CoFe Layer Thickness Research Articles

Simple electrodepositing of CoFe/Cu multilayers: Effect of ferromagnetic layer thicknesses

The CoFe/Cu magnetic multilayers were produced by changing CoFe ferromagnetic layers from 3nm to 10nm using electrodeposition. By now, the thinnest Cu (0.5nm) layer thicknesses were used to see whether the GMR effect in the multilayers can be obtained or not since the pinning of non-magnetic layer between the ferromagnetic layers is required. For the proper depositions, the cyclic voltammograms was used, and the current–time transients were obtained. The Cu and CoFe layers were deposited at a cathode potential of −0.3 and −1.5V with respect to saturated calomel electrode, respectively. From the XRD patterns, the multilayers were shown to be fcc crystal structures. For the magnetization measurements, saturation magnetization increases from 160 to 600kA/m from 3 to 8nm ferromagnetic layer thicknesses. And, the coercivity values increase until the 8nm of the CoFe layer thickness. It is seen that the thin Cu layer (fixed at 0.5nm) and pinholes support the random magnetization orientation and thus all multilayers exhibited the giant magnetoresistance (GMR) effect, and the highest GMR value was observed about 5.5%. And, the variation of GMR field sensitivity was calculated. The results show that the GMR and GMR sensitivity are compatible among the multilayers. The CoFe/Cu magnetic multilayers having GMR properties are used in GMR sensors and hard disk drive of the nano-technological devices.

CoFe Layers Thickness and Annealing Effect on the Magnetic Behavior of the CoFe/Cu Multilayer Nanowires

CoFe/Cu multilayer nanowires were electrodeposited into anodic aluminum oxide templates prepared by a two-step mild anodization method, using the single-bath technique. Nanowires with 30 nm diameter and the definite lengths were obtained. The effect of CoFe layers thickness and annealing on the magnetic behavior of the multilayer nanowires was investigated. The layers thickness was controlled through the pulses numbers: 200, 260, 310,360 and 410 pulses were used to deposit the CoFe layers, while 300 pulse for the Cu layers. A certain increase in coercivity and squareness of CoFe/Cu multilayer nanowires observed with increasing the CoFe layer thickness and annealing improved the coercivity and decrease squareness of CoFe/Cu multilayer nanowires. First order reversal curves after annealed showed amount domains with soft magnetic phase, it also shows decreasing spreading of distribution function along the Hu axis after annealed

Tunable interface anisotropy in a Pt/Co1−xFex/Pt multilayer

Interfacial magnetic anisotropy in a Pt/Co1−xFex/Pt multilayer is tuned by doping iron atoms into the cobalt layer. The perpendicular magnetic anisotropy and out-of-plane coercivity are found to decrease with increasing x. For a specific x, the out-of-plane coercivity acquires a maximal value as a function of the thickness of the CoFe layer. At low temperature, the coercivity is enhanced. Small coercivity but reasonably large perpendicular magnetic anisotropy can be obtained by controlling the x and CoFe layer thickness.

Study of Magnetization Reversal by Minor Loops in IrMn/CoFe Exchange-Biased Bilayers

We report a detailed investigation of the magnetization reversal by minor loops in Co75Fe25 (t) single layer and Ir22Mn78(10 nm)/CoFe(t) exchange-biased bilayers with different CoFe thicknesses. With increasing CoFe layer thickness in IrMn/CoFe bilayers, the magnetization reversal process shows a transition from the coherent rotation to the domain-wall motion, which is attributed to the competition among the antiferromagnetic domain wall energy, ferromagnetic domain wall energy, and the interface coupling between antiferromagnetic and ferromagnetic layers.

Research on enhanced perpendicular magnetic anisotropy in CoFe/Pd bilayer structure

A series of CoFe/Pd bilayer thin films is fabricated by introducing a native oxide layer to the interface or to the inside of CoFe layer in this paper. The results indicate that the magnetic anisotropy of the film is transformed from in-plane to out-of-plane after annealing by introducing the native oxide layer. For the samples with the introduction of native oxide layer into CoFe layer, the strong perpendicular magnetic anisotropy is maintained in a wide range of the effective thickness (1.22 nm) of magnetic layer. For the perpendicular magnetic films, the thickness of CoFe layer in this special bilayer structure is at least 1.4 nm, thicker than in common CoFe/Pd multilayer structure. The results in this paper are beneficial for the fabrication of the electrodes in perpendicular magnetic devices with high thermal stability.

Thickness Effect on Spin Moment in Amorphous Co<sub>0.9</sub>Fe<sub>0.1</sub> Films

Utilizing X-ray magnetic circular dichroism spectra the thickness effect on spin moment is examined in amorphous Co0.9Fe0.1films fabricated by RF magnetron sputtering. As film thickness increases from 5nm to 50nm, the variations of spin moments for Fe is a gradual decrease from 1.87μB to 1.70μB, while for Co it increases from 1.41μB to 1.69μB monotonously. Based on magnetic dead layer (MDL) model, the above changes are well explained, and the thickness of MDL, 0.83 nm, is estimated as well. That is not changed with increasing CoFe layer thickness.

Enhancement of Extraordinary Hall Effect in Pt/CoFe Multilayers With a Small Amount of Fe Doped Into Pt Layers

The extraordinary Hall effect (EHE) is investigated for the Pt/CoFe multilayers with a small amount of Fe doped into Pt layers. It is found that, through varying CoFe layer thickness and/or the content of Fe in Pt layers, high sensitivity linear EHE can be achieved in the Fe doped Pt/CoFe multilayers at room temperature. Most remarkably, both the saturation Hall resistivity and the Hall angle are significantly enhanced upon adding a small amount of Fe into Pt layers, reaching 1.2 μΩ·cm and 1.8%, respectively. The EHE sensor based on the Fe doped Pt/CoFe multilayers has the field sensitivity over 400 V/A T, which is twice as large as that of the pure Pt/CoFe multilayers and much higher than the best value ever achieved in Pt-based ferromagnetic alloy thin films. The present results suggest that, due to the large Hall effect and the adjustable interface anisotropy, the Fe doped Pt/CoFe multilayer film should be a potential candidate for magnetic field sensor application.

Influence of ferromagnetic current screen layer on current perpendicular to the plane-giant magnetoresistance

We investigated the influence of the ferromagnetic current screen layer on a current perpendicular to the plane-giant magnetoresistance (CPP-GMR). We prepared a bottom-type synthetic-pinned spin-valve film with a ferromagnetic current screen layer of naturally oxidized CoFe, which was separated magnetically from the free and pinned layers. When the CoFe layer thickness increased to above 1.0nm before oxidation, we observed a magnetic moment corresponding to the unoxidized CoFe. We also found that the MR ratio abruptly increased from 1.6% to 7.2% with the increase in the CoFe layer thickness from 1.0to3.7nm before oxidation, which was the same tendency observed in the magnetic moment. The MR ratio seemed to be strongly dependent on the magnetic moment of the current screen layer. The MR curve with the high MR ratio had two peaks near the zero magnetic fields. Based on the analysis of the magnetization configuration of the free, pinned, and current screen layers, we found that the ferromagnetic properties of the current screen layer contributed to the high MR ratio. From transmission electron microscopy observation and magnetic properties of the current screen layer, we estimated that the metal CoFe bridge exists in the current screen layer. We believe that the metal bridge made from the ferromagnetic metal in the current screen layer is important for enhancing the MR ratio of CPP-GMR for both current screening and spin dependent scattering.

Magnetic and microwave properties of CoFe∕PtMn∕CoFe multilayer films

CoFe ∕ PtMn ∕ CoFe films were deposited on seed layers of Ru or NiFeCr with CoFe film compositions being either Co-10at.%Fe or Co-16at.%Fe. Eight periods of the CoFe∕PtMn∕CoFe trilayers were also prepared. The magnetic properties and ferromagnetic resonance (FMR) of these films were characterized with vibrating-sample magnetometer, and field-sweep FMR system at X band (∼9.5GHz). The Ru-seeded CoFe∕PtMn∕CoFe sandwich films show excellent magnetic softness with a low hard axis coercivity of 2–4Oe, an easy axis Mr∕Ms of >98%, and a significantly enhanced in-plane anisotropy of 57–123Oe when CoFe layer thickness is above 200Å. Contrary to what was observed in the ferromagnetic/antiferromagnetic bilayer systems that have reduced FMR linewidth with the increase of film thickness, the CoFe∕PtMn∕CoFe trilayers with Ru seed layer show a minimum FMR linewidth of 45Oe at an intermediate CoFe layer thickness of 300Å at ∼9.5GHz.

Exchange coupling between ferromagnetic and laminated antiferromagnetic layers and its application

Exchange bias (Hex) and coercivity (Hc) of the NiFe layer in the NiFe/IrMn system can be tuned by inserting either spacer layers such as Cu, Ru, and Ta or ferromagnetic layers such as CoFe into IrMn since the antiferromagnetic spin structure of IrMn is altered in consequence. Hex usually decreases while Hc increases when the thin discontinued spacer layers are inserted into IrMn. The crossover from the unidirectional exchange-biased coupling to the uniaxial exchange-spring coupling has been successfully observed in the NiFe/[IrMn/CoFe(t)]3/IrMn (here, 3 means the number of the repeated periods of IrMn/CoFe double layer) system when the thickness of CoFe layer t exceeds 1 nm. It indicates that much of the physics and reversal mechanisms in the exchanged-biased systems are similar to that observed in exchange-spring systems where the hard layer replaces the antiferromagnetic layer as the biasing layer. Uniaxial spin valves (both of current in the plane and current perpendicular to the plane modes) and uniaxial magnetic tunneling junctions have been successfully fabricated by using this uniaxial exchange-spring system.

Magnetic surface anisotropy of fcc-Co-Fe[111]/Pd multilayers

We have studied the magnetic surface anisotropy (MSA) of fcc-Co-Fe[111]/Pd multilayers in order to investigate the relationship of the MSA with Co-Fe composition. Multilayers (Co/sub 100-x/Fe/sub x/ d/spl Aring//Pd 50 /spl Aring/)/spl times/5/Pd 200 /spl Aring/ were fabricated by DC sputtering on HF-treated Si[001] substrates. Co-Fe layer thickness d was varied from 3 to 7.5 /spl Aring/ at x=0, 8, and 14 at.%. All the samples showed perpendicular magnetic anisotropy, and the MSA decreased monotonically with Fe content x. This decrease of the MSA would be attributed to decrease of band filling by Co-Fe alloying.

Dependence of tunneling magnetoresistance on CoFe interfacial layer thickness in NiFe/Al/sub 2/O/sub 3//NiFe tunnel junctions

Magnetic tunnel junctions of Ta/Ni/sub 81/Fe/sub 19//Fe/sub 50/Mn/sub 50//Ni/sub 81/Fe/sub 19//Co/sub 50/Fe/sub 50//Al/sub 2/O/sub 3//Co/sub 50/Fe/sub 50//Ni/sub 81/Fe/sub 19/ were fabricated by a magnetron sputtering system. We have studied the change of tunneling magnetoresistance (MR) ratio and junction resistance as a function of CoFe interfacial layer thickness. The MR ratio rapidly increased and slowly decreased as the CoFe layer thickness increased. The junction resistance increased with the introduction of CoFe layer. The increase is due to more uniform Al layer formation on a CoFe layer than a NiFe layer.

Thermal Stability of Spin Valve Films with FeMn Layers

Spin valves with FeMn antiferromagnetic layers were investigated. Substitution of CoFe layers for NiFe layers in the pinning-layer side and both side interfaces of the Cu space layer increases the MR ratio. Any partial substitution at the interface of the Cu space layer of CoFe layers causes thermal instability. Only complete substitution of a CoFe layer for NiFe layer was effective for improving both the MR ratio and the thermal stability. The MR ratio was strongly correlated with ΔR and Rs in various type of spin valves. The thermal stability varies according to the CoFe layer thickness and the presence of substitution.