Search

We study the electric field (EF)-assisted magnetization switching in perpendicular magnetic free layer guided by an Oersted field using micromagnetic simulations. The EF is used to reduce the perpendicular magnetic anisotropy (PMA), and thus change the easy axis from the perpendicular to the in-plane. The Oersted field is used to guide the magnetization to the desired switching directions. The effects of various physical parameters, such as the damping constant, the PMA change, the PMA after EF, the saturation magnetization, and the Oersted field, on the switching times are examined. The simulation results indicate that the switching time decreases with the increase in the damping constant and the Oersted field. The EF efficiency has a significant effect on the switching performance. In order to make a fast and energy-saving switching, the PMA of the free layer needs to be properly controlled. Simulation results also show that a material with higher $M_{s}$ needs a lower EF efficiency for fast switching. For the merit of a fast switching, large damping constant ( $\alpha > 0.1$ ) should be used. In addition, large damping constant requires a small Oersted field for a reliable switching, which reduces the energy during writing. For $\alpha = 0.3$ , a fast total switching time within 3 ns can be achieved with an Oersted field as small as 1 mT.

We study the electric field (EF) effect on MgO/CoFeB/Ta/CoFeB/MgO free layers by varying the thickness of the top MgO layer. The two CoFeB/MgO interfaces oppose the change in magnetic anisotropy from each other and this can be understood by considering the voltage drop as well as the efficiency of the anisotropy modulation from both interfaces. These results are proven by monitoring both coercivity and anisotropy field as a function of the applied EF. From the fit to the model, we show that the bottom CoFeB/MgO interface has a higher EF efficiency than the top interface.

Electric field (EF)-assisted magnetization reversal is investigated in both top-pinned and bottom-pinned CoFeB/MgO/CoFeB magnetic tunnel junctions (MTJs). EF modulation in coercivity ( $H_{c}$ ) shows an increasing dependence with the thickness of the free layer ( $t_{\rm FL}$ ) at small $t_{\rm FL}$ values. This abnormal variation was attributed to possible Ta diffusion through the free layer to the interface with MgO barrier. It is found that the bidirectional switching is not achievable using unipolar EF only in our MTJ devices, which is due to small spin-transfer torque (STT) effect and switching uncertainty due to unipolar feature of EF-induced $H_{c}$ modulation. A bipolar external magnetic field should be applied to realize EF-controlled magnetic random access memory (MRAM). For quasistatic magnetization reversal, the required field can be as low as 10 Oe when $H_{c}$ is effectively modulated to nearly zero. Switching field as a function of switching time shows that the magnetization switching is dominated by thermal activation. Simulation results show that switching time is mainly determined by the damping constant and the EF efficiency. Different from STT-MRAM, a large damping constant is desired to achieve fast switching. Using a sweeping field method, we show that MTJs with a thermal stability factor as high as 58 can be reliably switched using an EF-modulated anisotropy scheme with a bipolar magnetic field as low as 10 Oe.

Magnetic single-domain islands based on in-plane anisotropy (usually, shape anisotropy) and their dipole—dipole interactions have been investigated extensively in recent years. This has been driven by potential applications in magnetic recording, spintronics, magneto-biology, etc. Here, we propose a concept of outof-plane magnetic clusters with configurable domain structures (multi-flux states) via dipole—dipole interactions. Their flux stages can be switched through an external magnetic field. The concept has been successfully demonstrated by patterned [Co/Pd] islands. A [Co/Pd] multilayer exhibits a large perpendicular anisotropy, a strong physical separation, and uniform intrinsic properties after being patterned into individual islands by electron beam lithography. A threeisland cluster with six stable flux states has been realized by optimizing island size, thickness, gap, anisotropy, saturation magnetization, etc. Using [Co/Pd] multilayers, we have optimized the island structure by tuning magnetic properties (saturation magnetization and perpendicular anisotropy) using Landau—Liftshitz—Gilbert (LLG) simulation/calculation. Potential applications have been proposed, including a flexi-programmable logic device with AND, OR, NAND, and NOR functionalities and a magnetic domino, which can propagate magnetic current as far as 1 µm down from the surface via vertical dipole—dipole interactions.

Ferromagnetic nanofilms with high saturation magnetization (Ms), particularly FeCo alloys with the highest Ms value (theoretically 2.45T), are promising candidates for emerging compact high-performance magnetoelectronic, microwave, and spintronic devices. Thin films with diverse and specific dynamic microwave properties are essential components for these different applications. For example, a high-frequency mobile phone requires a ferromagnetic element of high resonant frequency (fr) ; [4] a thin single-band microwave absorber requires ferromagnetic films with large resonance-type permeability (m), whereas a broadband absorber requires films with wide frequency dispersion or large relaxation-type m. The demand for a wide range of functions poses challenges for both scientific understanding and fabrication of these thin films, in particular, for applications in gigahertz (GHz) range. Hence despite being one of the earliest themes in magnetism, the topic of ferromagnetic thin films for high-frequency applications still generates much interest from scientists and engineers. Although the influence of the composition of materials on static or dynamic magnetic properties is well studied and described mathematically, for example, by Snoek’s law and constant (S), 3, 15] most formulae are insensitive to the crystal structure or nanostructure of thin ferromagnetic films. The understanding of the influence of an altered structure on the static and dynamic magnetic properties is still limited. A notable example is the preparation of appropriate nanostructure or crystal texture of soft ferromagnetic thin films with high Ms, such as FeCo, for achieving low coercivity (Hc 50 Oe), as well as ultrahigh fr ( 5 GHz) or wide frequency dispersion ( 3 GHz) by simple diverse atom arrangements without the addition of other materials. 17] Due to the inherent limitations of pure homogeneous ferromagnetic single-layer films (e.g. undesirable magnetic softness, anisotropy, or crystallinity of FeCo films), and a lack of evidence on the relationship between the nanostructure or crystal texture and dynamic microwave properties, doping or insertion of nonmagnetic materials is often used to address the stringent requirements of functional devices. This has be achieved by adding AlOx to a FeCo(HfO) film to attain a high fr ( 3 GHz), utilizing FeCo–MnIr exchange-coupled multilayers for wideband microwave noise filtering, or by doping Zr or B into a ferromagnetic film to adjust the m type. However, there are two critical challenges associated with these methods. The foreign elements decrease the Ms of the ferromagnetic film and subsequently deteriorate the device efficiency or performance. Moreover, most of the modifications are tailored The application of a pure FeCo film directly to devices is limited by the intrinsic properties of a homogeneous monolayer of the alloy, despite it having the highest saturation magnetization. A feasible methodology based on alternating current-density electrodeposition to tune the microwave properties of FeCo films through diverse atom-stacking arrangements is reported. The properties range from a large relative resonance permeability (up to 728 in the real part) to ultrahigh resonant frequency (up to 5.2 GHz), and extremely wide frequency dispersion (1.5–6.0 GHz); these are not observed in other materials or as a result of conventional doping methods. They are attained using different single-layer, semi-multilayer, and multilayer FeCo nanofilms, fabricated by diverse stacking arrangements of Fe and Co atoms during deposition in a single bath. This technique firstly exemplifies the significant effect of atom arrangement on magnetic inhomogeneity, nanoscale morphology, composition, crystal texture, stress, and damping, which in turn largely alters both the static and dynamic magnetic properties of the ferromagnetic film. These thin FeCo films might be used directly in various devices operating in the gigahertz frequency range.

Based on requirements for spin-transfer torque (STT)-magnetic random access memory (MRAM), fundamental challenges in current CoFeB- and MgO-based STT-MRAM with perpendicular magnetic anisotropy (PMA) are addressed when scaling down to sub-20 nm. Electric-field (EF)-induced PMA modulation has been proposed to significantly reduce the switching current. As EF alone is unable to induce the magnetization reversal but PMA reduction, additional mechanisms should be applied to realize EF switching. We discuss difficulties in the implementation of currently reported two switching approaches and propose a new approach using Oersted field guided EF switching in MRAM arrays. Our latest experimental results on the EF effect show that the spin reorientation transition can be realized at an EF of 0.8 V/nm for the top-pin CoFeB/MgO magnetic tunnel junctions (MTJs) with the thermal stability factor of as high as 57 in the absence of EF. However, the bidirectional switching of the free layer cannot be achieved at a fixed biasing field, which is attributed to small STT effect and switching uncertainty due to unipolar feature of EF-induced PMA modulation. Perspective of EF-MRAM is analyzed based on currently published data on EF efficiency. We show that the EF switching is very promising for future MRAM applications in spite of challenges in materials and MTJ stack engineering.

We present a detailed study of spin-transfer torque induced noise in self-biased differential dual spin valves (DDSV) which could be potentially used as magnetic read-heads for hard-disk drives. Micromagnetics studies of DDSV were performed in all the major magnetic configurations experienced by read-heads and we show that in every case, self-biased DDSV provide a much stronger stability against spin-transfer torque noise than conventional spin valves. Provided are also insights on the influence of the dipolar interlayer coupling, shape anisotropy, exchange bias and relative orientation between the 2 free layers. Our results demonstrate the viability of DDSV read-heads for future hard disk drives generations.

Several materials (Ta, Cu, Al, Ru) are investigated for the gap layer (GL) in a differential dual spin valve (DDSV) as a function of GL thickness in terms of the differential effect and interlayer coupling. High field measurements in current in the plane geometry show that similar GMR effect can be obtained for two spin valves (SVs) with Ta, Ru, and Cu GLs, while for Al GL, GMR ratio of the upper SV decreases as Al thickness increases. For Ta GL, the two free layers (FLs) may switch either simultaneously or separately, depending on which FL switches first due to the weak ferromagnetic (FM) Neel coupling between the FLs. For Ru GL, the switching behavior depends on the thickness of Ru, due to the oscillation of interlayer exchange coupling. Cu GL causes additional GMR resulted from the FL/GL/FL structure. Detailed investigation on thickness dependence of Ru GL shows that FM interlayer coupling is achieved with Ru thickness of 1.6, 2.4, and 4 nm. The good differential effect can be obtained till Ru = 8 nm, above which MR of the upper SV decreases. Patterned DDSV sensors with Ru GL = 2.4 nm shows an overall FM coupling between the FLs, implying FM exchange coupling is larger than the antiferromagnetic magnetostatic coupling at edges.

Miniaturization is very important in magnetic recording. Here, we have micromagnetically evaluated the respective effects of the free layer (FL) thickness and width on the downtrack and crosstrack responses for single spin valves (SSVs) and differential dual spin valves (DDSVs). Our micromagnetic results show that the linear resolution scales down with the free layer thickness for DDSVs, as is the case for SSVs found by the reciprocity theory. We have also found that the crosstrack resolution scales down with free layer width in both SSVs and DDSVs (correspondingly, the side reading increases, which needs to be mitigated). The corresponding scalings of the signal amplitudes with FL thickness and width in SSVs and DDSVs are also discussed in terms of the shape anisotropy of the free layers. Finally, we have found that side shields can provide bias fields for the free layers and, meanwhile, the improvement in track density and the reduction in side reading are not compromised; this bias point of view of side shields is an additional appreciation of the usual roles played by side shields.

A finite element method (FEM) model, with refinements for the free layers, is proposed for GMR-type differential readers (GDRs). Our purpose is to explore the underlying reasons for the effects of the gap length and bit length on the GDR responses and for the origin of the undershoots in the GDR pulses. Our major findings are that the maximum field within the free layers of GDRs increases with decreasing gap length due to flux concentration; and that the GDR pulse and the associated undershoot effect obtained from the FEM model proposed are consistent with those obtained from our micromagnetic modeling. It has been revealed, for the first time, that the undershoot effect in differential readers are related to that the downtrack profile of the mean field near a transition is non-monotonic.

For future magnetic recording, one challenge is that the shield to shield spacing (SSS) of readers cannot be scaled down to achieve the linear density requirement. A differential dual spin valve (DDSV) has been proposed to improve the linear resolution as it does not rely on the magnetic shields to diminish the interference from adjacent bits. The side reading becomes more and more challenging as the track width shrinks to below SSS to accommodate high track density, in particular for a DDSV reader in which no magnetic shield or larger SSS is used. A self-biased DDSV structure is proposed to replace the conventional abutted junction stabilization scheme. In the self-biased DDSV readers, two side shields are put at the both sides of the sensor across the track direction in the replacement of the hard bias (HB). The stray fields from the two free layers in the DDSV sensor bias each other to stabilize the domain structure of the free layers. Preliminary analysis shows that the self-bias DDSV is also robust against the spin torque-induced magnetic instability. Simulation results indicate that the self-biased DDSV reader has much better reading sensitivity for the opposing fields generated by magnetic transitions than HB-stabilized sensor. It is found that for DDSV readers, the mag-noise is less significant due to a larger signal field and thicker free layer. Current perpendicular to the plane (CPP)-DDSV sensors have been fabricated and show very good differential effect in the real operating mode. The magnetoresistance performance of individual spin valve in CPP-DDSV sensors has been obtained through measurements with applied field and pinning field parallel to the easy axis of the free layer.

The effect of itinerant spin moment (m) dynamic in spin transfer switching has been ignored in most previous theoretical studies of the magnetization (M) dynamics. Thus in this paper, we proposed a more refined micromagnetic model of spin transfer switching that takes into account in a self-consistent manner of the coupled m and M dynamics. The numerical results obtained from this model further shed insight on the switching profiles of m and M, both of which show particular sensitivity to parameters such as the anisotropy field, the spin torque field, and the initial deviation between m and M.

Microstructure, static magnetic properties and microwave permeability of sputtered FeCo films were examined. Fe 60 Co 40 films (100 nm in thickness) deposited on glass substrates exhibited in-plane isotropy and a large coercivity of 161.1 Oe. When same thickness films were deposited on 2.5 nm Co underlayer, well-defined in-plane anisotropy was formed with an anisotropy field of 65 Oe. The sample had a static initial permeability of about 285, maximum imaginary permeability of 1255 and ferromagnetic resonance frequency of 2.71 GHz. Cross-sectional TEM image revealed that the Co underlayer had induced a columnar grain structure with grain diameter of 10 nm in the FeCo films. In comparison, FeCo films without Co underlayer showed larger grains of 70 nm in diameter with fewer distinct vertical grain boundaries. In addition, the Co underlayer changed the preferred orientation of the FeCo from (1 0 0) to (1 1 0). The improvement in soft magnetic properties and microwave behavior originates from the modification of the film microstructure, which can be well understood by the random anisotropy theory.

We explore the lattice and the electronic band structures matching between the half-metallic Heusler alloys (half-Heusler NiMnSb and full-Heusler Co 2 MnSi) and several hypothetical non-magnetic Heusler alloys by using first principle calculations. The lattice and band structure matching are almost perfectly satisfied between the two materials of similar crystal structures: (i) NiMnSb and XYSb and (ii) Co 2 MnSi and X 2 YSi, where X , Y =Ni or Cu. Owing to the high interface spin scattering asymmetry, these materials are promising to realize a high giant magnetoresistance at room temperature.

The readback resolution of conventional CPP spin valve reader is mainly determined by the shield to shield spacing and partially affected by the head media spacing change. As the linear density grows continuously, the bit length will be reduced to sub-10 nm or even sub-5 nm in the future. In such, the shield to shield spacing has to be below 20 nm or even 10 nm. It gradually becomes not feasible to squeeze all the functional layers used by current reader, such as: AFM layer, SAF, tunnel barrier, free layer, and capping layer, in such a small spacing. The differential dual spin valve (DDSV) read head is one of the new reader structures that can provide better readback resolution. This work studied the sensitivity function of DDSV reader without and with shields, then, identified the waveform characteristics of readback signal at different head media spacing (HMS) and gap layer (GL) thickness. The readback resolution of DDSV reader is mainly determined by the thickness of the gap layer between the two free layers. The two shields are still necessary for the DDSV reader in order to have the free layers picking up more localized media flux. The shield to shield spacing at 35 nm helps to constrain the free layers to pick up media flux mainly from ±5 nm region.

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.

Commercial electron-beam resists are modified into semimetallic resists by doping with 1–3 nm metal nanoparticles, which improve the resolution, contrast, strength, dry-etching resistance, and other properties of the resist. With the modified resists, fine resist nanopatterns from electron-beam lithography are readily converted into 5–50 nm, high-quality multilayers for metallic nanosensors or nanopatterns via ion-beam etching. This method solves the problem of the fabrication of fine (

A multilayer structure magnetic force microscopy (MFM) tip coated with antiferromagnet/ferromagnet/Ru/ferromagnet/Ru/ferromagnet/antiferromagnet on one side of the tip has been fabricated and evaluated. The ferromagnet used was CoFe. The central CoFe layer is antiferromagnetically (AFM) coupled with the two-side CoFe layers via ultra-thin Ru layers through optimizing the Ru layer thickness. The strong antiferromagnetic coupling between the CoFe layers leads to a more stable magnetization configuration and confined tip stray field as compared to that of conventional single-layer coated tips. The former improves the signal-to-noise ratio of the detected signals and the latter leads to an improvement of spatial resolution. The performance of this kind of tip has been evaluated by imaging magnetic patterns and comparing them with the images taken by both ferromagnetically coupled multilayer tips and commercial tips. Micromagnetic modeling has been performed to gain an understanding of the experimental results.

Using the semiclassical Boltzmann theory, we have investigated the influences of pure interface, nonpure interface, bulk, and interface plus bulk scattering on the giant magnetoresistance (GMR) dependence on layer thickness of the bottom spin valve (BSV), synthetic antiferromagnetic (SAF) spin valve, and dual spin valve (DSV). Our work shows consistency with experiment and theory and may provide some useful guidelines for electrical and structural optimizations of spin valves

The domain structures in NiFe elements were studied by magnetic force microscopy measurement and micromagnetic modeling. The remanent states in the elements were dependent on the direction of the saturation field. The “S” and “U” states were observed at remanence by applying the saturation field at different directions. The “S” and “U” states are metastable: magnetic force microscopy tip field-induced switching from the “S” and “U” states to the flux closure configuration was observed.

The nano-oxide layer (NOL) inside the spin valve can smooth the surface topography, which results in two effects: suppressing the ferromagnetic Neel magnetostatic coupling and enhancing the RKKY exchange coupling between the free layer and the pinned layer. As a consequence, MR ratio is increased in the spin valve with NOL layer inside the pinned layer or on top of the free layer. Because of the enhancement of the specular reflectivity in the NOL added spin valves, the oscillation of the interlayer coupling field with respect to the thickness of the spacer layer and even the thickness of the cap layer has been observed. In terms of the performance of both electrical and magnetic properties of the spin valves, CoFe–O turns out to be the best materials inside the pinned layer. But, as a cap layer, ZnO is the best choice because of its crystalline growth on top of the free layer CoFe, which causes the enhancement of the MR ratio. About 4.5% of MR ratio has been achieved in a NOL added spin valve in the current-perpendicular-to-plane configuration. Large MR ratio observed in the NOL added CPP sensor is due to the increment of the interface scattering and current confined path in the NOL added pinned layer.

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 uniax...

Electron beam lithography and ion beam etching have been used to pattern a wire-like array in FeMn/NiFe bilayers. The variation of hysteresis loops with the etching depth in FeMn layer has been presented, and it has been found that with increasing etching depth the coercivity increases and M – H loops show an asymmetric kink. Detailed studies of the magnetic behaviors of the asymmetric kink in the patterned sample with 3.5 nm thick FeMn layer have been performed, and a magnetization component perpendicular to the wire direction has been observed.

High tunneling magnetoresistance ratios (TMR) up to 44.6% were observed at room temperature on magnetic tunnel junctions (MTJs) with Ta20/Ni 81 Fe 19 20/Co 90 Fe 10 2/Al(1 nm)-oxide/Co 90 Fe 10 2/Ni 81 Fe 19 7/Fe 50 Mn 50 20/Ta5 (the thickness of other layers is in nm) structures fabricated by using an inductively coupled plasma sputtering system operating at a base pressure of 5×10 −10 Torr. High field sensitivity up to 6.1%/Oe has been achieved in these MTJs with dimensions of 120 μm×120 μm by using extremely soft ferromagnetic (FM) Ni 81 Fe 19 /Co 90 Fe 10 electrode. Small ferromagnetic coupling field (11 Oe) between the top and bottom FM electrodes, high breakdown electrical field (1.2×10 7 V/cm), and high V h (340–414 mV) at which the TMR decreases to 50% of its initial value, were obtained as the surface roughness of the bottom FM electrode ( R ms A ) and Al-oxide ( R ms A ) layer have been improved.

Characteristics of silicon nitride (SiNx:H) films, grown by plasma enhanced chemical vapor deposition (PECVD) on various metals such as Ta, IrMn, NiFe, Cu, and CoFe at various temperatures down to 100 °C, were studied using measurements of BHF etch rate, surface roughness and Auger electron spectroscopy (AES). The results were compared with those obtained for SiNx:H films on Si. The deposition rate of SiNx:H films increased slightly as deposition temperature decreased, and showed a weak dependence on the underlying materials. The surface of the nitride films deposited on all underlying materials at lower temperatures (below 150 °C) became rougher. In particular, a bubble-like surface was observed on the nitride film deposited on NiFe at 100 °C. At higher deposition temperatures (above 200 °C), SiNx:H films on all the above metals had small RMS values, except for films on Cu which cracked at 250 °C. BHF (10:1) etch rate increased dramatically for nitride films deposited below 150 °C. For different underlying films, the BHF etch rate was quite different, but exhibited the same trend with decrease in deposition temperature. AES measurements showed that Si and N concentrations in the SiNx:H films were only slightly different for the various deposition temperatures and underlying materials. AES depth profile of nitride films indicated that both surface O content and the depth of oxygen penetrating into SiNx:H increased for low temperature-deposited films. However, there was no observed oxygen signal from within the films, even for films deposited at 100 °C, and both Si and N concentrations were uniform throughout the film.

Plasma-enhanced chemical-vapor deposition (PECVD) was employed to grow silicon nitride at various temperatures to find its application in magnetic random access memory. Diffusion and oxidation of PECVD nitride (SiNx:H) and underlying metals (Ta and Cu) have been studied through Auger electron spectroscopy measurements. Oxygen content on the SiNx:H surface and characteristic sputtering time (t0), after which the oxygen signal falls below the measuring errors of the system, were used to characterize the oxidation of SiNx:H films. It is found that both oxygen content and t0 increase significantly for decreasing deposition temperature. The oxygen content is larger for SiNx:H films with lower Si/N ratios. Cu oxidation was investigated through changing sample loading methods. Strong oxidation was observed for samples loaded at higher temperatures, while almost no oxidation was detected for samples loaded at room temperature and heated to the deposition temperature after pumping the chamber to high vacuum. Stron...

We report a methodology to fabricate ultrasoft NiFe films via electrodeposition in a sulfate solution. With a little addition of Cu 2+ into the solution, NiFe films become extremely soft: typically, the film coercivities in the hard and easy axes are 0.03 and 0.15 Oe, respectively. The maximum relative permeability is also significantly increased to the order of 1times104. Meanwhile, these achieved ultrasoft NiFe films show a small but finite anisotropic field and high magnetic moments ranging from 1.1 to 1.65 T. These kinds of films can be potentially applied in current and future magnetic recording systems as well as biotechnological and microelectronic devices

AlTiC etching in CF/sub 4/ and H/sub 2/ high-density plasma is investigated. Its etching rate is relatively high and it is not corrosive to the giant magnetoresistive elements. The effects of etching parameters such as pressure, gas flow rate, radio-frequency power, and inductively coupled plasma power on the etching rate, selectivity and surface roughness are studied. The etching parameters are optimized to balance the etching rates of Al/sub 2/O/sub 3/ and TiC in order to obtain a smooth etched surface. The etching wall profile and a fabricated 6-nm flying height femto slider are also presented.

The magnetoresistance (MR) properties of a basic Ta/NiFe/IrMn/CoFe/Ru/CoFe/Cu/CoFe/Cu/Ta synthetic spin valve (SV) system have been systematically studied by using O2-soaked layers in five different positions. It is found that about 10% of MR ratio enhancement can be achieved without sacrificing other merits of SVs when the O2-soaking dose is controlled in the vicinity of 10−3 Pa s. It is probably due to improvement of the spin-dependent scattering (increasing the spin-dependent transmission coefficient and reducing the diffusion scattering coefficient) after O2 soaking either within the pinned layers or within the spacer layer.

Exchange bias (Hex) between NiFe and IrMn across a spacer layer such as Ru, Cr, Cu, and Ta has been studied. Hex is almost destroyed when a 0.2-nm-thick Ta layer is inserted between NiFe and IrMn. Abnormal temperature (T) dependence of Hex (there is two magnetization hysteresis loops with different blocking temperatures; the T dependence is neither linear nor nature of Fermi-Dirac statistics, it is an exponential decay function) has been observed in the NiFe/Ta/IrMn system. The abnormal hysteresis loops are associated with two antiferromagnetic (AFM) phases formed due to interface diffusion after magnetic annealing. The exponential decay Hex with temperature is due to complicated coupling mechanisms involved in the system. It is suggested that the strength of the exchange bias should be the nature of long-range interaction while the blocking temperature of the system should be mainly determined by the structure of the FM/AFM interface.

The arrays of NiFe and CoNiFe nanowires were grown in anodic alumina (alumite) and track etched polycarbonate (PCTE) membranes with various pore sizes by pulsed electrodeposition. Magnetic properties of the array were studied as functions of wire material, length, and diameter as well as field orientation. In PCTE membranes, as high as 0.92 of remanent squareness (S) was obtained for the array with wire diameter of 30 nm. However, for the array of nanowires in anodic membranes, anisotropy with field applied in and out of plane is very low, and the obtained S is less than 10%. For nanowires in alumite with the same wire length, CoNiFe shows a higher anisotropic field (H/sub k/) than NiFe, leading to larger coercivity (H/sub c/) and S and a lower saturation field. Wire-length dependence was measured for alumite membranes. As wire length increases, H/sub k/, H/sub c/, and S decrease, but the saturation field increases. This magnetic behavior can be qualitatively explained by considering dipolar interactions among nanowires and shape anisotropy of an individual nanowire, but it remains difficult to give a quantitative explanation.

Stress-reducing technologies over the slider backside are studied for curvature adjustment. These technologies include lapping on a copper table with different size diamond, lapping on a tin table charged with diamond and etching using an inductive coupling plasma system. Results show that reactive ion etching gives the largest range for crown and camber adjustment. Curvature adjustment by lapping on a tin table is controllable as it changes in small increments, but such control is unachievable with different diamond sizes.

Antiferromagnetically coupled hard/Ru/soft triple layers have been fabricated using ultrahigh vacuum sputtering. A series of experiments has been carried out to study the dependence of the exchange-coupling field on the thickness of the soft layer which is either CoFe or NiFe, while the hard layer is CoCrPt. It was found that this type of synthetic structure exhibits a significantly higher exchange coupling field as compared to the conventional antiferromagnet/ferromagnet exchange coupled structures. The use of these synthetic structures as the pinned and pinning layers has resulted in spin valves with a magnetoresistance ratio in the range of 5%–7% and a thermal stability that is better than those of IrMn-based and comparable to those of PtMn-based spin valves.

The interlayer coupling field (Hint) between the free and pinned ferromagnetic (FM) layers in an exchange-biased spin valve deposited by magnetron sputtering is usually dominated by the Neel “orange peel” coupling. The orange peel coupling is suppressed dramatically when an oxide layer (OXL) is inserted into the free/pinned FM layers due to smoother surface roughness at the interface. Hint decreases with increasing oxygen exposure dose of the free/pinned FM layers to pure O2 gas. And it is found that Ruderman–Kittel–Kasuya–Yoshida exchange coupling dominates in OXL spin valves due to smoother surface roughness and enhanced specular electron scattering at the interface between OXL and pinned/free FM layers, which also results in enhancement of magnetoresistance effect.

The thermal stability of spin valves was studied through measuring the magnetoresistance response curves at different temperatures with the applied field set at different angles from the pinning field direction. According to a simple coherent rotation model, the magnetoresistance versus applied field curves should be symmetrical with respect to the zero field line when the applied field is perpendicular to the pinning field. The deviation from symmetry should be attributed to the canting of the pinning field direction. The deviation from symmetry should be attributed to the canting of the pinning field direction. Experiments have been carried out on spin valves with a structure of Si/SiO2/Ta(2 nm)/Ni80Fe20(2.5 nm)/CoFe(1 nm)/Cu(2 nm)/CoFe(2 nm)/IrMn(5 nm)/Ta(2 nm). The canting of the pinning field was seen clearly from the change of the magnetoresistance curves while the temperature was varied from 50 to 100 °C. A quantity (the relative change in the asymmetry of the response curve) was newly defined to e...

Heulser alloys Fe2Cr1−xCoxSi (FCCS) with different Co compositions x have been predicted to have high spin polarization. High perpendicular magnetic anisotropy (PMA) has been observed in ultra-thin FCCS films with magnetic anisotropy energy density up to 2.3 × 106 erg/cm3. The perpendicular magnetic tunnel junctions (p-MTJs) using FCCS films with different Co compositions x as the bottom electrode have been fabricated and the post-annealing effects have been investigated in details. An attractive tunneling magnetoresistance ratio as high as 51.3% is achieved for p-MTJs using Fe2CrSi (FCS) as the bottom electrode. The thermal stability Δ can be as high as 70 for 40 nm dimension devices using FCS, which is high enough to endure a retention time of over 10 years. Therefore, Heusler alloy FCS is a promising PMA candidate for p-MTJ application.

Magnetic and structural properties of Co/Pt multilayers with varying Co (tCo) and Pt (tPt) thickness grown on various seed layers have been examined. It is challenging to grow Co/Pt multilayers as a top electrode with high perpendicular magnetic anisotropy (PMA) for magnetic tunnel junctions which usually comprise of CoFeB/MgO/CoFeB. We show that a thicker Pt layer of 1.2 nm is necessary to attain effective anisotropy (Keff) up to 0.14 MJ/m3. On the other hand, Co/Pt multilayers with high PMA have been achieved for proper textured seed layers of Ru and Pt. In the case of Ru seed layer, a higher Keff = 0.45 MJ/m3 can be achieved for tCo = 0.5 nm and tPt = 0.2 nm. This can be attributed to the lower lattice mismatch (∼4%) within the multilayers and hence a more coherent CoPt (111) structure. Finally, we note that the film roughness could play an important role in influencing the PMA of the multilayers. The highest Keff ∼ 0.6 MJ/m3 is achieved for Pt seed layer.

We report the studies of magnetic tunnel junctions (MTJs) using epitaxially grown Fe2CrSi (FCS) as a bottom electrode. A tunnel magnetoresistance (TMR) ratio of 2.5% was obtained for MTJ at room temperature. The low TMR ratio is attributed to the oxidation of FCS at the interface with MgO barrier. With the insertion of 0.3 nm Mg layer between the FCS and MgO barrier layers, the TMR ratio increases to 8.1%. X-ray Photoelectron Spectroscopy results show that the FCS film is most likely terminated at Fe and Si atomic layers, which is found to be bonded to oxygen at the interface, while Cr remains at metallic state. Post-annealing effect shows that TMR first increases with annealing temperature (Ta) due to improvement in crystalline structure of MgO and top electrode and then decreases due to oxidation of the bottom electrode. The TMR finally disappears due to the depinning of top electrode induced by Mn diffusion at high Ta.