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Nanocomposite films hold great promise for multifunctional devices by integrating different functionalities within a single film. The microstructure of the precipitate/secondary phase is an essential element in designing composites' properties. The interphase strain between the matrix and secondary phase is responsible for strain-mediated functionalities, such as magnetoelectric coupling and ferroelectricity. However, a quantitative microstructure-dependent interphase strain characterization has been scarcely studied. Here, it is demonstrated that the PbTiO

Multiple phases coexist in manganite with simultaneously active couplings, and the transition among them depends on the relative intensities of different interactions. However, the melting path with variable intensities is unclear. The concentration and the ordering of oxygen vacancy in previous work are found to induce ferromagnetic charge-ordering insulator phase in [(La

Multiferroic oxide heterostructures consisting of ferromagnetic and ferroelectric components hold the promise for nonvolatile magnetic control via ferroelectric polarization, advantageous for the low-dissipation spintronics. Modern understanding of the magnetoelectric coupling in these systems involves structural, orbital, and magnetic reconstructions at interfaces. Previous works have long proposed polarization-dependent interfacial magnetic structures; however, direct evidence is still missing, which requires advanced characterization tools with near-atomic-scale spatial resolutions. Here, extensive polarized neutron reflectometry (PNR) studies have determined the magnetic depth profiles of PbZr0.2Ti0.8O3/La0.67Sr0.33MnO3 (PZT/LSMO) bilayers with opposite self-polarizations. When the LSMO is 2-3 nm thick, the bilayers show two magnetic transitions on cooling. However, temperature-dependent magnetization is different below the lower-temperature transition for opposite polarizations. PNR finds that the LSMO splits into two magnetic sublayers, but the inter-sublayer magnetic couplings are of opposite signs for the two polarizations. Near-edge X-ray absorption spectroscopy further shows contrasts in both the Mn valences and the Mn-O bond anisotropy between the two polarizations. This work completes the puzzle for the magnetoelectric coupling model at the PZT/LSMO interface, showing a synergic interplay among multiple degrees of freedom toward emergent functionalities at complex oxide interfaces.

The charge-density wave is correlated with the properties in transition metal oxides, and regulating this state is important to explore the potential of oxides. Defects could modulate the local environment, in which the effect is subject to the concentration and arrangement, and an artificial arrangement of defect-ordering is highly expected to design the material properties. In this work, the ordering of oxygen vacancies with a preferred location on the (001) La/SrO plane by self-structural optimization was induced in La0.7Sr0.3MnO3/SrTiO3 superlattices with medium oxygen pressure during SrTiO3 deposition, and then the ferromagnetic charge-ordering (CO)/charge-density-wave (CDW) state was formed in La0.7Sr0.3MnO3 with susceptibility to magnetic field, temperature, and superlattice configuration. In addition, re-entrance to the ferromagnetic insulator CO/CDW could be induced by a high magnetic field. The selective occupancy of oxygen vacancies on the (001) La/SrO plane and the phase fluctuation around the CO/CDW-to-ferromagnetic metal phase transition were critical to the above properties. The interfacial diffusion with atomic-level resolution to control oxygen vacancies could be used in other magnetoelectric systems and corresponding device applications.

The oxygen octahedral rotation around out-of-plane axis is explored to study its effect on metastable status, magnetic cluster glass in manganite. The antiphase rotation around the out-of-plane axis (TiO6 a0a0c-) of SrTiO3 enhances the Mn-O bond anisotropy along in-plane and out-of-plane directions, and weakens the ferromagnetic interactions in 12 nm Pr0.67Sr0.33MnO3 film on (001) SrTiO3 substrate, which together promote the formation of magnetic cluster-glassiness and enlarges the irreversible magnetoresistance effect with enhanced relaxation time of charge carrier. The effect of TiO6 a0a0c- in SrTiO3 substrate on materials properties is obvious with large irreversible magnetoresistance effect for thin film, which fades away with the increase of film thickness. At 10 K, the irreversible magnetoresistance is 0.91 for 12 nm film, and 0.22 for 30 nm film. This work extends current understanding on interfacial coupling to metastable status, and could help to explore other systems in perovskite structure with octahedral rotation.

Novel phenomena at the ferromagnetic/ferroelectric interface have generated much interest. Here, a ferromagnetic insulating state with the Curie temperature about 268-286 K in PbZr0.52Ti0.48O3/La0.67Sr0.33MnO3 heterostructures is induced and modulated by varying the PbZr0.52Ti0.48O3 thickness. An abnormally enlarged c/a ratio in La0.67Sr0.33MnO3 by strain-based coupling effect leads to d3z2-r2 orbital preferable occupancy. This orbital reconstruction modulates effective electron transfer and finally leads to a ferromagnetic insulating state. Valence change induced by charge-based coupling effect could be partially responsible for change in the Curie temperature in the strongly correlated electron system of La1-xSrxMnO3. This work provides a deeper understanding of strain effects near the ferromagnetic/ferroelectric interface, especially in a PbZr1-yTiyO3/La1-xSrxMnO3 heterostructure system.

Structural domains in ferroic materials can be manipulated to achieve novel properties and functionalities of devices with multiple tunabilities. Herein, we report a study of tunable domain structures in ferroelastic ${\mathrm{La}}_{0.67}{\mathrm{Sr}}_{0.33}{\mathrm{MnO}}_{3}$ (LSMO) films via interfacial engineering. Distinct domain structures are formed in rhombohedral LSMO films depending on the crystallographic orientations of the orthorhombic ${\mathrm{NdGaO}}_{3}$ (NGO) substrates. A unidirectional lattice modulation is observed in LSMO films grown on $\mathrm{NGO}{(110)}_{\mathrm{Or}}$ substrates, whereas a unidirectional twinned-domain structure is generated by $\mathrm{NGO}{(001)}_{\mathrm{Or}}$ substrates (where Or in the subscript denotes orthorhombic notation). The orientation-dependent domain structures in LSMO films are controlled by anisotropic strain as well as interfacial oxygen octahedral coupling at the heterointerface between LSMO and NGO. The orbital occupancy and in-plane magnetic anisotropy are markedly affected by strain relief induced by the unidirectional structural domains in LSMO films. In addition, the structural results observed in LSMO/$\mathrm{NGO}{(001)}_{\mathrm{Or}}$ films further demonstrate that anisotropic strain is capable to disturb octahedral connectivity in epitaxial films. Our findings provide future directions to understand and control the domain structures in ferroelastic heterostructures of perovskite materials and open a pathway towards tailoring the desirable physical properties.

The electronic excitation of 3d transition metal oxide depends on the hybridization between orbitals of different ions, and is related to the materials properties. In this work, we systematically study the effect of hydrostatic pressure up to ∼20 GPa on the crystal structure and electronic structure of Pr0.67Sr0.33MnO3 powder, using Mn K-edge X-ray absorption near edge structure and X-ray diffraction at room temperature. With the increase of pressure, the energy position of non-local screened feature moves towards feature without screening due to the enhanced transition energy; however, the intensity (probability) of non-local screened feature increases with the pressure. Further study suggests that the pressure-induced antiferromagnetic phase, affecting hybridization between neighboring Mn ions with spin sensitivity, increase the probability of non-local charge transfer and corresponding intensity of non-local screened feature. The spin-sensitivity of non-local screening may be a useful parameter for characterization of material properties.

Multiferroic oxide heterostructures consisting of ferromagnetic and ferroelectric components hold the promise for nonvolatile magnetic control via ferroelectric polarization, advantageous for the low-dissipation spintronics. Modern understanding of the magnetoelectric coupling in these systems involves structural, orbital, and magnetic reconstructions at interfaces. Previous works have long proposed polarization-dependent interfacial magnetic structures; however, direct evidence is still missing, which requires advanced characterization tools with near-atomic-scale spatial resolutions. Here, extensive polarized neutron reflectometry (PNR) studies have determined the magnetic depth profiles of PbZr

Room-temperature-high-efficiency light-emitting diodes based on metal halide perovskite FAPbI3 are shown to be able to work perfectly at low temperatures. A peak external quantum efficiency (EQE) of 32.8%, corresponding to an internal quantum efficiency of 100%, is achieved at 45 K. Importantly, the devices show almost no degradation after working at a constant current density of 200 mA m-2 for 330 h. The enhanced EQEs at low temperatures result from the increased photoluminescence quantum efficiencies of the perovskite, which is caused by the increased radiative recombination rate. Spectroscopic and calculation results suggest that the phase transitions of the FAPbI3 play an important role for the enhancement of exciton binding energy, which increases the recombination rate.

The oxygen octahedral rotation around the out-of-plane axis is explored to study its effect on metastable status, magnetic cluster glass in manganite. The antiphase rotation around the out-of-plane axis (TiO

Novel phenomena at the ferromagnetic/ferroelectric interface have generated much interest. Here, a ferromagnetic insulating state with the Curie temperature about 268-286 K in PbZr

We report on the efficient spin-orbit torque (SOT) switching in a single ferromagnetic layer induced by a new type of inversion asymmetry, the composition gradient. The SOT of 6- to 60-nm epitaxial FePt thin films with a $L{1}_{0}$ phase is investigated. The magnetization of the FePt single layer can be reversibly switched by applying electrical current with a moderate current density. Different from previously reported SOTs which either decreases with or does not change with the film thickness, the SOT in FePt increases with the film thickness. We found the SOT in FePt can be attributed to the composition gradient along the film normal direction. A linear correlation between the SOT and the composition gradient is observed. This Rapid Communication introduces a platform to engineer large SOTs for lower-power spintronics.

The chemical asymmetry at the hetero-structure interface offers an effective opportunity to design desirable electronic structures by controlling charge transfer and orbital hybridization across the interface. However, controlling the hetero-interface remains a daunting task. Here, we report the modulation of interfacial coupling of (La0.67Sr0.33MnO3)n/(SrTiO3)n superlattices by manipulating the periodic thickness with n unit cells of SrTiO3 and n unit cells of La0.67Sr0.33MnO3 with a fixed thickness of ~120 unit cells. The easy axis of magnetic anisotropy rotates ~45° towards the out-of-plane direction from n = 10 to n = 2 at reduced temperature TRe = T/TS = 0.87, where TS is the temperature at the onset of magnetization. Transmission electron microscopy reveals an enlarged tetragonal ratio >1 with breaking of volume conservation around the (La0.67Sr0.33MnO3)n/(SrTiO3)n interface and electronic charge transfer from Mn to Ti 3d orbitals across the interface. Orbital hybridization accompanying the charge transfer results in preferred occupancy of $${3d}_{3z^2-r^2}$$ orbitals at the interface and induces a stronger electronic hopping integral and interfacial magnetic anisotropy along the out-of-plane direction, which contributes to the rotation towards the out-of-plane direction of an effective magnetic easy axis for n = 2. We demonstrate that interfacial orbital hybridization with charge transfer in the superlattice of strongly correlated oxides may be a promising approach to tailor electronic and magnetic properties in device applications. A composite material with tuneable magnetic properties which could add novel functionality to electronic devices has been developed by scientists from Singapore and the USA. The interface between two crystalline materials can exhibit properties differing from those of either substance separately. These interface properties can be extended to three dimensions by stacking alternating thin layers of the two materials, creating a so-called superlattice. Bangmin Zhang from the National University of Singapore and co-workers used this concept to alter the magnetic response of a superlattice consisting of lanthanum strontium manganite and strontium titanate. They showed that they could rotate the direction along which the smallest magnetic field is required to magnetize the material by changing the thickness of the layers. This could be useful in devices that are controlled by interaction between electric and magnetic fields. The modulation of interfacial coupling of (La0.67Sr0.33MnO3)n/(SrTiO3)n superlattices with n unit cells of SrTiO3 and n unit cells La0.67Sr0.33MnO3, offers an effective opportunity to control charge transfer and orbital hybridization. The easy axis of magnetic anisotropy rotates ~45° towards the out-of-plane direction from n = 10 to n = 2 at reduced temperature TRe = T/TS = 0.87 (TS is onset of magnetization). Orbital hybridization accompanying the charge transfer results in preferred occupancy of $$3d_{3z_{2} - r_{2}}$$ orbital at the interface, and induces stronger electronic hopping integral and interfacial magnetic anisotropy along perpendicular direction, useful to tailor properties in device applications.

Out-of-plane ferroelectricity with a high transition temperature in nanometer-scale films is required to miniaturize electronic devices. Direct visualization of stable ferroelectric polarization and its switching behavior in atomically thick films is critical for achieving this goal. Here, ferroelectric order at room temperature in the two-dimensional limit is demonstrated in tetragonal BiFeO3 ultrathin films. Using aberration-corrected scanning transmission electron microscopy, we directly observed robust out-of-plane spontaneous polarization in one-unit-cell-thick BiFeO3 films. High-resolution piezoresponse force microscopy measurements show that the polarization is stable and switchable, whereas a tunneling electroresistance effect of up to 370% is achieved in BiFeO3 films. Based on first-principles calculations and Kelvin probe force microscopy measurements, we explain the mechanism of polarization stabilization by the ionic displacements in oxide electrode and the surface charges. Our results indicate that critical thickness for ferroelectricity in the BiFeO3 film is virtually absent, making it a promising candidate for high-density nonvolatile memories., High temperature perpendicular ferroelectricity in nano thin films is crucial for miniaturization of electronic devices. Here the authors show the presence of stable and switchable out-of-plane ferroelectricity in tetragonal BiFeO3 thin films at the two-dimensional limit and 370% tunneling electroresistance in ferroelectric tunnel junctions.

Brain-inspired computing is an emerging field, which intends to extend the capabilities of information technology beyond digital logic. The progress of the field relies on artificial synaptic devices as the building block for brainlike computing systems. Here, we report an electronic synapse based on a ferroelectric tunnel memristor, where its synaptic plasticity learning property can be controlled by nanoscale interface engineering. The effect of the interface engineering on the device performance was studied. Different memristor interfaces lead to an opposite virgin resistance state of the devices. More importantly, nanoscale interface engineering could tune the intrinsic band alignment of the ferroelectric/metal-semiconductor heterostructure over a large range of 1.28 eV, which eventually results in different memristive and spike-timing-dependent plasticity (STDP) properties of the devices. Bidirectional and unidirectional gradual resistance modulation of the devices could therefore be controlled by tuning the band alignment. This study gives useful insights on tuning device functionalities through nanoscale interface engineering. The diverse STDP forms of the memristors with different interfaces may play different specific roles in various spike neural networks.

Heteroepitaxial film growth is crucial for magnetic and electronic devices. In this work, we reported the effects of the large lattice mismatch and film thickness on the epitaxial growth and magnetic properties of FePt films on Zr x Ti 1−x N (0 0 1) intermediate layer. FePt films with different thickness were deposited on ZrTiN intermediate layers with various doping concentration of TiN in ZrN. The increase in doping concentration of TiN caused a decrease in the lattice parameters of ZrTiN intermediate layer. It was found that (0 0 1) epitaxy of FePt 10 nm films was only achieved on ZrTiN intermediate layer when the TiN composition was ≥25 vol%, while (0 0 1) texture of 5 nm films was achieved on ZrTiN intermediate layer with a minimum of 50 vol% TiN composition. The in-plane lattice constants of FePt and Zr 0.70 Ti 0.30 N (25 vol% TiN) were 3.870 A and 4.476 A, respectively, which resulted in a lattice mismatch as large as 15.7%. These large lattice mismatch heterostructures adopted 7/6 domain matching epitaxy. The magneto-crystalline anisotropy of FePt films was improved with the increase in lattice mismatch. Intrinsic magnetic properties were extrapolated for FePt (30 nm)/Zr 0.70 Ti 0.30 N (30 nm)/TaN (30 nm)/MgO, and the M s (0 K) and K 1 (0 K) were 1042 emu/cc and 5.10 × 10 7 erg/cc, respectively, which is comparable to that of bulk L1 0 FePt.

The structural stability of the organometal halide perovskites (CH3NHjPbX3, where X = Br, I, Cl) is highly correlated with the rotation of the methylammounium (MA) cations and the tilting of the PbX 6 octahedra. Hydrogen-bonding is the link between organic molecules and inorganic cages. In this study, the hydrogen-bonding status between the H atoms of the methylammonium (MA) cation and the halide ions is resolved through temperature-dependent experiments combined with theoretical analysis.

The polarization of $\mathrm{PbZ}{\mathrm{r}}_{0.52}\mathrm{T}{\mathrm{i}}_{0.48}{\mathrm{O}}_{3}$ thin film is switched by changing film thickness through the competition between the strain relaxation-induced flexoelectric fields and the interfacial effects. Without an applied electric field, this reversal of polarization is exploited to control the magnetic properties of $\mathrm{L}{\mathrm{a}}_{0.67}\mathrm{S}{\mathrm{r}}_{0.33}\mathrm{Mn}{\mathrm{O}}_{3}$ by the competition/cooperation between the charge-mediated and the strain-mediated effects. Scanning transmission electron microscopy, polarized near-edge x-ray absorption spectroscopy, and half-integer diffraction measurements are employed to decode the intrinsic magnetoelectric effects in the $\mathrm{L}{\mathrm{a}}_{0.67}\mathrm{S}{\mathrm{r}}_{0.33}\mathrm{Mn}{\mathrm{O}}_{3}/\mathrm{PbZ}{\mathrm{r}}_{0.52}\mathrm{T}{\mathrm{i}}_{0.48}{\mathrm{O}}_{3}$ heterostructures. With $\mathrm{PbZ}{\mathrm{r}}_{0.52}\mathrm{T}{\mathrm{i}}_{0.48}{\mathrm{O}}_{3}$ films $l48\phantom{\rule{0.16em}{0ex}}\mathrm{nm}$, the polarization-driven carrier density modulation around the $\mathrm{L}{\mathrm{a}}_{0.67}\mathrm{S}{\mathrm{r}}_{0.33}\mathrm{Mn}{\mathrm{O}}_{3}/\mathrm{PbZ}{\mathrm{r}}_{0.52}\mathrm{T}{\mathrm{i}}_{0.48}{\mathrm{O}}_{3}$ interface and the strain-mediated Mn $3d$ orbital occupancy work together to enhance the magnetism of 14-unit-cell $\mathrm{L}{\mathrm{a}}_{0.67}\mathrm{S}{\mathrm{r}}_{0.33}\mathrm{Mn}{\mathrm{O}}_{3}$ film; with $\mathrm{PbZ}{\mathrm{r}}_{0.52}\mathrm{T}{\mathrm{i}}_{0.48}{\mathrm{O}}_{3}$ layers $g48\phantom{\rule{0.16em}{0ex}}\mathrm{nm}$, the strain-induced change of bond length/angle of $\mathrm{Mn}{\mathrm{O}}_{6}$ accompanied with a modified spin configuration are responsible for the decrease in the Curie temperature and magnetization of 14-unit-cell $\mathrm{L}{\mathrm{a}}_{0.67}\mathrm{S}{\mathrm{r}}_{0.33}\mathrm{Mn}{\mathrm{O}}_{3}$ film.

Topologically protected magnetic states have a variety of potential applications in future spintronics owing to their nanoscale size (

We report on the study of both perpendicular magnetic anisotropy (PMA) and Dzyaloshinskii-Moriya interaction (DMI) at an oxide/ferromagnetic metal (FM) interface, i.e. BaTiO3 (BTO)/CoFeB. Thanks to the functional properties of the BTO film and the capability to precisely control its growth, we are able to distinguish the dominant role of the oxide termination (TiO2 vs BaO), from the moderate effect of ferroelectric polarization in the BTO film, on the PMA and DMI at the oxide/FM interface. We find that the interfacial magnetic anisotropy energy of the BaO-BTO/CoFeB structure is two times larger than that of the TiO2-BTO/CoFeB, while the DMI of the TiO2-BTO/CoFeB interface is larger. We explain the observed phenomena by first-principles calculations, which ascribe them to the different electronic states around the Fermi level at the oxide/ferromagnetic metal interfaces and the different spin-flip processes. This study paves the way for further investigation of the PMA and DMI at various oxide/FM structures and thus their applications in the promising field of energy-efficient devices., 14 pages, 4 figures, 1 table

Recent studies have highlighted the collective rotations of corner-shared oxygen octahedra in ABO3 functional perovskite oxides. However, experimental methods that allow direct measurements of oxygen octahedra, especially for the multilayer containing different types of oxygen octahedral rotations in each layer, are still rare. In this report, the correlation between oxygen octahedral rotation and cation-lattice symmetry is discussed by studying the interface-engineered perovskite La2/3Sr1/3MnO3 layers. The out-of-phase octahedral rotations remove the orthogonality between corresponding axes of the cation lattice, leading to the asymmetric diffraction pattern recorded by the reciprocal space mapping. More importantly, in the La2/3Sr1/3MnO3-multilayer heterostructure, the reciprocal space mapping can identify different octahedral rotations for each La2/3Sr1/3MnO3 layer, explaining the appearance of multiple Curie temperatures and coercive fields. Our results reveal the new understanding of the old reciprocal space mapping-based technique, based on the correlation between oxygen octahedral rotation and cation-lattice symmetry. The application of reciprocal space mapping to the La2/3Sr1/3MnO3-multilayers not only showcases the advantage of this technique but also extends our understanding of oxygen octahedral rotation to the more complicated oxide heterostructures.

The microstructure and magnetic properties of L1 0 FePt–C–SiO 2 films grown on TiON–MgO intermediate layer were studied. TiON–MgO layer was deposited by co-sputtering TiN and MgO–TiO 2 targets at 380 °C. With increasing MgO–TiO 2 doping concentration, the contact angle between FePt grains with intermediate layer gradually increased, and it was close to 90° when the volume percentage of MgO–TiO 2 reached 30%. At this condition, a high out-of-plane coercivity of 19.1 kOe was obtained, while the opening-up of in-plane M-H loop was very narrow. Moreover, it was found that the out-of-plane coercivity can be further improved to 21.6 kOe, by slightly increasing the percentage of MgO–TiO 2 to 35 vol%.

Topological Hall effect (THE), appearing as bumps and/or dips in the Hall resistance curves, is considered as a hallmark of the skyrmion spin texture originated from the inversion symmetry breaking and spin-orbit interaction. Recently, Néel-type skyrmion is proposed based on the observed THE in 5d transition metal oxides heterostructures such as SrRuO

Size control of nanocrystals is becoming more crucial in growing, for example, granular ferromagnetic thin films for heat-assisted magnetic recording, or self-assembled quantum dots for quantum computing. This study identifies granular patterns with surprisingly ``quantized'' feature sizes in Fe-Pt thin film grown on lattice-mismatched MgO. This arises from the periodic nature of the misfit-strain energy in such a system; island lengths that are integer multiples of the misfit dislocation period are energetically favored. These results point to synthesizing nanostructured materials with well-controlled grain size by tuning the interlayer lattice mismatch.

Interfaces with subtle difference in atomic and electronic structures in perovskite ABO 3 heterostructures often yield intriguingly different properties, yet their exact roles remain elusive. In this article, we report an integrated study of unusual transport, magnetic, and structural properties of Pr 0.67 Sr 0.33 MnO 3 (PSMO) films and La 0.67 Sr 0.33 MnO 3 (LSMO) films of various thicknesses on SrTiO 3 (STO) substrate. In particular, using atomically resolved imaging and electron energy-loss spectroscopy (EELS), we measured interface related local lattice distortion, BO 6 octahedral rotation and cation-anion displacement induced polarization. In the very thin PSMO film, an unexpected interface-induced ferromagnetic polaronic insulator phase was observed during the cubic-to-tetragonal phase transition of the substrate STO, due to the enhanced electron-phonon interaction and atomic disorder in the film. On the other hand, for the very thin LSMO films we observed a remarkably deep polarization in non-ferroelectric STO substrate near the interface. Combining the experimental results with first principles calculations, we propose that the observed deep polarization is induced by an electric field originating from oxygen vacancies that extend beyond a dozen unit-cells from the interface, thus providing important evidence of the role of defects in the emergent interface properties of transition metal oxides.

The microstructures and magnetic properties of FePt(-SiOx-C) thin films grown on TiON and TiON/TiN intermediate layers were studied. TiON possessed smaller surface energy and smaller lattice constant than TiN. With increasing TiOx doping concentration, FePt grain shape changed from semi-spherical to square and grain size was significantly reduced. Meanwhile, good perpendicular magnetic anisotropy was retained, indicating that TiON intermediate layer could achieve a good balance between island growth and epitaxial growth. Furthermore, using TiON/TiN combined intermediate layer, FePt grain size was further reduced and the opening-up of in-plane M-H loop diminished. With 45 vol.% SiOx-25 vol.% C doping, well-isolated FePt grains with an average size as small as 5.7 nm and the grain size distribution of 0.9 nm were achieved. It also exhibited good perpendicular magnetic anisotropy with an out-of-plane coercivity of 18 kOe.

Topological Hall effect (THE), appearing as bumps and/or dips in the Hall resistance curves, is considered as a hallmark of the skyrmion spin texture originated from the inversion symmetry breaking and spin-orbit interaction. Recently, Neel-type skyrmion is proposed based on the observed THE in 5d transition metal oxides heterostructures such as SrRuO3 /SrIrO3 bilayers, where the interfacial Dzyaloshinskii-Moriya interaction (DMI), due to the strong spin-orbit coupling (SOC) in SrIrO3 and the broken inversion symmetry at the interface, is believed to play a significant role. Here the emergence of THE in SrRuO3 single layers with thickness ranging from 3 to 6 nm is experimentally demonstrated. It is found that the oxygen octahedron rotation in SrRuO3 also has a significant effect on the observed THE. Furthermore, the THE may be continuously tuned by an applied electrical field. It is proposed that the large SOC of Ru ions together with the broken inversion symmetry, mainly from the interface, produce the DMI that is responsible for the observed THE. The emergence of the gate-tunable DMI in SrRuO3 single layer may stimulate further investigations of new spin-orbit physics in strong SOC oxides.

Hydrothermal method is a much simpler method of epitaxial multiferroic BiFeO 3 (BFO) film than physical/chemical vapor deposition methods. In this work, epitaxial BFO thin films were fabricated on (0 0 1)-oriented single-crystal SrRuO 3 (SRO)/SrTiO 3 (STO) structures by PVA-assistant hydrothermal method. The results of θ –2 θ scan, ω scan and reciprocal space mappings (RSMs) measured by synchrotron high resolution X-ray diffraction and high-resolution transmission electron microscopy (HRTEM) suggest that the BFO films have relaxed to a single-phase monoclinic structure. The electrical properties observed in BFO (0 0 1) thin films are superior to those of hydrothermal epitaxy reported previously, which indicates PVA plays an important role in fabricating BFO films by using hydrothermal method.

The microstructure and magnetic properties of granular FePt-SiNx-C films were modified by introducing an MgO nucleation layer grown on the TiN intermediate layer. It was found that the deposition of an ultra-thin MgO nucleation layer could reduce the FePt grain size, narrow grain size distribution and improve grain isolation by creating more nucleation sites. When MgO nucleation layer thickness varied from 0 to 0.36 nm, FePt grain size was reduced from 8.51 nm to 7.18 nm and the standard deviation of the grain size distribution was narrowed from 2.16 nm to 1.51 nm. Good L10 (001) texture was maintained and large out-of-plane coercivity (27.5 kOe) was obtained at the MgO thickness of 0.36 nm. Meanwhile, Δθ50 of FePt (001) peak decreased from 7.1° to 6.4°, indicating the improved easy axis distribution of FePt grains. However, with the further increase of the MgO nucleation layer thickness, MgO nuclei developed into a continuous layer, FePt (111) orientation appeared and the perpendicular magnetic anisotropy was deteriorated.

Monodisperse β-NaYF4:Yb,Er nanocrystals with mean sizes of 11, 40, and 110 nm were synthesized by a thermal decomposition solvothermal process to better understand the relationship between particle size and optical properties. A systematic study of luminescence intensity versus size revealed that both visible upconversion and infrared downconversion emission intensities decrease with decreasing nanocrystal size. The intrinsic quantum efficiency of the infrared 4I13/2 → 4I15/2 downconversion transition was studied in great detail since this specific transition allows us to quantify the contribution of nonradiative losses more easily than the observed upconversion transitions. The intrinsic quantum efficiency of the 4I13/2→4I15/2 transition decreased from 50% (110 nm) to 15% (11 nm). Multiphonon relaxation and −OH quenching was studied in these materials by measuring the vibrational characteristics of β-NaYF4:Yb,Er nanospheres. While multiphonon relaxation exhibited increased contribution to nonradiative de...

Heat-assisted magnetic recording is one of the most promising approaches to achieve extremely high density magnetic recording. A laser is used to temporarily heat the recording media film to render its switching field to become lower than the magnetic field of the writing head. After writing, the film material is cooled down to room temperature for data storage. In this dynamic writing process, the challenge is to tailor and optimize the time resolved structural/thermal/magnetic properties of the media films and their correlations during/after the laser heating. In this paper, the four dimensions of current progress in HAMR media research, i.e., structure, magnetic properties, thermal properties and time, are briefly overviewed and discussed. Their correlations are also emphasized.

The microstructure and magnetic properties of the FePt films grown on large mismatched ZrN (15.7%) intermediate layer were investigated. With using ZrN intermediate layer, FePt 10 nm films exhibited (001) texture except for some weaker FePt (110) texture. Good epitaxial relationships of FePt (001) //ZrN (001) //TiN (001) among FePt and ZrN/TiN were revealed from the transmission electron microscopy (TEM) results. As compared with TiN intermediate layer, although FePt-SiO2-C films grown on ZrN/TiN intermediate layer showed isotropic magnetic properties, the large interfacial energy and lattice mismatch between FePt and ZrN would lead to form columnar structural FePt films with smaller grain size and improved isolation. By doping ZrN into the TiN layer, solid solution of ZrTiN was formed and the lattice constant is increased comparing with TiN and decreased comparing with ZrN. Moreover, FePt-SiO2-C films grown on TiN 2 nm-20 vol.% ZrN/TiN 3 nm intermediate layer showed an improved perpendicular magnetic anisotropy. Simultaneously, columnar structure with smaller grain size retained.

Interfaces with subtle differences in atomic and electronic structures in perovskite ABO3 heterostructures often yield intriguingly different properties, yet their exact roles remain elusive. Here, we report an integrated study of unusual transport, magnetic, and structural properties of Pr0.67Sr0.33MnO3 film on SrTiO3 substrate. The variations in the out-of-plane lattice constant and BO6 octahedral rotation across the Pr0.67Sr0.33MnO3/SrTiO3 interface strongly depend on the thickness of the Pr0.67Sr0.33MnO3 film. In the 12 nm film, a new interface-sensitive ferromagnetic polaronic insulator (FI') phase is formed during the cubic-to-tetragonal phase transition of SrTiO3, apparently due to the enhanced electron-phonon interaction and atomic disorder in the film. The transport properties of the FI' phase in the 30 nm film are masked because of the reduced interfacial coupling and smaller interface-to-volume ratio. This work demonstrates how thickness-dependent interfacial coupling leads to the formation of a theoretically predicted ferromagnetic-polaronic insulator, as illustrated in a new phase diagram, that is otherwise ferromagnetic metal (FM) in bulk form.

The Mn K edge X-ray absorption near edge structure (XANES) of Pr0.67Sr0.33MnO3 films with different thicknesses on (001) LaAlO3 substrate was measured and the effects of strain relaxation on film properties were investigated. The films showed in-plane compressive and out-of-plane tensile strains. Strain relaxation occurred with increasing film thickness, affecting both lattice constant and MnO6 octahedral rotation. In polarization dependent XANES measurements using in-plane (parallel) and out-of-plane (perpendicular) geometries, the different values of absorption resonance energy Er confirmed the film anisotropy. The values of Er along these two directions shifted towards each other with increasing film thickness. Correlating with X-ray diffraction (XRD) results it is suggested that the strain relaxation decreased the local anisotropy and corresponding probability of electronic charge transfer between Mn 3d and O 2p orbitals along the in-plane and out-of-plane directions. The XANES results were used to explain the film-thickness dependent magnetic and transport properties.

FePt–SiN x –C films with high coercivity, (001) texture and small grain size were obtained by co-sputtering FePt, Si 3 N 4 and C on TiN/CrRu/glass substrate at 380 °C. Without C doping, FePt–SiN x films with good perpendicular anisotropy and a single layer structure were obtained. However, the grain size was still too large and the grain isolation was poor. When C was doped into the FePt–SiN x films, the out-of-plane coercivity increased due to the decrease of the exchange coupling. In addition, the grain size of the FePt films decreased, and well-separated FePt grains with uniform size were formed. The microstructure of [FePt–SiN x 40 vol%]−20 vol% C films changed from a single layer structure to a multiple layer structure when the FePt thickness was increased from 4 to 10 nm. By optimizing the sputtering process, the [FePt (4 nm)–SiN x 40 vol%]−20 vol% C (001) film with coercivity higher than 21.5 kOe, a single layer structure, and small average FePt grain size of 5.6 nm was obtained, which makes it suitable for ultrahigh density perpendicular recording.

Uniform bismuth ferrite BiFeO3 nanoparticles (below 60 nm) were successfully synthesized via a simple hydrothermal route with the assistance of KOH as mineralizer and EDTA as the chelating agent. The effects of mineralizer and chelating agent on the phase formation, and morphology of these particles were investigated. Size dependent magnetic properties of as-prepared particles at room temperature were investigated.

In this work, effects of exchange coupling of soft magnetic layer on switching field and magnetization reversal behaviour of CoPt-SiO2(soft)/CoPt-SiO2(hard) exchange coupled media were investigated. With increasing the thickness of the soft layer, both the coercivity and magnetization squareness of composite media decreased. Soft layer thickness 4 nm and below was more effective to significantly reduce the switching field than that above 4 nm. More incoherent switching behavior was observed with increasing soft layer thickness.

In order to demonstrate efficiency improvement of solar cells through utilization of frequency-shifted sub-band-gap photons, we prepared Y3Al5O12 transparent ceramics co-doped with 3.0 at% Yb3+ and 0.5 at% Er3+ (YAG:3.0Yb/0.5Er) by solid state reaction. The material’s upconversion luminescence was investigated and it was found that near-infrared light could be effectively converted to green light centered at 563 nm, where a dye-sensitized solar cell normally possessed high spectral response. Using a thin disk of YAG:3.0Yb/0.5Er transparent ceramics attached to the rear of the dye-sensitized solar cell, the near-infrared response of the dye-sensitized solar cell was enhanced, due to the frequency upconversion.

Hollow nanoparticles of hexagonal close-packed (hcp)-NaYF4:Yb,Er were synthesized by thermal decomposition of trifmoroacetate precursors at 340 °C via vacancy diffusion, likely due to the Kirkendall effect and Ostwald ripening mechanism. The average outer diameter, inner diameter, and shell thickness of these hollow particles were 14 ± 3 nm, 7 ± 2 nm, and 4 ± 1 nm, respectively. The surface effects on the fluorescence properties of these hollow particles were studied by comparing with that of solid NaYF4: Yb,Er (average size ~ 15 ± 3 nm) and solid NaYF4 core/NaYF4: Yb,Er shell (NaYF4 core ~10 ± 1 nm and NaYF4:Yb,Er shell ~3 ± 2 nm) nanoparticles containing similar composition of Yb and Er ions. The green, red, and total emission intensities decreased with increasing upconversion active volume-normalized surface area. Surface coatings of undoped NaYF4 on both inner and outer surfaces of the hollow nanoparticles enhanced the total emission intensity by ~ 19 and ~5 times compared with those of the hollow and solid NaYF4:Yb,Er nanoparticles, respectively.

A control strategy for tuning the film morphology of asymmetric polystyrene-b-poly(4-vinylpyridine) (PS-b-P4VP) block copolymers (BCPs) is reported. After preparation of the film by spin-coating method, the as-cast films were annealed in different solvent vapor. It is found that chloroform is a wonderful solvent for forming PS-b-P4VP regular pattern. Otherwise, with changing the concentration of PS-b-P4VP, cylindrical or parallel nanostructures could be attained. The PS-b-P4VP films with cylindrical structure are used as template to deposit FePt nanoparticles into the pores. Nanoparticles reaching the bottom of the holes form a disordered magnetic array.