Ferromagnetic Double Exchange Research Articles

Colossal Magnetoresistive Switching Induced by d0 Ferromagnetism of MgO in a Semiconductor Nanochannel Device with Ferromagnetic Fe/MgO Electrodes.

Exploring potential spintronic functionalities in resistive switching (RS) devices is of great interest for creating new applications, such as multifunctional resistive random-access memory and novel neuromorphic computing devices. In particular, the importance of the spin-triplet state of cation vacancies in oxide materials, which is induced by localized and strong O-2p on-site Coulomb interactions, in RS devices has been overlooked. d0 ferromagnetism sometimes appears due to the spin-triplet state and ferromagnetic Zener's double exchange interactions between cation vacancies, which are occasionally strong enough to make nonmagnetic oxides ferromagnetic. Here, for the first time, anomalous and colossal magneto-RS (CMRS) with very high magnetic field dependence is demonstrated by utilizing an unconventional RS device composed of a Ge nanochannel with all-epitaxial single-crystalline Fe/MgO electrodes. The device shows colossal and unusual behavior as the threshold voltage and ON/OFF ratio strongly depend on a magnetic field, which is controllable with an applied voltage. This new phenomenon is attributed to the formation of d0 -ferromagnetic filaments by attractive Mg vacancies due to the spin-triplet states with ferromagnetic double exchange interactions and the ferromagnetic proximity effect of Fe on MgO. The findings will allow the development of energy-efficient CMRS devices with multifield susceptibility.

Orbital-Selectivity-Induced Robust Quantum Anomalous Hall Effect in Hund's Metals MgFeP.

Ferromagnetic (FM) states with high Curie temperatures (Tc) and strong spin-orbit coupling (SOC) are indispensable for the long-sought room-temperature quantum anomalous Hall (QAH) effects. Here, we propose a two-dimensional (2D) iron-based monolayer MgFeP that exhibits a notably high FM Tc (about 1525 K) along with exceptional structural stabilities. The unique multiorbital nature in MgFeP, where localized and dxz/yz orbitals coexist with itinerant dxy and dz2 orbitals, renders the monolayer a Hund's metal and in an orbital-selective Mott phase (OSMP). This OSMP triggers an FM double exchange mechanism, rationalizing the high Tc in the Hund's metal. This material transitions to a QAH insulator upon consideration of the SOC effect. By leveraging orbital selectivity, the QAH band gap can be enlarged by more than two times (to 137 meV). Our findings showcase Hund's metals as a promising material platform for realizing high-performance quantum topological electronic devices.

Cationic mismatch effect on structural and magnetic behavior of La0.5-xEuxCa0.5-yBayMnO3 charge-ordered manganites

In this research, we have tried to investigate the effect of the cationic disorder on charge ordering and magnetic phase separation in La0.5-xEuxCa0.5-yBayMnO3 (x = 0, 0.05, and 0.1) compounds synthesized by using the sol-gel method. All the samples possess the same average ionic radius at A site <rA> and the same Mn3+/Mn4+ ratio. Our analysis confirmed the chemical composition by energy dispersive X-ray spectroscopy and verified the structural integrity and purity of the phase by X-ray diffraction, revealing an orthorhombic structure with Pnma space group, which is in agreement with the tolerance factor. The important mismatch effect observed in the substituted specimens induces drastic effects on the structural and microstructural properties. Magnetic measurements indicate a great reduction of Curie temperature for substituted samples (from 250 K for x = 0 to 90 K for x = 0.05 and 85 K for x = 0.1), which indicates a weakening of ferromagnetic double exchange interactions induced by cationic disorder. The Arrott plots and the magnetocaloric study of the Eu−based samples indicate the persistence of the antiferromagnetic charge-ordered state characterizing the pristine compound (x = 0) as well as the presence of a first-ordered metamagnetic transition for all the studied samples, which is ascribed to the presence of antiferromagnetic domains. Such transition induced the appearance of a shoulder peak near 100 K in the magnetic entropy change curves for high magnetic field values, resulting in an extra cooling efficiency.

Effect of A-site ionic disorder on structure, magnetic and magnetocaloric properties of La0.85-xNdxAg0.15-yKyMnO3 manganites

In this paper, the effect of A-site ionic disorder (σ2) on the structure, magnetic and magnetocaloric properties in La0.85-xNdxAg0.15-yKyMnO3 have been investigated. X-ray diffraction analysis using Rietveld refinement shows that the crystal structure of the perovskite manganites changes from rhombohedral (space group R3 ͞C) to orthorhombic (space group Pnma) structure with the increasing in σ2. Magnetization measurements showed that, upon increasing σ2, ferromagnetic double exchange interaction of the perovskite manganites diminishes, and as a result, Curie temperature (TC) of the samples decrease linearly. The inverse of susceptibility shows a downturn with decreasing temperature before TC indicating the existence of the Griffiths phase for La0.62Nd0.23Ag0·099K0·051MnO3 (σ2 = 0.004). The magnetic phase transitions of all the samples are belongs to second order transition.

Effect of Chromium Substitution on Microstructure and Magnetic Properties of La&lt;sub&gt;0.7&lt;/sub&gt;Sr&lt;sub&gt;0.2&lt;/sub&gt;Ba&lt;sub&gt;0.1&lt;/sub&gt;Mn&lt;sub&gt;1-&lt;/sub&gt;&lt;i&gt;&lt;sub&gt;x&lt;/sub&gt;&lt;/i&gt;Cr&lt;i&gt;&lt;sub&gt;x&lt;/sub&gt;&lt;/i&gt;O&lt;sub&gt;3&lt;/sub&gt; (&lt;i&gt;x&lt;/i&gt; = 0, 0.03, 0.05, 0.07, 0.1)

Structure, morphology, and magnetic properties of perovskite La0.7Sr0.2Ba0.1Mn1-xCrxO3 (x = 0; 0.03; 0.05; 0.07 and 0.1) synthesized via sol-gel method have been studied. X-ray diffraction studies confirm the Rhombohedral structure with R-3c space groups for all samples. The magnetization measurements clearly show that magnetization decreases with increasing Cr substitution concentration. The partial substitution of Cr3+ in the Mn site weakens the ferromagnetic double exchange interaction of the Mn3+–O–Mn4+ bond. It is caused by the emergence of the Cr3+–O–Cr3+ antiferromagnetic interaction. As known, the structural parameters affect the magnetic properties of perovskite manganese materials in the double exchange interaction. As the Cr3+ concentration increases, the average Mn-O bond length also increases, and the average Mn-O-Mn bond angle decreases, which dramatically weakens the Mn3+–O–Mn4+ double exchange interaction.

High entropy effect on double exchange interaction and charge ordering in half doped Nd0.5Sr0.5MnO3 manganite

The entropy stabilized oxides i.e., the so-called high-entropy oxides are of great interest in recent time due to their intriguing physical properties. This new category of advanced materials is stabilized by the high configurational entropy of randomly mixed elements, where a specific lattice site is populated by five or more elements. The present study is devoted to explore the high entropy effect in well-known charge ordered manganite Nd0.5Sr0.5MnO3 where a delicate balance exists between the ferromagnetic double exchange and the antiferromagnetic superexchange interactions. Powder X-ray diffraction analyses confirm phase purity of the samples. FE-SEM imaging revealed the microstructure and elemental mapping confirmed the chemical homogeneity of the samples as well as nominal cationic composition. Bond valence sum (BVS) calculation using refinement parameters supports the expected cationic valence in all the samples. Replacement of Nd3+ by five trivalent cations as in (La0.1Pr0.1Nd0.1Gd0.1Bi0.1)Sr0.5MnO3 with larger average A-site ionic radius,<rA>and smaller size variance, σ2 compared with Nd0.5Sr0.5MnO3 dramatically suppressed the ferromagnetic double exchange interaction. This observation is in contrast with the expected variation in<rA>and σ2. In (La0.1Nd0.1Gd0.1Bi0.1Y0.1)Sr0.5MnO3 with smaller<rA> and marginally higher σ2 the ferromagnetic state ceases to exist. In both the multicationic compositions, a long-range antiferromagnetic state is evolved around 200 K with the retention of charge ordering. In the high entropy (La1/6Nd1/6Dy1/6Ca1/6Ba1/6Sr1/6)MnO3 composition with nominal<rA> and larger σ2 values the high temperature long-range ordering is completely suppressed and a new antiferromagnetic state is evolved at 45 K without manifestation of any charge ordering. This composition also avoids magnetic frustration unlike the dopant variant with larger σ2. The present investigation thus highlights the role of local lattice distortion or high entropy effect apart from the<rA>and σ2 in manganites.

Superior oxygen evolution reaction performance of NiCoFe spinel oxide nanowires in situ grown on β-Ni(OH)2 nanosheet-decorated Ni foam: case studies on stoichiometric and off-stoichiometric oxides

This work proposes a new direction towards rational design of highly efficient NiCoFe oxide based OER electrocatalysts where induced oxygen vacancies and enhanced ferromagnetic double exchange interactions resulted in the favourable configuration.

Spin-orbital liquids and insulator-metal transitions on the pyrochlore lattice

The two orbital Hubbard model, with the electrons additionally coupled to a complex magnetic background, arises in the pyrochlore molybdates. The background involves local moments Hund's coupled to the electrons, driving double exchange ferromagnetism, and antiferromagnetic (AF) tendency arising from competing superexchange. The key scales include the Hubbard repulsion and the superexchange, both of which can be tuned in these materials. They control the phase transition from a ferromagnetic metal to a spin-glass metal and then to a spin-glass (Mott) insulator. We provide a comprehensive description of the ground state of this model using an unrestricted Hartree-Fock scheme implemented via a simulated annealing procedure and establish the metal-insulator transition line for varying Hubbard interaction and superexchange. The electrons see an effective disorder, due to orbital frustration, already in the ferromagnetic phase. The disorder is further enhanced by antiferromagnetic coupling and the resulting magnetic disorder. As a result, increasing AF coupling shifts the metal-insulator transition to lower Hubbard interaction and gives it an additional ``Anderson'' character. We provide detailed results on the magnetic and orbital correlations, the density of states, and the optical conductivity.

Pressure-induced first-order antiferromagnetic to ferromagnetic transition in MnN

MnN systems have been widely used to investigate Mn incorporated into Ш–V compounds, which combines the spin and electron charge as promising diluted magnetic semiconductors (DMS). However, few experiments have demonstrated the magnetic transformation of MnN with lattice constant changes, although it has been mentioned many times in previous theoretical calculations. In this study, we synthesize MnN single crystal under high pressure and temperature. Furthermore, we perform high-pressure resistance, magnetic resistance and synchrotron radiation on MnN single crystal/polycrystalline and observe the first-order phase transition accompanied with antiferromagnetic (AFM) to ferromagnetic (FM) magnetic structure transition under 34 GPa. The experimental result and first-principles calculations reveal the same magnetic and structural transition of MnN in the compression process from equilibrium volume 18.2 to16 Å3. An analysis of electronic structure and magnetic interactions in terms of the Heisenberg Hamiltonian indicates a strong FM coupling in the [001] plane due to the double exchange mechanism of Mn eg orbitals. With the reduced Mn-N bond length under high pressure, the enhanced FM double exchange interactions could induce the magnetic transition from AFM to FM and subsequently lead to a structural transition from a face-centered tetragonal structure to a cubic structure. These findings provide the foundations for GaMnN or MnN layer DMS.

Nematic order driven by superconducting correlations

The interplay of nematicity and superconductivity has been observed in a wide variety of quantum materials. To explore this interplay, we consider a two-dimensional (2D) array of nematogens, local droplets with Z3 nematicity, coupled to a network of Josephson junction wires. Using finite temperature classical Monte Carlo simulations, we elucidate the phase diagram of this model and show that the development of superconducting correlations and the directional delocalization of Cooper pairs can promote nematogen ordering, resulting in long-range nematic order. We obtain the transport properties of our model within an effective resistor network picture. We discuss these ideas in the context of the 2D electron gas at the (111) KTaO3 interface and the doped topological insulators NbxBi2Se3 and CuxBi2Se3. Our work makes contact with Phil Anderson’s numerous contributions to broken symmetries driven by the saving of kinetic energy, including double exchange ferromagnetism and the interlayer tunneling theory of high Tc superconductivity.

Structural, magnetic and magnetocaloric effect studies of Nd0.6Sr0.4AxMn1-xO3 (A=Co, Ni, Zn) perovskite manganites

The effect of B-site substitution by other transition elements on the structural, magnetic, and magnetocaloric effect properties of Nd0.6Sr0.4AxMn1-xO3 (x = 0.1 and x = 0.2, A=Co, Ni, and Zn) nanopowders has been reported in this study. Auto-combustion sol-gel method was used to synthesize all the nanopowder samples. Room temperature X-ray diffraction shows that all the nanopowders have orthorhombic structure of Pnma space group crystallography, confirming the purity of the single phase. Also, the average nanosized scale of these powder samples is ~ 43 nm, revealing a spherical shape with a packed and homogenous structure. The Mn4+/Mn3+ ratio in these nanopowder compounds is highly dependent on the dopants concentration (x), which shows a significant diminishes as the dopants introduce into the parent compound (Nd0.6Sr0.4MnO3). The decrease in the Mn4+/Mn3+ ratio enhances in the antiferromagnetic (AFM) super exchange interaction (SE) due to the lack of Mn3+— O—Mn4+ ferromagnetic (FM) double exchange (DE). The magnetization measurements indicate that all samples exhibit a ferromagnetic (FM) to paramagnetic (PM) transition with increasing temperature. The Curie temperature (TC) is also affected by the dopants concentrations where considerable decrease has been noticed for all compounds compared to the parent compound. The M-H curves for all compounds reveal PM behavior at 300 K, whereas FM behavior characterized the magnetic hysteresis at low temperature (2 K) which also shows the presence of exchange bias effect. The magnetic entropy change |−∆SMMax| has shown bigger effect for Co dopant (5.92 J/kg.K) compared to Ni and Zn dopants with values of 5.19 J/kg.K, and 4.28 J/kg.K respectively at an applied magnetic field of 9 T. Despite substituting at Mn-site by other transition elements lower the Tc, |−∆SMMax| and RCP, the obtained results are promising for magnetic cooling materials and further investigation.

Polarity and charge redistribution induced emergent interfacial ferromagnetism in non-magnetic LaNiO3/SrMnO3 superlattices

Artificial heterostructures composed of strongly correlated oxides can host many up-and-coming phenomena. The interfacial ferromagnetism can be observed at the interface of paramagnetic LaNiO3 (LNO) and G-type antiferromagnetic SrMnO3 (SMO). Through the macroscopic magnetic and transport measurements and the microscopic x-ray magnetic circular dichroism signals, the obvious interfacial ferromagnetic behavior exhibited in the thicker superlattices. Using x-ray absorption spectroscopy and x-ray photoelectron spectroscopy measurements, the polar mismatch-induced charge redistribution in Ni and Mn ions accurately demonstrates the dependence on the varying thickness of LNO/SMO superlattices. These results suggest that the ferromagnetic double-exchange interaction of Mn3+–Mn4+ increases and the ferromagnetic super-exchange interaction of Ni2+–Mn4+ decreases with the increasing thickness of LNO/SMO superlattices. Consequently, the obvious ferromagnetic behavior in the thicker superlattices is induced by the double-exchange interaction. For the thinner LNO/SMO superlattice, the interfacial super-exchange ferromagnetic state is offset by the double-exchange ferromagnetism. This is the crucial reason behind the fact that ferromagnetism is hard to exist in the prior LNO/SMO superlattices. Our findings highlight the intrinsic mechanism responsible for the interfacial ferromagnetism and the significance of understanding polar mismatch at the interface of heterostructures.

Giant magnetocaloric effect and magnetic properties of nanocomposites of manganite Nd1-xSrxMnO3 (0.0 ≤ x ≤ 0.8) synthesized using modified sol-gel method

The magnetocaloric effect in an array of nanocomposites manganite Nd1-xSrxMnO3 (x = 0.0, 0.2, 0.4, 0.6 and 0.8) was reported in this study. The nanocomposites were synthesized using auto-combustion sol-gel technique where replacing Nd3+ by Sr2+ influence the structure and hence enhancing the magnetic properties and magnetocaloric effect. The synthesized nanocomposites form an orthorhombic crystal structure with Pnma space group No.62 and the average crystallite size was found to be ∼30 nm. The tunning (Mn4+/Mn3+) ratio varies in the nanocomposites with different concentration where the Nd0.6Sr0.4MnO3 nanocomposite exhibits maximum (Mn4+/Mn3+) ratio. The ZFC-FC magnetization measurements indicate that all samples exhibit ferromagnetic (FM) to paramagnetic (PM) transition with increasing temperature and other phase transitions are observed for all samples except Nd0.6Sr0.4MnO3 which also shows a peak Curie temperature (TC = 256 K) in the vicinity of room temperature. The presence of FM in NdMnO3 sample is highly enhanced via FM double exchange (DE) interaction due to self-doping process. Room temperature hysteresis loop reveals paramagnetic (PM) behaviour whereas the pronounced effect presents in Nd0.6Sr0.4MnO3 compound compared to other compounds. However, all compounds exhibit FM behaviour at low temperature measurements with saturation magnetization (Ms) raising up gradually and reaching its maximum at x = 0.4. The magnetic entropy change | ΔSM | is calculated through isotherms measurements and Nd0.6Sr0.4MnO3 nanocomposite exhibits a relatively giant value of magnetic entropy (12.71 J/kg.K and 7.78 J/kg.K at around 257.5 K) under a maximum applied magnetic field of 9 T and 5 T respectively. The corresponding relative cooling power (RCP) for this compound is found accordingly as 636.9 J/kg and 349.8 J/kg. The obtained results in the wide range of temperature starting from very low temperature up to room temperature recommend Nd0.6Sr0.4MnO3 compound as a good potential material for magnetic cooling.

Coupling Stacking Orders with Interlayer Magnetism in Bilayer H-VSe2**Supported by the National Natural Science Foundation of China (Grant No. 51272291), the Distinguished Young Scholar Foundation of Hunan Province (Grant No. 2015JJ1020), the Young Scholar Foundation of Hunan Province (Grant No. 2016JJ3142), the Central South University Research Fund for Sheng-Hua Scholars, Central South University State Key Laboratory of Powder Metallurgy, and

Stacking-dependent magnetism in van der Waals materials has caught intense interests. Based on the first principle calculations, we investigate the coupling between stacking orders and interlayer magnetic orders in bilayer H-VSe2. It is found that there are two stable stacking orders in bilayer H-VSe2, named AB-stacking and A′B-stacking. Under standard DFT framework, the A′B-stacking prefers the interlayer AFM order and is semiconductive, whereas the AB-stacking prefers the FM order and is metallic. However, under the DFT+U framework both the stacking orders prefer the interlayer AFM order and are semiconductive. By detailedly analyzing this difference, we find that the interlayer magnetism originates from the competition between antiferromagnetic interlayer super-superexchange and ferromagnetic interlayer double exchange, in which both the interlayer Se-4pz orbitals play a crucial role. In the DFT+U calculations, the double exchange is suppressed due to the opened bandgap, such that the interlayer magnetic orders are decoupled with the stacking orders. Based on this competition mechanism, we propose that a moderate hole doping can significantly enhance the interlayer double exchange, and can be used to switch the interlayer magnetic orders in bilayer VSe2. This method is also applicable to a wide range of semiconductive van der Waals magnets.

Room temperature multiferroic properties and polymorphic phase transition-induced noticeable magnetodielectric anomalies in Fe/Co co-doped (K0.52Na0.48)NbO3 ceramics

Abstract Polycrystalline ceramics of (K0.52Na0.48)Nb1-x(FeCo)xO3 (0 ≤ x ≤ 0.02) are synthesized using solid-state reaction method. Appropriate Fe/Co doping (x = 0.010 and 0.015) not only optimizes room temperature ferroelectricity of KNNFC ceramics, but also effectively introduces room temperature ferromagnetism and large magnetodielectric effects. The Fe2+/3+-O-Co2+/3+ ferromagnetic double exchange is considered the main reason for the enhancement in ferromagnetic. Moreover, magnetic anomalies and noticeable magnetodielectric (MD) peaks are found near the ferroelectric rhombohedral-orthorhombic (R–O) polymorphic phase transition, indicating the presence of spin-lattice coupling in these samples. Meanwhile, the Fe2+-Fe3+, Co2+-Co3+, and/or Fe2+/3+-Co2+/3+ local dipoles that begin to appear near the R–O phase transition temperature can also contribute to the MD effect. When x = 0.015, the MD peak is as large as +12% (0.9 T, 106 Hz, 120 K), and the room temperature MD value reaches −7% (0.9 T, 106 Hz).

Elastic strain control of electronic structure, and magnetic properties of [Pr1−xCaxMnO3/SrTiO3]15 superlattices

We report the growth, electronic structure, and in-plane magnetic properties of pulsed laser deposition grown 2D superlattice structures [Pr0.7Ca0.3MnO3/SrTiO3]15 and [Pr0.5Ca0.5MnO3/SrTiO3]15 on (001) oriented SrTiO3 and LaAlO3 single crystal substrates. The x-ray reflectivity measurements reveal well-defined interfaces between the manganite and titanate layers along with the existence of Kiessig fringes, providing the evidence for the smooth periodic superlattice structure. The reciprocal space mapping provides signature of tetragonal distortion in all the superlattices. The electronic structure determined from the x-ray photoelectron spectroscopy reveals divalent Sr and Ca, tetravalent Ti, and mixed valent Mn with a pronounce shift of binding energy peaks toward the higher energy side in the superlattices grown on (001) oriented LaAlO3 as compared to those grown on SrTiO3. These superlattices exhibit highly anisotropic ferromagnetic character. We used the law of approach to saturation to determine the anisotropy field (HK) and cubic anisotropy constant (K1) for all the investigated superlattices. This analysis yields the highest HK∼9 kOe and K1∼8×105 erg/cc for the [Pr0.7Ca0.3MnO3/SrTiO3]15 superlattice system. Furthermore, significant enhancement of the overall magnetic moment and a decrease in TC (&amp;lt;100 K) was observed in the case of LaAlO3 grown superlattice, which indicates a substantial role of residual elastic strain on the magnetic ordering. Our results indicate that the strain induced elongation of MnO6 octahedra leads to finite possibility of non-orthogonal overlapping of orbitals in the presence of large crystal field splitting of eg levels, which, in turn, causes suppression of the ferromagnetic double exchange interaction.

New Universality Class Associated with Jahn–Teller Distortion and Double Exchange

The scaling of the magnetic heat capacity in the two manganites La0.85Ag0.15MnO3 and Sm0.55Sr0.45MnO has given the critical exponents α = –0.23 and ν = 0.7433 of the heat capacity and correlation radius of the magnetic order parameter, respectively, which do not belong to any known universality class. These results cannot be attributed to chemical inhomogeneities and/or structural imperfections because the samples are of a high quality. Thus, unusual critical exponents can be associated not only with the chemical disorder and/or structural defects but also with the collective behavior of the lattice. An analogy has been revealed between the effects of the magnetic field and doping on ternary oxides of transition metals: the magnetic field affecting lattice distortions through the orientation of t2g orbitals acts as chemical doping. It seems that scaling relations are more stable than critical exponents in them. The synchronism of lattice distortions and ferromagnetism leads to a novel criticality, but their desynchronization induced by magnetostructural disorder results in the violation of scaling relations between isothermal and isomagnetic exponents. Although double-exchange systems demonstrate novel criticality, they satisfy scaling relations until the magnetic behavior is synchronized with the coherent lattice behavior in the form of cooperative Jahn–Teller distortions. Breaking of double exchange bonds leads to the formation of metamagnetic clusters with magnetic dipole–dipole interaction between them, which desynchronizes lattice distortions and ferromagnetism, resulting in the violation of scaling relations. The proposed new universality class includes diverse materials such as manganites, cobaltites, crystalline Fe–Pt and amorphous Fe–Mn alloys, and high-Tc superconductors. Unusual criticality in double-exchange systems is due to an unusual semiclassical nature of double-exchange ferromagnetism caused by real exchange, i.e., electron current through Mn3+–O–Mn4+ chains with the conservation of the spin rather than by virtual exchange as in a usual ferromagnet. Double-exchange ferromagnetism arises only because to freely itinerate, electrons orient the magnetic moments of Mn cations in a single direction.

Effect of yttrium doping on the structure, dielectric multiferroic and magnetodielectric properties of Bi5Ti3FeO15 ceramics

Multiferroic Bi5−xYxTi3FeO15 (BYTF-x, x = 0, 0.1, 0.3, 0.5, 0.7) ceramics were synthesized through the conventional solid-state reaction. The structure, dielectric, multiferroic and magnetodielectric properties of BYTF-x were investigated in detail. X-ray diffraction confirmed that all the samples were layered Aurivillius structure. Upon increasing Y content, the grain size of samples slightly decreases. The dielectric permittivity increased with Y doped. The Y doping has no effect on microstructural changes of plate-like grains which verified though field-emission scanning electron microscopy. The minimum remanent polarization (2Pr = 2.48 μc/cm2) was observed in BYTF-0.3 ceramic and the maximum magnetodielectric coefficient value of 1.23% was obtained in BYTF-0.3 ceramic perhaps result from the coexistence of Fe2+ and Fe3+. Additionally, weak ferromagnetic is only found in BYTF-0.3 ceramic. The ferromagnetism can be attributed to ferromagnetic double exchange interactions (Fe2+–O–Fe3+) and the spin canting of tilting FeO6 octahedra via the Dzyaloshinskii–Moriya interaction. These results indicate that Y doping Aurivillius phase may be the potential candidates for exploring superior room-temperature multiferroics.

Nature of novel criticality in ternary transition-metal oxides

There are the chains of transition-metal cations alternating with the anions of oxygen in ternary transition-metal oxides. When a p-orbital of the oxygen connects the half-filled and empty d-orbitals of adjacent transition-metal cations, double-exchange ferromagnetism takes place. Although double exchange has been well explored, the nature of novel criticality, induced by it, is yet not uncovered. We explored the magnetic-field scaling in the heat capacity of a Sm0.55Sr0.45MnO3 manganite, one of the best ternary transition-metal oxides as it is completely ferromagnetic, and found novel criticality - unordinary critical exponents which are the consequence of coherence of Coulomb lattice distortion and ferromagnetism. The coherence is caused by the trinity of the mass, the charge and the spin of an electron. When the d and p orbitals overlaps, it quickly walks from one site to the another due its lightest mass. And due to its electric charge, it equalizes the valences of the transition-metal cations in the chains and so diminishes the Coulomb lattice distortion. At last, its spin forces magnetic moments of transition-metal cations to ferromagnetically arrange. The disappearance of Coulomb distortions widens the overlap and lowers the elastic lattice energy, so that not only the spin of an electron, but also its electric charge strengthens ferromagnetism. That nonlinear effect strengthens the critical behaviour and critical exponents come off any known universality classes. Thus, the symbiotic coherence of annihilating Coulomb distortions and arising ferromagnetism is a reason of the novel criticality.

Critical phenomena in the double-exchange ferromagnet La0.8Na0.2Mn1-xNixO3 around the critical temperature

The research results of magnetocaloric effect and critical properties of La0.8Na0.2Mn1-xNixO3 (0 ≤ x ≤ 0.06) manganite are reported. Using the Banerjee's criteria, Franco method and Landau theory, we proved the second order ferromagnetic-paramagnetic phase transition for all samples. The critical exponents values β, γ and δ are determined using modified Arrott plot (MAP), Kouvel Fisher technique and the critical isotherm. Indeed, comparing our determined exponent values with those of standards model, there is a shifting tendency from the mean field model for the compositions La0.8Na0.2MnO3 and La0.8Na0.2Mn0.97Ni0.03O3 to those of the 3D-Ising model for La0.8Na0.2Mn0.94Ni0.06O3 sample. Thus, reflect that the magnetic coupling tends to change from the long-range to the short-range interaction as increasing Ni content. Particularly, by performing the Landau theory we suggest that the magnetoelastic contribution and the electron interaction should be associated with the Jahn Teller interaction in the determination of ΔSM magnetic entropy change effect in our compounds.