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.

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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 have grown high quality single crystals of the Kondo compound CeTe and its reference compounds LaX c 's with X c =S,Se,Te, and measured the de Haas-van Alphen effect of these compounds and the magnetic properties of CeTe. The Fermi surface of each LaX c is centered at the X points of the Brillouin zone and has a nearly ellipsoidal shape. The cyclotron effective masses are very close to the electron rest mass. On the other hand, CeTe has a rather complicated magnetic phase diagram which is different from that predicted by previous works. In the induced ferromagnetic phase of CeTe, the Fermi surface is found to be similar to that of LaTe but it splits into the majority and minority spin Fermi surface due to the exchange interaction between the 4f and conduction electrons. We have also observed strongly enhanced cyclotron effective masses in that phase. Interestingly, the mass enhancement of the minority spin surface differs with that of the majority spin surface by about a factor of 2.

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