Thermal Stability of CoFe/Cu/CoFe/IrMn Top Spin Valve

We present a study of thermal stability of the top spin valve with a structure of seed Ta （Snm）/Co75Fe25 （5 nm ） /Cu （2.5 nm） /Co75Fe25 （5 nm ） /Ir20Mn80（12 nm） /cap Ta （8 nm） deposited at room temperature by magnetron sputtering. A vibrating sample magnetometer fixed with a heater was used to record the magnetic hysteresis loops at variational temperatures and x-ray diffraction was performed to characterize the structure of the multilayer. The exchange field Hex and the coercivity of the pinned CoFe layer Hop decrease monotonically with increasing temperature. The coercivity of the free CoFe layer Hcf in the spin valve shows a maximum at 498K. The temperature dependences of Hex, Hop and Hcf have also been discussed.     

Tuning exchange coupling by replacing CoFe with amorphous CoFeB in the CoFe/Ru/CoFe synthetic antiferromagnetic structure

We studied exchange coupling in the CoFe/Ru/CoFe synthetic antiferromagnetic structure with systematical replacement of the crystalline CoFe with amorphous CoFeB. Antiferromagnetic exchange coupling intensity decreases with an increase in the replacement in the bottom magnetic layer, which indicates that exchange coupling intensity could be tuned by the replacement. The origin of weakening antiferromagnetic exchange coupling is attributed to the amorphous CoFeB replacement inducing incomplete crystallization and disordered orientation in the Ru layer.     

Hot-electron transport properties of CoFe/n-Si and CoFe/Cu/n-Si junctions

The hot-electron transport properties of different thickness of CoFe films deposited on n-Si substrate with and without Cu layer were investigated. Diode characteristics were tested to obtain the heights of Schottky barrier for different samples. The dependences of Schottky heights on CoFe thickness were studied. The research shows that the height of the Schottky barrier can be adjusted and a good Schottky diode can be obtained by controlling the thickness of CoFe film accurately. The results are very important for the application of spintronic devices, such as spin valve transistor (SVT) and magnetic tunnel transistor (MTT).     

Magnetoresistance study and interlayer coupling of CoFe/Os/CoFe thin films

The CoFe/Os/CoFe thin films were deposited on natural oxidized Si(1 0 0) substrates at room temperature by an ultra-high vacuum DC-magnetron sputtering system with a base pressure less than 1×10⁻⁸ Torr. The thickness of the ferromagnetic layers was 100 Å in all cases and a series of trilayers with Os spacer ranging from 3 to 20 Å was made. Effects of the Os layer thickness on the magnetoresistance (MR) and magnetic properties were investigated. The results showed that the magnetism switched from ferromagnetic (Os thickness=3, 5 Å) to antiferromagnetic (Os thickness=7–13 Å) and then ferromagnetic (Os thickness=20 Å) again. From the MR study, we see that the AMR ratio decreased from 4.64% to the minimum value 0.69% at 9 Å and then increased; GMR ratio increased from 0.01% to the maximum value 0.43% at 9 Å and then decreased. From the hysteresis loops, the results exhibited that coercivity increased from 16 Oe to the maximum value 92 Oe at 9 Å and then decreased, and squareness value decreased from 0.97 to the minimum value 0.17 at 9 Å and then increased. Dependence of saturation field on Os spacer-layer thickness for CoFe trilayers showed a maximum value 216 Oe at 9 Å. This suggests that the small GMR effect may be related to the small exchange coupling strength in CoFe/Os/CoFe thin films.     

反铁磁Cr插入层对CoFe/MgO/CoFe磁性隧道结的隧穿磁电阻的影响

利用基于密度泛函理论和非平衡态格林函数的第一性原理计算研究了CoFe/MgO/CoFe磁性隧道结的隧穿磁电阻效应。给出了该隧道结隧穿磁电阻与偏压的依赖关系,并计算了平行结构与反平行结构相应的I-V特性曲线和传输谱。通过在一侧电极与势垒层之间插入反铁磁金属Cr层,观察到了隧穿磁电阻、电导随插入层Cr层数增加发生衰减和2个原子层周期的振荡现象,这主要是由于Cr拥有反铁磁结构,在Cr/MgO界面形成了与Cr磁矩取向相关的界面散射。     

反铁磁Cr插入层对CoFe/MgO/CoFe磁性隧道结的隧穿磁电阻的影响

利用基于密度泛函理论和非平衡态格林函数的第一性原理计算研究了CoFe/MgO/CoFe磁性隧道结的隧穿磁电阻效应。给出了该隧道结隧穿磁电阻与偏压的依赖关系,并计算了平行结构与反平行结构相应的I-V特性曲线和传输谱。通过在一侧电极与势垒层之间插入反铁磁金属Cr层,观察到了隧穿磁电阻、电导随插入层Cr层数增加发生衰减和2个原子层周期的振荡现象,这主要是由于Cr拥有反铁磁结构,在Cr/MgO界面形成了与Cr磁矩取向相关的界面散射。     

High temperature magnetoresistance in (Co,CoFe and NiFe)/Cu/CoFe/IrMn spin-valves

The MR characteristics of temperature variations ranging from room temperature to 570 K for IrMn spin-valves which consist of free layer Co, CoFe and NiFe were studied. Co-SV had the highest MR value in all temperature ranges among them and even at 510 K the MR ratio held more than half of room temperature value. Whereas CoFe-SV had a slightly higher MR than NiFe-SV below 450 K, above 450 K CoFe-SV showed a lower MR ratio than NiFe-SV. MR loops of large coercivity such as CoFe free magnetic layer collapsed in the lower elevated temperature compared to NiFe and Co. Small coercivity of the free magnetic layer would be preferable to spin-valves.     

Influence of temperature on thermal relaxation of exchange bias field in CoFe/Cu/CoFe/IrMn spin valve

A multilayered spin valve film with a structure of Ta(5 nm)/Co_(75)Fe_(25)(5 nm)/Cu(2.5 nm)/Co_(75)Fe_(25)(5 nm)/Ir_(20)Mn_(80)(12 nm)/Ta(8 nm) is prepared by the high-vacuum direct current(DC) magnetron sputtering. The effect of temperature on the spin valve structure and the magnetic properties are studied by x-ray diffraction(XRD), atomic force microscopy(AFM), and vibrating sample magnetometry. The effect of temperature on the exchange bias field thermomagnetic properties of multilayered spin valve is studied by the residence time of samples in a reverse saturation field. The results show that as the temperature increases, the Ir Mn(111) texture weakens, surface/interface roughness increases, and the exchange bias field decreases. Below 200℃, the exchange bias field decreases with the residence time increasing, and at the beginning of the negative saturation field, the exchange bias field Hex decreases first quickly and then slowly gradually. When the temperature is greater than 200℃, the exchange bias field is unchanged with the residence time increasing.     

Transient NMR/ON of56CoFe

Adiabatic Fast Passage NMR/ON measurements on single crystal⁵⁶CoFe indicate a unique electric field gradient when the applied field is parallel to the 100 direction.A well defined spin echo has been observed with pulsed NMR/ON using the 847 keV gamma and the echo amplitude decay followed for pulse separations out to 75 ms. The decay of the echo is non exponential, being essentially constant for pulse separations of 75 s, 750 s and 7.5 ms. The echo is significantly attenuated at 75 ms. This may be contrasted with an effective nuclear spin lattice relaxation time of T ₁ 30 s.     

Influence of Ga+ ion irradiation on the magnetisation reversal process and magnetoresistance in CoFe/Cu/CoFe/IrMn spin valves

Ga+ion irradiation is performed on the surfaces of IrMn-based spin valves and the effects of ion irradiation on the magnetisation reversal process and magnetoresistance(MR) are investigated.The results show that the exchange bias field and magnetoresistance ratio of the spin valve decrease with the increase of ion dose.The width of the forward step between the free layer and the pinned layer becomes gradually smaller with the increase of ion dose whilst the recoil step tends to be narrower with ion dose increasing up to 6×10 13 ions/cm 2 and the step disappears afterwards.Two peaks in the R-H curve are found to be asymmetric.     

Antiferromagnet IrMn thickness dependence in exchange-biased perpendicular magnetic anisotropy based on CoFe/Pt/CoFe/[IrMn(tIrMn)] multilayers

The effect of the antiferromagnetic IrMn thickness upon the magnetic properties of CoFe/Pt/CoFe/[IrMn(t_IrMn)] multilayers is studied. An oscillatory interlayer coupling (IEC) has been shown in pinned CoFe/Pt(t_Pt)/CoFe/IrMn multilayers with perpendicular anisotropy. The period of oscillation corresponds to about 2 monolayers of Pt. The oscillatory behavior of IEC depends on the nonmagnetic metallic Pt thickness and is thought to be related to the antiferromagnetic ordering induced by the IrMn layer. From the extraordinary Hall voltage amplitude (EHA) curves as function of IrMn thickness, we report that the oscillation dependence of IEC for the [CoFe/Pt/CoFe] multilayer system induced by IrMn with spacer-layer thickness is a important features of perpendicular exchange biased system.     

Inverse TMR in a nominally symmetric CoFe/AlOx/CoFe junction induced by interfacial Fe3O4 investigated by STEM-EELS

We have found inverse tunneling magnetoresistance (TMR) with a non-symmetric bias voltage dependence in a nominally symmetric Si (001)/Ag/CoFe/AlO_x/CoFe/IrMn/Ag magnetic tunnel junction after field cooling. The O K edge fine structure extracted from electron energy loss spectroscopy spectrum images taken at the interfaces of junctions with inverse TMR shows a thin, discontinuous Fe₃O₄ layer at the CoFe/AlO_x interfaces. The Fe L_2,3 edge core level shifts are also consistent with those of Fe₃O₄. We find no Fe₃O₄ layer in junctions with normal TMR. We believe this Fe₃O₄ layer is responsible for the inverse TMR.     

Electric-field-induced changes in magnetization in PZT/Insulator/CoFe nanometer multilayer

The PZT/Insulator/CoFe nanometer multilayer has been proposed for applications of the spin-dependent devices in this paper. With the strains as a response of PZT layer to an applied electric field in the structure, the magnetization in CoFe layer can be significantly altered, leading to a significance change in magnetoresistance. Our numerical results have demonstrated that the magnetization states in CoFe layer can be tuned by an electric field without a magnetic field being present.     

Superlattice CoCrPt/Ru/CoFe structure fabricated by pulsed laser deposition

The synthetic antiferromagnets (SAF) have been used in spin-valve sensor in data storage industry [1]. We report a new hard/Ru/soft sandwich structure (SHBL) fabricated by pulsed lased deposition to replace current single layer structure for information recording application. SHBL consists of two magnetic layers separated by thin nonmagnetic layers, typically with Ru layers of 0.7-1.2 nm, through which antiferromagnetic coupling is induced. Varying the relative thickness of the magnetic layers, the spacer layers, and the type of magnetic materials can alter magnetic properties of CoCrPt/Ru/CoFe superlattice. The coercivity H_c and grain size of magnetic layer is also dependent on the laser fluence. High laser fluence results in both small grain size and high H_c. The observed phenomena are related to high quenching and deposition rates during PLD at high fluence, resulting in more pronounced phase segregation.     

Brillouin light scattering of CoFe/IrMn-based top and bottom spin-valves

The spin-wave Brillouin light scattering (BLS) was observed from CoFe/IrMn-based bottom and top spin-valve structures. The magnitude of perpendicular magnetic anisotropy of these structures was investigated by means of BLS. The experimental spin-wave frequency was simulated using a simple model which includes crystallographic, exchange, in-plane uniaxial, and in- and out-of-plane anisotropies and takes the exchange interaction between the two ferromagnetic layers into account. This enabled us to determine, in addition to the other magnetic parameters, both in- and out-of-plane anisotropy constants near the surface. It was found that the top spin-valve is in a strong out-of-plane anisotropy whereas in-plane anisotropy is dominant for the bottom spin-valve.     

Magnetization reversal in the pinned layer of CoFe/PtMn bilayers

The magnetization reversal of the ferromagnetic (FM) layer in CoFe/PtMn exchange-coupled bilayer films has been investigated using bulk magnetometry. These films exhibit very complex angular dependence and the easy axis is perpendicular to the field applied during deposition and post-annealing. Holding the film at negative saturation of the FM layer for up to 17 h results in no change in the exchange field. We believe that this is a thermally stable exchange-coupled system. Only limited thermal activation with a small time constant appears and no thermally activated reversal of the antiferromagnetic layer with a large time constant exits.     

Electrochemical characterization of core@shell CoFe2O4/Au composite

Quantum dots (QDs) have received considerable attention due to their unique optical and electrical properties. Although substantial research has focused on the potential applications and toxicological impacts of QDs, far less effort has been directed toward understanding their fate and transport in the environment. In this work, the effect of four coatings, polyethylene glycol functionalized polymer (PEGP), carboxyl derivatized polymer (COOHP), linoleic acid (LA), and polyacrylic acid-octylamine (PAA-OA), on the transport and retention of QDs in porous media were evaluated under environmentally relevant conditions. Aqueous QD suspensions (ca. 10 nM) were introduced into water-saturated columns packed with 40–50 mesh Ottawa sand at a pore-water velocity of 7.6 m/day. At an ionic strength (IS) of 3 mM and pH of 7, PEGP-coated QDs were completely retained within the column, while more than 60 % of COOHP-coated QDs were transported through a column run under identical conditions. When PAA-OA and LA were used as coatings, effluent QD recoveries increased to more than 65 and 89 % of the injected mass, respectively. Additionally, a decrease in pH from 9.5 to 5.0, or an increase of IS from 0 to 30 mM reduced the eluted mass of PAA-OA-coated QDs by more than 2 and 15 times, respectively. The relative mobility of coated QDs (LA > PAA-OA > COOHP > PEGP) was consistent with total interaction energy profiles between QDs and sand surfaces calculated based on Derjaguin–Landau–Verwey–Overbeek (DLVO) theory. At an IS of 3 mM (NaCl) and pH 7, a linear correlation was obtained between the fraction of eluted QDs and the magnitude of the primary interaction energy barrier. These findings demonstrate the strong dependence of QD transport on coating type and indicate that interaction energies based on DLVO theory can be used to predict the relative mobility of QDs in porous media.     

Tuneable magnetic properties of hydrothermally synthesised core/shell CoFe2O4/NiFe2O4 and NiFe2O4/CoFe2O4 nanoparticles

The aim of this study was to prepare a novel targeting nano drug delivery system of 2-methoxyestradiol (2-ME) based on the folic acid-modified bovine serum albumin, in order to improve the clinical application disadvantages and antitumor effect of 2-ME. In this study, 2-methoxyestradiol-loaded albumin nanoparticles (2-ME-BSANPs) were prepared by desolvation method, and then the activated folic acid was conjugated to 2-ME-BSANPs by covalent attachment (2-ME-FA-BSANPs). The size and zeta potential of 2-ME-FA-BSANPs were about 208.8 ± 5.1 nm and ?32.70 ± 1.01 mV, respectively. 2-ME loading efficiency and loading amount of the nanoparticles were 80.49 ± 3.80 and 10.25 ± 1.59 %, respectively. SEM images indicated that 2-ME-FA-BSANPs were of a round shape, similar uniform size, and smooth surface. Studies on drug release indicated that 2-ME-FA-BSANPs had the properties of sustained and controlled release, which provided them with the ability to fight continually against cancer cells. Internalization analysis demonstrated that 2-ME-FA-BSANPs-targeting drug delivery system could get efficiently transferred into the cells through the folic acid-mediated endocytosis, leading to higher apoptosis and affording higher antitumor efficacy against SMMC-7721 cells in vitro compared with 2-ME alone. Furthermore, the cell-cycle arrest of 2-ME-FA-BSANPs on the SMMC-7721 cells occurred at G2/M phase, and 2-ME-FA-BSANPs did not change the inhibition of the tumor mechanisms of 2-ME. Based on these results, it was concluded that albumin nanoparticles could be the promising nano carrier for 2-ME, and 2-ME-FA-BSANPs-targeting drug delivery system may be promising candidate for providing high treatment efficacy with minimal side effects in future cancer therapy.     

Ultrathin (CoFe/Pt)n multilayers with tuned magnetic properties

Perpendicular magnetic anisotropy (PMA) has been investigated in ultrathin (CoFe [0.2] nm/Pt [0.2] nm)_n multilayers. The Pt layers show an fcc crystal structure with a preferred [111] orientation. The multilayers with n=3, 4 show PMA in the as-grown state, which can be enhanced by thermal annealing. However, no PMA is observed in the as-grown state with higher repetitions (n>&=5), although it is observed after thermal annealing. For 1=&<n=&<8, the anisotropy energy is around 10⁵ J/m³ for all (CoFe [0.2]/Pt [0.2])_n stacks. The perpendicular anisotropy is related to layer thickness and interface roughness.     

引入纳米氧化层的CoFe/Pd双层膜结构中增强的垂直磁各向异性研究

制备了CoFe/Pd双层结构的界面处或CoFe层 内部引入纳米氧化层后的系列薄膜. 研究结果显示, 引入纳米氧化层后, 可以使薄膜的磁各向异性在退火后从面内转到垂直膜面方向. 并且对于在CoFe层内部引入纳米氧化层的这类样品, 其强烈的垂直磁性可以在相当宽的有效磁性层厚度范围内(1.2-2 nm)维持. 在保持垂直磁性的前提下, 这种特殊的双层膜结构中CoFe磁性层厚度比常规CoFe/Pd 多层膜中的CoFe层厚度至少多出1.4 nm. 本文的研究有助于制备出具有较高热稳定性的垂直磁性器件电极.