The coexistence of ferroelectricity and ferromagnetism in Mn-doped BaTiO3 thin films

Due to the fault of the first author, this article entitled “The coexistence of ferroelectricity and ferromagnetism in Mn-doped BaTiO3 thin films”, published in “Chinese Physics B”, 2011,Vol.20, Issue 12, Article No. 127701, has been found to copy from the article entitled“Decisive role of oxygen vacancy in ferroelectric versus ferromagnetic Mn-doped BaTiO3 thin films”, published in “Journal of Applied Physics”, 2011,Vol.109, Issue 8, article No. 084105. So the above article in “Chinese Physics B” has been withdrawn from the publication.<     

Influence of nanoparticle surface chemistry on the thermomechanical and magnetic properties of ferromagnetic nanocomposites

The effect of nanoparticle surface chemistry on the thermal, mechanical, and magnetic properties of poly(methyl methacrylate) (PMMA) nanocomposites with cobalt ferrite nanofillers was studied by comparing nanofillers coated with oleic acid (OA; which does not covalently bond to the PMMA matrix) and 3‐methacryloxypropyltrimethoxysilane (MPS, which covalently bonds to the PMMA matrix). Thermogravimetric analysis revealed an increase in the thermal degradation temperature of the nanocomposites compared with the neat polymer. The effect of cobalt ferrite nanofiller on the glass transition temperature (T_g) of the nanocomposite was evaluated by differential scanning calorimetry. The T_g value of the material increased when the particles were introduced. Dynamic mechanical analysis indicated an increase in the storage modulus of the nanocomposite because of the presence of nanofiller and a shift in the peak of loss tangent toward higher temperature. Magnetic measurements indicated that both nanocomposites had a small hysteresis loop at 300 K and no hysteresis at 400 K. However, estimates of the nanofiller's rotational relaxation times and measurements of the zero field cooled temperature‐dependent magnetization indicate that the observed lack of hysteresis at 400 K is likely because of particle rotation in the polymer matrix. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Double-Exchange Magnetic Interactions in High-Temperature Ferromagnetic Iron Chalcogenide Monolayers

Smythite ( ) is an iron-based chalcogenide with a lamellar structure, different from the compositionally identical mineral greigite. Owing to their natural abundance, such transition metal chalcogenides are promising materials for low-cost spintronic-based devices. Herein, we discuss the charge transfer processes and complex magnetic ordering in a two-dimensional (2D) smythite lattice. We find that redox couple and complex magnetic ordering are governing factors in the charge transfer processes. A very strong ferromagnetic in-lattice coupling is also observed, which is attributed to the presence of three Fe-centres. To describe the magnetic behaviour molecular and periodic approaches have been considered. We found a substantial increase in Curie temperature with applied mechanical stress due to opening of the double exchange interaction angle. We also observe an in-plane Jahn−Teller distortion, which is further confirmed by the spin−orbit counter plot. Our study thus provides an insight into the double exchange mechanism favoured by the redox couple and results in a strong ferromagnetic ordering.     

Electronic structure and magnetic properties of （Mn,N）-codoped ZnO

The electronic structures and magnetic properties of（Mn, N）-codoped Zn O are investigated by using the firstprinciples calculations. In the ferromagnetic state, as N substitutes for the intermediate O atom of the nearest neighboring Mn ions, about 0.5 electron per Mn^2＋ion transfers to the N^2-ion, which leads to the high-state Mn ions（close to ＋2.5）and trivalent N3-ions. In an antiferromagnetic state, one electron transfers to the N2-ion from the downspin Mn2＋ion,while no electron transfer occurs for the upspin Mn^2＋ion. The（Mn, N）-codoped Zn O system shows ferromagnetism,which is attributed to the hybridization between Mn 3d and N 2p orbitals.     

A Delicate Balance between Antiferromagnetism and Ferromagnetism: Theoretical and Experimental Studies of A2MRu5B2 (A=Zr,Hf; M=Fe,Mn) Metal Borides

Metal-rich borides with the Ti₃Co₅B₂-type structure represent an ideal playground for tuning magnetic interactions through chemical substitutions. In this work, density functional theory (DFT) and experimental studies of Ru-rich quaternary borides with the general composition A₂MRu₅B₂ (A=Zr, Hf, M=Fe, Mn) are presented. Total energy calculations show that the phases Zr₂FeRu₅B₂ and Hf₂FeRu₅B₂ prefer ground states with strong antiferromagnetic (AFM) interactions between ferromagnetic (FM) M-chains. Manganese substitution for iron lowers these antiferromagnetic interchain interactions dramatically and creates a strong competition between FM and AFM states with a slight preference for AFM in Zr₂MnRu₅B₂ and for FM in Hf₂MnRu₅B₂. Magnetic property measurements show a field dependence of the AFM transition (T_N): T_N is found at 0.1 T for all phases with predicted AFM states whereas for the predicted FM phase it is found at a much lower magnetic field (0.005 T). Furthermore, T_N is lowest for a Hf-based phase (20 K) and highest for a Zr-based one (28 K), in accordance with DFT predictions of weaker AFM interactions in the Hf-based phases. Interestingly, the AFM transitions vanish in all compounds at higher fields (>1 T) in favor of FM transitions, indicating metamagnetic behaviors for these Ru-rich phases.     

室温铁磁Sr4-xErxCo4O10.5+δ(0.6≤x≤1.2)多晶电输运和磁性能

采用固相反应法制备Sr4-xErxCo4O10.5+δ(0.4≤x≤1.2)多晶,系统研究了Er掺杂对体系结构、电输运和磁性质的影响.X射线衍射结果表明室温下x=0.4时多晶为立方晶系,空间群为P3m3,0.6≤x≤1.2时,为四方晶系,空间群为I4/mmm,四方相晶格常数随着Er含量增加而减小.扫描电子显微镜结果表明,随着Er掺杂量增加,晶粒细化,晶界增加.采用四探针法测量多晶的电阻率-温度曲线,结果表明多晶样品在80～ 300 K为半导体电输运行为,且随Er化学计量比增加样品电阻率和热激活能增大.采用超导量子干涉仪测量多晶的磁化强度-温度曲线和磁滞回线,结果表明0.6≤x≤1.2时Sr4-xErxCo4O10.5+δ多晶具有室温铁磁性,Tc≈320 ～ 335 K,室温铁磁性可能源于A位Sr和Er离子有序及CoO4.5+δ层中Co离子自旋倾斜净磁矩不为零.     

Role of vacancy-type defects in magnetism of GaMnN

Role of vacancy-type(N vacancy(VN) and Ga vacancy(VGa)) defects in magnetism of GaMnN is investigated by first-principle calculation.Theoretical results show that both the VNand VGainfluence the ferromagnetic state of a system.The VNcan induce antiferromagnetic state and the VGaindirectly modify the stability of the ferromagnetic state by depopulating the Mn levels in GaMnN.The transfer of electrons between the vacancy defects and Mn ions results in converting Mn~(3+)(d~4) into Mn~(2+)(d5).The introduced VNand the ferromagnetism become stronger and then gradually weaker with Mn concentration increasing,as well as the coexistence of Mn~(3+)(d~4) and Mn~(2+)(d~5) are found in GaMnN films grown by metal–organic chemical vapor deposition.The analysis suggests that a big proportion of Mn~(3+)changing into Mn~(2+)will reduce the exchange interaction and magnetic correlation of Mn atoms and lead to the reduction of ferromagnetism of material.     

Aggregation of ferromagnetic and paramagnetic atoms at edges of graphenes and graphite

In this work we report that when ferromagnetic metals (Fe,Co and Ni) are thermally evaporated onto n-layer graphenes and graphite,a metal nanowire and adjacent nanogaps can be found along the edges regardless of its zigzag or armchair structure.Similar features can also be observed for paramagnetic metals,such as Mn,Al and Pd.Meanwhile,metal nanowires and adjacent nanogaps cannot be found for diamagnetic metals (Au and Ag).An external magnetic field during the evaporation of metals can make these unique features disappear for ferromagnetic and paramagnetic metal;and the morphologies of diamagnetic metal do not change after the application of an external magnetic field.We discuss the possible reasons for these novel and interesting results,which include possible one-dimensional ferromagnets along the edge and edge-related binding energy.     

Synthesis and characterization of nano ZnS doped with Mn

Nanocrystalline samples of Zn_1‐xMn_xS (x = 0.0, 0.02, 0.04) were synthesized by chemical precipitation method and characterized for magnetism. EPR studies showed an evidence of ferromagnetism around room temperature. Hysterisis from vibrating sample magnetometer supports the observation. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

点缺陷引起中子辐照MgO(110)单晶的铁磁性

对MgO(110)单晶进行中子辐照,辐照剂量从1.0 × 10¹⁶到1.0 × 10²⁰ cm^-2。基于黄昆漫散射理论,我们计算了MgO晶体中的立方缺陷和偶极力缺陷引起的X射线漫散射强度分布图。通过X射线漫散射及紫外-可见光(UV-Vis)吸收光谱实验表征了晶体的点缺陷组态,并利用超导量子干涉仪(SQUID)测量了样品的磁性。ω–2θ和摇摆曲线说明MgO单晶经中子辐照后产生了晶格畸变,晶体中存在一定浓度的点缺陷。倒易空间图(RSM)显示中子辐照的MgO单晶存在漫散射现象。与计算得到的漫散射分布图对比分析可知,中子辐照的MgO(110)单晶中产生了弗仑克尔缺陷。UV-Vis吸收光谱表明所有辐照晶体中存在阴离子单空位缺陷。辐照剂量较高(1.0 × 10¹⁹和1.0 × 10²⁰ cm^-2)的样品中存在O空位的聚集。磁性测量显示中子辐照后的MgO(110)单晶在室温下依然是抗磁性,但在低温下具有铁磁性,最大饱和磁化强度达到0.058 emu·g^-1。通过中子辐照的方法,可以使MgO(110)单晶产生点缺陷引起的低温铁磁性。利用F色心交换机制可以解释中子辐照MgO晶体中的O空位缺陷与铁磁性之间的关系。