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I-V curves of magnetic tunnel junctions are measured in a temperature range of 5-305 K. The study shows that the additional hopping conductance helps explain the observed temperature dependence and bias dependence of magnetic tunnel junction conductance.

Tunneling magnetoresistive (TMR) readers capable of 150 Gb/[in.sup.2] of areal density- magnetic recording for hard disk drive were demonstrated with bit-error-rate performance. The head design used is basically a bottom type stack of Ta/PtMn/CoFe/ Ru/CoFe/oxide barrier/CoFe/NiFe/Ta cap with abutted hard bias stabilization. The electrical reader width is about 4 [mu]' to reach a very high track density and shield-to-shield spacing is about 700 [Angstrom] for high linear density. On-track bit error floor is better than [10.sup.-5] at a linear density of 900 KBPI and the recording system noise is dominated by the media, The best areal density achieved (using -4 OTC reference level) is 143 Gb/[in.sup.2] using symmetric squeeze and 152 Gb/[in.sup.2] using asymmetric squeeze method, respectively. It was found that the TMR head has several decibels more signal-to-noise ratio gain over spin valve readers at 150 Gb/[in.sup.2] and beyond. The TMR head is also suitable for perpendicular recording application. Index Terms--Areal density, current-perpendicular-to-plane (CPP) geometry, perpendicular recording, signal-to-noise ratio (SNR), tunneling magnetoresistive (TMR) heads.

Spin tunneling recording heads above 20 Gb/[in.sup.2] have been fabricated using a bottom tunneling junction stack. The spin tunneling stack is made of Ta/PtMn/CoFe/Ru/CoFe/AlO/NiFe/Ta and stabilized by a permanent magnet abutted junction. The effective junction width is about 0.4 [micro]m wide and lapped to the junction with an optimum stripe height. The barrier has resistance area product of 15-20 [OMEGA][micro][m.sup.2], leading to a typical head resistance of around 50 [OMEGA]. Isolated pulses during the spin-stand test shows large signal up to 10 mV. On track error rate floor is better than [10.sup.-9] and the head signal-to-noise ratio is also better than that of a conventional spin valve GMR head. The areal density estimated (using BER of [10.sup.-5]) is above 20 Gb/[in.sup.2]. Index Terms--Areal density, micromagnetic modeling, spin-stand test, spin tunneling heads, TGMR.

The prediction of half metallicity in epitaxial NiMnSb has been tested using direct measurement of the conduction electron spin polarization.

The two dimensional current crowding effect in magnetic tunnel junctions is examined with the help of an analytical method. The junction resistance increases faster than the lead resistance when the junction radius becomes smaller.

The shape of the dynamic conductance versus voltage of NiFe/AlO(sub x)/NiFe tunnel junctions is correlated with the intensity and duration of oxidation. Annealing of the junctions makes the tunnel barrier effectively thinner and taller, as implified by a fit to the parabolic conductance.

Two breakdown mechanisms are observed in magnetic tunnel junctions having an ultrathin alumina barrier. The two breakdown mechanisms manifest themselves differently when considering large ensembles of nominally identical devices under different stress conditions. The results suggest that one type of breakdown occurs because of the intrinsic breakdown of a well-formed oxide barrier that can be described by the E model of dielectric breakdown. The other is an extrinsic breakdown related to defects in the barrier rather than the failure of the oxide integrity. The characteristic of extrinsic breakdown suggests that a pre-existing pinhole in the barriers grows in area by means of dissipative (Joule) heating and/or an electric field across the pinhole circumference. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The tunneling criteria are evaluated using magnetic tunnel junctions having ultrathin alumina barrier with and without pinholes. It is shown that the tunneling criteria formulated by Rowell [J. Appl. Phys. 41, 1915 (1970)] clearly do not rule out the presence of pinholes in an ultrathin insulating barrier. In particular, the third criterion, a downward temperature dependence of resistance, cannot be used to decisively rule out the presence of pinholes. Examination of the breakdown mechanism will reveal the true nature of the barrier quality, and thus should be applied alongside the tunneling criteria to identify tunneling and the presence of pinholes. [ABSTRACT FROM AUTHOR]

Research is done on the exchange coupling between half-metallic Fe3O4 and antiferromagnetic CrMnPt films, which was examined, with the goal of inducing unidirectional anisotropy in the Fe3O4 film having hard magnetic properties. In conclusion, the strong unidirectional anisotropy constant is thought to have been caused by large stress relief in the NiO film resulting from the thermal annealing that acted to increase the c/a ratio in the CrMnPt film, inducing so-called stress-induced anisotropy in the CrMnPt film.

We demonstrate the feasibility of a read head using a high-resistance spin-dependent tunneling (SDT) junction. The head consists of a 1.5 [micro]m or 1.7 [micro]m wide flux guide on top of the junction. The junction is about 0.8 [micro]m wide and varies in height. There is a pinned layer at the bottom of the stack. The tunnel barrier is made by plasma oxidation of about 10 [Angstrom] of aluminum. The barrier has resistance of about 3.7 k[Omega] [micro][m.sup.2], leading to a typical head resistance of a few k[Omega]. The heads are lapped to the edge of the junction, and show 5% to 8% TMR during transfer curve measurement. Isolated pulses during the spin stand test shows large signal up to 5.7 mV. We find a voltage sensing preamp is a better choice over a current sensing one. Index Terms--(GMR) heads, magnetic spin tunneling, heads test and characterization.

Copyright of Scientific Papers of Silesian University of Technology. Organization & Management / Zeszyty Naukowe Politechniki Slaskiej. Seria Organizacji i Zarzadzanie is the property of Silesian Technical University, Organisation & Management Faculty and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Scientific Papers of Silesian University of Technology. Organization & Management / Zeszyty Naukowe Politechniki Slaskiej. Seria Organizacji i Zarzadzanie is the property of Silesian Technical University, Organisation & Management Faculty and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

An analytical method was developed to compute the current crowding effect in two dimensions when the lead width and length are much larger than the tunnel junction radius. In a typical four-terminal geometry, current crowding gives rise to an extra lead resistance which can result in a larger measured resistance and lower tunneling magnetoresistance ratio than the intrinsic values of the magnetic tunnel junction. This extra lead resistance is approximately R[sub lead,4-terminal] ∼ 0.1 × (R[sub sheet, Top] + R[sub sheet, Bottom]) × ln(lead-width/junction-radius), where R[sub sheet, Top/Bottom] is the sheet resistance of the top/bottom lead. [ABSTRACT FROM AUTHOR]

From wafers where the AlO[sub x] barrier varies from junction to junction, we determine the proper oxidation conditions for spin-dependent tunnel junctions. We obtain large variation in the resistance×area product (R×A) of the junctions within a wafer by either using nonuniform plasma oxidation on uniform Al films, or using uniform oxidation on Al films with a wedge thickness profile. When plotted against R×A, the tunneling magneto-resistance (TMR) for all junctions on the wafer falls on one curve that exhibits a broad maximum in the TMR. We propose that this maximum is where most metal Al has been oxidized while the oxidation of the bottom electrode is minimal. With annealing, we achieved our highest TMR, 38%, in highly resistive Co–AlO[sub x]–Co junctions. The most conductive junctions we made have about 18% TMR and R×A of 140 Ω μm2. They are made by natural oxidation on about 5 Å of Al. For barriers thinner than 13 Å Al, we start to lose TMR for junctions larger than 2 μm2. This is possibly caused by pinholes in thin barrier and indicates the importance of studying small size junctions. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Micromagnetic structures in submicron size circular permalloy elements of various thickness (5–50 nm) have been experimentally studied using a magnetic force microscope (MFM). One and two vortex micromagnetic states were observed in the elements. It was found that one vortex state is more favorable under external field of low values, while two vortex state forms under high fields. Switching between one and two vortex states results in a hysteresis in the micromagnetic response of the elements. The transition field from one to two vortex state increases with the increase of element thickness and, therefore, with the increase of the demagnetizing effect of the element edges. The two vortex state was not observed in the elements with a thickness of 50 nm or greater. The micromagnetic behavior correlates with hysteresis loops of a free layer in a magnetic tunnel junction of size, shape, and free layer thickness similar to elements examined with the MFM. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]