Orthorhombic DyMnO3 Research Articles

Room-temperature spin reorientation transition and low-temperature significant magnetothermal effect in Mn-doped DyFeO3 single crystals

Rare-earth orthoferrites (RFeO3) promise in spin storage and spin sensing, but the majority of the magnetic phase transition and intriguing properties occur at low temperatures. Searching for higher-temperature or even room-temperature spintronics devices has been a critical challenge in the development of spintronics. We doped Mn ions into Fe sites of DyFeO3 in 10%–50 % ratios to coexist antiferromagnetic and ferromagnetic coupling in the ab plane and elevate their spin reorientation transition (SRT) temperatures. The structural, magnetic, and magnetothermal properties of the Mn-doped DyFeO3 single-crystal system are investigated. With increasing doping ratio, the Néel temperature progressively falls, while the SRT temperature (TSR) continuously rises to the room temperature of 307 K with a 40 % doping ratio, making it promising for room-temperature spin storage devices. When the ratio reaches 50 % (half doping), the magnetic configuration of Dy sublattices changes and a significant magnetothermal effect is observed. Because of low-field metamagnetic phase transition, the magnetic entropy change along the c-axis approaches 10.41 J/kg·K for the half doping crystal at 5 K (0 J/kg·K for DyFeO3, 0.93 J/kg·K for orthorhombic DyMnO3). The large adiabatic temperature change contributed by magnon indicates the exceptional refrigeration efficiency in a direct way. Therefore, it is possible to convert DyFeO3 into a room-temperature spin storage device material or a magnetic refrigeration contender at low temperatures.

Inverse and direct magnetoelectric effects in orthorhombic DyMnO3 manganite single crystals

Correlations between the direct and inverse magnetoelectric effects in orthorhombic DyMnO3 single crystals have been investigated. In the inverse magnetoelectric effect, the magnetic moment of the crystal appears to have a contribution that is sinusoidal oscillating in ac electric fields below the temperature TFE of ferroelectric phase transition. The first and the second harmonics of the inverse magnetoelectric effect are clearly detected. The magnetoelectric susceptibilities α and β, corresponding to first and second harmonics, are found to correlate with the derivative of polarization with respect to the magnetic field. The influence of the magnetic and electric regimes during cooling on magnetoelectric effects has also been studied. The maximum change in the magnetic moment of a sample under the action of electric fields is observed under the same (T, H) conditions as the rotation of the spontaneous polarization vector from the crystallographic c direction to the a axis in the magnetic field H || b.

The effect of rare-earth Gd-substitution on the structural, magnetic and specific heat properties in orthorhombic DyMnO3 ceramics

The acrylamide polymer gel template method has been adopted to synthesize single phase Dy1–xGdxMnO3 (DGMO, x= 0, 0.05, 0.1, 0.15, 0.2) ceramics. The Rietveld refinement of x-ray diffraction patterns recorded at room temperature suggests that DGMO ceramics are stabilized in an orthorhombic crystal structure with a Pnma space group. Gd3+ cations play an important role in stabilizing the orthorhombic phase and the unit cell volume increases with x. We report the phonon spectra of pure and Gd-substituted DyMnO3 (DMO) and their mode assignments. Raman modes are softened with x due to the relaxation in the stiffness constants upon the increase in the volume of the unit cell. The magnetic transition temperatures corresponding to TN(Dy) and Tlock decrease with the increase in Gd concentration as inferred from the temperature dependent magnetization data (M–T curve). The magnetization value increases below TN(Dy) with the increase in the Gd concentration as observed from the M–T plot. The magnetic hysteresis loop is fitted to extract ferromagnetic and antiferromagnetic/paramagnetic contributions for each composition x. Fittings of M–H loops indicate the increase in the magnetic contribution below TN(Dy) upon increasing the Gd dopant concentrations, while that decreases above TN(Dy). The temperature dependent specific heat data identifies these magnetic transition temperatures TN(Dy), Tlock and TN(Mn). Furthermore, magnetic field dependencies on TN(Dy), Tlock and TN(Mn) are studied in an elaborate manner. Both DMO and DGMO samples are found to be viable candidates for magnetic refrigeration applications in cryogenic temperature region.

Structure and Magnetic Properties of Multiferroic DyMnO₃ Epitaxial Thin Films Grown on Different Substrates

Fabrication of thin films is crucial in the study of fundamental properties of matter and designs of devices. In this work, multiferroic dysprosium manganites DyMnO₃ thin films were grown epitaxially on SrTiO₃ (001) and yttrium stabilized zirconia (111) [YSZ (111)] substrates by pulsed laser deposition technique. The fabricated films showed perfectly orthorhombic crystallization on SrTiO₃ (001) and hexagonal crystallization on YSZ (111) substrates. At low temperatures, the magnetic measurements revealed three magnetic transitions at 10 K, 21 K and 43 K for orthorhombic DyMnO₃ film, 7 K, 38 K and 58 K for hexagonal DyMnO₃ film, respectively. The results are consistent with those observed in bulk materials, corresponding to magnetic ordering of the Dy<SUP>3+</SUP> ion spins, antiferromagnetic transitions and spin reorientation respectively. This work provides a convenient method to manipulate the film structure by choosing suitable substrates, and it can be used in the study of magnetic properties of multiferroic manganites and related device fabrication.

Dielectric Properties of Orthorhombic Dysprosium Manganites

Orthorhombic dysprosium manganite DyMnO3 with single phase is synthesized using solid-state reaction technique and the crystal structure and dielectric properties as functions of temperature and frequency are investigated. Thermally activated dielectric relaxations are shown in the temperature dependence of the complex permittivity, and the respective peaks are found to be shifted to higher temperatures as the measuring frequency increases. In Arrhenius plots, activation energies of 0.32 and 0.24 eV for the high- and low-temperature relaxations are observed, respectively. Analysis of the relationship between the real and imaginary parts of the permittivity and the frequencies allows us to explain the dielectric behavior of DyMnO3 ceramics by the universal dielectric response model. A separation of the intrinsic grain and grain boundary properties is achieved using an equivalent circuit model. The dielectric responses of this circuit are discerned by impedance spectroscopy study. The determined grain and grain boundary effects in the orthorhombic DyMnO3 ceramics are responsible for the observed high- and low-temperature relaxations in the dielectric properties.

Studies of magnetic phase transitions in orthorhombic DyMnO3 ceramics prepared by acrylamide polymer gel template method

Abstract Single phase polycrystalline DyMnO3 (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; Tlock) and antiferromagnetic (AFM) ordering of Dy spin (around 8 K; TN (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; TN(Mn)), (ii) Tlock transition and (iii) TN(Dy) transition. The effect of magnetic field to the transitions were studied using specific heat capacity measurement. The peak intensity of TN(Dy) decreases on the application of magnetic field whereas peak intensity of Tlock increases with increase in magnetic field in specific heat measurement. Further the third anomaly, TN (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.

Impedance Spectroscopy Analysis of Orthorhombic DyMnO3 Ceramics

Orthorhombic DyMnO3 ceramics were synthesized by means of standard high-temperature solid-state reaction technique. Impedance spectroscopy analysis (complex impedance Z* and complex modulus M*) were performed by using the nondestructive complex impedance spectroscopy technique in the frequency range of 100–10 MHz at different temperatures. The impedance spectroscopic plots were used to discern the intrinsic DyMnO3 grain and grain boundary contributions to the dielectric responses. The radii of semicircles in Z″ vs. Z′ plot (Z′ and Z″ are real and imaginary parts of Z*) increased with decreasing temperature, which suggest the increased grain resistance. Similarly, the radii of semicircles in M″ vs. M′ plot (M′ and M″ are real and imaginary parts of M*) suggest that the grain capacitance increased as the temperature decreased. The resistance and capacitance of grain boundaries seem to be independent of the investigated temperatures. The dielectric response from electrodes with demarking frequency was extracted from the presentation of Z′ vs. Z″/f, where f is the frequency of the applied field.

Ferroelectric ordering and magnetoelectric effect of pristine and Ho-doped orthorhombic DyMnO3 by dielectric studies

In this paper, the magnetoelectric coupling and ferroelectric ordering of the orthorhombic Dy1-xHoxMnO3 (x = 0 and 0.1) are studied from the magnetodielectric response of the polycrystalline samples. The dielectric study on the DyMnO3 reveals ferroelectric transition at 18 K along with an addition transition at 12 K. We suggest that the transition at 12 K could have originated from the polarization flop rather than being the rare earth magnetic ordering. The magnetodielectric study reveals a magnetoelectric coupling strength of 10%, which is stronger by two orders of magnitude in comparison to the hexagonal manganites. Surprisingly, the Ho3+ substitution in DyMnO3 suppresses the magnetoelectric coupling strength via the suppression of the spiral magnetic ordering. In addition, it also reduces the antiferromagnetic ordering and ferroelectric ordering temperatures. Overall, the studies show that the rare earth plays an important role in the magnetoelectric coupling strength through the modulation of spiral magnetic structure.

Size-dependent structure and magnetic properties of DyMnO3 nanoparticles

The structure and magnetic properties of orthorhombic DyMnO3 nanoparticles with different particle sizes are investigated in this paper. With decreasing particle size, all the lattice parameters a, b, and c gradually decrease, whereas the orthorhombic distortion increases. Magnetic measurements reveal that the antiferromagnetic interaction of Mn ions is weakened due to the decrease in Mn-O-Mn bond angle. Above a critical field H*, DyMnO3 undergoes a field-induced metamagnetic transition at 4 K, which is related to the spin reversal of Dy moments. The critical field H* increases monotonically with size reduction, indicating an enhancement of the antiferromagnetic interaction of Dy ions due to the decreased distance between rare earth ions. The magnetization at 4 K and 5 T, i.e., M(4 K, 5 T) shows a non-monotonic variation with particle size d, i.e., M(4 K, 5 T) initially increases with size reduction but decreases again for d &amp;lt; 68 nm. A modified core-shell model, in which the ferromagnetic ordering (Dy magnetic structure) and antiferromagnetic ordering (Mn magnetic structure) coexist in the core, is proposed to explain this behavior.

Pressure and Temperature Dependence of Local Structure and Electronic Structure of Orthorhombic DyMnO3

The dependence on pressure and temperature of the local structure and electronic state for MnO6 octahedra in orthorhombic DyMnO3 is investigated with Raman scattering, lifetime-broadening-suppressed x-ray absorption spectra and x-ray emission spectra. With increasing pressure, all Raman-active modes of DyMnO3 persist and shift monotonically to greater wavenumbers, implying that no structural change occurs under an external pressure up to \({\sim}32\) GPa. The spectral weight of the white line in Mn \(K\)-edge x-ray absorption spectra of DyMnO3 increased progressively, whereas the pre-edge feature gradually shifted to smaller energy upon increasing pressure. The Jahn–Teller distortion of MnO6 octahedra in DyMnO3 is progressively diminished with increasing pressure. The energy of the pre-edge line increased upon cooling from 300 to 10 K, in contrast with the pressure effect. A gradual breakdown of the high-spin state for MnO6 octahedra in DyMnO3 is observed. This work provides insight into structural modifi...

Magnetic properties and anisotropy of orthorhombic DyMnO3 single crystal

An orthorhombic DyMnO3 single crystal has been studied in magnetic fields up to 14T and between 3K and room temperature. The field dependent ordering temperature of Dy moments is deduced. The paramagnetic Curie Weiss behavior is related mainly to the Dy3+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 9K, when relatively weak magnetocrystalline anisotropy is overcome by magnetic fields up to 1.6T.

Static and dynamic magnetic properties and interplay of Dy3+, Gd3+ and Mn3+ spins in orthorhombic DyMnO3 and GdMnO3 nanoparticles

Single-phase orthorhombic DyMnO3 and GdMnO3 nanoparticles in the size range 60–70 and 35–45 nm, respectively, were synthesized using a modified hydrothermal method. The magnetic property measurements of DyMnO3 nanocrystals show anomalies around ∼43 K (antiferromagnetic (AFM) coupling between Mn3+ spins) and at 7 K in the form of a peak in the zero-field-cooled curve (AFM coupling between Dy3+ spins). Whereas, GdMnO3 undergoes a phase transition at ∼42 K from paramagnetic to an incommensurate-antiferromagnetic phase (ICAFM) followed by a second anomaly at ∼22 K, which could be associated with the transition from ICAFM into a canted A-type AFM ordering of the Mn3+ spins. This transition is followed by a long-range ordering of the Gd3+ moments at 6 K yielding the canting of the Gd3+ spins with a ferromagnetic (FM) component antiparallel to the FM moment of the canted Mn3+ spins. No anomaly near the Néel temperature of the Mn moments for both DyMnO3 and GdMnO3 nanoparticles was observed in ac magnetization which were observed in dc magnetization. The room temperature Raman spectra of DyMnO3 shows two most intense Raman modes at 480 and 609 cm−1 which can be assigned to an antisymmetric Jahn–Teller stretching mode and a symmetric or breathing stretching mode, respectively, involving Mn–O bond stretching.

Observation of anomalous phonons in orthorhombic rare-earth manganites

We observe the appearance of a phonon near the lock-in temperature in orthorhombic REMnO3 (RE denotes rare earth) (RE: Lu and Ho) and anomalous phonon hardening in orthorhombic LuMnO3. The anomalous phonon occurs at the onset of spontaneous polarization. No such changes were found in incommensurate orthorhombic DyMnO3. These observations directly reveal different electric polarization mechanisms in the E-type and incommensurate-type orthorhombic REMnO3.

Modifications of MnO6 octahedra in DyMnO3 under high pressure

Local geometry and electronic states of octahedrally coordinated Mn ions in orthorhombic DyMnO3 have been studied by partial-fluorescence-yield spin-selective x-ray absorption spectroscopy and in-situ Raman scattering. As evidenced in absorption near-edge structure and Raman spectra, the external pressure alleviates the MnO6 octahedral distortion and Jahn-Teller effect with enhanced octahedral tilt.

Phase Equilibria in the System Al2O3-CaO-CoO and Gibbs Energy of Formation of Ca3CoAl4O10

The floating-zone method with different growth ambiences has been used to selectively obtain hexagonal or orthorhombic DyMnO3 single crystals. The crystals were characterized by x-ray powder diffraction of ground specimens and a structure refinement as well as electron diffraction. We report magnetic susceptibility, magnetization and specific heat studies of this multiferroic compound in both the hexagonal and the orthorhombic structure. The hexagonal DyMnO3 shows magnetic ordering of Mn3+ (S = 2) spins on a triangular Mn lattice at T-N(Mn) = 57 K characterized by a cusp in the specific heat. This transition is not apparent in the magnetic susceptibility due to the frustration on the Mn triangular lattice and the dominating paramagnetic susceptibility of the Dy3+ (S = 9/2) spins. At T-N(Dy) = 3 K, a partial antiferromagnetic order of Dy moments has been observed. In comparison, the magnetic data for orthorhombic DyMnO3 display three transitions. The data broadly agree with results from earlier neutron diffraction experiments, which allows for the following assignment: a transition from an incommensurate antiferromagnetic ordering of Mn3+ spins at T-N(Mn) = 39 K, a lock-in transition at Tlock-in = 16 K and a second antiferromagnetic transition at T-N(Dy) = 5 K due to the ordering of Dy moments. Both the hexagonal and the orthorhombic crystals show magnetic anisotropy and complex magnetic properties due to 4f-4f and 4f-3d couplings.

Multiferroic properties of epitaxially stabilized hexagonal DyMnO3 thin films

The authors fabricated epitaxial thin films of hexagonal DyMnO3, which otherwise form in a bulk perovskite structure, via deposition on Pt(111)‖Al2O3(0001) and YSZ(111) substrates, each of which has in-plane hexagonal symmetry. The polarization hysteresis loop demonstrated the existence of ferroelectricity in our hexagonal DyMnO3 films at least below 70K. The observed 2.2μC∕cm2 remnant polarization at 25K corresponded to a polarization enhancement by a factor of 10 compared to that of the bulk orthorhombic DyMnO3. Interestingly, this system showed an antiferroelectriclike feature in its hysteresis loop. Our hexagonal DyMnO3 films showed an antiferromagnetic Néel temperature around 60K and a spin reorientation transition around 40K. The authors also found spin-glass-like behavior, which was likely to arise from the geometric frustration of antiferromagnetically coupled Mn spins with an edge-sharing triangular lattice.

P.3.e.003 Dissociation of working memory from decision-making in schizophrenia

A large magnetocaloric effect can be obtained around TN, Dy ̴8 K simply by spinning the orthorhombic DyMnO3 single crystal within the cb-plane in a constant magnetic field, instead of the standard magnetization–demagnetization process. Under 7 T, the maximum rotating entropy change (−ΔSR, cb) and the associated adiabatic temperature change (ΔTad, cb) are 16.3 J/kg K and 11 K, respectively. The corresponding refrigerant capacity is 440 J/kg, with no thermal and field hysteresis losses. Our findings show that the orthorhombic DyMnO3 could be used as a good refrigerant in more compact and efficient cryomagnetocaloric refrigerators.