We have found that the addition of Cu to an FePt alloy film is an effective approach for reducing the ordering temperature of FePt. The coercivity of the FePtCu film is around 5 kOe after annealing at 300 °C, whereas that of FePt shows several hundred Oe. In the FePtCu film annealed at 700 °C, the coercivity is almost the same as for the FePt films. Therefore, the FePtCu film displays a hard-magnetic property similar to that of the FePt film. The results of x-ray diffraction indicate that a ternary FePtCu alloy is formed. Thus, the formation of the ternary FePtCu alloy is considered to play an important role in reducing the ordering temperature.

Spin transfer (ST) switching in the TbCoFe∕CoFeB∕MgO∕CoFeB∕TbCoFe magnetic tunnel junction (MTJ) was studied. The TbCoFe∕CoFeB free layer with a large coercive field of 1.2kOe and a large thermal stability factor of 107 at room temperature was switched by a 100ns pulse current with a current density of 4.7MA∕cm2. This is the first report of ST switching in a MTJ with perpendicular magnetic anisotropy. The temperature dependence of the coercive field was also investigated to estimate the magnetic anisotropy in the case of rising temperature due to the Joule heating effect. The measured coercive field at 87°C, which was the simulated temperature during the switching pulse current, was about 0.34kOe. The ratio of the switching current density to the coercive field under the switching current in the MTJ with the TbCoFe∕CoFeB free layer is smaller than that in a typical MTJ with an in-plane magnetized CoFeB free layer. This result indicates that a MTJ with perpendicular magnetic anisotropy is advantageous for realizing low switching current magnetoresistive random access memory.

We investigate extremely low programming current and fast switching time of a perpendicular tunnel-magnetoresistance (P-TMR) for spin-transfer torque using a P-TMR cell of 50nm-diameter. A L1 0 -crystalline ordered alloy is used as a free layer that has excellent thermal stability and a damping constant of about 0.03. The programming current of 49 uA and the switching time of 4 nsec are also demonstrated. IntroductionRecently, magnetoresistive random access memory (MRAM) based on spin-transfer torque (STT) switching has been intensively developed as a most promising non-volatile random access memory. The reasons are the good scalability, good non-volatility, and fast-switching time (1). The STT switching of a TMR element with perpendicular magnetic anisotropy has attracted considerable attention in recent years (2-7), because of small cell size of 6F 2 and the lower programming current than that of a TMR element with in-plane shape magnetic anisotropy (I-TMR) (2). L1 0 -crystalline ordered alloy like FePt is one of candidates for the P-TMR because of large anisotropic energy Ku of order of 10 7 erg/cc and high thermal stability (3).In this paper, we have designed and fabricated a P-TMR element using L1 0 -crystalline ordered alloy as the free layer and successfully demonstrated low-current and fast switching time. We fabricated 1kbit array of P-TMR elements to show memory performance.

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We report on the spin-transfer magnetization switching properties of CoFe/Pd-based perpendicularly magnetized giant magnetoresistive cells over a wide current pulse duration time range. Analytic expressions without empirical parameters like attempt frequency are tested experimentally for the thermally assisted and precessional regimes. Good agreement with the experiment data is obtained using a common parameter set in both regimes, which leads to a comprehensive understanding of the switching properties including the origin of the attempt frequency.

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