Haruyuki Morita

Low resistance and high thermal stability of spin-dependent tunnel junctions with synthetic antiferromagnetic CoFe/Ru/CoFe pinned layers

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.

ESD induced pinned layer reversal in spin-valve GMR heads

Magnetization direction of the pinned layer in the Spin-Valve giant magnetoresistive (SV) heads has been found to be reversed easily by electrostatic discharge (ESD). Thermal stress and magnetic field from ESD cause this phenomenon. This phenomenon happens only when the bias field direction by ESD current Is opposite to the magnetization of the pinned layer. The energy of magnetization reversal of the pinned layer from ESD is found to be a quarter of the ESD breakdown energy. For SV heads which consist of an AF film with higher blocking temperature, the energy becomes higher.

Electrical breakdown of the magnetic tunneling junction with an AlOx barrier formed by radical oxidation

In this work, the dielectric breakdown in magnetic tunnel junctions (MTJs) was studied. The MTJ structure is Ta50/NiFe100/Co20/AlOx/Co30/RuRhMn100/Ta50 with the bottom lead of Ta50/Cu500/Ta50 and the top lead of Cu2000/Ta50 (in A), where the tunneling barrier was formed by 2–20 min radical oxygen oxidation of a 10 A-thick Al layer. The junctions with area from 2×2 to 20×20 μm2 were patterned using the photolithography process, leading to tunneling magnetoresistance up to 17.2% and resistance-area product ranging from 350 Ω μm2 to 200 kΩ μm2. The junctions studied show dc breakdown voltage from 0.7 to 1.3 V, depending on the junction area and the oxidation time. Long oxidation time up to 14 min and a small junction area results in a large dc breakdown voltage. The electrostatic discharge (ESD) of MTJs was tested by using a human body model. The ESD breakdown voltage increases with decreasing junction resistance. These results are discussed in terms of the E-model based on the field-induced distortion of at...

Evaluation of front flux guide-type magnetic tunnel junction heads

Magnetic tunnel junction (MTJ) heads have been successfully fabricated using the free layer as flux guide to prevent electrical short during the definition of the air bearing surface (ABS). For a 6 Gbits/in/sup 2/ design, an output as high as 5740 /spl mu/Vpp was achieved for 3 mA sense current, and the output waveform was stable and noise free. Noise analysis confirmed that shot noise is prevailing in these MTJ heads, suggesting that the junction resistance has to be further reduced to challenge spin-valve heads in terms of signal to noise ratio. Landau-Lifshitz-Gilbert simulations showed that for 20 Gbits/in/sup 2/ application, the flux guide height should not exceed 0.1 /spl mu/m.

The distribution of blocking temperature in NiFe-Ru/sub x/Rh/sub y/Mn bilayers

We report the distribution profiles of blocking temperature (T/sub b/) in Ru/sub x/Rh/sub y/Mn-NiFe interfaces with comparisons of FeMn, NiMn, and PtMn. The distribution of T/sub b/ at the temperature around 120/spl sim/150/spl deg/C decreased with increasing Rh content. The FWHM of the distribution profile in Ru/sub 4/Rh/sub 14/Mn is one half of that in ordered phase NiMn and PtMn. The unblocked ratio at 125/spl deg/C decreases with increasing Rh content, and becomes a minimum in Ru/sub 4/Rh/sub 14/Mn, which is one half of FeMn.

New antiferromagnetic RuRhMn film and its application for spin-valves

We have successfully developed new RuRhMn antiferromagnetic (AF) films for spin-valves. The spin-valves with RuRhMn exhibit larger unidirectional anisotropy (Hua), higher blocking temperature (Tb), higher thermal stability and higher corrosion resistance than those with FeMn films. The MR ratio of 7.4% and Tb of 250/spl deg/C are obtained for glass/Ta(5)-NiFe(7)-Co(0.5)-Cu(3)-Co(2.5)-RuRhMn(10)-Ta(5), unit nm, spin-valve with Hua of 350 Oe. The rest potential of RuRhMn films is listed between one of NiFe and Co films and is much better than that of FeMn films.

Which spin valve for next giant magnetoresistance head generation? (invited)

To maintain a challenging 100%/year growth rate of the areal density, new spin valve (SV) structures have recently emerged. This work reviews the transport properties of hybrid free, synthetic, and specular SV at film level and discusses their potential for read head application. High sensitivity can be achieved using hybrid free and synthetic free SV due to their small net magnetic moment, but the longitudinal biasing of synthetic free SV is a critical issue. Good thermal stability was obtained in both synthetic pinned and specular SV due to high effective exchange field or good protection from interdiffusion. Moreover, specular SV also shows large output. With structure having different benefits, the next generation of SV head should be a combination to optimize all properties. Nevertheless, it raises many technological issues, related to the processing of very thin layers, which should be solved to meet the requirements of reproducibility and high yield from mass production.

A new approach to the synthesis of cobalt modified iron oxide

The new approach to the synthesis of cobalt modified iron oxide with an autoclave in a hydrogen atmospher is reported. The acicular particles of magnetite used for this technique are the following three kinds: (1) The magnetite made by usual preparation method. (2) The magnetite made from goethite whose surface was treated with SiO 2 . (3) The magnetite obtained by annealing of the magnetite in (2). The product has a black acicular crystalline structure. The analysis of magnetic measurements proved that the surface localization of cobalt compounds is very important in order to improve the magnetic stability.

Extra current channels in longitudinally biased magnetic tunnel junctions

Experiments on the longitudinal biasing of microsized magnetic tunnel junctions have been conducted using permanent magnets partially overlapping the junction area. The tunneling magnetoresistance ratio showed a strong dependency on the overlap length, since even a 10% overlap of the sensor length resulted in a 25% drop from its initial value without overlap. Analytical and micromagnetic analyses have demonstrated that this decrease comes from extra current channels, located in the regions below the permanent magnets, that shorted a large amount of the sense current from the central active region in the antiparallel magnetization state. The high uniaxial anisotropy field, induced by the permanent magnets in the overlapped regions, created particular magnetic configurations responsible for these low resistance paths. Several alternatives, using antiferromagnetic material in place of the permanent magnets or a modified design of the magnetic tunnel junction structure, are presented and discussed to prevent ...

Exchange coupling and GMR properties in ion beam sputtered hematite spin-valves

We have succeeded in fabricating hematite (/spl alpha/-Fe/sub 2/O/sub 3/) antiferromagnetic (AF) thin films by the ion beam sputtering method, which give unidirectional anisotropy to the adjacent ferromagnetic layer. Its exchange bias energy (J/sub ex/) is 0.03 erg/cm/sup 2/, and blocking temperature (T/sub b/) is 250/spl deg/C. Spin-valve films with the hematite AF layer were also fabricated. They exhibit GMR property with unidirectional anisotropy of the pinned layer. Spin- valve films of which magnetic layers consist of only NiFe exhibit relatively low MR ratio and poor thermal stability. However, the spin-valve using Co as the pinned layer and the free layer at the Cu interface exhibits MR ratio of more than 6% and excellent thermal stability.