The structural and electronic properties of the Ca 1−x Na x V 2 O 5 system, where the composition CaV 2 O 5 exhibits an isolated dimer-like spin-gap state, and NaV 2 O 5 indicates a linearchain magnetic behaviour and undergoes a spin-singlet transition at T c = 34 K, have been explored by means of x-ray four-circle diffraction and through magnetization and electron paramagnetic resonance measurements. The crystal structures with 0 < x 0.1 and 0.8 x 1 are isomorphous with that of CaV 2 O 5 , where the space group is P mmn. The effective V valence is correlated with the V-O bond length in the VO 5 pyramid, and the transfer integral for the nextnearest-neighbour V-V path is suggested to be larger than those for other paths, which may be consistent with the formation mechanisms of the dimer in the Ca-rich compounds and the V-O-V molecular orbital in the Na-rich compounds. The magnetic properties for 0 < x 0.1 are interpreted as being governed by contributions from the dimer which is formed between the V zigzag chains and from the isolated spins that are present due to the breaking of the dimer. On the other hand, the properties for 0.9 x < 1 still exhibit linear-chain behaviours, and for x 0.97 the singlet transition with a large reduction of the exchange coupling constant disappears, and no magnetic ordering takes place. The characteristic spin dynamics for the Na-rich compounds is also discussed.

In this work, submicron-size (down to 0.273 μm2) spin–dependent tunnel junctions with resistance as low as ∼30 Ω μm2 have been fabricated, where the tunneling barrier of AlOx was formed by in situ natural oxidation. These junctions annealed at 250 °C for 5 h showed tunneling magnetoresistance (TMR) of 14.3% and 25.8% for the pinned layers of CoFe/RuRhMn and CoFe/PtMn, respectively, while the TMR is further increased to 31.6% for a synthetic antiferromagnetic pinned layer of CoFe/Ru/CoFe/PtMn due to less interdiffusion at CoFe/Ru interface. The investigation has indicated that the growth of ultrathin Al layer is very sensitive to the surface roughness of bottom ferromagnetic electrode, and large surface roughness leads to small junction resistance.

In this work, a technique, gas cluster ion beam (GCIB), was introduced to smooth the bottom NiFe magnetic shield for magnetic tunnel junction (MTJ) read heads. The GCIB treatment can bring the surface roughness of the shield from 15 to 20 Å to around 5 Å, and the most of scratch marks can be removed. The efficiency of the GCIB process is dependent on the initial surface morphology. The MTJs grown on the magnetic shield smoothed by the GCIB show that the resistance area product RA is increased from 60 to ∼100 Ω μm2 with the GCIB dose up to 1×1016 ions/cm2, arising from a smooth insulating layer, meanwhile, the tunneling magnetoresistance (TMR) is almost constant or slightly decreases. This GCIB process can also improve breakdown voltage (approximately 0.019 V per 1015 ions/cm2) of the MTJs, and slightly increase the ferromagnetic coupling mainly due to the change of the surface morphology. Using this technology, an RA as low as 3.5–6.5 Ω μm2 together with a TMR of 14%–18% can be obtained for MTJs grown on the GCIB treated NiFe magnetic shield.

Tunnel giant magnetoresistance (TMR) heads at 50 Gb/in 2 have been fabricated using improved lapping process. Together with writer of 2.0 T pole materials, recording performance has been demonstrated at magnetic write width of 0.28 m and magnetic read width of 0.18 m. The resistance area product of final wafer data is around 5 m 2 , with lead and contact resistance included, resulting in a final head resistance of around 200 . The output voltage achieved for 1 mA bias current is 42 mV/ m, and the isolated pulses are stable.With a discrete preamplifier, the track density as measured by "747 curve" is 94 kTPI at a bit-error rate of 10 4 and the linear density is 508 kBPI, achieving an areal density of 48 Gb/in 2 . The noise analysis reveals that the noises come mainly from media and shot noise.

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