The phase diagram of Gd1-xYxMnO3, 0 <= x <= 0.4, is presented and the role of the driving mechanisms in stabilizing both magnetic and ferroelectric orderings is discussed in the framework of the Dzyaloshinskii-Moriya model. The (x, T) phase diagram reflects the effect of lattice distortions induced by the substitution of Gd3+ ion by smaller Y3+ ions, which gradually unbalances the antiferromagnetic against the ferromagnetic exchange interactions, enabling the emergence of ferroelectricity for higher concentrations of yttrium. (C) 2015 Elsevier Ltd. All rights reserved.

This paper reports on structural, magnetic, dielectric, thermodynamic, and magnetodielectric properties of Eu${}_{1\ensuremath{-}x}$Lu${}_{x}$MnO${}_{3}$, with 0 \ensuremath{\leqslant} $x$ \ensuremath{\leqslant} 0.2, towards the ($x$, $T$) phase diagram. The phase diagram reflects the effect of lattice distortions induced by the isovalent substitution of Eu${}^{3+}$ by smaller Lu${}^{3+}$ ions, which gradually unbalances the antiferromagnetic against the ferromagnetic exchange interactions, enabling the emergence of both ferroelectricity and magnetoelectric coupling. For $x$ 0.1, the paramagnetic phase is followed by a presumably incommensurate collinear antiferromagnetic phase AFM-1, and then a weak ferromagnetic phase seems to be established, with a canted $A$-type antiferromagnetic order. For 0.1 \ensuremath{\leqslant} $x$ \ensuremath{\leqslant} 0.2, the AFM-1 phase is followed by an antiferromagnetic phase AFM-2 with modulated spiral spin arrangement, compatible with ferroelectricity. The disappearance of hysteresis cycles $P$($E$) at low temperatures, clearly indicates the existence of an antiferromagnetic phase AFM-3, whose spin structure is not compatible with both the ferroelectric and ferromagnetic components. The magnetic behavior of EuMnO${}_{3}$ and Eu${}_{0.9}$Lu${}_{0.1}$MnO${}_{3}$ suggests the existence of a phase line separating the AFM-1 phase from the AFM-2 and AFM-3 phases, which is observed for $x$ $=$ 0.1. Magnetodielectric coupling was evidenced for both $x$ $=$ 0.1 and 0.2 compositions. Ferroelectric polarization and magnetodielectric coupling coefficient are larger for the latter composition.

The present study deals with the design, synthesis and characterization of magnetic glass-ceramics along diopside (CaMgSi2O6)–aegirine (NaFeSi2O6) join targeted towards their final application as thermoseeds in hyperthermia. The glass-ceramics were prepared from the sintering and crystallization of glass powders obtained through melt-quenching technique. The sintering behavior of glass powders was studied by hot-stage microscopy (HSM) while differential thermal analysis (DTA) was used to study the non-isothermal crystallization kinetics of the as prepared glasses. In order to analyze the crystallization behavior of glasses, the glass powder compacts were sintered at 900°C for 1h under non-isothermal conditions. The qualitative as well as quantitative crystalline phase analysis of glass-ceramics has been made by X-ray diffraction (XRD)-adjoined with Rietveld-RIR technique. Augite crystallized as the primary phase in all the compositions. The scanning electron microscopy (SEM) was used to shed light on the microstructure of the glass-ceramics while the magnetic properties of glass-ceramics were studied by vibration sample magnetometer (VSM). All the investigated glass-ceramics exhibited ferromagnetic behavior the intensity of which increased with increase in Fe content in the samples. The dependence of magnetic properties on the composition of glass-ceramics has been explained.

This work reports an experimental investigation of the ferroelectric character of magnetic phases of the orthorhombic Eu1-xYxMnO3 system at low temperatures. The temperature dependence of the polarization curves clearly reveals the existence of a re-entrant improper ferroelectric phase for x = 0.2, 0.3 and 0.5. A ferroelectric phase is also stable for x = 0.4, and we have no experimental evidence for its vanishing down to 7 K. From these and early results obtained using other experimental techniques, the corresponding (x, T) phase diagram was traced, yielding significant differences with regard to the ones previously reported. (C) 2010 Elsevier Ltd. All rights reserved.

This work is addressed to study the crystal structure and morphology, as well as the thermodynamic, dielectric and magnetic properties of Eu0.8Y0.2MnO3 ceramics, synthesized by urea sol-gel combustion method. The experimental results were systematically compared with data available for the corresponding single crystals. Though the effect of the anisotropy on both dielectric and magnetic properties is missing, they enabled us to investigate the main physical mechanisms associated with their magnetoelectric properties, in particular the one which drives the ferroelectric phase. The phase sequence and critical temperatures are in good agreement with the corresponding values reported for single crystals. Similarly, structural results evidence strong distortions of the crystal lattice, enhancing the ferromagnetic interactions over the antiferomagnetic ones. A significant contribution of the magnetic fluctuations above TN was also evidenced from the magnetization studies.

Correlation between spin-phonon coupling and the magnetoelectric properties of EuMnO3 and GdMnO3 were investigated using ceramic samples in this work. The experimental results evidence a stronger spin-phonon coupling in GdMnO3 than in EuMnO3, as well as a clear anomaly in the phonon contribution for the dielectric constant. This anomaly is located at the paramagnetic-incommensurate antiferromagnetic phase-transition temperature of GdMnO3, corroborating the existence of a magnetoelectric effect in this system. The absence of the magnetoelectric effect in EuMnO3 is due to the existing disorder revealed in this compound by the striking thermal metastability and the large decrease in the activation energy associated with the dielectric relaxation processes. This kind of behavior has no counterpart in GdMnO3. In fact, it has been confirmed that the existence of spin-phonon coupling is not a sufficient condition for the existence of magnetoelectric property, and other mechanisms have to be considered in order to understand the magnetoelectric properties.

Bi 1 − x A x Fe O 3 ceramics (A=Ca,Sr,Pb) were sintered by conventional mixed oxide route. The crystallographic structure of all samples is characterized by the rhombohedral symmetry (space group R3c). The existence of switchable ferroelectric polarization is verified by piezoresponse force microscopy that is proven to be a useful technique in semi-insulating ferroelectrics. Magnetic properties of Ca and Sr-doped ceramics are found to reproduce the antiferromagnetic behavior of undoped BiFeO3 without any enhancement of the magnetization. On the contrary, Pb-doped compound demonstrates appearance of a weak ferromagnetism. It is thus shown that Pb doping of BiFeO3 is a promising way for preparing multiferroic materials.

Polymer composites have recently received a considerable amount of scientific and technological interest, because their properties can be properly controlled, choosing the adequate doped particles, their size and concentrations, and the synthesis conditions.