formalism involving Gilbert-Landau-Lifshits equation. Below TD = 359.6 K at the stage of domain formation, a weak interaction of matrix and cluster subsystems leads to their mutual ordering, which is accompanied by a sharp decrease of the nonlinear response to a weak ac field in small steady field H. The latter suggests an “antiferromagnetic” type of arrangement of these subsystems that provides decreasing the magnetostatic energy of the sample.

Magnetization Dynamics and Electron Transport in the La0.7Sr0.3MnO3/Y3Fe5O12 Hybrid Structures

We present the results of investigations of the spin-polarized current and spin dynamics in the hybrid structures ferrimagnetic insulator/ferromagnetic metal subjected to microwave radiation. We studied the La0.7Sr0.3MnO3/Y3Fe5O12 bilayer films on the Gd3Ga5O12 substrate. It was experimentally established that under the action of spin pumping the resistance of the La0.7Sr0.3MnO3 film changes. The value of ΔR is maximum in the sample with a La0.7Sr0.3MnO3 layer thickness of 10 nm and sharply drops as the manganite film thickness is increased. The resistance decreases in the paramagnetic region and grows in the ferromagnetic region at temperatures below the metal-insulator transition point. The variation in the resistance of the manganite film can be attributed to the correlation of the spin dynamics and transport properties of conduction electrons in the structure.

Effect of Cobalt Deficiency on Physical Properties of the GdBaCo2-xO5+δ Single Crystal

The effect of cobalt deficiency in a single crystal of double layered cobaltite GdBaCo1.86O5.32 on the magnetic properties was investigated. We have found that in the region 210 - 400 K the sample has the ferrimagnetic state with the Neel temperature (TN ~ 400 K) which is above the Curie temperature (TC ~ 262 K). In the paramagnetic region T = 410 - 650 K the effective magnetic moment is μeff = 8.78 μB, that points out the intermediate spin state (IS) of Co3+ ions.