Heating Efficiency of CoFe2-xRExO4 (RE=Dy, Yb, Gd) Magnetic Nanoparticles for Hyperthermia Applications

Cobalt ferrite nanoparticles (NPs) doped with rare earth (RE) metals with general formula CoFe2-xRExO4 (RE=Yb, Dy, Gd; x = 0.0 - 0.3) were synthesized by the co-precipitation method followed by post thermal treatment. The influence of RE doping on structural, magnetic and thermal properties and potential biomedical applications like magnetic hyperthermia has been investigated. In the as-prepared samples RE cations enter the spinel lattice as detected by X-ray diffraction. Thermal treatment leads to thermodynamically stable and relaxed single-phase spinel structures only for lower RE content, x = 0.01-0.05. However, annealed samples present higher mass magnetization values (MS), up to 83 Am2/kg. RE content also affects MS, especially in the case of annealed samples where it decreases linearly with x from about 80 Am2/kg (x = 0.01) to about 60 Am2/kg (x = 0.30). Thermal treatment induces a reduction in coercivity from 60-100 mT for as-prepared samples to 18-33 mT for annealed samples, in a nonlinear manner with respect to RE content. Heating efficiency, i.e., Specific Loss Power (SLP), of all samples has been studied using both magnetometric and calorimetric method to deeper examine the energy loss mechanisms involved.

Influence of mechanical activation and heat treatment on magnetic properties of nanostructured mixture Ni85.8Fe10.6Cu2.2W1.4

The mechanical activation of the Ni85.8Fe10.6Cu2.2W1.4 powder mixture in the time intervals of 30-210 min in combination with thermal treatment at 393-873 K resulted in microstructural changes, forming the nanostructured mixture of the same composition but improved magnetic properties. The best result were achieved for mechanical activation during 120 min and thermal treatment at temperatures close to the Curie temperature (693K), enhancing the mass magnetization of the starting powder mixture by about 57%. The microstructural changes, which include the structural relaxation, decrease in free volume, density of dislocation and microstrain, improve structural characteristics of material, enabling better mobility of walls of magnetic domains and their better orientation in applied magnetic field and consequently enabling better mass magnetization of the material. With longer time of milling, the growing stress introduced in the sample undergoes easier relief, relocating stress-relieving processes toward lower temperatures.

Dispersion of dielectric permittivity and magnetic properties of solid solution PZT–PFT

In this paper we present the results of investigations into ceramic samples of solid solution (1-x)(PbZr0.53Ti0.47O3)- x(PbFe0.5Ta0.503) (i.e. (1-x)PZT-xPFT) with x = 0.25, 0.35 and 0.45. We try to find the relation between the character of dielectric dispersion at various temperatures and the composition of this solution. We also describe the magnetic properties of investigated samples. With increasing the content of PFT also mass magnetization and mass susceptibility increase (i.e. magnetic properties are more pronounced) at every temperature. The temperature dependences of mass magnetization and re­ciprocal of mass susceptibility have similar runs for all the compositions. However, our magnetic investigations exhibit weak antiferromagnetic ordering instead of the ferromagnetic one at room temperature. We can also say that up to room tempera­ture any magnetic phase transition has not occurred. It may be a result of the conditions of the technological process during producing our PZT-PFT ceramics.

MICROSCOPIC QUANTUM MECHANICAL FOUNDATION OF FOURIER'S LAW

Besides the growing interest in old concepts such as temperature and entropy at the nanoscale, theories of relaxation and transport have recently regained a lot of attention. With the electronic circuits and computer chips getting smaller and smaller, a fresh look on the equilibrium and nonequilibrium thermodynamics at small length scales far below the thermodynamic limit, i.e. on the theoretical understanding of original macroscopic processes, e.g. transport of energy, heat, charge, mass, magnetization, etc., should be appropriate. Only from the foundations of a theory its limits of applicability may be inferred. This review tries to give an overview on the background and recent developments in the field of nonequilibrium quantum thermodynamics, focusing on the transport of heat in small quantum systems.