Colossal magnetoresistance of Nd-doped LaCaMnO3 polycrystalline ceramics

The cation doped polycrystalline compound La0.5Nd0.15Ca0.35MnO3 has been synthesized by a conventional solid state reaction method. The Rietveld analysis of the powder XRD of the composites reveals an orthorhombic structure with Pbnm space group symmetry. The cell parameters are a = 5.4505 ?, b = 5.4457 ? and c = 7.6876?. The AC magnetization studies show a semiconducting paramagnetic to metallic ferromagnetic transition at a temperature below the Curie temperature TC which is found to be 206.3K. It is also observed that metal to semiconductor transition temperature TMS is very close to TC. The sample also possesses high magnetoresistance, which is revealed in MR studies.

Empirical Expression for AC Magnetization Harmonics of Magnetic Nanoparticles under High-Frequency Excitation Field for Thermometry

The Fokker–Planck equation accurately describes AC magnetization dynamics of magnetic nanoparticles (MNPs). However, the model for describing AC magnetization dynamics of MNPs based on Fokker-Planck equation is very complicated and the numerical calculation of Fokker-Planck function is time consuming. In the stable stage of AC magnetization response, there are differences in the harmonic phase and amplitude between the stable magnetization response of MNPs described by Langevin and Fokker–Planck equation. Therefore, we proposed an empirical model for AC magnetization harmonics to compensate the attenuation of harmonics amplitude induced by a high frequency excitation field. Simulation and experimental results show that the proposed model accurately describes the AC M–H curve. Moreover, we propose a harmonic amplitude–temperature model of a magnetic nanoparticle thermometer (MNPT) in a high-frequency excitation field. The simulation results show that the temperature error is less than 0.008 K in the temperature range 310–320 K. The proposed empirical model is expected to help improve MNPT performance.

Influence of annealing temperature on nanocrystalline alloy’s excess loss parameters

In this paper, both nanocrystalline alloy (Fe73.5Cu1Nb3Si15.5B7) ribbon samples and toroidal samples (wound ribbon) are annealed at different temperatures in order to consider the influence of inner stress on the magnetization properties. Then the AC magnetization properties of these samples are measured. Combined with the measured results, the influence of inner stress on nanocrystalline alloy’s microstructure is analyzed quantitatively based on the loss separation principle and the statistical theory of loss. By comparing measured macroscopic magnetization characteristics and excess loss, the equivalent stress state of the toroidal sample is evaluated. Furthermore, two kinds of samples’ excess loss under different annealing temperatures are analyzed, and the effectiveness of stress relief at optimal annealing temperature is validated.

The Impact of the Composition Effect on Ferromagnetic Properties of Tb2Co2Ga

The ferromagnetic properties of Tb2Co2Ga, crystallizing into an orthorhombic W2CoB2-type structure, were investigated by preparing 11 polycrystalline samples with different starting atomic compositions. We found that Tb2Co2Ga possesses a homogeneity range in the ternary phase diagram. The Curie temperature TC is sensitive to the atomic composition and ranges rather widely, i.e., from 75 to 145 K. For the samples with a TC above 90 K, the nearest Tb–Tb and the Tb–Co distances would be important factors deciding TC, considering the RKKY interaction through the hybridization between Tb and Co atoms. An anisotropic change of two kinds of Co–Tb–Co angles in the octahedron formed by two Tb and four Co atoms occurs in the samples with a TC lower than 90 K. Such a change of octahedral parameters seems to be related to a difference of shapes in the ac magnetization anomaly at TC between the samples in the lowest TC (~ 75 K) group and those in the other groups.