Interaction Effects in SmCo/FeCo Bilayer Film Media

The magnetic property of Sm22Co78/Fe65Co35 bilayer film media prepared by magnetron sputtering was measured. All the samples have in-plane anisotropy and the hysteresis loops are simple single loops, indicating that the two phases are strongly exchange-coupled. The reduced remanence (Mr/Ms) was found to increase from 0.58 to 0.8 with increasing Fe65Co35 layer thickness (d) for a fixed Sm22Co78 layer thickness. The coercivity was found to increase with increasing a few Fe65Co35 layer, and then to decrease with continuously increasing Fe65Cos5 layer. The intergranular exchange and magnetostatic interaction effects were measured from their remanence magnetization curves.     

A novel fabrication method of magnetic Co/Ni0.4Zn0.6Fe2O4 coaxial nanocables

A highly ordered Co/Ni0.4Zn0.6Fe2O4 coaxial nanocable array has been synthesized based on porous anodized aluminum oxide template via a new approach, which combines an improved sol-gel template method and alternating current electrochemical deposition. Scanning electron microscopy and transmission electron microscopy images show the nanocables are uniform with outer diameter of about 50 nm and inner diameter of about 17 nm. X-ray diffraction patterns and energy dispersive spectrometer confirm that Co nanowires are successfully deposited into the pores of the Ni0.4Zn0.6Fe2O4 nanotubes. Normalized magnetic hysteresis loops demonstrate the coercive force and the squareness with the applied field parallel to the axis of the nanocables increase dramatically compared with that of the nanotubes.     

Positive and negative exchange bias in IrMn/NiFe bilayers

We present the observation of double shifted hysteresis loops in IrMn/NiFe bilayer structures. The bilayer structures were fabricated using high vacuum DC magnetron sputtering system. The hysteresis loops of the as deposited samples show the double shifted loops at NiFe layer thicknesses 5 nm and 6 nm, whereas the IrMn layer thickness was kept constant at 15 nm. The results were interpreted as the contribution of both positive and negative exchange bias fields. We suppose that this phenomenon is occurring due to the ferromagnetic (FM) layer exchange coupled with the antiferromagnetic (AFM) layer in two different magnetization directions. The ferromagnetic coupling of the interface spins in some regions of the film generates the hysteresis loop shift toward negative fields and antiferromagnetic coupling toward positive fields in the other regions. The double shifted hysteresis loops disappeared after magnetic field annealing of the samples above Neel temperature of the AFM layer. The X-ray diffraction patterns of the sample show the IrMn (111) crystalline growth necessary for the development of exchange bias field in this system. The correlation between the Magnetic Force Microscopy (MFM) domain structures of the as deposited sample and the magnetization reversal process of the double shifted hysteresis loops were discussed. The results suggest that the larger multidomain formation in the AFM layer with different magnetization directions was responsible for the positive and negative exchange bias fields in IrMn/NiFe bilayer samples.     

The magnetic and magnetooptical properties of Fe/Ti, Zr, Pt and Fe/Ti, Zr, Pt/Fe thin-film magnetic structures

The results of investigation of the magnetic and magnetooptical properties of two-layer Fe/Ti, Zr, Pt and three-layer Fe/Ti, Zr, Pt/Fe thin-film magnetic structures are presented. The nonmagnetic layer exhibits a strong effect on the magnetic properties of samples. The magnitude of the saturation field of three-layer magnetic structures oscillates as a function of thickness of the nonmagnetic layer; the period of this oscillation depends on the thickness of the Fe layer. The Pt layer strongly affects the spectral dependences of the equatorial Kerr effect in the structures investigated.     

单相Bi0.95Eu0.05Fe0.95Co0.05O3纳米颗粒的结构及其铁磁特性

采用溶胶-凝胶法制备了单相Bi0.95 Eu0.05Fe0.95 Co0.05 O3纳米粉末。用X射线衍射仪(XRD)和扫描电子显微镜(SEM)测量分析了其结构和形貌,结果表明样品仍为钙钛矿菱方结构。样品Fe2p的X射线吸收谱(XAS)表明样品中Fe的价态处于Fe2+和Fe3+的混合态。利用振动样品磁强计(VSM)测量样品的磁性特征,结果表明样品具有完整闭合的磁滞回线,表现出室温的铁磁性,相比BiFeO3样品磁性得到明显增强。     

溶胶-凝胶法制备Bi0.975La0.025Fe0.975Ni0.025O3铁电薄膜的结构及物理性能

采用溶胶-凝胶法在Pt/Ti/SiO_2/Si(111)衬底上制备了Bi_(0.975)La_(0.025)Fe_(0.975)Ni_(0.025)O_3(BLFNO)铁电薄膜。利用X射线衍射(XRD)、原子力显微镜(AFM)及其压电模式(PFM)对薄膜的晶体结构、表面形貌以及铁电畴结构进行了研究。研究发现,BLFNO为结晶良好的钙钛矿结构多晶薄膜,且薄膜表面颗粒生长均匀。PFM测试图显示铁电薄膜在自发极化下的铁电畴结构清晰,铁电电容器具有良好的铁电性能。应用铁电测试仪对Pt/BLFNO/Pt电容器进行测量,得到了饱和性良好的电滞回线。在828kV/cm的外加电场下,Pt/BLFNO/Pt电容器的剩余极化强度为74.3μC/cm~2,表明La、Ni的共掺杂没有明显抑制铁电电容器的剩余极化强度,铁电电容器具有良好的铁电性能。漏电流研究结果表明,La、Ni元素的共掺杂有效降低了薄膜的漏电流密度,在277.8kV/cm外加电场下漏电流密度在10-4 A/cm2量级,明显小于纯BFO薄膜的漏电流密度。正半支漏电流曲线满足SCLC导电机制,对于负半支曲线,当电场强度大于22.2kV/cm时,同样遵循SCLC导电机制;但是,当电场强度小于22.2kV/cm时,曲线斜率约为4.8,表明参与导电贡献的电子数较多,归因于极浅陷阱俘获的电子在外加电场作用下参与了导电行为。室温下磁滞回线测试结果表明BLFNO薄膜具有反铁磁性质。     

SmCo/FeCo/SmCo三层膜中的剩磁增强效应

系统地研究了磁控溅射制备的Sm22Co78/Fe65Co35/Sm22Co78三层膜系统中，当软磁相的体积分数一定时，矫顽力和剩磁比随FeCo软磁层厚度（d)的变化，所有样品的磁滞回线均为单一硬磁相特征：说明FeCo软磁层与SmCo硬磁层之间的交换相互作用，使两相很好地复合在一起。当软磁相的体积分数为15％，20％，30％的情况下，矫顽力随d的变化都出现峰值，而剩磁比则单调增加，当体积分数为50％时，矫顽力随d的增加滑有峰值，但剩磁比还是单调增加，随着软磁体积分数的增加，矫顽力峰值及峰值位置都是单调减少。     

Microstructure,Magnetic and Magnetoresistance Properties of Electrodeposited [Fe/Pt] Granular Multilayers

In this paper, we report experimental results concerning the magnetic properties and the magnetoresistance effect of [Fe/Pt] _n and [Pt/Fe] _n electrodeposited multilayers. Two series of multilayers starting with Pt and Fe layers, respectively, were grown onto glass substrate covered with electroless deposited amorphous Ni. We investigated the effect of the seed layer (Pt or Fe) and Pt layer thicknesses on the magnetic and magnetoresistance properties of electrodeposited multilayers. The structure and morphology of the samples were characterized by X-ray diffraction (XRD) and atomic force microscopy (AFM). The hysteresis loops of the [Fe/Pt] _n and [Pt/Fe] _n multilayers showed that the magnetic properties strongly depend on the Pt thickness and on the seed layer (the first layer deposited onto the glass substrate). [Fe/Pt] _n and [Pt/Fe] _n electrodeposited multilayers display magnetoresistance (∼15%) effect which can be explained mainly by the spin-dependent scattering of conduction electrons between Fe layers through a Pt layer and by the existence of anti-ferromagnetic coupling between subsequent Fe layers. The existence of a GMR effect in Fe/Pt multilayers is very promising for technological applications (e.g., magnetoresistance sensors).     

巨磁电阻材料A0.05Co0.95Cr2S4(A=Zn、Ni、Cd、Fe)的输运行为及磁性能研究

过渡金属尖晶石型硫化物具有包括超巨磁电阻(CMR)效应在内的多种物理性能, 其CMR效应机理的研究对开发巨磁电阻材料有重要价值。目前, 铬基硫族尖晶石的CMR效应尚未深入研究。本论文通过固相反应法制备A_0.05Co_0.95Cr₂S₄(A=Zn、Ni、Cd、Fe)样品, 研究磁性和非磁性元素掺杂对CoCr₂S₄晶体结构和磁性能的影响。XRD检测表明, 掺杂的A_0.05Co_0.95Cr₂S₄(A=Zn、Ni、Cd、Fe)均呈现纯的尖晶石结构, 掺杂导致的晶胞参数变化与掺杂元素的离子半径成比例。磁电阻测定表明A_0.05Co_0.95Cr₂S₄(A=Zn、Ni、Fe)均具有巨磁电阻效应。掺杂削弱了铁磁相互作用, 导致A_0.05Co_0.95Cr₂S₄(A=Zn、Ni、Cd、Fe)的居里温度T_C降低。在0.01 T下, A_0.05Co_0.95Cr₂S₄(A=Zn、Ni、Cd、Fe)的零场冷却(ZFC)和加场冷却(FC)曲线均呈现磁性不可逆现象。A_0.05Co_0.95Cr₂S₄(A=Zn、Ni、Cd、Fe)呈现典型的亚铁磁性磁滞回线, 其中Zn_0.05Co_0.95Cr₂S₄的矫顽场最大。     

Features of the magnetic properties of Co/Si/Co thin-film systems

The magnetic properties of Co/Si/Co thin-film structures grown by magnetron sputtering have been studied using magnetooptical techniques. It is established that the saturation field (H _S) of trilayers exhibits oscillations as a function of the thickness of the semiconductor (silicon) interlayer. This behavior is explained by structural features of the Co/Si/Co system and the presence of antiferromagnetic exchange coupling between magnetic layers via the silicon interlayer.     

Processing of magnetic properties of nearly zero magnetostrictive glass-coated microwires by current annealing

The effect of dc current annealing (with length up to 80 min and current density j up to 250 A/mm/sup 2/), with or without dc axial magnetic field, on the magnetic properties of Co/sub 55.7/Fe/sub 5.9/Ni/sub 9.9/B/sub 17.7/Si/sub 10.8/ and Co/sub 68/Mn/sub 7/Si/sub 10/B/sub 15/ glass-coated microwires has been studied. Such thermal treatments, especially performed under magnetic field, modify the magnetic parameters, such as coercivity, remanent magnetization, magnetic permeability, and overall shape of the hysteresis loops. Such phenomenology can be interpreted by considering the noticeable longitudinal magnetic anisotropy induced by the combined effects of the magnetic field and internal stresses arising from the coating during the thermal treatment.     

Exchange-coupled Fe3O4/L10-FePt bilayer films by controlled oxidation of Fe/Pt multilayer

A Fe₃O₄/L1₀-FePt bilayer thin-film magnet was fabricated via a simple one-step process by annealing Fe/Pt multilayer thin films in a N₂ gas flow. X-ray diffraction and plane-view selected-area electron diffraction results are identified with magnetite phase (Fe₃O₄) and L1₀-FePt. Cross-sectional transmission electron microscopy images show the two phases form a bilayer structure. Magnetic hysteresis loops of the bilayer show single phase behavior which is interpreted as a result of the soft Fe₃O₄ phase exchange-coupled with the hard L1₀-FePt phase, consistent with micromagnetic simulation prediction. Such bilayer structure may have potential for coercivity control in high density magnetic recording application.     

静电纺丝法制备的Co0.6Ni0.3Cu0.1Fe2O4和Co0.6Ni0.3Zn0.1Fe2O4纳米纤维的结构及磁性能

采用静电纺丝技术制备出表面光滑、直径均匀的Co_(0.6)Ni_(0.3)Cu_(0.1)Fe_2O_4/PVP和Co_(0.6)Ni_(0.3)Zn_(0.1)Fe_2O_4/PVP纳米纤维前驱丝,经500~900℃煅烧后得到Co_(0.6)Ni_(0.3)Cu_(0.1)Fe_2O_4和Co_(0.6)Ni_(0.3)Zn_(0.1)Fe_2O_4纳米纤维。用TG-DSC、XRD、SEM及VSM现代测试分析手段对Co_(0.6)Ni_(0.3)Cu_(0.1)Fe_2O_4和Co_(0.6)Ni_(0.3)Zn_(0.1)Fe_2O_4纳米纤维的结构、形貌及磁学性能进行测试表征。结果表明:在空气气氛中经500~900℃煅烧后可得到纯尖晶石相、结晶度良好的纳米纤维或短纤维;当温度为700℃时,Co_(0.6)Ni_(0.3)Cu_(0.1)Fe_2O_4和Co_(0.6)Ni_(0.3)Zn_(0.1)Fe_2O_4纳米纤维的形貌细长而光滑且直径相对均匀,大约为80nm;此时Co_(0.6)Ni_(0.3)Cu_(0.1)Fe_2O_4纳米纤维则保有较高的剩磁比(M_r/M_s)及矫顽力,分别为0.56和1 088.87Oe。在500℃、600℃、700℃、800℃、900℃煅烧后,Co_(0.6)Ni_(0.3)Zn_(0.1)Fe_2O_4纳米纤维的饱和磁化强度分别比Co_(0.6)Ni_(0.3)Cu_(0.1)Fe_2O_4纳米纤维增大了14.5%、7%、16%、10.7%、8%,而矫顽力则分别降低了38%、51%、50%、46%、46.7%。两种纳米纤维的饱和磁化强度及矫顽力存在差异,为CoNi铁氧体在电磁方面的应用提供了很好的参考。     

Study of the interfacial magnetism in NiO/NiFe system

The interfacial magnetism of NiO/NiFe bilayers with different NiFe layer thicknesses, produced by DC and RF magnetron sputtering, has been studied by magnetometry and X-ray magnetic circular dichroism (XMCD). In magnetic hysteresis loops, the exchange bias field was found to be inversely proportional to the NiFe layer thickness. The fit using the Meiklejohn and Bean model gives a coupling energy at the NiO/NiFe interface of approximately 0.027 mJ/m². The analysis of the XMCD spectra of Fe and Ni, using the sum rules, shows a reduction of the effective spin magnetic moments in bilayers with NiFe thickness less than 4 nm. This reduction is attributed to hybridization of ferromagnetic and antiferromagnetic atoms d orbitals near the interface and/or formation of antiferromagnetic alloys due to atomic diffusion at the interfaces.     

Sr、Co共掺多铁性材料BiFeO3的性能

利用溶胶-凝胶法制备了BiFeO_3、Bi_(0.95)Sr_(0.05)FeO_3、BiFe_(0.95)Co_(0.05)O_3和Bi_(0.95)Sr_(0.05)Fe_(0.95)Co_(0.05)O_3样品,并对样品的结构、形态、元素含量、铁电性和铁磁性进行了研究。结果表明,共掺杂样品Bi_(0.95)Sr_(0.05)Fe_(0.95)Co_(0.05)O_3的晶体结构发生了变化,铁电性明显增强,但漏电流变大;Bi_(0.95)Sr_(0.05)FeO_3、BiFe_(0.95)Co_(0.05)O_3样品的磁性都有所增强,但Bi_(0.95)Sr_(0.05)Fe_(0.95)Co_(0.05)O_3样品的磁性并没有随着Sr和Co的共同掺杂而进一步提高,从氧空位浓度、Fe-O共价键结构的变化和晶体尺寸三个方面对产生这种现象的原因进行了分析。     

Effect of Variable Biquadratic Exchange Coupling on the Magnetic Hysteresis of Uniaxial Antiferromagnetic Co/Ru/Co Films

We investigated biquadratic exchange coupling strength in sputtered uniaxial antiferromagnetic Co/Ru/Co trilayers, which can be tuned by applying a magnetic field perpendicular to the sample surface during deposition. The perpendicular field induces a columnar grain structure that results in a perpendicular magnetic anisotropy for single Co layers. The perpendicular magnetic anisotropy is detected by combined magnetization and Brillouin light scattering measurements. In trilayers, increasing the perpendicular field during deposition results in a monotonic increase of the biquadratic exchange coupling strength, so these samples provide an experimental realization of the effect of variable biquadratic coupling strength on magnetic hysteresis behavior. The hard-axis remanence is a direct measure of biquadratic exchange coupling strength, which we demonstrated both by experiment and by a Stoner-Wohlfarth model that includes the relevant magnetic parameters.     

Key Properties of Ni?Mn?Ga Based Single Crystals Grown with the SLARE Technique

Magnetic shape memory alloys (MSMAs), exhibit large strains and hence are materials, which could substitute giant magnetostrictive and piezoelectrical materials in actuating devices. The actuation stress needed to induce the strain is much lower than in other actuator materials. Since the strain can be induced without phase transformation by a magnetic field, the development of actuators with high working frequencies is possible. However, for reasonable applications, large strains have to be induced with small magnetic fields. Up to now repeatable magnetically induced strains of 5–10% in magnetic fields of less than 500 mT have been achieved only in single crystals. The production of Ni? Mn? Ga based single crystals is difficult and time consuming. The crystal quality is affected by porosity and impurities. With the Bridgeman based method called Slag Remelting and Encapsulation (SLARE) single crystalline ingots of Ni? Mn? Ga, Ni? Mn? Ga? Fe, and Ni? Mn? Ga? Co of high quality were grown and characterized. The results show that MSMA properties depend on the position within the single crystalline rods due to a composition gradient. The influence of surface treatment demonstrates that the decrease of surface roughness leads to a decrease of twinning stress. MSMAs with twinning stresses above 1 MPa show a magnetic field induced strain (MFIS) when tilting is not restricted by constraints. Softer samples can adapt to constraints much better and show large MFIS. Substituting Ni by Fe and Co, shifted the phase transitions successfully to higher temperatures. Ni? Mn? Ga alloyed with up to 6 at.% Co showed three different martensite structures: a non‐modulated tetragonal structure, a modulated tetragonal structure, showing the same behavior as Ni? Mn? Ga with identical structures and a non‐modulated orthorhombic structure with a stress–strain‐behavior explainable by the double twinning mechanism.     

Magnetic anisotropies in single and multilayered thin films grownby bowed-substrate sputtering

Thin-film structures composed of nearly nonmagnetostrictive single-layer Co₇₆Fe₄B₂₀ or magnetostrictive Fe₈₀B₂₀ and Co₇₅Si₁₅B₁₀ amorphous layers have been deposited on bowed glass substrates using the RF-sputtering technique. The fabrication procedure induces a postdeposition compressive stress in the thin-film structure when the sample is retrieved from an arching device in the sputtering chamber. This results in an induced magneto-elastic anisotropy that governs the magnetic easy axis of the film, depending on the sign of the magnetostriction constant of each layer. Particular attention is paid here to heterogeneous structures made of bi- or multilayers with magnetic easy axis oriented in a different direction in each layer. Bulk magnetic properties were evaluated from hysteresis loops and thermomagnetization measured by vibrating sample magnetometry (VSM) and quantum interference device (SQUID) magnetometry. Magnetic domain walls and out-of-plane magnetized domains were observed by a Kerr imaging system and magnetic force microscopy. The combination of microstructure and strains induced in the layers determines the orientation of the observed magnetic anisotropies, which vary from high in-plane anisotropies up to out-of-plane orientations for selected films. The results, which provide reassurance that effective anisotropies are induced in each of the layers, are discussed in terms of the interactions between magnetic phases with different induced easy magnetization axes     

Hysteresis properties of sintered Sm Co5permanent magnets

The magnetic properties of individual SmCo5particles have been extensively studied in the literature. In the present work, initial magnetization curves and hysteresis loops of sintered SmCo5magnets have been drawn with a hysteresigraph. The observed properties depend on the previous magnetic treatment of the sample. After thermal demagnetization, the initial susceptibility is very high; after dc field demagnetization, it is very weak. The inner hysteresis loops are often unsymmetrical. Results are interpreted by considering the magnets as particle assemblies related together by dipolar interactions.     

Ab initio study of structure and magnetism of late transition metal oxide TMnOm clusters (TM = Fe, Co, Ni, n = 1, 2, m = 1-6)

We systematically investigate the structural and magnetic properties of late transition metal oxide clusters, TMnOm (TM = Fe, Co, Ni; n = 1, 2; m = 1-6) by using ab initio density functional theory approach. FenOm clusters prefer to adopt three dimensional configurations, while ConOm and NinOm clusters are apt to form planar structures. The O atoms are all atomic bonding to Fe atoms in the FenOm clusters, and are partly molecularly adsorbed to Co(Ni) in ConOm(NinOm) clusters, such as Co2O(5-6) (NiO3, and Ni2O(4-6)). The average binding energies per atom of TMnOm show a monotonous increase trend with the increase of O atoms for both n = 1 and 2 for TM = Fe, Co and Ni, and reach the peak at m = 4 for TM2Om and decrease a little bit afterwards. The odd-even magnetic oscillation is major trait with the peaks at odd and bottoms at even sizes for Fe2Om and Ni2Om (m = 2-6), respectively and large magnetic moments are found in Co2O3 and Co2O6.