Small polaron migration associated multiple dielectric responses of multiferroic DyMnO3 polycrystal in low temperature region (original) (raw)
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Single phase polycrystalline DyMnO 3 (DMO) was synthesized using acrylamide polymer gel template method. We report the structural, magnetic, specific heat and dielectric properties of DMO over wide experimental conditions. Room temperature XRD pattern shows the formation of singe phase material without any impurity. The magnetic properties such as magnetization versus temperature (M vs. T) and magnetization versus magnetic field (M vs. H) were studied around the transition temperatures region. The temperature dependent magnetization data suggest two phase transitions corresponding to the lock-in temperature below which ferroelectric ordering exist (around 19 K; T lock ) and antiferromagnetic (AFM) ordering of Dy spin (around 8 K; T N (Dy)). The magnetic hysteresis obtained were fitted to extract weak ferromagnetic (FM) and antiferromagnetic/paramagnetic (AFM/PM) contribution to the magnetic data. The order of magnetic transitions were analyzed from Arrott plot. The temperature dependent specific heat measurement shows all three phase transitions corresponding to (i) AFM ordering of Mn spin (around 38 K; T N (Mn)), (ii) T lock transition and (iii) T N (Dy) transition. The effect of magnetic field to the transitions were studied using specific heat capacity measurement. The peak intensity of T N (Dy) decreases on the application of magnetic field whereas peak intensity of T lock increases with increase in magnetic field in specific heat measurement. Further the third anomaly, T N (Mn) remains more or less unaffected by the application of magnetic field. The intrinsic dielectric behaviour of the material was observed up to 160 K, above this temperature there is large increase in dielectric value due to the contribution from Maxwell-Wagner polarization.
Magnetic properties and anisotropy of orthorhombic DyMnO3 single crystal
Journal of Magnetism and Magnetic Materials, 2013
An orthorhombic DyMnO 3 single crystal has been studied in magnetic fields up to 14 T and between 3 K and room temperature. The field dependent ordering temperature of Dy moments is deduced. The paramagnetic Curie Weiss behavior is related mainly to the Dy 3 þ sublattice whereas the Mn sublattice contribution plays a secondary role. DC magnetization measurements show marked anisotropic features, related to the anisotropic structure of a cubic system stretched along a body diagonal, with a magnetic easy axis parallel to the crystallographic b axis. A temperature and field dependent spin flop transition is observed below 9 K, when relatively weak magnetocrystalline anisotropy is overcome by magnetic fields up to 1.6 T.
Interplay of structural distortions, dielectric effects and magnetic order in multiferroic GdMnO3
Journal of the Korean Physical Society, 2013
Multiferroic materials are characterized by simultaneous magnetic and ferroelectric ordering making them good candidates for magneto-electrical applications. We conducted thermal expansion and magnetostriction measurements in magnetic fields up to 14 T on perovskitic GdMnO3 by highresolution capacitive dilatometry in an effort to determine all longitudinal and transversal components of the magnetostriction tensor. Below the ordering temperature TN = 42 K, i.e., within the different complex (incommensurate or complex) antiferromagnetic phases, lattice distortions of up to 100 ppm have been found. Although no change of the lattice symmetry occurs, the measurements reveal strong magneto-structural phenomena, especially in the incommensurate sinusoidal antiferromagnetic phase. A strong anisotropy of the magnetoelastic properties was found, in good agreement with the type and propagation vector of the magnetic structure. We demonstrate that our capacitive dilatometry can detect lattice expansion effects and changes of the dielectric permittivity simultaneously because the sample is housed inside the capacitor. A separation of both effects is possible by shielding the sample. Dielectric transitions could be detected by this method and compared to the critical values of H and T in the magnetic phase diagram. Dielectric changes measured at 1 kHz excitation frequency are detected in GdMnO3 at about 180 K, and between 10 K and 25 K in the canted antiferromagnetic structure which is characterized by a complex magnetic order on both the Gd-and Mn-sites.
Phase transitions and rare-earth magnetism in hexagonal and orthorhombic DyMnO 3 single crystals
Journal of Physics: Condensed Matter, 2009
Multiferroic manganites of the type RMnO 3 (R=rare-earth) have attracted a great deal of attention due to two main reasons: First, on the technological front multiferroics are promising materials for potential spintronic applications such as four-state memory devices . For their application, however, a better understanding of their fundamental properties is necessary. Second, these materials belong to a class of complex oxides with various coupled ordering phenomena and rich phase diagrams . Generally, RMnO 3 crystallizes in an orthorhombic, perovskite-like structure (space group P nma), if the rare-earth ionic radius is large enough, i.e. r R > r Dy . Thus, the manganites with R = La, Pr, Nd etc. are orthorhombic, whereas the RMnO 3 manganites for R = Y, Tm, Yb, Lu, Er with an ionic radius smaller than that of Dy usually crystallize in hexagonal structure (space group P 6 3 cm). Since the transition between hexagonal and orthorhombic crystal structure of RMnO 3 occurs in the rare-earth series for the ionic radius of Dy or Ho, RMnO 3 with r R r Dy can be synthesized in both structures by applying different growth conditions .
Determination of the intrinsic ferroelectric polarization in orthorhombic HoMnO3
New Journal of Physics, 2010
Whether large ferroelectric polarization P exists in the orthorhombic HoMnO 3 with the E-type antiferromagnetic spin ordering or not remains as one of unresolved, challenging issues in the physics of multiferroics. The issue is closely linked to an intriguing experimental difficulty for determining P of polycrystalline specimens that conventional pyroelectric current measurements performed after a poling procedure under high dc electric fields are subject to large errors due to the problems caused by leakage currents or space charges. To overcome the difficulty, we employed the PUND method, which uses successively the two positive and two negative electrical pulses, to directly measure electrical hysteresis loops in several polycrystalline HoMnO 3 specimens below their Néel temperatures. We found that all the * These authors equally contributed to this work. HoMnO 3 samples had similar remnant polarization P r values at each temperature, regardless of their variations in resistivity, dielectric constant, and pyroelectric current levels. Moreover, P r of~0.07 µC/cm 2 at 6 K is consistent with the P value obtained from the pyroelectric current measurement performed after a short pulse poling. Our findings suggest that intrinsic P of polycrystalline HoMnO 3 can be determined through the PUND method and P at 0 K may reach~0.24 µC/cm 2 in a single crystalline specimen.
Physical Review B, 2011
We investigate the structural, magnetic, and specific heat behavior of the hexagonal manganite Dy 0.5 Y 0.5 MnO 3 in order to understand the effect of dilution of Dy magnetism with nonmagnetic yttrium. In this compound, the triangular Mn lattice orders antiferromagnetic at T Mn N ≈ 68 K observed experimentally in the derivative of magnetic susceptibility as well as in specific heat. In addition, a low-temperature peak at T Dy N ∼ 3 K is observed in specific heat which is attributed to rare earth order. The T Mn N increases by 9 K compared to that of hexagonal (h)DyMnO 3 while T Dy N is unchanged. A change in slope of thermal evolution of lattice parameters is observed to occur at temperature close to T Mn N. This hints at strong magnetoelastic coupling in this geometric multiferroic. In magnetization measurements, steplike features are observed when the magnetic field is applied along the c axis which shift to higher fields with temperature and vanish completely above 40 K. The presence of different magnetic phases at low temperature and strong magnetoelastic effects can lead to such field-induced transitions which resemble metamagnetic transitions. This indicates the possibility of strong field-induced effects in dielectric properties of this material, which is unexplored to date.
Polar octahedral rotations, cation displacement and ferroelectricity in multiferroic SmCrO3
Our thorough synchrotron diffraction studies provide a clue on the origin of ferroelectricity in SmCrO3. Careful observation demonstrates that polar order develops in the paramagnetic state. Rietveld refinement of the diffraction data confirms that emergence of polar order is correlated with the structural transformation from centrosymmetric P bnm to noncentrosymmetric P na21 space group of the distorted orthorhombic structure. Rotations of polar CrO6 octahedra and Sm displacement are proposed to be correlated with the emergence of polar order, which is extended over a wide temperature range and increases gradually with decreasing temperature. This is consistent with the relaxor behavior as evident from the frequency-dependent dielectric response satisfying the Vogel-Fulcher law. A non-collinear to collinear spin transformation is suggested well below the spin reorientation transition. Appearance of ferroelectricity without any correlation to the antiferromagnetic order in SmCrO3 suggests a new class of ferroelectricity. All-electron full-potential first-principles calculation demonstrates significant Sm-Cr hybridization near the Fermi level, which substantiates the experimental findings.
Journal of Alloys and Compounds, 2018
In the present work, we report a comprehensive investigation of dielectric and magnetic phase transition in single phase Dy(Fe 0.5 Cr 0.5)O 3 (DFC) bulk ceramics. The Rietveld refinement suggests that DFC exhibit orthorhombic crystal system with Pnma space group. The observed magnetic and structural properties of Dy(Fe 0.5 Cr 0.5)O 3 are distinct from both the parent compound DyFeO 3 and DyCrO 3. Temperature dependent dc-magnetic studies exhibit a complex sequence of three magnetic transitions (T N1 ¼ 261 K, T N21 15 K & T N3~1 4 K) below 300 K. The diffuse dielectric peaks were observed in high temperature dielectric studies near at 578 K, indicates diffuse relaxor like dielectric transition. The complex impedance spectroscopic analysis suggests that Non-Debye type dielectric relaxation process is detected.
Investigations on the defect dipole induced pyroelectric current in multiferroic GdMnO3 system
Journal of Applied Physics, 2018
Pyroelectric current measurements on the orthorhombic GdMnO3 polycrystalline sample are done to explore the intrinsic and extrinsic contributions. The measurements reveal poling temperature dependent pyrocurrent peaks at 20, 50 and 108 K. The pyrocurrent at 20 K and at 108 K are attributed to ferroelectric transition induced by the incommensurate spiral magnetic ordering of Mn spins and the release of trapped charges from the localized states, respectively. A detailed analysis on the broad pyrocurrent signal at 50 K suggests that it could be attributed to the thermally stimulated depolarization current effect due to the relaxation of defect dipoles induced by negatively charged Mn3+ ions and excess holes localized at Mn4+ sites. Importantly, the effect of the electric field due to the defect dipoles on the ferroelectric state is highlighted. The temperature dependent dielectric measurements under the magnetic field brought out the correlation between pyroelectric and dielectric prop...