A structure of exchange biased FM1/AFM1/FM2/AFM2 multilayers is proposed and giant magnetoresistance effect is used as a probe of magnetization reversal. A spin valve structure of NiFe (2 nm)/CoFe (1 nm)/Cu (2.2 nm)/NiFe (12 nm/IrMn (3 nm)/NiFe (6 nm)/IrMn (12 nm) is fabricated to investigate the magnetization reversal in NiFe (12 nm)/IrMn (3 nm)/NiFe (6 nm)/IrMn (12 nm) multilayers. In the decreasing field process, magnetization reversal can well be understood by the reversal of magnetization due to decreasing magnetization and increasing resistance. In the Increasing field process, magnetization and resistance increase sharply at the field around -20 Oe. Hysteresis loop of the sample are also investigated.
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 /spl mu/m/spl middot/0.05 /spl mu/m to 0.4 /spl mu/m/spl middot/ 0.5 /spl mu/m with different free- layer structures have been investigated by means of the first method.
A magnetoresistance random access memory (MRAM) with a guided synthetic antiferromagnet (SAF) and direct writing scheme is presented to reduce the writing time. The MRAM cell includes not only the balanced SAF trilayers but also one more guiding layer, which is weakly exchange-coupled with one of the SAF layers. The two orthogonally oriented digital and word lines are aligned at 45deg with respect to the easy axis of the cell. With the exchange-coupling field from the guiding layer, the MRAM cell can be written directly by the combined field induced by current of the digital and word line. However, the cell cannot be switched by any single field induced by either current due to the balanced SAF structure before saturation. The switching field has been reduced and the writing operation margin has been improved with the use of the exchange-coupling field. Both simulation and the experiments have been carried out to verify this scheme. The write operation margin-H disturb /H sw of more than 4.3 has been achieved for the magnetic tunnel junction MRAM cell
A detailed work on the enhancement of the interlayer exchange coupling (IEC) in the nano-oxide added spin valves when metallic Al is used as the cap layer is presented. The interlayer coupling field and MR ratio as a function of the thickness of the Al was measured for two series of spin valves with the structures of Ta/NiFe/IrMn/CoFe/Ru/CoFe/CoFe/Cu/CoFe/Al/AlO and Ta/NiFe/IrMn/CoFe/Ru/CoFe/Cu/CoFe/Al/AlO. It is concluded that huge enhancement of the interlayer coupling observed in nano-oxide added spin valves is ascribed to the quantum size effect caused by the non-oxidized metallic Al layer between the free layer and AlO cap layer.
The stray field detection of the periodically magnetic dot array is performed using a commercial giant magnetoresistance read head which is attached to a static spin stand setup. The magnetization reversal process is compared to the measurement of magnetic force microscopy image and M-H curve measured by AGM.
Summary form only given. The storage density of MRAMs can be increased via either reducing the cell size or increasing the number of bits stored in one cell. A three-level and six-state multilevel MRAM has been proposed. However, it is difficult to write a cell independently in an MRAM array using this structure. Here we propose a multilevel MRAM that writes data at the Curie point and reads data using the angular-dependent magnetoresistance. The former has been proposed by Beech et al. (2000) for a spin-valve based single level MRAM. In our structure, a pinned ferromagnetic layer (CoFe/IrMn) is used as the recording layer in a MTJ device.
A track width reduction and an area resistance (RA) reduction scheme are presented to meet the requirement of the reader for ultrahigh density recording. The side reading effect worsens the performance of the track-width-gradient-reduction design even if a side-shield layer is applied due to the overlap between the backend and the side-shield. However, the side-reading effect can be significantly suppressed in the long-height design after the introduction of the side-shield. Using the long-height sensor design, the RA, the track width and the signal level may meet the requirement of reader for ultra-high density recording. The back flux-guide design can further improve the sensitivity of the tunneling magneto resistance (TMR) sensor
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