-
[show abstract]
[hide abstract]
ABSTRACT: Recently, a differential dual spin valve (DDSV) has been proposed to enhance the downtrack
resolution for the application in the hard disk drive recording at 10 Tb/in2 and beyond. The following key issues for the implementation of a high-quality DDSV have been addressed. I. Formation of the antiparallel arrangement of the reference magnetization of two spin valves (SVs) with high pinning stability. II. Differential effect of a DDSV. To achieve perfect differential effect in a DDSV, not only should two SVs have the same giant magnetoresistance effect, but their free-layer (FL) magnetization should also respond to a field identically. Using 2.4 nm ruthenium as the gap layer to form a ferromagnetic interlayer coupling between FLs, a good differential effect is achieved. III. Quasistatic characterization of a DDSV. As there is no output from a DDSV under a uniform field, it would be difficult to evaluate performances of a DDSV. By varying the annealing field direction, field response of each SV as well as differential effect can be identified.
Journal of Applied Physics 03/2011; 109(7):07B707-07B707-3. · 2.17 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Field dependence of low frequency noise in tunnel magnetoresistance (TMR) heads with different barrier materials of TiO <sub>2</sub> , Al <sub>2</sub> O <sub>3</sub> , and MgO has been studied. It is found that for MgO-TMR heads, the noise amplitude increases as the sensor is driven from parallel to antiparallel magnetization configurations. However, this field dependence of the noise is not magnetic in origin and can be accounted for by the coherent tunneling mechanism in MgO-TMR heads. For TiO <sub>2</sub> - and Al <sub>2</sub> O <sub>3</sub> -TMR heads, low frequency noise is generally independent of magnetic field when the heads are biased properly by hard bias. A noise spike related to a resistance jump in the transfer curve is measured in a head without proper hard bias. Field-dependent low frequency noise is observed for TMR heads without hard bias. The noise amplitude follows the sensitivity function of the sensor and can be attributed to the thermally activated magnetization fluctuations. Spin transfer (ST) effect on low frequency noise was examined by noise measurements of field dependence at different current directions. Extra noise appears when the TMR head is in antiparallel magnetization configurations. The results suggest that the ST-induced extra noise can be either pure 1/f noise or the combination of both 1/f and random telegraph noises.
Journal of Applied Physics 06/2010; · 2.17 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Two series of Co <sub>2</sub> Mn Al (CMA) and Co <sub>2</sub> Mn Al O (CMAO) thin films deposited on Si (100) coated with thermo- Si O <sub>2</sub> by using two CoMnAl targets were studied. One target is oxygen-free and the other one contains 0.8% oxygen. The properties of the two series CMA (O) films strongly depend on deposition conditions and seed layers. The oxygen impurity is a key factor to influence the properties. It would obviously increase the thickness of magnetic dead layer, weaken the magnetic anisotropy, and significantly decrease the spin polarization in CMA film. The magnetoresistance ratios of IrMn pinned top-type magnetic tunnel junctions by utilizing CMAO/CMA as the bottom ferromagnetic electrode were 19% and 68%, respectively.
Journal of Applied Physics 05/2009; · 2.17 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Hard bias effect on thermally activated magnetic noise has been investigated through changing the biasing direction in three types of tunnel magnetoresistive (TMR) heads with different head structures and sensor widths. It is found that characteristic variation in the noise spectra is different for different TMR heads. The results can be explained through stiffness field difference in different TMR heads. No additional ferromagnetic resonance (FMR) was observed in accompanying with the hard bias weakness. The resonant frequency as a function of field at different bias angles can be qualitatively accounted for by relevant stiffness field variations.
IEEE Transactions on Magnetics 12/2008; · 1.36 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The peak value ( PSD <sub>p</sub>) from power spectral density (PSD) curves was obtained as a function of burning current before and after the breakdown in tunnel magnetoresistive (TMR) heads. The obtained PSD <sub>p</sub> versus current curves can be classified into two categories. For one set of TMR heads, an abnormal peak was observed just before the breakdown of TMR heads. For another set of TMR heads, PSD <sub>p</sub> shows a nearly linear current dependence as expected from the mag-noise theory. After the pinhole growth, the abnormal PSD <sub>p</sub> peak disappears, implying that it is related to the pinhole-free barrier. Spin transfer effect was examined to understand the abnormal increases in PSD <sub>p</sub> by both reversing current direction and reducing measuring current. The result shows that the spin transfer effect is not important for the presence of the abnormal increase in PSD <sub>p</sub> . In spite of the lack of a full understanding, we will give discussions on possible mechanisms.
Journal of Applied Physics 05/2008; · 2.17 Impact Factor
-
Y. K. Zheng,
G. C. Han,
K. B. Li,
J. J. Qiu,
Z. B. Guo,
P. Luo,
L. An,
S. G. Tan,
Z. Y. Liu,
L. Wang, B. Y. Zong,
B. Liu
[show abstract]
[hide abstract]
ABSTRACT: A read sensor working in the toggle mode is presented. The free layer comprises a balanced synthetic-antiferromagnetic (SAF) multilayer. The magnetization of the free SAF layer is perpendicular to the air-bearing surface (ABS) when bias field is applied in the direction of the ABS. The magnetization of the reference layer is fixed to be parallel to the ABS instead of perpendicular as is the conventional case. The sensitivity of the toggle read sensor (for small track width) improves significantly compared to the conventional abutted junction bias type. For a toggle sensor with long height structure, performance in both the sensitivity and linearity has also been improved because increased sensor height can be used for the lower bias field. The lower bias field is also compatible with the small gap structure of an in-stack bias scheme. Simulation results also show that the thermal magnetic noise in the toggle sensor is much smaller than that in the conventional biased sensor. Experimental results for both the current-in-plane (CIP) and tunneling-magneto-resistive (TMR) sensors with toggle mode are consistent with our calculation results
IEEE Transactions on Magnetics 03/2007; · 1.36 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Temperature dependence of thermally activated ferromagnetic resonance (FMR) has been studied for two kinds of tunneling magnetoresistive (TMR) heads with a track width of about 100 nm. It is found that the power spectral density (PSD) is composed of a FMR peak and a resonance kink at slightly lower frequency. For the TMR head with a well-defined magnetization state (single domain) of the free layer, the kink is much smaller than the peak in amplitude, and the FMR peak increases in its amplitude and shifts to lower frequency as temperature increases. However, for the TMR head with a hysteretic magnetization behavior, the FMR peak is blurred by the kink and no discernible shift of its position can be detected as temperature increases. It is observed that the noise power can be redistributed among different resonance modes at different temperatures and fields
IEEE Transactions on Magnetics 03/2007; · 1.36 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The magnetostriction coefficient (λ<sub>s</sub>) of ultrathin sputtered polycrystalline as-deposited and annealed Ta / Ni <sub>81</sub> Fe <sub>19</sub>(t)/ Ta films was studied as a function of the thickness. λ<sub>s</sub> and magnetoresistance (MR) of bottom-type spin valves (SVs) with nano-oxide layer (NOL) added in the pinned layer were investigated by using NiFe, Co <sub>90</sub> Fe <sub>10</sub> , and Co Fe / Ni Fe / Co Fe layers as free layer (FL), respectively. λ<sub>s</sub> of SV with NOL increased slightly except that of CoFe FL. NOLs were added at different positions to study the effects of NOL on λ<sub>s</sub> of CoFe FL. All λ<sub>s</sub> of CoFe FL change from negative to positive and its absolute value also increases significantly with Co Fe O <sub>x</sub> related NOL added below. Our λ<sub>s</sub> and surface roughness results indicated that the structure of the film not the roughness dominates λ<sub>s</sub> of ultrathin FL in SVs.
Journal of Applied Physics 06/2006; · 2.17 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Two sets of processes for sub-100-nm current-perpendicular-to-plane (CPP) spin-valves (SVs) were developed. In the first method, a CPP SV was fabricated by using via-hole instead of small cell patterning. This method makes it easy to characterize the CPP spin valve films. The shunting effect has been analyzed in this method. In the second method, a resist layer for planarization, ion-milling, and wet etching for self-opening via-hole in a self-aligned fashion by making use of the height difference between the cell and surrounding regions was introduced. This method is suitable for the actual recording heads with small dimension even without an ion-beam-deposition system. CPP sensors with size from 0.05 μm·0.05 μm to 0.4 μm· 0.5 μm with different free- layer structures have been investigated by means of the first method.
IEEE Transactions on Magnetics 08/2004; · 1.36 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Magnetization properties of magnetic nanowire arrays are studied on various ferromagnetic materials grown in anodic alumina (alumite) and track etched polycarbonate (PCTE) membranes by pulsed electrodeposition. Magnetization curves were measured as functions of wire material, field orientation, and wire length. The coercivity (Hc) and remanent squareness (S) of the various wire arrays were derived from hysteresis loops as a function of angle (θ) between the field and wire axis. For PCTE membranes, Hc(θ) curves for CoNiFe, NiFe, and Co nanowire arrays all show an otherwise-bell-type variation, while they change shapes from the otherwise bell to bell type for Ni nanowire arrays as the wire diameter decreases to 30 nm. These characteristics can be understood based on different magnetization reversal mechanisms of small wires. The effect of magnetostatic interaction among wires on the magnetic properties was examined by changing the wire lengths in alumite membranes. It is found that the interaction reduces Hc and S values significantly and may cause the overall easy axis change from parallel to perpendicular to the wire axis. However, the interaction is much weaker than expected from an independent precession theory. The strong coupling among the wire may also induce a change of magnetization reversal mechanism. © 2003 American Institute of Physics.
Journal of Applied Physics 05/2003; 93(11):9202-9207. · 2.17 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: 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</sub>) than NiFe, leading to larger coercivity (H<sub>c</sub>) and S and a lower saturation field. Wire-length dependence was measured for alumite membranes. As wire length increases, H<sub>k</sub>, H<sub>c</sub>, 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.
IEEE Transactions on Magnetics 10/2002; · 1.36 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: For the double exchange-biased IrMn/NiFe/FeMn structures, the pinning directions at IrMn/NiFe and NiFe/FeMn interfaces were set either parallel or antiparallel to each other by field annealing. Exchange bias and magnetotransport properties in IrMn/NiFe/FeMn trilayers were studied and compared with those of IrMn/NiFe and NiFe/FeMn bilayers. The dependence of exchange bias on the thickness of NiFe layer was different for parallel and antiparallel pinnings. A remarkable increase in resistance was observed which should be attributed to domain-wall resistance induced by the twisted spin structure. The spin configuration of twisted spin structure was simulated by one-dimensional atomic model.
Phys. Rev. B. 78(18).
