Simultaneous control of ferromagnetism and ferroelasticity by oxygen octahedral backbone stretching

Coexistence of ferromagnetism and ferroelasticity in a single material is an intriguing phenomenon,but has been rarely found.Here we studied both the ferromagnetism and ferroelasticity in a group of LaCoO3 films with systematically tuned atomic structures.We found that all films exhibit ferroelastic domains with four-fold symmetry and the larger domain size(higher elasticity)is always accompanied by stronger ferromagnetism.We performed synchrotron x-ray diffraction studies to investigate the backbone structure of the CoO6 octahedra,and found that both the ferromagnetism and the elasticity are simultaneously enhanced when the in-plane Co–O–Co bond angles are straightened.Therefore the study demonstrates the inextricable correlation between the ferromagnetism and ferroelasticity mediated through the octahedral backbone structure,which may open up new possibilities to develop multifunctional materials.

High-temperature ferromagnetism and strongπ-conjugation feature in two-dimensional manganese tetranitride

Two-dimensional(2D)magnetic materials have attracted tremendous research interest because of the promising application in the next-generation microelectronic devices.Here,by the first-principles calculations,we propose a twodimensional ferromagnetic material with high Curie temperature,manganese tetranitride MnN4monolayer,which is a square-planar lattice made up of only one layer of atoms.The structure is demonstrated to be stable by the phonon spectra and the molecular dynamic simulations,and the stability is ascribed to theπ–d conjugation betweenπorbital of N=N bond and d orbital of Mn.More interestingly,the MnN_(4)monolayer displays robust 2D ferromagnetism,which originates from the strong exchange couplings between Mn atoms due to theπ–d conjugation.The high critical temperature of 247 K is determined by solving the Heisenberg model using the Monte Carlo method.

Spontaneous isospin polarization and quantum Hall ferromagnetism in a rhombohedral trilayer graphene superlattice

Moiré superlattices in van der Waals heterostructures have recently attracted enormous interests, due to the highly controllable electronic correlation that gives rise to superconductivity, ferromagnetism, and nontrivial topological properties. To gain a deep understanding of such exotic properties, it is essential to clarify the broken symmetry between spin and valley flavors which universally exists in these ground states. Here in a rhombohedral trilayer graphene crystallographically aligned with a hexagonal boron nitride, we report various kinds of symmetry-breaking transition tuned by displacement fields(D) and magnetic fields:(ⅰ) While it is well known that a finite D can enhance correlation to result in correlated insulators at fractional fillings of a flat band, we find the correlation gap emerges before the flavor is fully filled at a positive D, but the sequence is reversed at a negative D.(ⅱ) Around zero D, electronic correlation can be invoked by narrow Landau levels, leading to quantum Hall ferromagnetism that lifts all the degeneracies including not only spin and valley but also orbital degrees of freedom. Our result unveils the complication of transitions between symmetry-breaking phases, shedding light on the mechanisms of various exotic phenomena in strongly correlated systems.

Enhanced ferromagnetism and conductivity of ultrathin freestanding La_(0.7)Sr_(0.3)MnO_(3)membranes

We report a universal method to transfer freestanding La_(0.7)Sr_(0.3)MnO_(3)membranes to target substrates.The 4-unit-cell-thick freestanding La_(0.7)Sr_(0.3)MnO_(3)membrane exhibits the enhanced ferromagnetism,conductivity and out-of-plane magnetic anisotropy,which otherwise shows nonmagnetic/antiferromagnetic and insulating behavior due to the intrinsic epitaxial strain.This work facilitates the promising applications of ultrathin freestanding correlated oxide membranes in electronics and spintronics.

The room temperature ferromagnetism in highly strained twodimensional magnetic semiconductors

In spintronics,it is still a challenge in experiments to realize the ferromagnetic semiconductors with Curie temperature Tc above room temperature.In 2017,the successful synthesis of two-dimensional(2D)van der Waals ferromagnetic semiconductors,including the monolayer CrI3 with Tc=45 K[1]and the bilayer Cr2Ge2Te6 with Tc=28 K[2]in experiments,has attracted extensive attention in the 2D ferromagnetic semiconductors.One of the key problems is to find suitable 2D magnetic semiconductors,which can have room-temperature operation as required in applications.

Microstructure and ferromagnetism of heavily Mn doped SiGe thin flims

Heavily Mn-doped SiGe thin films were grown by radio frequency magnetron sputtering and then treated by postgrowth thermal annealing.Structural characterizations reveal the coexistence of Mn-diluted SiGe crystals and Mn-rich nanoclusters in the annealed films.Magnetic measurements indicate the ferromagnetic ordering of the annealed samples above room temperature.The data suggest that the ferromagnetism is probably mainly contributed by the Ge-rich nanoclusters and partially contributed by the tensile-strained Mn-diluted SiGe crystals.The results may be useful for room temperature spintronic applications based on group IV semiconductors.

Room temperature ferromagnetism of boron-doped ZnO nanoparticles prepared by solvothermal method

In this study, B-doped ZnO nanoparticles were synthesized by template-free solvothermal method. X-ray diffraction analysis reveals that B-doped ZnO nanoparti- cles have hexagonal wurtzite structure. Field emission scanning electron microscopy observations show that the nanoparticles have a diameter of 50 nm. The room tem- perature ferromagnetism increases monotonically with increasing B concentration to the ZnO nanoparticles and reaches the maximum value of saturation magnetization 0.0178 A.ma.kg-1 for 5 % B-doped ZnO nanoparticles. Moreover, photoluminescence spectra reveal that B doping causes to produce Zn vacancies （Vzn）. Magnetic moment of oxygen atoms nearest to the B-Vzn vacancy pairs can be considered as a source of ferromagnetism for B-doped ZnO nanoparticles.

Effect of vanadium on the room temperature ferromagnetism of V-doped 6H-SiC powder

This study focuses on the effect of V-doping on the ferromagnetism（FM） of 6H-SiC powder.The X-ray diffraction results indicate that V is inserted into the 6H-SiC lattice.The Raman spectra reveal that with a V concentration of 25 ppm,the crystalline quality and carrier concentration of 6H-SiC are hardly varied.It is found that after the V-doping process,the saturation magnetization（Ms） and the vacancy concentration of 6H-SiC are both increased.From these results,it is deduced that the effect of V might contribute mainly to the increase of vacancy concentration,thus resulting in the increase of Ms of V-doped 6H-SiC.

Defect types and room-temperature ferromagnetism in undoped rutile TiO_2 single crystals

Room-temperature ferromagnetism has been experimentally observed in annealed rutile TiO2 single crystals when a magnetic field is applied parallel to the sample plane.By combining X-ray absorption near the edge structure spectrum and positron annihilation lifetime spectroscopy,Ti^3＋-V O defect complexes（or clusters） have been identified in annealed crystals at a high vacuum.We elucidate that the unpaired 3d electrons in Ti^3＋ ions provide the observed room-temperature ferromagnetism.In addition,excess oxygen ions in the TiO2 lattice could induce a number of Ti vacancies which obviously increase magnetic moments.

Half-metallic ferromagnetism in C-doped zinc-blende ZnO: A first-principles study

We perform a first-principles study of electronic structure and magnetism of C-doped zinc-blende ZnO using the full-potential linearized augmented plane wave method. Results show that C-doped zinc-blende ZnO exhibits half-metallic ferromagnetism with a stable ferromagnetic ground state. The calculated magnetic moment of the 32-atom supercell containing one C dopant is 2.00 μ B , and the C dopant contributes most. The calculated low formation energy suggests that C-doped zinc-blende ZnO is energetically stable. The hole-mediated double exchange mechanism can be used to explain the ferromagnetism in C-doped zinc-blende ZnO.

Synthesis and Room Temperature Ferromagnetism in Fe-Doped CuAlO_2 Semiconductor

The synthesis and characterization of Fe-doped CuA102 semiconductor were reported. The samples were synthesized by a simple and cost effective spin-on technique from solid state reaction of Cu20 and A1203 on sapphire （001） substrate. Appropriate ethyl-cellulose （EC） and terpineol are useful for the formation of Fe-doped CuA102 films. X-ray diffraction （XRD） revealed the growth of pure delafossite CuA102 phase ruled out elemental metallic Fe clusters in all the Fe incorporated CuA102 films. The existence of ferromagnetism at room temperature is evidenced by well-defined hysteresis loops. Specially, the saturation magnetization （Ms） values at room temperature have been monotonously enhanced with the increase of Fe composition from 1% to 5%.

Toward intrinsic room-temperature ferromagnetism in two-dimensional semiconductors

Two-dimensional (2D) ferromagnetic semiconductors have been recognized as the most promising candidates for next-generation low-cost, high-performance and nano-scale spintronic applications such as spin field-effect transistors and quantum computation/communication. However, as one of the 125 important scientific issues raised by Science journal in 2005 that "is it possible to create magnetic semiconductors that work at room temperature?", how to achieve a feasible ferromagnetic semiconductor with high Curie temperature is still a long-standing challenge despite of tremendous efforts have been devoted in this field since 1960s. The recent discovery of 2D ferromagnetic semiconductors Cr2Ge2Te6 and CrI3 has evoked new research interests in 2D intrinsic ferromagnetic semiconductors. But the low Curie temperature (<45 K) of these materials is still badly hindering their industrial applications.

Ferromagnetism of Ni-Doped ZnO Powders Prepared by Sol-Gel Method above Room Temperature

The magnetic and structural properties of 2% Ni-doped ZnO powers prepared by sol-gel method were studied. X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM) of the sample do not show existence of any signal of second phase. The X-photoelectron spectroscopy (XPS) of the sample shows the chemical valence of Ni is +2 and the real Ni concentration is 2.19% determined by X-ray fluorescence spectra (XRFS). The magnetic property performed with superconducting quantum interference device (SQUID) shows that the sample exhibits ferromagnetism above room temperature and the Curie temperature (TC) is about 600 K.

Room Temperature Ferromagnetism in Co-doped CuAlO_2 Nanofibers Fabricated by Electrospinning

One-dimensional, diluted magnetic semiconductor nanofibers have attracted increasing attention for their unique magnetic properties, large specific surface area, and high porosity. These qualities lead to excellent performance in magneto-optical devices, magnetic resonance imaging, ferrofluids and magnetic separation. The purpose of this study is to fabricate P-type one dimensional CuAlO2-based diluted magnetic semiconductor nanofibers. First, we fabricated CuAl0.95Co0.05O2 nanofibers with an average diameter of 1 μm with the electrospinning method. The annealed nanofibers were thermally treated at a temperature of 1 100℃ and then shrunk to a diameter of about 650 nm. We used X-ray diffraction measurements and Raman spectra to confirm that the CUAl0.95CO0.05O2 nanofihers had a single impurity free delafossite phase. The X-ray photoelectron spectroscopy analysis indicates that Co was present in the ＋2 oxidation state, resulting in an room temperature ferromagnetism in the CHAl0.95Co0.05O2 fiber. This contrststs with nonmagnetism in pristine CuAlO2 fiber. The coercivity （Hc） value of 65.26 Oe and approximate saturation magnetization （Ms） of 0.012 emu/g demonstrate good evidence of ferromagnetism at room temperature for CuAl0.95Co0.05O2 nanofibers.

First Principle Study of Ferromagnetism in Cr-Doped In_2O_3

We present a first principle study of Cr-doped In2O3 system using density functional theory. The obtained results show that the Cr ion prefers the cation site of the center of trigonally distorted octahedron and converges to high spin-polarized configuration in the ground state. The hybridization between d-states and the donor states is strong, and the spin-split donor impurity-band model is found to be the most favorable mechanism for the ferromagnetism in this system. The good ferromagnetic property of high Curie temperature is discussed in view of the electronic structure analyses.

First-principles study on nonlocal ferromagnetism in (Cu, N)-codoped ZnO

First-principles calculations based on spin density functional theory are performed to study the spin-resolved elec- tronic properties of ZnO codoped with Cu and N. （Cu, N）-codoped ZnO exhibits magnetism, and the total magnetic mo- ment mainly originates from the p--d hybridization of Cu-N and Cu-O as well as p--p coupling interaction between N and O at the Fermi level. The Zn34Cu2035N1 favors energetically a ferromagnetic ground state due to the existence of stable Cu-N-Cu complex. These results imply that the （Cu, N）-codoped ZnO is a promising dilute magnetic semiconductor free of magnetic precipitates, which could broaden the horizon of currently known magnetic systems.

Effect of phase transition on room temperature ferromagnetism in cerium doped ZnS nanorods

The effects of Ce doping on the structure,optical,oxidation,thermal and magnetic properties of ZnS:Ce nanorods synthesized by a chemical co-precipitation method were reported.The crystalline phase transformation from cubic to hexagonal structure was observed upon doping ZnS with Ce.Magnetic measurements showed the existence of room temperature ferromagnetism in Ce-doped ZnS nanorods.X-ray photoelectron spectroscopic(XPS)measurements provided evidence for Zn-S bonds and oxidation state of Ce in the near-surface region.Raman spectrum provided evidence for the presence of defects as well as hexagonal structure of 5 wt.%Ce doped ZnS nanorods.Ce substitution induced shape evolution was studied by using TEM.DRS spectra further validated the incorporation of Ce^3+ions.The present study reveals that Ce doped ZnS nanorods may find applications in spintronic devices.

Room temperature ferromagnetism in un-doped amorphous HfO_2 nano-helix arrays

Amorphous HfO2 nano-helix arrays with different screw pitches were fabricated by the glancing angle deposition technique. Room temperature ferromagnetism was achieved in this undoped amorphous HfO2 nanostructure, which is attributed to singly charged oxygen vacancies. The different magnetic behavior and photoluminescence in flat film and nano-helix arrays originate from the distinction of defect components. This study could facilitate the understanding of ferromagnetism origin in undoped HfO2, it also suggests a possible way to alter the intrinsic defects in amorphous HfO2.

The coexistence of ferroelectricity and ferromagnetism in Mn-doped BaTiO_3 thin films

5-at% Mn-doped and undoped BaTiO3 thin films have been grown under different oxygen partial pressures by Pulsed Laser Deposition （PLD） on platinum-coated sapphire substrates. X-ray diffraction （XRD） measurements for all the thin films reveal a similar polycrystalline single-phase perovskite structure. Ferroelectricity is observed in the Mn-doped and undoped BaTiO3 thin films grown under relatively high oxygen partial pressure. Ferromagnetic coupling of the Mn dopant ions, on the other hand, is only seen in Mn-doped BaTiO3 thin films prepared under low oxygen partial pressure in a wide temperature range from 5 K to 300 K, and is attributed to the enhanced exchange coupling between Mn dopants and electrons at oxygen vacancies. Our results show that the leakage current is decreased with the doped Mn, but increases the dielectric loss and decreases the dielectric constant, and the ferroelectricity is impaired. To produce ferromagnetism, oxygen vacancies are necessary, which unfortunately increase the leakage current. This confirms that the mutual interplay between the ferroelectricity and ferromagnetism can be tuned by exchange coupling of the doped-Mn and oxygen vacancies in the BaTiO3 thin films.

Room Temperature Ferromagnetism in Ga1-xHoxN （x=0.0 and 0.05） Diluted Magnetic Semiconductor Thin Films

Holmium doped GaN diluted magnetic semiconductor thin films have been prepared by thermal evaporation technique and subsequent ammonia annealing. X-ray diffraction mea- surements reveal all peaks belong to the purely hexagonal wurtzite structure. Surface mor- phology and composition analysis were carried out by scanning electron microscopy and energy dispersive spectroscopy respectively. The room temperature ferromagnetic proper- ties of Gal-xHoxN （x=0.0, 0.05） films were analyzed using vibrating sample magnetometer at room temperature. Magnetic measurements showed that the undoped films （i.e. GaN） exhibited diamagnetic behavior, while the Ho-doped （Gao.95Hoo.05N） film exhibited a ferro- magnetic behavior.