NiFe/Pt薄膜中角度相关的逆自旋霍尔效应

NiFe/Pt双层薄膜样品在铁磁共振时, NiFe磁矩进动所产生的自旋流注入到Pt层中, 由于逆自旋霍尔效应产生直流电压V_ISHE, 此电压会叠加到NiFe薄膜由于自旋整流效应而产生的电压V_SRE 上, 实验测量所得电压为V_ISHE和V_SRE的叠加. 为了区分这两种不同机理对电压的贡献, 本文采取旋转外加静磁场的方法, 通过分析所测电压随磁场角度的变化从而分离出V_ISHE 的大小. 研究结果表明, 相比于单层NiFe(20 nm)薄膜样品, NiFe(20 nm)/Pt(10 nm)双层膜样品中由于NiFe自旋注入到Pt 中导致铁磁共振线宽增加. 与逆自旋霍尔效应产生的电压相比, 自旋整流效应的贡献较小, 但不可忽略. 本文工作有助于认清铁磁/非磁性金属材料中的自旋相关效应, 并提供了一种准确的分析逆自旋霍尔效应的方法.     

Multilevel interaction between layers in layered film structures

An analysis was carried out of the mechanism underlying magnetic interlayer interaction in film structures. The investigation was based on the assumption that interlayer bonding affects film hysteresis. This was based on experimental data on the coercive force, the domain structure parameters, and the microstructure of Fe₁₉Ni₈₁/Cr/Fe₁₉Ni₈₁ and Fe₁₅Co₂₀Ni₆₅/Cr/Fe₁₅Co₂₀Ni₆₅ films. Theoretical estimates show that, as the thickness of the Cr interlayer increases, the exchange interaction between the ferromagnetic layers can be replaced by the magnetostatic interaction whose effectiveness is determined by surface irregularities and layer ‘magnetization ripples’. Fiz. Tverd. Tela (St. Petersburg) 39, 2191–2194 (December 1997)     

Giant magnetic impedance of film nanostructures adapted for biodetection

A comparative study of the magnetic properties and giant magnetic impedance of Fe₁₉Ni₈₁/Su/Fe₁₉Ni₈₁ film structures fabricated by the method of ion-plasma evaporation is performed versus the geometry of an impedance element. The geometrical parameters of the Fe₁₉Ni₈₁/Сu/Fe₁₉Ni₈₁ structures are estimated from the viewpoint of obtaining strong magnetic impedance effect and possible application of these structures for detection of bioelements with magnetic markers. Widening of the structures necessary for increasing their active surface area weakens the magnetic impedance effect, and the length increase is limited by the optimal working biodetector frequencies and electromagnetic wave propagation processes.     

Vortex Pinning due to Dynamic Spin-Vortex Interaction in aSuperconductor/Ferromagnet Multilayer

We investigate the mutual interaction between superconductivity and ferromagnetism in a Nb/Ni81 Ee19 multilayer by ac susceptibility measurements. Compared with a pure superconducting Nb film, the critical current density of the multilayer is apparently enhanced in a low magnetic field region but remains nearly the same in high magnetic fields, which indicates that a continuous ferromagnetic layer with in-plane magnetization can produce strong vortex pinning in a low field region. We interpret this unusual vortex-pinning phenomenon as a consequence of dynamic spin vortex interaction which induces a spin rotation following vortex movement. In addition, we propose that this dynamic interaction could be used for spin manipulation via a superconductor.     

Abnormal spin-pumping effect at Pt/NiFe interface by an oxidation of ferromagnet

The Inverse Spin Hall Effect (ISHE) voltage induced by spin-pumping was measured in Pt/[nonoxidized or oxidized NiFe] samples. The spectrum shape of the DC voltage signal was well-reproduced by simple Lorentzian functions, which were consistent with the prediction of ISHE in Pt/nonoxidized NiFe sample. On the other hand, the voltage signal from the Pt/oxidized NiFe was significantly decreased in accordance with abnormal ferromagnetic resonance (FMR) behavior. The origin of the ISHE voltage degradation was investigated by the FMR spectrum and X-ray photoelectron spectroscopy (XPS) analyses. The spin-pumping was suppressed by the oxidation of NiFe layer and deficient Pt/NiFe interface. The well-defined ferromagnet and clear interface with a normal spin mixing conductance were experimentally demonstrated to be reasonable spin-pumping.     

Local charge and spin currents in magnetothermal landscapes

A scannable laser beam is used to generate local thermal gradients in metallic (Co2FeAl) or insulating (Y3Fe5O12) ferromagnetic thin films. We study the resulting local charge and spin currents that arise due to the anomalous Nernst effect (ANE) and the spin Seebeck effect (SSE), respectively. In the local ANE experiments, we detect the voltage in the Co2FeAl thin film plane as a function of the laser-spot position and external magnetic field magnitude and orientation. The local SSE effect is detected in a similar fashion by exploiting the inverse spin Hall effect in a Pt layer deposited on top of the Y3Fe5O12. Our findings establish local thermal spin and charge current generation as well as spin caloritronic domain imaging.     

The observation of inherent spin Seebeck effect in Rh/YIG hybrid structure

Rhodium (Rh) is a 4d metal possessing a large spin orbit coupling strength and spin-Hall conductivity with a very small magnetic susceptibility, implying an insignificant magnetic proximity effect (MPE). We report here the observation of longitudinal spin Seebeck effect (LSSE) using Rh as a normal metal. A Rh film was sputtered on nanometer thick YIG films of highly crystalline nature and extremely low magnetic damping to obtain Rh/YIG hybrid structure. A clear thermal voltage V_th (SSE voltage) was obtained when a temperature gradient was applied on the Rh/YIG hybrid. The Rh film showed a very weak anomalous Hall resistance and the magneto-resistive testing clearly ruled out the magnetization of the Rh films via MPE. The anisotropic magnetoresistance (AMR) revealed a clear spin hall magnetoresistance (SMR) signal in Rh film implying a purely intrinsic spin current generation, free from any parasitic magnetic effects. The work can open a new window in the study of pure and uncontaminated spin current, generated in ferromagnetic insulators, using Rh as spin current detector.     

Magnetic exchange bias enhancement through seed layer variation in FeMn/NiFe layered structures

The exchange bias and crystalline texture of the multilayer structure (Ta/Al/seed/Fe₅₀Mn₅₀/Ni₈₁Fe₁₉/Al₂O₃/Ni₈₁Fe₁₉/Al/Ta with seed=Ni₈₁Fe₁₉ or Ni₈₁Fe₁₉/Cu) has been characterized. Measurements indicate an abrupt decrease in exchange bias of the Ni₈₁Fe₁₉ pinned layer for samples with very thin seed layers, and exchange bias as high as 325 Oe for thicker seed layers. Fluctuation of exchange bias with thickness was greatly reduced for the Ni₈₁Fe₁₉/Cu seed configuration. X-ray diffraction measurements demonstrate a correlation between exchange bias and strong (1 1 1) texture of FeMn. The results suggest a high sensitivity of Ni₈₁Fe₁₉ roughness and texture on deposition conditions, and corroborate previous observations of roughness in ultrathin NiFe films.     

Thickness-dependent magnetic properties of Ni81Fe19, Co90Fe10 and Ni65Fe15Co20 thin films

We present results of magnetization and magnetic anisotropy measurements in thin magnetic films of the alloys Ni₈₁Fe₁₉, Co₉₀Fe₁₀ and Ni₆₅Fe₁₅Co₂₀ that are commonly used in magnetoelectronic devices. The films were sandwiched between layers of Ta. At room temperature the critical thickness for all the films to become ferromagnetic is in the range 11–13 Å. In Co₉₀Fe₁₀ the coercivity and the anisotropy field both depend strongly on layer thickness.     

The origin of spin current in YIG/nonmagnetic metal multilayers at ferromagnetic resonance

Spin pumping in yttrium-iron-garnet(YIG)/nonmagnetic-metal(NM) layer systems under ferromagnetic resonance(FMR) conditions is a popular method of generating spin current in the NM layer.A good understanding of the spin current source is essential in extracting spin Hall angle of the NM and in potential spintronics applications.It is widely believed that spin current is pumped from precessing YIG magnetization into NM layer.Here,by combining microwave absorption and DC-voltage measurements on thin YIG/Pt and YIG/NM_1/NM_2(NM_1 =Cu or Al,NM_2 =Pt or Ta),we unambiguously showed that spin current in NM,instead of from the precessing YIG magnetization,came from the magnetized NM surface(in contact with thin YIG),either due to the magnetic proximity effect(MPE) or from the inevitable diffused Fe ions from YIG to NM.This conclusion is reached through analyzing the FMR microwave absorption peaks with the DC-voltage peak from the inverse spin Hall effect(ISHE).The voltage signal is attributed to the magnetized NM surface,hardly observed in the conventional FMR experiments,and was greatly amplified when the electrical detection circuit was switched on.     

Electric manipulation of spin relaxation using the spin Hall effect

Using the spin Hall effect, magnetization relaxation in a Ni_{81}Fe_{19}/Pt film is manipulated electrically. An electric current applied to the Pt layer exerts spin torque on the entire magnetization of the Ni81Fe19 layer via the macroscopic spin transfer induced by the spin Hall effect and modulates the magnetization relaxation in the Ni81Fe19 layer. This method allows us to tune the magnetization dynamics regardless of the film size without applying electric currents directly to the magnetic layer.     

Comparison of parallel and perpendicular ferromagnetic resonance in an exchange-biased bilayer

We have investigated the ferromagnetic resonance spectra of an exchange-biased Ni₈₀Fe₂₀/CoO bilayer between room temperature and 4 K. Primary attention has been paid to the effect of the antiferromagnetic CoO film on the temperature-dependent resonance field shift of the ferromagnetic Ni₈₀Fe₂₀ film with respect to that of an unbiased film. At low temperatures, the field shift with the magnetic field applied perpendicular to the plane was determined to be more than twice the magnitude of the parallel field shift, and of the same sign, while an unoxidized single ferromagnetic film has much smaller parallel and perpendicular low-temperature shifts (here defined with respect to room temperature) of opposite sign. This observation implies that the anisotropy axis can rotate with the applied field, provided that the primary cause of the anisotropy is the interaction between the adjacent ferromagnetic and antiferromagnetic films. Since the perpendicular shift is more than a factor of two larger than the parallel field shift, the rotatable anisotropy is, in fact, anisotropic in this bilayer.     

Electron scattering characteristics of polycrystalline metal transition films by in-situ electrical resistance measurements

In-situ electrical resistance measurements were performed to obtain the scattering characteristics of very thin polycrystalline metal transition magnetic alloys grown by ion beam deposition (IBD) on specific underlayers. The experimental curves show size effects at small film thicknesses and important differences between Co₈₅Fe₁₅ and Ni₈₁Fe₁₉ thin layers grown on identical underlayers of Ta70 Å/Ru13 Å. The largest difference was observed in Ni₈₁Fe₁₉ films grown on underlayers of amorphous Ta70 Å. The experimental curves of electrical resistivity/conductivity variation with layer thickness were well fit within the Mayadas and Shatzkes (M-S) model, assuming specific formulations for grain growth with layer thickness.     

Micromagnetism of two-dimensional permalloy particles with different aspect ratios

Micromagnetic properties of the Fe₁₉Ni₈₁ (5 nm)/NiO (50 nm)/Fe₁₉Ni₈₁ (30 nm) structured system have been investigated in a photoemission electron microscope in the magnetic X-ray circular dichroism operating mode. The microstructured Fe₁₉Ni₈₁ (5 nm) film contained two-dimensional islands with the aspect ratio varying from 1:1 to 10:1, and the linear size of their long axis comprised 24, 12 and 6 μm. It is shown that the magnetic domains have the direction of magnetization preferentially parallel and antiparallel to the magnetic field direction in which this system was prepared. Their number is determined by the particles’ sizes, their shape as well as by the direction of the external magnetizing field and can be characterized by a non-monotonic size dependence. The magnetization of domains with different lateral sizes was found to be 0.4 T with an accuracy better than 20%. Received: 29 May 2002 / Accepted: 17 July 2002 / Published online: 22 November 2002 RID="*" ID="*"Corresponding author. Fax: +49-6131/392-3807, E-mail: nepijko@mail.uni-mainz.de     

合成反铁磁Ni81Fe19/Co90Fe10/Ru/Co90Fe10/Ni81Fe19的研究

采用直流磁控溅射方法制备了一系列的合成反铁磁及以其为自由层的自旋阀.研究发现,在Ni₈₁Fe₁₉与Ru层之间插入适当厚度的Co₉₀Fe₁₀层后,可有效地提高合成反铁磁两磁性层间的反铁磁耦合强度,得到具有饱和场H_s更高、饱和磁化强度M_s更低、热稳定性更好的合成反铁磁.另外,以这种合成反铁磁作自旋阀的自由层时,可有效提高自旋阀的稳定性. 关键词： 合成反铁磁 退火 自旋阀     

Spin-torque ferromagnetic resonance induced by the spin Hall effect

We demonstrate that the spin Hall effect in a thin film with strong spin-orbit scattering can excite magnetic precession in an adjacent ferromagnetic film. The flow of alternating current through a Pt/NiFe bilayer generates an oscillating transverse spin current in the Pt, and the resultant transfer of spin angular momentum to the NiFe induces ferromagnetic resonance dynamics. The Oersted field from the current also generates a ferromagnetic resonance signal but with a different symmetry. The ratio of these two signals allows a quantitative determination of the spin current and the spin Hall angle.     

Planar Hall effect and magnetoresistance in Ni81Fe19 and Co square shaped thin films

Ni₈₁Fe₁₉ and Co thin films have been fabricated and their transport properties have been investigated for potential applications in ultra sensitive magnetic field sensors. The Ni₈₁Fe₁₉ films exhibit an anisotropic magnetoresistance (AMR) of 2.5% with a coercivity 2.5 Oe and the Co films exhibit an AMR of 0.7% with coercivity 11 Oe. Large planar Hall effect magnetoresistance values at room temperature are reported for both cases. An unbalanced Wheatstone bridge model is proposed to describe quantitatively the observed experimental Planar Hall Effect data.     

Nanostructuring effects in soft magnetic films and film elements with magnetic impedance

The magnetization reversal and magnetic impedance (MI) of films and film elements based on Fe₁₉Ni₈₁ and Fe_72.5Cu_1.1Nb_1.9Mo_1.5Si_14.2B_8.7 alloys with a varied thickness, heat-treatment temperature, and the number of thin Cu interlayers are studied. The dependences of the coercive force and the magnitude of MI on these parameters are found. Layered structuring is shown to be an effective method for improving the functional characteristics of MI elements. In elements containing nanocrystalline Fe₁₉Ni₈₁ layers, this is related to the restructuring of a magnetic structure; in elements containing amorphous Fe_72.5Cu_1.1Nb_1.9Mo_1.5Si_14.2B_8.7 layers, this improvement is likely to be caused by a decrease in the effective electrical resistivity.     

掺铌SrTiO_3中的逆自旋霍尔效应

采用磁控溅射法在未掺杂和掺杂的SrTiO_3基片上沉积了NiFe薄膜,通过翻转测试法分离出掺杂样品中的自旋整流电压和逆自旋霍尔电压.研究结果表明:在未掺杂的SrTiO_3基片中,翻转前后测试的电压曲线基本一致,为NiFe薄膜自旋整流效应产生的电压.对于掺Nb浓度x为0.028, 0.05, 0.1, 0.15, 0.2的SrTiO_3基片,分离出的逆自旋霍尔电压随掺杂浓度增加而减小,在掺杂浓度为0.15和0.2的样品中没有探测到明显的逆自旋霍尔电压.本文的结果表明,在SrTiO_3中掺入强自旋轨道耦合的杂质,通过掺杂浓度可以实现对SrTiO_3中逆自旋霍尔效应的调控,这类可调控的自旋相关研究为自旋电子器件的研究和开发提供了更多的可能性,具有很大的潜在应用价值.     

Ni81Fe19/Cr82Al18双层膜中的交换偏置

研究了直流磁控溅射法制备的Ni₈₁Fe₁₉/Cr₈₂Al₁₈双层膜中的交换耦合.样品的室温矫顽力与1/t^{3/2_FM(t_FM为铁磁层厚度）近似成正比例关系,从而表明在Ni₈₁Fe₁₉/Cr₈₂Al₁₈中交换耦合为铁磁/反铁磁界面的随机相互作用.另外还讨论了反铁磁层厚度对交换偏置的影响. 关键词：}