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Magnetoresistance (MR) phenomenon couples the electron transport with magnetic field, which has been at the forefront of condensed matter physics and materials science. Large-MR behaviors are of particularly importance for magnetic sensor and information memory applications, and their scarcity has aroused intensive research. Moreover, due to the different physical origins, combination of large positive and negative MR (pMR and nMR) in one single compound has rarely been reported. In present work, we achieved a coexistence of large pMR and nMR in Cr2Si2Te6 ferromagnetic semiconductor single crystal with different field configurations. Specifically, a large nMR of about −60% was obtained under the in-plane field, while a large pMR higher than 1000% took over in the out-of-plane direction. We attribute this field direction-sensitive dualistic large MR behavior to the competition and cooperation effect from the ferromagnetic interaction, orbital scattering and electronic correlation that coexist in Cr2Si2Te6, which contribute to nMR, pMR, and nMR, respectively, in dominated temperature and field ranges, and show different weights under different field directions. The elucidated multiple MR mechanism in this ferromagnetic semiconductor will shed light on the pursuit of coexistence of large pMR and nMR for field-sensitive device applications.

In this work, polycrystalline Pr1-xBaxMnO3 (0.25 ≤ x ≤ 0.36) ceramics were synthesized, and their magnetic and electrical transport properties were systematically studied. All samples show two metal-insulator transitions (MITs) corresponding to the high temperature TMI1 and low temperature TMI2, respectively, besides the non-Griffith phase above the ferromagnetic (FM) transition temperature TC. Combining the results of the transport and magnetic properties, it is found that the FM transition temperature TC coincides with the temperature TMI1, which is linearly related to the A-site ionic radius mismatch variance σ2, indicating the enhancement of FM interactions due to the increase of the degree of B-site ordering of Mn3+/Mn4+ ions. The positive correlation between ferromagnetic insulators (FMI) and magnetic interactions, including the FM and short-range antiferromagnetic (AFM) interactions, is confirmed. It is suggested that the first MIT at TMI1 is attributed to the Mn3+/Mn4+ double exchange interactions and the second MIT at TMI2 is closely related to the suppression of the AFM interactions under the internal FM field induced by the Mn3+/Mn4+ DE interactions. This work provides not only a theoretical understanding on the origin of MIT at low temperature, but also a new way for adjusting the FMI in perovskite manganese oxide Pr1-xBaxMnO3 for application.

Pursuing new ferromagnetic systems could bring about research breakthroughs for magnetism. Currently, studies of magnetic ordering are expanding from interatomic to intermolecular exchange interactions to produce ferromagnets in inorganic/organic crystals. To date, the crystalline framework used for stabilizing parallel spin alignment via an ordered lattice seems to be indispensable to ferromagnetism. In our case, we demonstrated room-temperature long-range ferromagnetic order in two-dimensional confined cobaltocene (Co(Cp)2) molecular monolayers. In a confined van der Waals (vdW) interlayer space, spontaneous uniform spin orientation of Co(Cp)2 can be settled. Ferromagnetic coupling is established by an intermolecular vibronic superexchange interaction, a new long-distance exchange interaction in a cooperative dynamic Jahn-Teller (J-T) Co(Cp)2 monolayer. As expected, the confined Co(Cp)2 monolayers exhibit a high ferromagnetic transition temperature (above room temperature) with a saturation magnetization up to 4 emu.g-1.

BiTe is a potentially attractive candidate for thermoelectric applications because it is the structural analogue of the state-of-the-art thermoelectric material, bismuth telluride (Bi2Te3). However, BiTe has attracted little attention due to its small band gap and high electron concentration. In this study, remarkable increase in thermoelectric performance in the n-type Bi1−xSbxTe compounds through tuning the carrier concentration with chemical doping is shown. The Seebeck coefficient of Bi1−xSbxTe increases remarkably while the electronic thermal conductivity decreases gradually as Sb content is increased, leading to enhanced thermoelectric figure of merit (ZT). Moreover, the simultaneous optimization of the electrical and thermal transport properties leads the peak temperature of the figure of merit to shift toward lower temperature with Sb content increasing in Bi1−xSbxTe, thus making Bi1−xSbxTe a potential alternative to bismuth telluride for near-room-temperature thermoelectric applications. In addition, the presence of multiple low-frequency optical phonons and their coupling with the long-wavelength heat carrying acoustic phonons in all the Bi1−xSbxTe investigated are revealed based on the combined Debye−Einstein model. The present results provide the underlying mechanism connecting thermoelectric performance and lattice dynamics in Bi1−xSbxTe compounds. 因其与成熟的室温热电材料Bi2Te3具有类似的结构, BiTe被认为在热电材料领域具有潜在的应用价值。但是, 受限于禁带宽度较小、载流子浓度过高等特点, BiTe的热电性能依旧处于很低的水平。本工作通过在BiTe样品中掺入Sb元素的方法来调节材料的载流子浓度, 从而显著提高了n型Bi1−xSbxTe化合物的热电性能。研究发现, 随着Sb含量的增加, Bi1−xSbxTe的塞贝克系数显著增加、电子热导率逐渐降低, 从而使得Bi1−xSbxTe材料的热电优值得以提高。进一步发现, 电、热输运行为的协同优化会导致Bi1−xSbxTe的热电优值峰值温度随着Sb含量的增加而逐渐向低温端移动, 这使得Bi1−xSbxTe成为近室温热电应用领域的明星材料Bi2Te3的潜在替代品。此外, 基于德拜—爱因斯坦模型, 本工作揭示了Bi1−xSbxTe材料中多个低频光学声子的存在以及这些光学声子与载热的声学声子之间的耦合关系, 从而将Bi1−xSbxTe化合物的热电性能与晶格动力学联系起来。

The R-dependent structural and magnetic properties of the disordered RFe0.5Cr0.5O3 (R = Ce, Pr, Nd, Sm) ceramics are systemically investigated. Based on the model composed of the paramagnetic R sub...

Understanding the origin of intrinsic lattice thermal conductivity in crystalline solids is critical to research fields ranging from thermoelectric materials to thermal barrier coatings. This work ...

The Sm-doping effect on the crystal structure, dielectric and magnetic properties of CeFeO3 ceramics are systemically investigated. A giant dielectric response with high dielectric constant and low dielectric loss at room temperature (RT) is observed in Ce0.5Sm0.5FeO3 compounds. The increase of the dielectric constant is attributed to the increase of the ratio of Fe2+/Fe3+ ionic contents due to the charge transfer between Ce3+ and Fe3+ ions induced by Sm doping. Besides, the starting temperature T1 of spin-reorientation transition from Γ4 (Gx, Ay, Fz) to Γ1 (Ax, Gy, Cz) increases with Sm doping, and even reaches to a higher one than RT. Meanwhile, composite spin configurations of Fe3+ ions containing Γ1 and/or Γ2 (Fx, Cy, Gz) are found at RT in 0.2≤x ≤ 0.5 samples (x is Sm doping level), besides Γ4 state, whose formation originates from the strengthening of the anisotropic exchange interactions between Fe3+ and Ce3+/Sm3+ spins and the coexistence of Ce- and Sm-rich regions caused by Sm doping. It is suggested that the combining and competing functions of the Fe2+-Fe3+ ferromagnetic double-exchange interaction related to the Fe2+ ionic content and the composite spin configurations of Fe3+ ions containing Γ1 and/or Γ2 dominate the dielectric loss of Ce1-xSmxFeO3 ceramics. The results provide a different view for the physical theory and adjustment of the dielectric properties for applications.

Quantum Griffiths singularity (QGS) is among the remarkable phenomena induced by disorder in quantum phase transitions (QPTs). In recent years, experimental progresses have been made in ultrathin s...

Spin-reorientation (SR) transition as a kind of magnetic phase transition is the most peculiar and interesting phenomenon for rare-earth orthoferrites RFeO3, the research on which is important not ...

The cerium orthoferrite (CeFeO3) ceramics were synthesized successfully by solid-state method and the room-temperature multiferroic properties of CeFeO3 annealed under different atmospheres were investigated. A clear ferroelectric hysteresis loop with Pr = 0.8 μC/cm2 measured under 10 kV/cm is observed at room temperature in the CeFeO3 annealed under oxygen, implying the nature of ferroelectricity existing in the material which is ascribed to the crystal structure change and local lattice distortion closely related to the mixed valences of Ce and Fe ions, as revealed by X-ray diffraction, Raman spectra, and XPS analysis. Besides, Magnetic study reveals that CeFeO3 is a weak ferromagnetic material and the saturation magnetization increases with oxygen vacancies decreasing. The coexistence of the induced ferroelectricity and the improved ferromagnetism confirms that the better multiferroic property exists in CeFeO3 ceramics and the oxygen content (Ce valence) has a critical role in the ferroelectric property.

The successful fabrication of freestanding two-dimensional (2D) crystals that exhibit unprecedented high crystal quality and macroscopic continuity renovates the conventional cognition that 2D long-range crystalline order cannot stably exist at finite temperatures. Current progresses are primarily limited to van der Waals (vdW) layered materials, while studies on how to obtain 2D materials from nonlayered bulk crystals remain sparse. Herein, we report the experimental realization of vdW-like cubic ZrN single crystal and emphasize the significant role of confined electrons in stabilizing the atomic structure at the 2D limit. Furthermore, the exfoliated ZrN single-crystal films with a few nanometers thick exhibit dimensional crossover effect of emerging 2D superconductivity with the unconventional upper critical field beyond Pauli paramagnetic limit, which suggests a dimensional effect in the pairing mechanism of dimensionally confined superconductors.

Perovskite oxides are significant candidates to develop electrochemical catalysts for water oxidation in consideration of their high catalysis capacity, low costing and excellent stability. Rational design of coordination structure and overcoming poor electronic transport are regarded as critical factors for outstanding perovskite-based oxygen evolution reaction (OER) catalysts. Herein, we report a mild chemical oxidation method to realize ligancy engineering from strongly-correlated brownmillerite Sr2Co2O5 to perovskite phase Sr2Co2O55, along with abundant oxygen vacancies formation and greatly boosted electric conductivity, which helps to form the active species of Co hydroxide/oxide on the surface of catalysts. The coupling effect of catalytic kinetics and unimpeded electronic movement brings high OER activities in Sr2Co2O55with a low onset potential and a small Tafel slope. Our work not only displays in-depth understanding into the relationship among catalysis performance and multiple physical degrees of freedom, but also paves a new path to develop high-efficient electrochemical catalysts.

BiFeO3 is the most well-known single-phase material for multiferroic and photovoltaic applications because of its large ferroelectric polarization and high operating temperature. However, direct ma...

We explore the role of oxygen vacancies in the oxygen evolution reaction (OER) for double perovskite PrBaCo2O6-δ. Interestingly, we find that largely increasing oxygen vacancies leads to a significant reduction in the intrinsic OER activity. Structural studies reveal that oxygen vacancies tend to orderly align in PrO1-δ. This ordered structure not only lowers the cobalt oxidation states but also triggers a spin-state transition from high-spin to low-spin states for cobalt ions, both greatly slowing the OER kinetics.

Controlling lattice vibrations to obtain intrinsic low thermal conductivity play a critical role in thermal management of electronic and photonic devices, energy converters, and thermal insulation, which necessitates exploring new compounds and a thorough understanding of their chemical structure, bonding, and lattice dynamics. Herein, a new chalcogenide, Ga

Double perovskites Dy2CoMnO6 (DCMO) was synthesized by a sol-gel method and the structure and magnetic properties were systematically investigated. Both X-ray diffraction and Raman spectrum indicate that double pervoskite DCMO has a monoclinic structure with a space group P21/n. A Griffiths phase is confirmed to be existing in DCMO by the magnetic behaviors, which is significantly different from the behaviors of the non-Griffiths phase of Gd2CoMnO6 (GCMO) recently reported in reference. It is suggested that the origins of the different short-range magnetic orders of them can be attributed to the different 3d-4f exchange interactions in DCMO and GCMO, besides the effect of the unavoidable anti-site disorder, interrupting the long-range ferromagnetic (FM) order of Co2+-O-Mn4+, resulting in the formation of short-range FM order. The effects of A-site rare-earth Re3+ ions on the magnetism of double perovskite Re2Co(Ni)MnO6 are dominated by the combining and competing functions of the radius and the moments of rare earth ions (or the 3d-4f exchange interactions). The FM/AFM coupling is not only related to the most outer 4f electrons of the rare earth ions, but also to the inner 5d/6s orbital electrons.

Since the rise of two-dimensional (2D) semiconductors, it seems that electronic devices will soon be upgraded with spintronics, in which the manipulation of spin degree of freedom endows it obvious advantages over conventional charge-based electronics. However, as the most crucial prerequisite for the above-mentioned expectation, 2D semiconductors with adjustable magnetic interaction are still rare, which has greatly hampered the promotion of spintronics. Recently, transition metal phosphates have attracted tremendous interest due to their intrinsic antiferromagnetism and potential applications in spintronics. In the work described herein, parasitic ferromagnetism is achieved for the first time by exfoliating an antiferromagnetic chalcogenophosphate to a few layers. Taking the transition metal chalcogenophosphate Mn2P2S6 as an example, the antiferromagnetic transition at the Neel temperature is completely suppressed, and the magnetic behaviors of the as-obtained few-layered Mn2P2S6 are dominated by parasitic ferromagnetism. We experimentally verify an electron redistribution by which part of the Mn 3d electrons migrate and redistribute on P atoms in few-layered Mn2P2S6 due to the introduced Mn vacancies. The results demonstrated here broaden the tunability of the material's magnetic properties and open up a new strategy to rationally design the magnetic behaviors of 2D semiconductors, which could accelerate the applications of spintronics.

Appearance of disorder is commonly known as detrimental to two-dimensional (2D) superconductivity, and typically results in decrement of the critical transition temperature ( Tc). Herein, an anomalous enhancement of superconductivity was observed in TaS2 monolayer with function of disorder induced by structural defect. Owing to controlled pore density by acid concentration during chemical exfoliation, the disorder level in TaS2 framework can be effectively regulated. Dome-shaped behavior was uncovered in disorder dependence of superconductivity toward the chemically functionalized TaS2 monolayers, with Tc enhanced from 2.89 to 3.61 K when below critical disorder level. The disorder-engineered Tc enhancement, which distinctly differs from monotonic decrement in deposited 2D superconductors, can be ascribed to the increment of carrier density induced by Ta atom absence. The exotic superconducting enhancement would give help to deeply understand the correlation between superconductivity and disorder in 2D system.

Exploring efficient and economical electrocatalysts for the oxygen evolution reaction (OER) is of great importance for large-scale water splitting. Transition-metal oxides and their derivatives hav...

A series of Bi2MoO6 (BMO) nanoplates with a heterogeneous Bi2MoO6-x@Bi2MoO6 core/shell structure were successfully obtained by reduction with CaH2 at 140 °C and subsequent reoxidation in air under low temperatures (≤250 °C). It is found that the oxygen vacancies mainly exist in the core, while the shell is formed by surface disorder layer with few oxygen vacancies, which is almost stoichiometric. The controllable growth of the surface disorder layer can be realized by the reduction and/or reoxidation temperatures. The reoxidized BMO with the surface disorder layer exhibits about five times higher visible-light photocatalytic activity toward phenol degradation and an order of magnitude higher activity toward methylene blue (MB) degradation than those of the unmodified sample. The visible-light absorption is mainly dominated by the oxygen vacancies through the modulation of the band gap structure, which promote the solar light utilization and photogenerated charge carriers. Density functional theory calculation shows that BMO is a direct band gap semiconductor. It is suggested that the surface disorder layer could suppress the direct recombination of photogenerated carriers and improve surface reactivity, and results in the enhancement of the photocatalytic activity. In addition, the existence of the stoichiometric surface disorder can promote the catalyst stability. It is demonstrated that the reduction- reoxidation method applied here is simple, easily control, and beneficial for the design and realization of heterogeneous core-shell nanostructured photocatalysts to improve visible and infrared optical absorption by engineering the surface disorder and the oxygen vacancies inside core of Bi2MoO6 nanoplates and the related nanostructured photocatalysts.

Polycrystalline Bi2Fe4O9 and Bi2Fe3.6Me0.4O9 (Me = Al and Ti) ceramics were prepared using a modified Pechini method. It is observed that the introduction of Ti apparently increases low-temperature magnetization of Bi2Fe4O9, while the Al substitution has weakly effect. Meanwhile, the optical bandgap reduces from 2.06 eV for Bi2Fe4O9 to1.86 eV for Ti substitution, and 2.01 eV for Al substitution, respectively. All results may be ascribed to the random replacement of both octahedral and tetrahedral Fe ions for Al substitution while preferly replacement of octahedral sites for Ti substitution, as confirmed by the Rietveld refinement and Raman spectra.

The perovskite manganese oxides La 0.3 Ce 0.2 Ca x Sr 0.5-x MnO 3 (0 ≤ x ≤ 0.25) have been synthesized by a solid-state reaction, and their transport and magnetic properties have been systemically studied. It is found that the temperature dependent resistivity shows a maximum at T max below Curie temperature T c with temperature decreasing, which is correlated to the Ce 3+ spin-dependent scattering. Moreover, T max is almost unchanged for x ≤ 0.15, but decreases quickly and is closing on the temperature of T c while x > 0.15, which indicates the increase of Ce ionic valence. Meanwhile, the saturation magnetic moment Ms decreases with x increasing to 0.15, and increases anomaly when x > 0.15. XANES results reveal that when x ≤ 0.15, the valence of Mn ion is almost unchanged, but when x > 0.15, it obviously shifts from tetravalence to trivalence with Ca substitution. Meanwhile, XPS spectra results indicate the similar trend of Ce valence changing from trivalence to tetravalence. It is suggested that Ca substitution changes not only the chemical pressure, but also the valence of Ce ion. There is a threshold value for the chemical pressure corresponding to Ca- substitution content at around x = 0.15 (or A > tv = 1.2395 A), which is the starting point of charge transfer appearance in Ca-substituting La 0.3 Ce 0.2 Sr 0.5 MnO 3 compound. The transport and magnetic properties of the half-doped manganties La 0.3 Ce 0.2 Ca x Sr 0.5-x MnO 3 are dominated by the competition/cooperation of Ce 3+ spin-dependent scattering, interaction between Mn ions controlled by A-site ion-size, and the charge transfer from Ce ions to Mn ions.

Bi1−x(Sr1/2Pb1/2)xFeO3 (0.10 ≤ x ≤ 0.30) multiferroic compounds have been synthesized by a conventional solid-state reaction. The influences of A-site Sr/Pb co-doping on the structure, dielectric and magnetic properties of BiFeO3 are investigated systematically. X-ray diffraction reveals that the crystal structure of Bi1−x(Sr1/2Pb1/2)xFeO3 transforms from the rhombohedral symmetry (space group R3c) to the cubic symmetry (space group Pm 3 ¯ m) with Sr/Pb concentration increasing. Meanwhile, the intensities of Bi O bond vibrations continuously decrease and finally disappear. The RT polarization versus electric field (P-E) curves confim the ferroelectric nature for all the samples. Furthermore, it is found that the dielectric constant and dielectric loss tangent of the samples measured in the frequency range of 100–107 Hz decrease drastically at room temperature. A considerable reduction in the leakage current is observed for BFO with Sr/Pb doping content increasing. The ferromagnetic property enhances with the Sr/Pb substitution increasing, which is ascribed to the cooperation of the Fe2+ O Fe3+ double exchange interaction and the effective suppression of antiferromagnetic cycloidal spin structure caused by the crystalline structure transformation. All results indicate that the Sr and Pb co-doping can effectively improve the magnetic and high-frequency dielectric properties of the multiferroic BiFeO3 compounds.

Electronic state transitions, especially metal–insulator transitions (MIT), offer physical properties that are useful in intriguing energy applications and smart devices. But to-date, very few simple metal oxides have been shown to undergo electronic state transitions near room temperature. Herein, we demonstrate experimentally that chemical induction of double-exchange in two-dimensional (2D) nanomaterials brings about a MIT near room temperature. In this case, valence-state regulation of a 2D MnO2 nanosheet induces a Mn(III)–O–Mn(IV) structure with the double-exchange effect, successfully triggering a near-room-temperature electronic transition with an ultrahigh negative magneto-resistance (MR). Double-exchange in 2D MnO2 nanomaterials exhibits an ultrahigh MR value of up to −11.3% (0.1 T) at 287 K, representing the highest reported negative MR values in 2D nanomaterials approaching room temperature. Also, the MnO2 nanosheet displays an infrared response of 7.1% transmittance change on going from 270 to...

The orthorhombic La0.7Ca0.3MnO3/DyMnO3 (LCM/DMO) bilayers and referenced LCM single-layer films were epitaxially deposited by polymer-assisted deposition on (001)- and (011)-oriented SrTiO3 (STO) substrates, respectively, and the effects of interfacial coupling, oxygen deficiency, and orbital reconstruction on the physical properties of the LCM/DMO bilayers have been investigated. It is found that the magnetic and transport properties of LCM/DMO bilayers are weaker than those of LCM referenced films, due to the orientation-adjusted interfacial coupling and oxygen deficiency. More importantly, the introduced larger strain from DMO layer promotes the eg orbital splitting with consequences for orbital reconstruction and the enhancement of antiferromagnetic phase in LCM layer, which strongly affects the physical properties of LCM/DMO bilayers cooperated with interfacial coupling and oxygen deficiency.

The development of transition metal dichalcogenides has greatly accelerated research in the 2D realm, especially for layered MoS

The double-perovskite Nd2CoMnO6 (NCMO) thin films were epitaxially grown on LaAlO3 and SrTiO3 substrates with different orientations by the polymer-assisted deposition technique. A well crystallization quality of the films is confirmed by x-ray diffraction. The magnetism measurement suggests that all the films have a single ferromagnetic (FM) transition, but its substrate-orientational dependence is different from those in normal perovskite ABO3. By the analysis of the valence states of cations combining with the single FM transition, we suggest that the ionization degree of Co and Mn can be stimulated under both tensile and compressive strain, which can weaken the magnetic interaction. Thus, there are two aspects that competitively affect the magnetism [M(T) and Tc] of the NCMO film, i.e., the variation of oxygen octahedron similar to that in the normal perovskite ABO3 film and the degree of Co/Mn ionization, without changing the order of Co–O–Mn chain arrangement, resulting in the different orientation-dependent magnetism in NCMO films from that normally observed in ABO3 films. Our results give a systematic understanding of the substrate-induced-strain influence on the magnetic interaction in NCMO thin films and widen its practical application.

One-dimensional (1D) transition metal oxide (TMO) nanostructures are actively pursued in spintronic devices owing to their nontrivial d electron magnetism and confined electron transport pathways. However, for TMOs, the realization of 1D structures with long-range magnetic order to achieve a sensitive magnetoelectric response near room temperature has been a longstanding challenge. Herein, we exploit a chemical hydric effect to regulate the spin structure of 1D V-V atomic chains in monoclinic VO2 nanowires. Hydrogen treatment introduced V(3+) (3d(2) ) ions into the 1D zigzag V-V chains, triggering the formation of ferromagnetically coupled V(3+) -V(4+) dimers to produce 1D superparamagnetic chains and achieve large room-temperature negative magnetoresistance (-23.9 %, 300 K, 0.5 T). This approach offers new opportunities to regulate the spin structure of 1D nanostructures to control the intrinsic magnetoelectric properties of spintronic materials.

The activity of electrocatalysts exhibits a strongly dependence on their electronic structures. Specifically, for perovskite oxides, Shao-Horn and co-workers have reported a correlation between the oxygen evolution reaction activity and the eg orbital occupation of transition-metal ions, which provides guidelines for the design of highly active catalysts. Here we demonstrate a facile method to engineer the eg filling of perovskite cobaltite LaCoO3 for improving the oxygen evolution reaction activity. By reducing the particle size to ∼80 nm, the eg filling of cobalt ions is successfully increased from unity to near the optimal configuration of 1.2 expected by Shao-Horn's principle. Consequently, the activity is significantly enhanced, comparable to those of recently reported cobalt oxides with eg∼1.2 configurations. This enhancement is ascribed to the emergence of spin-state transition from low-spin to high-spin states for cobalt ions at the surface of the nanoparticles, leading to more active sites with increased reactivity., The activity of electrocatalysts exhibits a strong dependence on their electronic structures. Here, the authors manipulate the eg filling of perovskite cobaltite LaCoO3 nanoparticles by changing particle size and show improved oxygen evolution activity with increased numbers of surface high-spin cobalt ions.

The graphene system is actively pursued in spintronics for its nontrivial sp electron magnetism and its potential for the flexible surface chemical tuning of magnetoelectronic functionality. The magnetoresistance (MR) of graphene can be effectively tuned under high magnetic fields at cryogenic temperatures, but it remains a challenge to achieve sensitive magnetoelectric response under ambient conditions. We report the use of surface modulation to realize superparamagnetism in reduced graphene oxide (rGO) with sensitive magnetic field response. The superparamagnetic rGO was obtained by a mild oxidation process to partially remove the thiol groups covalently bound to the carbon framework, which brings about large low-field negative MR at room temperature (-8.6 %, 500 Oe, 300 K). This strategy provides a new approach for optimizing the intrinsic magnetoelectric properties of two-dimensional materials.

The epitaxial films of LaMnO3 were fabricated via a simple polymer-assisted deposition method. The effects of substrate orientation and annealing condition on the structure and properties of LaMnO3 films have been investigated. It is found by X-ray diffraction and Raman spectroscopy that increase in the oxygen content results in a decrease in unit cell volume along with a reduction in Jahn–Teller distortion. Besides, with increase in annealing temperature, the resistivity of the film decreases and the insulator–metal transition temperature TIM shifts to higher temperature. The maximum of the resistivity is highly substrate-orientation dependent in the ascending order of (1 0 0) ( 1 1 1). Furthermore, the TIM of LaMnO3 film increases with the substrate orientation changing from (1 1 1) to (1 0 0). It is shown that magnetic order correlates well with an insulator to metal behavior. All results reveal that the lattice distortion of MnO6 octahedron can be tuned by different annealing condition and the substrate orientation, which can be effective methods to adjust the structure, electrical and magnetic properties of LaMnO3 films.

La2CoMn1-xAlxO6 (0 ≤ × ≤ 1.00) samples were synthesized by sol–gel method, and their crystal structure and magnetic properties were investigated. X-ray diffraction reveals a structural transition from monoclinic (space group P21/n) to rhombohedral phase (space group R-3c) with Al content increasing. As envisioned and expected, the remanent magnetization Mr and ferromagnetic (FM) transition temperature TC dramatically decrease with the increment of Al doping, which is due to the destruction of the long-range Co2+-O-Mn4+ FM super-exchange interaction induced by Al ion doping. However, abnormally increase of coercive field HC and effective magnetic moment μeff appear for × = 0.25. The results of infrared spectrum, Raman spectrum, and X-ray photoelectron spectroscopy illustrate that this anomaly can be attributed to the spin-state transition of Co3+ ions from intermediate spin (IS) to high spin (HS) state with × increasing to 0.25, rather than the valence changes of the magnetic ions. This spin-state transition is probably due to the increase of crystal symmetry with high disorder and the suppression of Jahn-Teller distortion. The suppressing Jahn-Teller distortion favors the stability of the HS state of Co3+ ions.

The magnetoresistance (MR) and magnetism of PrBaCo2O5+δ (PBCO) with different oxygen content are systematically investigated. It is found that with the temperature lowing, the MR effect changes from positive to negative for the sample annealed in Ar with low oxygen content, and is negative and increases in magnitude for the as-prepared and O2-annealed samples (AP-PBCO, O2–PBCO). A higher MR effect with ∼38% at around 70 K and 9 T for AP-PBCO is obtained. Besides, an abnormal decrease in magnitude for MR is observed for AP-PBCO and O2–PBCO. It is suggested that the spin disorder related polaron hopping energy WP is crucial for the MR effect in PBCO, besides the competition of AFM and FM interactions, which rests with the crystal structure dominated by the content and order of the oxygen vacancies. The observed abnormal MR can be attributed to the reduced polaron hopping energy WP related to the AFM order. The results not only experimentally confirm that the MR effect can be easily adjusted by the oxygen vacancies but also open up a new way for developing the high MR in layered double perovskites for application.

Appearance of disorder is commonly known as detrimental to two-dimensional (2D) superconductivity, and typically results in decrement of the critical transition temperature ( T

Two-dimensional (2D) materials with robust ferromagnetism have played a key role in realizing nextgeneration spin-electronic devices, but many challenges remain, especially the lack of intrinsic ferromagnetic behavior in almost all 2D materials. Here, we highlight ultrathin Mn3O4 nanosheets as a new 2D ferromagnetic material with strong magnetocrystalline anisotropy. Magnetic measurements along the in-plane and out-of-plane directions confirm that the out-of-plane direction is the easy axis. The 2D-confined environment and Rashba-type spin-orbit coupling are thought to be responsible for the magnetocrystalline anisotropy. The robust ferromagnetism in 2D Mn3O4 nanosheets with magnetocrystalline anisotropy not only paves a new way for realizing the intrinsic ferromagnetic behavior in 2D materials but also provides a novel candidate for building next-generation spin-electronic devices.