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Transport and magnetic properties of LaMnO3+δ nanoparticles with average size of 18 nm have been investigated. The ensemble of nanoparticles exhibits a paramagnetic to ferromagnetic (FM) transition at TC∼246 K, while the spontaneous magnetization disappears at T≈270 K. It was found that the blocking temperature lies slightly below TC. The temperature dependence of the resistivity shows a metal–insulator transition at T≈192 K and low-temperature upturn at T

Magnetic properties of Pr0.5Ca0.5Mn1−xCrxO3 (0.015⩽x⩽0.5) samples were investigated under pressures up to 11 kbar. For x=0.015 and 0.03 samples, an applied pressure enhances significantly the Curie temperature (dTC/dP∼2 K/kbar), enhances the ferromagnetic phase volume below TC, and narrows appreciably the hysteresis in the vicinity of TC. For x=0.2 and 0.5 samples, pressure does not affect practically the magnetic transition temperature, but reduces noticeably the magnetization in a wide temperature range. Observed phenomena for x=0.015 and 0.03 samples are related to the interfacial elastic energy at the interface of different magnetic phases and to the suppression of the Jahn–Teller distortions under pressure. For higher doped samples, pressure possibly increases antiferromagnetic interactions between Cr3+ and Mn4+ ions.

Magnetic and transport properties of polycrystalline CaMn 1− x Ru x O 3 ( x = 0 – 0.4 ) perovskites were investigated under pressures up to 12 kbar. It was found that an applied pressure suppresses ferromagnetism and increases resistivity. The results are discussed in the context of phase separation and valence effects.

Measurements of electrical resistance and magnetization of an La 0.8 Ca 0.2 MnO 3 single crystal were carried out at temperatures below and above the Curie temperature, T C =183.5±1 K. The effect of applied hydrostatic pressure P and magnetic field H on the magnetization and the resistive properties were also investigated. It was found that the pressure coefficient of the Curie temperature is rather small d T C /d P ≈0.3 K/kbar. At low temperatures a positive magnetoresistance was found. A nonlinear dependence of resistivity as a function of DC current was revealed. The results are interpreted in the frame of phase separation scenario.

In this paper, we report on the effect of excess manganese on the magnetic properties of the (La0.7Ca0.3)1−xMn1+xO3 perovskites. All samples display a colossal magnetoresistance effect which becomes considerably enhanced with increasing manganese content. The magnetic behaviour of manganites studied was shown to depend strongly on the values of manganese doping and applied magnetic field. For the samples with x=0.1 and 0.2, in addition to an anomaly connected with paramagnet–ferromagnet transition, there are anomalies in the field-cooled (FC) and zero-field-cooled (ZFC) magnetization at low temperatures. In low magnetic fields (H 200 Oe, a jump upwards takes place in the MFC(T) and MZFC(T) curves at the same temperature. A low-temperature anomaly in AC susceptibility also indicates a change in magnetic ordered state. From M(T,H) and χ(T) dependencies, one can assume the existence of regions with different magnetic order at T

Magnetization, electrical resistivity and magnetoresistance of Pr 0.50 Ba 0.50 MnO 3− δ manganites with perovskite structure have been investigated as a function of preparation conditions. It was found that the as-prepared samples (prepared in air) show T C =110 K (first order phase transition), whereas for those annealed in flowing argon the T C value increases up to 340 K without change of cubic symmetry (second order phase transition). Ferromagnet–paramagnet transition is accompanied by both a metal–insulator transition and a magnetoresistance peak. The X-ray study has revealed that the samples annealed in argon have broad peaks apparently due to microstrains and crystal structure defects. The argon-treated samples improve the magnetization after subsequent annealing in air at T ⩽1000°C. T C of argon-treated samples is stable with respect to annealing in air up to 1300°C where it becomes again 110 K. In contrast, a treatment in vacuum destroys the ferromagnetic order. Auger-spectroscopy has not revealed any additional ions except Pr, Ba, Mn and O for all the samples. External pressure enhances the Curie point of the sample prepared in air at a rate of 43 K/GPa. We have observed that the samples Pr 1− x Ba x MnO 3− δ , x⩾ 0.30, exhibited the above-mentioned effect of increasing T C after treatment in flowing argon without changes of the phase state, whereas the samples x T C after argon treatment is supposed to result from microstrains and crystal structure defects in the sample.

The data of low-temperature magnetic measurements of the monoclinic KDy(WO 4 ) 2 crystal are used to calculate the exchange and dipole–dipole interactions energy. The last are used for the determination of the magnetic structure of the ground state.

Magnetization, FMR and sound velocities were measured in La 0.8 Sr 0.2 MnO 3 single crystals in the vicinity of the structural phase transition ( T s ). A strong jump in sound velocities was observed near T s . The temperature dependences of sound velocities and magnetization show the hysteresis characteristic of a first-order phase transition. The magnetization behavior indicates that the structural phase transition is accompanied by a magnetic phase transition of the spin reorientation type. It was shown that properties of the investigated single crystals are influenced by the presence of a twin structure. The existence of the twin structure was confirmed by FMR measurements.

Magnetic and transport properties of Pr 0.8 Ca 0.2 MnO 3 crystal have been studied. It was found that the magnetic anisotropy in (1 0 0) plane increases with decreasing temperature and increasing pressure. The resistivity for T >140 K obeys Arrhenius law with an activation energy E a =130 meV, while at T E a =62 meV. The magnetoresistance maximizes near the Curie temperature of Mn moments T C1 =130 K. The dynamic resistivity shows a marked dependence on a bias current I at T T C1 . The results are discussed in the frame of magnetic phase separation and spin-density wave scenario.