Thermomagnetic data writing and erasing in DyCo/NiFe (TbFe/NiFe) film structures

A new principle of data writing and erasing is proposed based on the exchange coupling between magnetic layers with mutually orthogonal orientations of the effective magnetization. The new method provides for a significant decrease in energy consumption. The possibility of using bilayer magnetic films of the (rare earth metal-transition metal)/NiFe type possessing unidirectional anisotropy as the media for thermomagnetic writing and erasing of magnetooptical data is studied.     

Specific features of unidirectional anisotropy in exchange-coupled DyCo/NiFe film structures

The dependence of the unidirectional anisotropy in a DyCo/NiFe bilayer system on the thickness of the magnetically soft layer has been studied using dynamic and static techniques. The magnitude of the exchange interaction between layers evaluated using the ferromagnetic resonance method is two times that determined from an analysis of the hysteresis loops. It is established that this difference is related to features of the magnetic microstructure of the DyCo layer.     

Peculiarities of magnetization reversal in exchange-coupled ferro/ferromagnet NiFe/CoP film structures

The effect of layer thicknesses on the magnetic properties and mechanism of magnetization reversal in exchange-coupled NiFe/CoP film structures has been studied. The process of magnetization reversal was studied by analysis of the magnetic-induction and magneto-optical hysteresis loops. It is established that, as the thicknesses of layers in the NiFe/CoP film structure are increased, the system exhibits a transition from homogeneous magnetization reversal in the structure to exchange spring formation in the soft magnetic layer.     

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.     

Ferromagnetic resonance in multilayer structures with bilinear and biquadratic exchange coupling

The resonance magnetization dynamics in multilayer nanostructures exposed to transverse and longitudinal magnetic fields is investigated with allowance for biquadratic exchange coupling between the magnetic moments of neighboring layers. It is found that the crystallographic magnetic anisotropy leads to the appearance of a minimum on the field dependence of the resonance frequency for the “acoustic” mode and the accompanying maximum in the magnetic susceptibility.     

Thickness dependence of interlayer fringe-field coupling in submicrometer NiFe/Cu multilayered pillars

The effect of fringe-field coupling on the magnetization reversal process in submicrometer scale giant magnetoresistive pillars consisting of [NiFe/Cu]/sub 6/ has been investigated by means of current perpendicular to plane magnetoresistance measurements and numerical simulations. The parabolic and reversible magnetoresistance curves due to an opposite rotation of magnetization in neighboring NiFe layers were observed. To explain the field sensitivity of the pillars quantitatively, we have proposed a modified single-domain model, where the magnetic energy of the system is reconstructed using the result of the micromagnetic simulation of a magnetostatically coupled bilayer system. The calculated magnetoresistance curves are consistent with the experimental ones. From the calculated results, the amplitude of the saturation field is found to be proportional to the thickness of the ferromagnetic layer and inversely proportional to the square root of the nonmagnetic layer thickness.     

Epitaxial growth and exchange coupling of spinel ferrimagnet Ni0.3Zn0.7Fe2O4 on multiferroic BiFeO3

Thin films of the zinc nickel ferrite, Zn_0.7Ni_0.3Fe₂O₄ (ZNFO), were deposited by the RF magnetron sputtering on a number of substrates, including (001) oriented single crystals of LaAlO₃ (LAO) and SrTiO₃ (STO), polycrystalline Pt/Si, and epitaxial films of BiFeO₃ (BFO) and LaNiO₃ (LNO). Except for the films on Pt/Si, the ZNFO films grown on other substrates were epitaxial and their magnetic properties were affected by the heteroepitaxy induced strains. Typically, the coercivity (H_c) was increased with the strain, i.e. H_c varied from 31 Oe for the 150 nm thick polycrystalline films grown on Pt/Si, to 55 Oe and 155 Oe for the 20 nm thick epitaxial films grown on BFO and LAO, respectively. The saturation magnetization of the epitaxial films was reduced accordingly to about 470 emu/cm³ from 986 emu/cm³ in the polycrystalline films. The all-oxide architecture allowed field-annealing to perform at the temperature above the Neel temperature of BFO (~ 370 °C), after which clear exchange bias was observed.     

Interface Reaction of Ta/NiFe and NiFe/Ta and the Dead Layer

The structures of Ta/Ni_(81)Fe_(19) and Ni_(81)Fe_(19)/Ta are commonly used in magnetoresistance multilayers. It is found that the thickness of dead layer in Ta/Ni81Fe19/Ta was about 1.6±0.2 nm. X-ray photoelectron spectroscopy (XPS) was used to study the interfaces of Ta/Ni_(81)Fe_(19) and Ni_(81)Fe_(19)/Ta. The results show that there is a reaction at the two interfaces: 2Ta+Ni=NiTa_2, which caused the thinning of the effective NiFe layer. Furthermore, this reaction could also explain the phenomenon that the dead layer thickness of spin valves multilayers prepared by MBE is thinner than those prepared by magnetron sputtering.     

Co/Cu多层膜层间耦合作用的调节

利用在Fe（5nm）/[Co/Cu]30多层膜的隔离层（Cu）中掺入磁性元素Co，引入与相邻Co层之间反铁磁的RKKY作用相竞争的直接的铁磁耦合作用，降低了相邻Co层间的交换耦合作用。在Cu层中掺入不同原子数比例的磁性元素时，饱和磁场有所降低，从而提高了多层膜对外磁场变化的灵敏度。     

插层Bi对NiFe/FeMn双层膜交换偏置场的影响及其XPS分析

在Ta／Cu／NiFe／FeMn／Ta薄膜中,我们曾发现Cu在NiFe层的表面偏聚导致NiFe／FeMn薄膜的交换偏置场降低。为了抑制Cu的表面偏聚,我们在Ta／Cu／NiFe／FeMn／Ta薄膜中在Cu／NiFe界面沉积Bi插层。实验发现,沉积适当厚度的Bi插层可以将NiFe／FeMn双层膜的交换偏置场提高1倍。XPS分析表明,在Cu／NiFe界面沉积的插层Bi有效地抑制了Cu在NiFe表面的偏聚,提高了交换偏置场。     

Asymmetry of Magnetization Reversal of Pinned Layer in NiFe/Cu/NiFe/IrMn Spin-Valve Structure

Two types of asymmetry in giant magnetoresistance (GMR) are observed which are not related to a training effect, but indicate different mechanisms of magnetization reversal of the pinned layer in spin-valve (SV) structures for ascending and descending field scans. GMR, exchange bias and coercivity in Si/Ta/NiFe/Cu/NiFe/IrMn/Ta SV-structures were investigated as functions of the thickness of the nonmagnetic spacer. The spacer thickness effects are discussed in correlation with layers microstructure and interfaces morphology variations.     

Enhanced exchange field of NiO/NiFe biyer by dual ion beam sputtering process control

Dual IBS (Ion Beam Sputtering) technique was used to fabricate NiO/NiFe bilayers. Various process conditions were examined to enhance the exchange field of the bilayer. Ion beam sputtering with an ion beam voltage above the threshold voltage and with the optimum ion beam current produced a fine-grained and smooth NiO film. This fine-grained surface followed by optimum etching exhibited an enhanced exchange field of 100 Oe. Growing NiO films were ion bombarded with a secondary ion-beam source having various beam voltages. The texture, surface roughness and grain size of the NiO films changed due to the ion bombardment; however, the grain size and/or surface roughness rather than texture was found to be responsible for controlling the exchange coupling. Furthermore, it was demonstrated that an optimum etching time of the NiO film prior to the depositing of NiFe for a large exchange field exists. With this optimum etching of the NiO film, surface segregated impurities could be eliminated without deteriorating the surface unnecessarily. Exchange fields and coercivities of the NiO/NiFe bilayers were measured with a MOKE (Magneto–Optic Kerr Effect) hysteresis looper and the surface properties of NiO films were examined with an AFM (Atomic Force Microscope) and an AES (Auger Electron Spectroscope).     

Magnetic coupling phenomena in EuS/Pb thin film double layers

The magnetic properties of EuS/Pb double layers (a ferromagnetic insulator on a superconducting metal) were investigated by means of 50 Hz hysteresis. The magnetic coupling between the two layers does not set in spontaneously. Two procedures for achieving magnetic coupling are described: first, by means of a d.c. magnetic field perpendicular to the film plane; secondly, with an a.c. field in the film plane. The coupled states are characterized by a slowing of the 50 Hz magnetization reversals. The degree of slow-down depends on the strength of the magnetic coupling.     

Optical quenching of photocurrent in CdSe/dielectric thin film structures

The influence of additional illumination on the photoconductivity of planar cadmium selenide/poly(ethylene terephthalate) (CdSe/PET) thin-film structures has been studied. The dependence of the photoconductivity of CdSe/PET samples on the wavelength and intensity of additional illumination is determined. The effect of the frequency of modulation of the exciting light on the spectra of optical quenching of photocurrent is considered.     

硬磁/反铁磁交换耦合对反铁磁FeMn稳定性影响研究

采用磁控溅射方法在SiO2基体上制备了FePt/FeMn/NiFe/Ta多层膜样品,通过FeMn/NiFe双层膜交换偏置的变化研究了硬磁FePt不同磁化状态对反铁磁层FeMn的影响。实验表明,磁化了的L10相FePt能使FeMn在较薄的情况下(4.5nm)对NiFe产生比较强的交换偏置;而未被磁化的FePt对FeMn/NiFe交换偏置影响并不明显。认为更薄的反铁磁层对另外的铁磁层产生交换偏置是由于硬磁与反铁磁的界面交换耦合作用能增强反铁磁的稳定性。     

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.     

花岗岩/硅烷偶联剂/水泥浆界面层的形成机理

用硅烷偶联剂(SCA)处理粗骨料,用分光光度法、接触角测定仪、傅里叶变换红外光谱(FTIR)和X射线光电子能谱(XPS)分析SCA与花岗岩表面的结合形式及其影响因素.结果表明,在常温下SCA与花岗岩表面可形成较强结合,包括化学键合.对花岗岩/SCA/水泥浆界面层的扫描电镜观测结果表明,水解SCA的羟基和间断分布的有机基团是界面结合增强的主要原因.     

Tuning the exchange bias in NiFe/Fe-oxide bilayers by way of different Fe-oxide based mixtures made with an ion-beam deposition technique

We have investigated the structural and magnetic properties of ion-beam deposited polycrystalline NiFe (25 nm)/Fe-oxide (35 nm) bilayers. A film prepared with an assist beam O2 to Ar gas ratio of 0% during deposition had a bottom layer that consisted of pure b.c.c. Fe (a = 2.87 A) whereas films prepared with 19%O2/Ar and 35%O2/Ar had either Fe3O4 (a = 8.47 angstroms) or alpha-Fe2O3 (a = 5.04 angstroms, c = 13.86 angstroms) bottom layers, respectively. Cross-sectional transmission electron microscopy revealed a smooth interface between the top nano-columnar NiFe and bottom nano-columnar Fe-oxide layer for all films. At room temperature, the observed coercivity (Hc approximately 25 Oe) for a film prepared with 19% O2/Ar indicates the existence of a magnetically hard ferrimagnetic Fe3O4 phase that is enhancing the plain NiFe (Hc approximately 2 Oe) by way of exchange coupling. A significant amount of exchange bias is observed below 50 K, and at 10 K the size of exchange bias hysteresis loops shift increases with increasing oxygen in the films. Furthermore, the strongest exchange coupling (H(ex) approximately 135 Oe at 10 K) is with alpha-Fe2O3 (35% O2/Ar) as the bottom film layer. This indicates that the pure antiferromagnetic phases work better than ferrimagnetic phases when in contact with ferromagnetic NiFe. H(ex) (T) is well described by an effective AF domain wall energy that creates an exchange field with a (1 - T/T(crit)) temperature dependence. Hc (T) exhibits three distinct regimes of constant temperature that may indicate the existence of different AF spin populations that couple to the FM layer at different temperatures.     

Effect of gas adsorption on the photoconductivity of CdSe/dielectric thin film structures

The sensitivity of CdSe/PETP thin-film structures with respect to the adsorption of ammonia, aqueous ammonia, and water vapor from the gas phase at room temperature has been studied. The photoconductivity of the best samples exhibited reversible variations within two orders of magnitude in response to the presence of ammonia vapor. The concentration of ammonia in the gas phase can be measured in the interval from 0.25 to 25 vol %.     

Interfacial effects on the magnetic profiles and interlayer exchange coupling of Co/CoSi multilayers

Density functional calculations are conducted to investigate the interlayer exchange coupling (IEC) between ferromagnetic Co slabs mediated by a CoSi spacer in Co/CoSi(001) multilayers with CsCl crystalline structure. For both sharp and mixed Co-Si interfaces we calculated the magnetic moment distribution and the energy stability for ferromagnetic (F) IEC and antiferromagnetic (AF) IEC between the Co slabs as function of the spacer thickness. We show that mixing near to the interface noticeably modifies the IEC to the extent that this can change from an oscillatory IEC as function of the spacer thickness to an exponentially decaying AF behavior.