Single-phase polycrystalline samples of La0.8-x Ndx Na0.2 MnO3 (x = 0.00, 0.05, 0.10, 0.15 and 0.20) were prepared by the sol–gel method. Investigations of Curie temperature and magnetic entropy change were carried out in the temperature range 240–340 K and magnetic field range 0–1 T. It was found that the Curie temperature TC decreases with increasing x, and that the maximum magnetic entropy change △S M , for x = 0.20, is 0.3692 J/mol K near the temperature 295 K. The results suggested that these perovskite manganites have some appropriate properties for a good candidate as magnetic refrigeration in the room temperature range.

Ionic size is considered to be an important factor influencing the unit cell volume of manganites with an ABO3 structure. For La1-xSrxMnO3, however, although the average effective ion radius of all cations taken together increases with increasing x, the unit cell volume decreases for x<0.5. In the case of La1-xNaxMnO3, the unit cell volume reaches a minimum when x = 0.3. Up to now, no satisfactory explanation of these phenomena has been found. In this letter, an explanation based on the ionic cohesive energy with a small additional metallic cohesive energy is described.

The magnetic aftereffects of Fe3O4 nano-particles were simulated by Preisach hysteresis model, the results showed excellent agreement with the experiment data. The simulating results showed that due to the wide distribution of interaction field, magnetization decay followed typical logarithmic time dependence, and the decay occurred more rapidly for field closer to the coercivity. The thermal fluctuation field and activation volume were also obtained, which are the main characteristics of the thermal fluctuations in magnetic recording medium. From the fact that activation volume is larger than the mean particle size, we deduced the reversal magnetization mechanism. One set of parameters used in simulating hysteresis loops and magnetic aftereffects has unified the hysteresis and magnetic aftereffect phenomena. The aftereffects under double-field were calculated, and the condition under which the time dependence of magnetization was non-monotonic was given.

Zno.96Mn0.04O powder and thin films were prepared by standard solid-state reaction processes and radio-frequency (RF) magnetron sputtering. Magnetic measurements indicate that the powder is paramagnetic for temperatures above 3K, while the thin films annealed in vacuum are ferromagnetic at room temperature with a transition temperature of about 400K. The largest saturated magnetization (Ms) was found to be about 1.05

A quantum-mechanical potential barrier model for estimating the number ratio between different valence cations in multiatom compounds is proposed. It is supposed that there is a potential barrier between a cation-anion pair. The height of the potential barrier is proportional to the ionization energy of the cation, and the width of the potential barrier is related to the distance between neighboring cations and anions. As examples for using this model, the distribution of cations with different valences in some ABO3 lanthanum manganites is explained satisfactorily.