Bottom Magnetic Layer Research Articles

Enhancement of tunneling magnetoresistance by inserting an amorphous nonmagnetic FeZr layer in magnetic tunnel junctions

An amorphous metallic FeZr layer is inserted inside the bottom magnetic layer in exchange-biased CoFe/Al2O3/CoFe magnetic tunnel junctions (MTJs). At room temperature, the tunneling magnetoresistance (TMR) increases from 25% to 36% before annealing, and from 45% to 52% after annealing. The junction resistance also increases with the FeZr thickness. The higher quality of the MTJ is attributed to the improved Al-oxide barrier due to the amorphousness of the FeZr layer.

Optimization of a tunneling barrier in magnetic tunneling junction by tilted-plasma oxidation

Oxidation of an AlOx insulating barrier in a magnetic tunneling junction (MTJ) was carried out by a tilted-plasma oxidation method. It was found that the tilted-plasma oxidation induced a gradual change in the extent of oxidation of an insulating layer, which consequently led to a gradual change in the tunneling magnetoresistance (TMR) and specific junction resistance (RA) of the MTJ. We found a linear relation in the TMR versus RA curve with positive and negative slopes for less- and overoxidized junctions, respectively, and a parabolic relation for optimally oxidized junctions. The crossover in the TMR versus RA curves provides an effective and useful way to optimize (and monitor) the oxidation condition of a tunneling barrier in MTJs especially of a tunneling barrier less than 10Å thick. The tunneling junctions were also investigated after thermal annealing at various temperatures. The observations after thermal annealing were found to be consistent with transmission electrons microscopy images and a scenario of the partial formation of an additional ultrathin tunneling barrier at the top surface of the bottom magnetic layer.

Interdiffusion and thermal stability in magnetic tunnel junction ferromagnet/insulator/ferromagnet trilayer structures

We used molecular beam epitaxy grown magnetic tunnel junction structures for thermal stability studies using x-ray photoelectron spectroscopy (XPS) and in situ scanning tunneling microscopy (STM). Unannealed trilayers show no oxidation of the bottom magnetic layer for barriers thicker than 1.1 nm. However, upon annealing, we find that the metallic XPS peak of the top layers decrease dramatically, while that of the bottom and barrier layers increases. STM images of the Co top layer on the Al–oxide barrier show that the Co does not agglomerate upon annealing up to 500 °C, which suggests interdiffusion is the most likely explanation for the XPS data.

Ferromagnetic resonance in coupled ultrathin films

Ferromagnetic resonance (FMR) is known to be one of the most informativetechniques to measure basic physical quantities such as magnetic anisotropy energies,the gtensor in solids or the interlayer exchange couplingJinter.We investigate prototype Cu/Ni/Cu/Ni/Cu(001) and Ni/Cu/Co/Cu(001)trilayers as well as Fen/Vm superlattices. We show for the case oftrilayers how in situ ultrahigh vacuum FMR can be used to determineJinterin absolute energy units in a straightforward way: we first prepare andmeasure the bottom magnetic layer together with the Cu spacer in situ andthen evaporate the second magnetic film on top. Thus, it is possible toinvestigate the FMR signal before and after the two magnetic films becomecoupled. We discuss results, showing that the temperature dependence ofJinterfollows a T3/2law over a wide temperature range. This indicates that thermally excited spin wavesat the interface of the ferromagnetic layers dominate the temperature dependence ofJinter.The second part focuses on the measurement of theg value. Fromthe g value, theratio of orbital to spin magnetic moment can be obtained via the relation μL /μS = (g − 2)/2.We show for Fen/Vm superlattices how μL /μSincreases with decreasing Fe-layer thickness.

이중절연층 산화공정에서 플라즈마 산화시간에 따른 터널자기저항 효과

자성터널접합(magnetic tunnel junction: MTJ)소자의 AlO<TEX>$_{x}$</TEX>터널장벽 절연층을 플라즈마 산화법으로 2번에 나누어 금속증착.산화를 반복하여 만들어 보았다. 이중산화I그룹은 10A의 <TEX>$\AA$</TEX>의 Al 하부 절연막을 증착하고 산화시간을 10 s로 완성한 후 그 위에 13<TEX>$\AA$</TEX>의 Al을성막하고 50, 80, 120s간 산화시켜 완성한 절연막의 특성을 알아보았다. 이중산화II그룹은 10<TEX>$\AA$</TEX>봐 Al하부 절연막의 산화시간을 30~120 s간 달리하고 그 위에 13 <TEX>$\AA$</TEX>의 Al을 성막하고 210 s간 산화시켜 완성한 절연막의 특성을 알아보았다. 이중산화공정으로 제조된 시편은 전 실험범위에서 자기저항비(magnetoresistance： MR)는 27% 이상으로 우수하였고, 이는 13 <TEX>$\AA$</TEX>의 Al을 증착하고 한번만 산화시키는 통상의 단일산화에 비해 MR비가 우수하고 공정범위가 넓었다. 수직단면 투과전자현미경(transmission electron microscope： TEM)으로 미세구조를 확인한 결과 이중산화가 단일산화보다도 더 얇고 균일한 두께를 유지함을 알 수 있었다 X선광전자분석(X-ray photoelectron spectroscopy： XPS)으로 확인한 결과 이중산화는 절연막층 하부 CoFe 자성층의 Fe의 산화를 방지하여, 결과적으로 단일산화법에 비해서 하부자성층의 산화를 방지하여 긴 산화시간 공정 범위에서도 우수한 MR비를 가질 수 있었다. We fabricated MTJ devices that have doubly oxidized tunnel barrier using plasma oxidation method to from oxidized AlO<TEX>$\sub$</TEX>x/ tunnel barrier. Doubly oxidation I, which sputtered 10 <TEX>${\AA}$</TEX>-bottom Al layer and oxidized it with oxidation time of 10 s. Subsequent sputtering of 13 <TEX>${\AA}$</TEX>-Al was performed and the metallic layer was oxidized for 50, 80 and 120 s., respectively. Doubly oxidation II, which sputtered 10 <TEX>${\AA}$</TEX>-bottom Al layer and oxidized it varying oxidation time for 30∼120 s. Subsequent sputtering of 13 <TEX>${\AA}$</TEX>-Al was performed and the metallic layer was oxidized for 210 sec. Double oxidation process specimen showed MR ratio of above 27％ in all experiment range. Singly oxidation process. 13 <TEX>${\AA}$</TEX>-Al layer and oxidized up to 210 s, showed less MR ratio and more narrow process window than those of doubly oxidation. Cross-sectional TEM images would that doubly oxidized barrowers were thinner and denser than singly oxidized ones. XPS characterization confirmed that doubly oxidation of Fe with bottom insulating layer. As a result, doubly oxidation could have superior MR ratio in process extent during long oxidation time because of preventing oxidation of bottom magnetic layer than singly oxidation.

Crystallographic stacking faults in antiferromagnetically coupled media

Synchrotron x-ray scattering has been used to examine stacking faults in the constituent layers of an antiferromagnetically coupled (AFC) media film. By varying the x-ray incident angle, we have varied the x-ray penetration depth and, hence, the layer under examination. Three films were studied, one consisting of a full AFC media structure and the other two consisting of a single magnetic layer with the thicknesses of the constituent layers in the AFC medium. The stacking faults in the bottom magnetic layer were investigated using the single layer film. The stacking fault density in the top AFC media layer was measured using careful depth profiling to ensure that the penetration depth of the x rays remained within the top layer. We were unable to estimate the stacking faults in the bottom layer film but the stacking fault densities are constant at approximately 5% for the top layer of the AFC media and the top layer single film within a relatively large error of 3%.

Magnetization reversal analysis for antiferromagnetic-coupled films with magnetic field angle dependence

In this article, theoretical analysis for the antiferromagnetically coupled films (two layers system) with magnetic field angle dependence is presented. The nonlinear simulative equations for such medium have been deduced and solved by the graphic solution method. Through the analysis of the solutions of different magnetic parameters (K1, K2, M1, M2, t1, t2, and J) and applied magnetic field angle (θ), the relationship between the magnetic switching fields (h1n,h2n) for each layer and the above magnetic parameters have been determined. The hysteresis loop with an applied field angle can be calculated and one example is plotted. By comparing the magnetic switching properties (h1n,h2n) with that of single layer (hn), it has been found that for both the top-magnetic layer and bottom-magnetic layer, the difference of the switching field (h1n−hn) and (h2n−hn), which are brought by the antiferromagnetical coupling effect (J), are closely correlated with the applied field angle.

Exchange coupling and edge pinning in vertical head sensors

Calculations which were done for an idealized geometry, showed that exchange coupling around the of a sandwich structure formed by folding the top magnetic layer around the and connecting to the bottom magnetic layer, increases the field necessary to nucleate the rotational reversal of the magnetization by a factor of more than 9. In a more realistic case, the coupling material is likely to be less uniform and somewhat irregular providing an additional contribution to the magnetization coercive force. Edge coupling is a major contributor to the high coercive force for hard edge sensors.

In situdetection of two ferromagnetic resonance modes in coupled Ni/Cu/Co/Cu(001) trilayer structures

Ultrathin Ni and Co films, separated by Cu spacer layers with thicknesses in the range 4--15 monolayers, are prepared and measured in situ via ferromagnetic resonance (FMR) between 50 and 400 K. Due to the interlayer exchange coupling two resonance modes are observed, corresponding to in- and out-of-phase precession of the rf magnetizations in the two magnetic layers, i.e., the acoustic and optic mode. The fields for resonance ${H}_{\mathrm{res}}$ and the linewidths $\ensuremath{\Delta}{H}_{\mathrm{pp}}$ of the exchange coupled FMR modes are measured as a function of temperature. Since all the measurements are performed in situ, we can compare the signal of the first (bottom) magnetic layer before and after the evaporation of the second (topmost) one. For the coupled films we observe an increase of $\ensuremath{\Delta}{H}_{\mathrm{pp}}$ compared to the uncoupled case. From the shift of ${H}_{\mathrm{res}}$ after the deposition of the second layer the sign and relative strength of the coupling is derived.

内部銅導体ライン，誘電体層および接地金属磁性層から成る伝送線路ローパスフィルタの試作

This paper describes a low-pass filter with a distributed constant circuit, which has electrically grounded top and bottom metallic magnetic layers, dielectric layers, and inner conductor lines. A trial large-scale device was used as an output noise filter in a 5 MHz switching boost micro dc-dc converter. With the new low-pass filter, the output spike noise was strongly suppressed.