Chunhong Hou

Enhancement of exchange field and reduction of GMR in PtMn-based spin valves by ion irradiation

C-ion irradiation was performed on PtMn-based spin valves and the effects of ion irradiation on magnetoresistance(MR) and on the exchange field were investigated. When ion irradiation was performed prior to post-annealing, the exchange field was substantially enhanced after annealing, especially for an annealing temperature below 240 ° C . The enhancement could be related to the formation of PtMn(C) phase, which might accelerate the formation of ordered PtMn phase and might increase the anisotropy of PtMn. Although the majority of C ions located in capping layers Ta and PtMn, small amounts of C ions may go into the interface of CoFe/Cu/CoFe, leading to a small MR.

Dispersion of the pinning field direction of a ferromagnet/antiferromagnet coupled system

The exchange bias field of a ferromagnet/antiferromagnet bilayer is usually measured by the unidirectional shift of the hysteresis loop of the ferromagnetic layer. The exchange bias field results from interfacial exchange coupling between the spins in the ferromagnetic and antiferromagnetic layers. In general, the spins of the antiferromagnetic layer can vary locally in their anisotropy directions resulting in a distribution in local pinning directions. This letter reports a quantitative study on this distribution or dispersion using the anisotropic magnetoresistive (AMR) effect in a small rotating magnetic field. The AMR data as a function of the rotating angle of the field measured at a low field reveal the dispersion inside the ferromagnetic layer and at the interface of a ferromagnet/antiferromagnet system. The interaction between the domains within the ferromagnetic layer also plays a significant role in the dispersion inside the ferromagnetic layer.

Field dependent anisotropic magnetoresistance measurements on CoFe/IrMn bilayers

The exchange anisotropy field, along with the qualitative distribution of the local pinning field at the ferromagnetic/antiferromagnetic interface, has been studied in polycrystalline CoFe/IrMn bilayers. The exchange anisotropy was studied using both the anisotropic magnetoresistance (AMR) technique and hysteresis loop measurements. The AMR technique determines a larger value for the exchange anisotropy than the hysteresis loop technique. It is observed that Hea extracted via the AMR technique for the majority of samples shows a quantifiable dependence on the applied measurement field, even at fields much less than the exchange bias measured by hysteresis loop. It is believed that a reversible measurement of the soft dispersive moments takes place at these low fields, and that the field dependence is indicative of a distribution of the local magnetization direction.

Rotational hysteresis of torque curves in polycrystalline ferro/antiferromagnetic systems

Rotational hysteresis of ferromagnetic (F)/antiferromagnetic (AF) exchange coupled systems was studied by using NiFe/IrMn, NiFe/FeMn, and NiFe/NiMn samples sputter deposited under almost the same conditions, although the sample of NiFe/NiMn was annealed later to obtain the antiferromagnetic phase for the NiMn layer. The rotational hysteresis of each sample exhibited quite a different feature from each other, especially in the rotational hysteresis–magnetization angle curves. The NiFe/IrMn bilayer showed a dip at around the antiparallel direction to the applied field direction during sample preparation (pinning direction), while the NiFe/NiMn bilayer exhibited a large peak in that direction. The NiFe/FeMn bilayer did not show any noticeable structure in the rotational hysteresis–magnetization curve. Based on the analysis of those data done by using the model recently proposed by the authors, the following was inferred: (1) The distribution of the anisotropy easy axes of IrMn of the NiFe/IrMn bilayer grains...

Exchange bias measurements of CoFe/IrMn

The exchange bias anisotropy field in CoFe/IrMn ferromagnetic/antiferromagnetic bilayers has been investigated by two different experimental probes. One was the traditional hysteresis loop shift technique and the other was a recently developed technique which monitors small reversible rotations of the magnetization with the anisotropic magnetoresistance (AMR). All the samples show approximately twice the exchange bias anisotropy field measured with the AMR technique compared to that measured with the traditional hysteresis loop method. Based on similar experiments in other materials, there is a portion of the exchange bias uniaxial anisotropy which rotates in a hysteresis loop measurement. It is surmised it is this energy which the hysteresis loop technique neglects and that the AMR technique is a better measure of the exchange bias anisotropy energy.

Vertical GMR recording heads for 100 Gb/in/sup 2/

Vertical giant magnetoresistive (GMR) recording head designs have been proposed to achieve the optimum bias point and magnetic stability. Using a micromagnetic model, several design options were simulated and a test feature was built to validate the model prediction. The vertical GMR head uses a front lead to connect the GMR element to shield at the air-bearing surface (ABS) and the sense current passes vertically from ABS to the back lead through the active elements. Canted stabilization fields are needed for proper bias for vertical GMR (VGMR) heads. A design proposal for 100 Gb/in/sup 2/ is presented.

Vertical GMR recording heads

A vertical head was proposed for various groups for AMR, spin valve and GMR.Vertical GMR readers for areal density from 50 to 100Gbits/in/sup 2/. The head has a vertical layout with two layers moving against the bit.