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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A spin transfer torque magnetoresistive random access memory (STT-MRAM) is the most promising candidate for a non-volatile random access memory, because of its scalability, high-speed operation, and unlimited read/write endurance. An ion beam etching (IBE) is one of the promising etching methods for a magnetic tunnel junction (MTJ) of the STT-MRAM, because it has no after-corrosion and oxidation problems. In this work, we developed the multiple-step wafer-tilted IBE using computer calculation. Using optimized multiple-step IBE conditions, we fabricated MTJs without barrier-short defects.

Spin-polarized tunneling was studied on Co surfaces of exchange coupled Co/Cu/Co samples, using an Fe tip. A spin-polarized surface state of Co(0001) was found to exist at -0.43 eV relative to E(F), with FWHM of 0.23 eV in the spectra. The state exhibits negative magnetoresistance with an effective spin polarization of less than -23%, suggesting negatively high spin polarization of the surface state. Our first-principles calculations have supported the existence of the surface state. From the calculation, the state is identified as a minority spin Gamma-centered d(2)(z)-like surface state.