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The magnetic and dielectric polarization properties of the single crystal samples of CuFe1-xGaxO2 (x=0 and 0.02) are investigated. Experimental results show that the magnetization and dielectric polarizations are anisotropy and coupled together. Compared with pure CuFeO2, in the case with the magnetic field parallel to the c axis, a field-induced phase transition with a hysteresis is clearly observed between the five-sublattice (5SL) and three-sublattice (3SL) phases. Specially, an obvious spontaneous dielectric polarization is observed in CuFe0.98Ga0.02O2 in a lower magnetic field region, indicating that the Ga doping has an effect on the enhancement of spontaneous dielectric polarization. Based on the dilution effect, change of exchange interaction, and partial release of the spin frustration due to the structural modulation of the Ga ion dopant, the origin of the magnetization, and spontaneous polarization characteristics are discussed and the complete dielectric polarization diagrams are assumed. [ABSTRACT FROM AUTHOR]

Magnetoelectric effects and their dynamic behavior in a CuFeO2 single crystal grown by the floating zone technique are investigated at low temperature in pulsed high magnetic fields. Experimental results show that the magnetization, dielectric polarization, and magnetoelectric coupling are anisotropic. In the magnetization, a field-induced multi-step-like transition with hysteresis is observed, in which the critical magnetic fields are independent of the field sweep rate. In the dielectric polarization, the field-induced dielectric polarization with hysteresis (or partial irreversible) is only observed in the incommensurate-noncollinear phase. In particular, no obvious spontaneous dielectric polarization is observed in the lower magnetic field regime. Using a pulsed high magnetic field with various magnetic field strength and field sweep rates, the coupling behavior between the magnetic moment and the dielectric polarization is investigated. Experimental results show that the dielectric polarization is weakly related to the field sweep rate. In the field-decreasing branch, the magnetic field is higher, the magnetic field region of the dielectric polarization remains is lower, indicating that the pulsed high magnetic field has an effect on the enhancement of the spontaneous dielectric polarization. [ABSTRACT FROM AUTHOR]

The particle size dependent training effect has been investigated on the exchange coupled NiFe2O4/NiO nanogranular systems, with average particle size (DNFO) of NiFe2O4 ranging from ~3nm to ~55 nm. For all samples, analysis of the field cycles (n) dependence on exchange bias fields (HEB) suggests the existence of two distinct forms of training mechanism during training procedure. One is related to an athermal contribution leading to the abrupt single cycle training, the other is the conventional thermal activation mechanism responsible for the gradual reduction of HEB during the subsequent cycles. With the increase of particle size, the relative change of HEB and enhanced coercivity (ΔHC) after training display a nonmonotonic size-scaling behavior and reaches the maxima for DNFO~22 nm. In this system, this largest reduction reveals the weakest dynamic stability of the interfacial exchange coupling energy during field cycle process. Moreover, different decay rate of HEB and DHC with field cycles are observed supporting the dual behavior of the interfacial uncompensated spins. The interfacial frozen spins are suggested to account for the appearance of HEB, while the rotatable spins are linked to the DHC. [ABSTRACT FROM AUTHOR]

The magnetic and dielectric polarization properties of the single crystal samples of CuFe1-xGaxO2 (x=0 and 0.02) are investigated. Experimental results show that the magnetization and dielectric polarizations are anisotropy and coupled together. Compared with pure CuFeO2, in the case with the magnetic field parallel to the c axis, a field-induced phase transition with a hysteresis is clearly observed between the five-sublattice (5SL) and three-sublattice (3SL) phases. Specially, an obvious spontaneous dielectric polarization is observed in CuFe0.98Ga0.02O2 in a lower magnetic field region, indicating that the Ga doping has an effect on the enhancement of spontaneous dielectric polarization. Based on the dilution effect, change of exchange interaction, and partial release of the spin frustration due to the structural modulation of the Ga ion dopant, the origin of the magnetization, and spontaneous polarization characteristics are discussed and the complete dielectric polarization diagrams are assumed. [ABSTRACT FROM AUTHOR]