ABSTRACT
The structural and magnetic properties of the Y1-x Tb x MnO3 (0.1 ⩽ x ⩽ 0.3) compounds were investigated. Neutron diffraction patterns for all three samples, recorded at room temperature (RT), were fitted to the nuclear structure confirming the paramagnetic nature of the compounds. At 2.8 K, for the x = 0.1 sample magnetic moments of the Tb3+ ionic as well as Mn3+ ionic were ordered. At 5 K for the x = 0.2 sample only the Mn3+ ionic magnetic moments were ordered. There were six sites for Mn atoms. Three on the z = 0 plane and three on the z = 0.5 plane (where z corresponds to +c axis).The Mn3+ionic moments were confined to the a-b plane with a net magnitude of 2.78(3) µ B, and 2.90(3) µ B for the x = 0.1 and the x = 0.2 samples. The Tb3+ionic moments had a magnitude of 1.36(4) µ B at 2.8 K and were aligned antiferromagnetically along the crystallographic c-axis for the x = 0.1 sample. The low moment in comparison with Mn3+ free ions has been attributed to crystalline electric fields similar to that found in the parent compound YMnO3 and also in another rare earth manganite viz HoMnO3. The x = 0.3 sample was found to be a canonical spin glass. To investigate the role of the above spin ordering in Y1-x Tb x MnO3 in governing the phonon dynamics, temperature dependent Raman measurements were carried out. We observed the deviation of the phonon frequency near 685 cm-1 and its line-width from the expected anharmonic behaviour around magnetic ordering temperature for Tb substituted compounds with x = 0.1 and 0.2. This was attributed to the spin-phonon coupling in these systems. The anomalous behaviour of this phonon mode in the canonical spin glass compound with x = 0.3, indicated that the coupling sustained even in the presence of only local magnetic ordering.
ABSTRACT
We report the synthesis and electric properties of nano-crystalline Tb1-xYxMnO3 (x = 0, 0.1, 0.2, 0.3 and 0.4) compounds prepared by gel-combustion method. These samples were characterized by a number of techniques including X-ray diffraction (XRD), Raman spectroscopy, specific-heat measurement, neutron diffraction, and magnetic field dependent pyrocurrent measurement. All the samples crystallize in the orthorhombic structure with space group Pnma at room temperature. Anomalies were observed in low temperature specific-heat measurement corresponding to magnetic and electric phase transitions. The magnetic phase transitions occurred at ~35, ~22-28 and ~7 K for all the samples. Signatures of coupling between magnetic and electric order parameters were revealed by pyrocurrent measurements carried out in presence of magnetic fields.
ABSTRACT
Structural, magnetic, specific heat, and dielectric studies were carried out on Y substituted (30 at. %) GdMnO(3) compound as a function of temperature. Anomalies occur at ~41 and 18 K, in the specific heat measurements and are ascribed to paramagnetic, to sinusoidal incommensurate antiferromagnetic transition (ICAFM) and ICAFM to commensurate antiferromagnetic transitions, respectively. Changes in the lattice parameters across these temperatures indicate magneto-elastic coupling present in the compound. However, in the dielectric measurements, an anomaly at 18 K alone is observed and is ascribed to a ferroelectric transition, giving rise to spontaneous ferroelectric ordering at low temperatures. This observation is supported by an anomaly in lattice parameters, across the transition temperature. From the frequency dependent dielectric studies, a strong coupling between Gd(3+) and Mn(3+) magnetic sublattices is inferred and Y substitution results in substantial changes in the relaxation process compared to that of GdMnO(3).
ABSTRACT
The room temperature multiferroic properties of bulk BiFeO3 are not exciting enough for its application in devices. Here, we report the sonochemical synthesis of scandium and titanium codoped BiFeO3 nanoparticles which exhibit improved magnetic and ferroelectric properties at room temperature. The nanoparticles have been checked for phase purity and composition using powder X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS). The size and morphology of the nanoparticles have been confirmed using scanning electron microscopy (SEM), and both low and high resolution transmission electron microscopy (TEM/HRTEM). The breaking of the spin cycloid due to the smaller size and slight structural distortion caused by the doping has been found to be instrumental for the enhancement of multiferroic properties. The electrical polarization increases significantly in the case of BiFe(0.925)Sc(0.05)Ti(0.025)O3 nanoparticles. A marked reduction in the leakage current was seen compared to undoped BiFeO3. Magnetoelectric coupling was also observed in the BiFe(0.925)Sc(0.05)Ti(0.025)O3 sample. Our results demonstrate that codoping with Sc and Ti ions is an effective way to rectify and enhance the multiferroic nature of BiFeO3.
