Prediction of one-dimensional CrN nanostructure as a promising ferromagnetic half-metal

Searching for one-dimensional(1D)nanostructure with ferromagnetic(FM)half-metallicity is of significance for the development of miniature spintronic devices.Here,based on the first-principles calculations,we propose that the 1D CrN nanostructure is a FM half-metal,which can generate the fully spin-polarized current.The ab initio molecular dynamic simulation and the phonon spectrum calculation demonstrate that the 1D CrN nanostructure is thermodynamically stable.The partially occupied Cr-d orbitals endow the nanostructure with FM half-metallicity,in which the half-metallic gap(?s)reaches up to 1.58 eV.The ferromagnetism in the nanostructure is attributed to the superexchange interaction between the magnetic Cr atoms,and a sizable magnetocrystalline anisotropy energy(MAE)is obtained.Moreover,the transverse stretching of nanostructure can effectively modulate?s and MAE,accompanied by the preservation of half-metallicity.A nanocable is designed by encapsulating the CrN nanostructure with a BN nanotube,and the intriguing magnetic and electronic properties of the nanostructure are retained.These novel characteristics render the 1D CrN nanostructure as a compelling candidate for exploiting high-performance spintronic devices.

Prediction of LiCrTe_(2)monolayer as a half-metallic ferromagnet with a high Curie temperature

By using first-principles electronic structure calculations,we predict a new two-dimensional half-metallic ferromagnet(2DHMF)with distorted square structure,i.e.,the LiCrTe_(2) monolayer.The results show that the LiCrTe_(2) monolayer is dynamically,thermally,and mechanically stable,and takes a large in-plane magnetic anisotropy,a wide spin gap,a large magnetization,and a very high Curie temperature.Under a biaxial strain ranging from-5% to+5%,the ferromagnetism,half-metallicity,and high Curie temperature are maintained well.Both tensile and compressive strains can significantly increase the magnitude of the magnetocrystalline anisotropy energy(MAE)and a transition from in-plane easy-x(y)-axis to out-of-plane easy-z-axis occurs when the compressive strain exceeds 1%.Our systematic study of the LiCrTe_(2) monolayer enables its promising applications in spintronics.

Exploring ferromagnetic half-metallic nature of Cs2NpBr6 via spin polarized density functional theory

By employing the spin resolved density functional theory, half-metallic character is investigated in Cs2NpBr6 having a K2PtCl6-type structure. The results precisely predict the half-metallic behavior of Cs2NpBr6. In spin-down state it presents an indirect band gap, while in spin-up channel it turns metallic. The structure optimization confirms the half-metallic nature in ferromagnetic configuration. The calculated magnetic moment is 3 μB toward which the main contributor is the Np atom.Furthermore, all the computed results are compared with the available experimental and theoretical values. According to the present analysis, we recommend Cs2NpBr6 for spintronic applications.

Spin-flip process through double quantum dots coupled to two half-metallic ferromagnetic leads

We investigate the spin-flip process through double quantum dots coupled to two half-metallic ferromagnetic leads in series. By means of the slave-boson mean-field approximation, we calculate the density of states in the Kondo regime for two different configurations of the leads. It is found that the transport shows some remarkable properties depending on the spin-flip strength. These effects may be useful in exploiting the role of electronic correlation in spintronics.

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.

Magnetic properties of several potential rocksalt half-metallic ferromagnets based on the first-principles calculations

Several rocksalt Sr4X3N （X = O, S, Se, and Te） are predicted to be potential half-metallic ferromagnets free of transition-metal and rare-earth elements by performing the first-principles calculations. Then their magnetic properties, such as the half metallicity and the crystal-cell magnetic moments are investigated. The Sr4X3N possibly have higher Curie temperatures and have more stable half metallicity than the Sr4X3C. Their crystal-cell magnetic moments are all 1.00 μB. The crystal-cell magnetic moments and the half metallicity arise mainly from the N ions. The main mechanism is the strong covalent interaction leading to the sp2 hybridized orbitals in the Sr4X3N. Then two Sr-5s and three N-2p electrons enter into three sp2 hybridized orbitals. Among these five electrons, four electrons are paired and one is unpaired, so there are three spin-up electrons and two spin-down electrons in these sp2 hybridized orbitals.

A Chemical Synthesis of Ferromagnetic Zn0.99Co0.01O Nano-Needles

Zn0.99Co0.01O nano-needles are synthesized by using pure ZnO powder as the starting material via chemical reactions in ammonia aqueous solution. The nano-needles show the room-temperature ferromagnetism （RTFM） characterized by using a superconducting quantum interference device. Non-reductive chemical synthesis steps ensure to prevent forming Co-metal nanoclusters within the doped sample. All the results of thermal gravimetric analysis, Fourier transform infrared spectroscopy, x-ray diffraction and ultraviolet spectroscopy demonstrate that Co ions have doped into ZnO lattices and occupied some Zn sites without changing the wurtzite structure of ZnO lattices, and no potential second phase except for the doped Co ions substituting the Zn sites in ZnO lattice can account for the observed RTFM behaviour. Moreover, the synthesis process is of high reproducibility over 80% which is higher than that of commonly-used sol-gel method.

Homogeneous and inhomogeneous magnetic oxide semiconductors

Magnetic oxide semiconductors are significant spintronics materials.In this article, we review recent advances for homogeneous and inhomogeneous magnetic oxide semiconductors.In the homogeneous magnetic oxide semiconductors,we focus on the various doping techniques including choosing different transition metals, codoping, non-magnetic doping,and even un-doping to realize homogeneous substitution and the clear magnetic origin.And the enhancement of the ferromagnetism is achieved by nanodot arrays engineering, which is accompanied by the tunable optical properties.In the inhomogeneous magnetic oxide semiconductors, we review some heterostructures and their magnetic and transport properties, especially magnetoresistance, which are dramatically modulated by electric field in the constructed devices.And the related mechanisms are discussed in details.Finally, we provide an overview and possible potential applications of magnetic oxide semiconductors.

Effect on Defect in N or F-Doped Ferromagnetic Zn_1-xCu_xO: First-Principles Study

We investigated the electronic and magnetic properties for O or Zn defect of (Cu, N) or (Cu, F)-co- doped ZnO with the concentration of 2.77% - 8.33% by using the first-principles calculations. The ferromagnetic coupling of Cu atoms in (Cu, N)-codoped ZnO can be attributed to the hole-mediated double-exchange through the strong 2p-3d coupling between Cu and neighboring O (or N) atoms. The ferromagnetism in Cu-doped ZnO is controllable by changing the carrier density. The Cu magnetic moment in low Cu concentration (2.77%) is increased by the N-doping, while for the F-doping it decreases. For two Cu atoms of Zn0.9445Cu0.0555O with O vacancy, the antiferromagnetic state is more energetically favorable than the ferromagnetic state.

CrO_(2)单层:一种兼具高居里温度和半金属特性的二维铁磁体

半金属铁磁体在费米能级附近具有特殊的能带结构,电子极化率可高达100%,在自旋电子学领域备受关注.但是大部分铁磁半金属材料的居里温度远低于室温,这大大限制了二维铁磁半金属材料的实际应用.因此寻找具有高居里温度的半金属铁磁体是一项具有挑战性的工作.本文基于密度泛函理论框架下的第一性原理方法,研究了过渡金属氧化物CrO_(2)单层的晶体结构、电子特性、基态磁性和铁磁相变.形成能计算、声子谱计算和分子动力学模拟表明CrO_(2)具有动力学稳定性和热稳定性,弹性常数计算表明CrO_(2)具有力学稳定性.基于GGA+U和SCAN方法的自旋极化计算表明CrO_(2)单层的磁基态是铁磁态.采用GGA+U方法计算了CrO_(2)的电子态密度和能带结构,CrO_(2)被确认为一种宽带隙的二维铁磁半金属.运用蒙特卡罗模拟方法求解Heisenberg模型,得到CrO_(2)单层是一种居里温度超过400 K的二维本征半金属铁磁体.CrO_(2)单层的高居里温度在二维铁磁材料中并不多见,在半金属材料中更为稀少,这将使它成为制备自旋电子器件和研究自旋量子效应的理想材料.

Controllable high Curie temperature through 5d transition metal atom doping in CrI_(3)

Two-dimensional(2D) CrI_(3) is a ferromagnetic semiconductor with potential for applications in spintronics. However,its low Curie temperature(T_(c)) hinders realistic applications of CrI3. Based on first-principles calculations, 5d transition metal(TM) atom doping of CrI_(3)(TM@CrI_(3)) is a universally effective way to increase T_(c), which stems from the increased magnetic moment induced by doping with TM atoms. T_(c) of W@CrI_(3) reaches 254 K, nearly six times higher than that of the host CrI_(3). When the doping concentration of W atoms is increased to above 5.9%, W@CrI_(3) shows room-temperature ferromagnetism. Intriguingly, the large magnetic anisotropy energy of W@CrI_(3) can stabilize the long-range ferromagnetic order. Moreover, TM@CrI_(3) has a strong ferromagnetic stability. All TM@CrI_(3) change from a semiconductor to a halfmetal, except doping with Au atom. These results provide information relevant to potential applications of CrI_(3) monolayers in spintronics.

Room temperature ferromagnetic property of Fe-Y(Fe:Y-6.5) composite oxide nano-cluster via an extremely easy and scalable method

A novel Fe-Y composite oxide(Fe:Y-6.5) nanocluster was synthesized by self-assembly approach.The α-Fe_(2)O_(3) and cubic-Y_(2)O_(3) nanocrystalline with diameter around 10 nm are homogeneously assembled to form a cluster architecture which are constituted of Fe6.5Y composite oxide particles.Additional oxygen vacancies are introduced with cubic-Y_(2)O_(3),and the oxygen vacancies as Fe^(3+)-V_(0)-Y^(3+) between α-Fe_(2)O_(3) and cubic-Y_(2)O_(3) nanocrystalline are generated by self-assembly process.Magnetic hysteresis loops recorded by vibrating sample magnetometry at 273 K display a ferromagnetic order,related to the fact that Fe^(3+)-V_(o)-Y^(3+) act as defect centers in the bound magnetic polaron model for Fe-Y composite oxide nanomaterial.The ferromagnetic prope rties are proportional to oxygen vacancy co ntents,and maximum magnetization(M_(m)) value of the nano-cluster reaches 5.14 A·m^(2)/g.

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.

Room-temperature ferromagnetism induced by Cu vacancies in Cu_x(Cu_2O)_(1-x) granular films

Cux（Cu2O）1-x（0.09 x 1.00） granular films with thickness about 280 nm have been fabricated by direct current reactive magnetron sputtering. The atomic ratio x can be controlled by the oxygen flow rate during Cux（Cu2O）1-x deposition. Room-temperature ferromagnetism（FM） is found in all of the samples. The saturated magnetization increases at first and then decreases with the decrease of x. The photoluminescence spectra show that the magnetization is closely correlated with the Cu vacancies in the Cux（Cu2O）1-x granular films. Fundamentally, the FM could be understood by the Stoner model based on the charge transfer mechanism. These results may provide solid evidence and physical insights on the origin of FM in the Cu2O-based oxides diluted magnetic semiconductors, especially for systems without intentional magnetic atom doping.

Theoretical Study on the Ferromagnetism of Cr-doped In_2O_3

Density functional theory （DFT） calculations are performed to investigate the electronic structure and ferromagnetism of （In, Cr）2O3. The densities of states suggest that the Cr dopants provide nearly 100% polarization of the conduction carriers and the ferromagnetic ground state in Cr-doped In2O3 can be explained from p-d hybridization mechanism. The calculation results also show that the ferromagnetism is strengthened in the presence of oxygen vacancy.

Room-temperature ferromagnetism observed in Nd-doped In_2O_3 dilute magnetic semiconducting nanowires

Nd-doped In_2O_3 nanowires were fabricated by an Au-catalyzed chemical vapor deposition method.Nd atoms were successfully doped into the In_2O_3 host lattice structure,as revealed by energy dispersive x-ray spectroscopy,x-ray photoelectron spectroscopy,Raman spectroscopy,and x-ray diffraction.Robust room temperature ferromagnetism was observed in Nd-doped In_2O_3 nanowires,which was attributed to the long-range-mediated magnetization among Nd^（3＋）-vacancy complexes through percolation-bound magnetic polarons.

磁力扰动法测量铁磁性锅炉管氧化皮堵塞

为解决铁磁性锅炉管氧化皮堵塞检测难题,提出一种磁力扰动法的无损检测方法。首先,采用数值模拟方法对正交放置的两电磁铁作用下的铁磁性锅炉管进行磁场分布特征分析,并通过实验验证仿真结果的正确性;其次,使用声发射技术对磁场作用下氧化皮碰撞管壁发出的声音进行采集,建立波形特征参数与氧化皮堵塞面积比的定量关系。结果表明:铁磁性锅炉管磁导率的非线性特点使得两电磁铁在管道内形成一种能穿透管壁直接吸引氧化皮的独特磁场,其吸引能力下限低至10%堵塞面积比;以幅值绝对值为权重的声信号加权平均时间可以作为判定被检管道堵塞面积比是否超标的依据。该方法具有一定的工程应用前景。

钴氧化物中晶格与自旋的关联耦合效应研究

强关联电子体系具有多序参量耦合且极易受到外场高效调控的特性.钴氧化物(LaCoO3)是一类典型的多铁性(兼具铁弹性和铁磁性)氧化物材料,受到了研究者们广泛和深入的研究.过去,针对钴氧化物的研究都集中于应力作用下的铁弹性相变和结构调控方面.近年来,研究人员新奇地发现钴氧化物薄膜在张应力作用下发生顺磁到铁磁相转变,但其根源一直存在较大争议.部分实验证据表明应力将会导致钴离子价态降低产生自旋态转变,而另一些研究者认为应力诱导的纳米畴结构会呈现高自旋态的长程有序排列,才是钴氧化物薄膜铁磁性的主要原因.本综述主要介绍近几年来钴氧化物薄膜和异质结中自旋与晶格之间关联耦合效应的系列进展.在保持钴离子价态不变时,通过薄膜厚度、晶格失配应力、晶体对称性、表面形貌、界面氧离子配位和氧八面体倾转等结构因素诱导钴氧化物薄膜的自旋态可逆转变,从而形成高度可调的宏观磁性.进而,研究者们利用原子级精度可控的薄膜生长技术构筑了单原胞层钴氧化物超晶格,通过高效的结构调控,实现了超薄二维磁性氧化物材料.这些系列进展不仅澄清了强关联电子体系中晶格与自旋等序参量之间的强耦合关系,而且为实现氧化物自旋电子器件所需的超薄室温铁磁材料提供了优良的候选者.

Defect-manipulated magnetoresistance and above-room-temperature ferromagnetism in two-dimensional BaNi_(2)V_(2)O_(8)

The intricate correlation between multiple degrees of freedom and physical properties is a fascinating area in solid state chemistry and condensed matter physics.Here,we report a quantum-magnetic system BaNi_(2)V_(2)O_(8)(BNVO),in which the spin correlation was modulated by unusual oxidation state,leading to different magnetic behavior.The BNVO was modified with topochemical reduction(TR)to yield TR-BNVO with partially reduced valance state of Ni^(+)in the two-dimensional NiO_(6)-honeycomb lattice.Accordingly,the antiferromagnetic order is suppressed by the introduction of locally interposed Ni^(+)and oxygen vacancies,resulting in a ferromagnetic ground state with the transition temperature up to 710 K.A positive magnetoresistance(7.5%)was observed in the TR-BNVO at 40 K under 7 T.These findings show that topological reduction is a powerful approach to engineer low-dimensional materials and accelerate the discovery of new quantum magnetism.

Emergent ultra-high temperature ferromagnetism in La_(2)CoO_(4±x) thin films

Searching for novel ferromagnetic oxides with high Curie temperature(TC)has been one of the main goals for oxide spintronics.The well-known perovskite cobaltate LaCoO_(3)is a classical ferromagnet in its thin-film form;however,it suffers from a low TC(~85 K).Here we report a new type of ferromagnetic La-Co-O films with an ultrahigh TC of~820 K.They are fabricated by pulsed laser deposition from a LaCoO_(3)target at low oxygen partial pressures.Detailed structural analysis indicates that they crystallize in terms of the Ruddlesden–Popper phase of La_(2)CoO_(4±x).In sharp contrast to the antiferromagnetism of bulk La_(2)CoO_(4),the strong ferromagnetism in the La_(2)CoO_(4±x) thin films is firmly demonstrated by magnetometry measurements,X-ray magnetic circular dichroism characterization,and magnetotransport experiments.More importantly,density functional theory calculations indicate that the nonstoichiometric oxygen induces an antiferromagnetic-to-ferromagnetic phase transition,accompanied by the orbital reconstruction of Co 3d electrons.Thus,our study provides an attractive strategy for designing or synthesizing exotic magnetic oxides with high ordering temperatures.