Materials with perpendicular magnetic anisotropy for magnetic random access memory

Materials with perpendicular magnetic anisotropy (PMA) are being investigated for magnetic random access memory (MRAM) and other spintronics applications. This article is an overview of the developments in this topic. At first, a historical overview of the magnetic memory is presented along with the fundamentals of MRAM using the field-assisted scheme. Later on, the principle of spin-transfer torque (STT) is explained briefly along with the STT-MRAM design requirements. Here, it is described that the MRAM design is a challenge where a choice has to be made to meet five criteria, a phenomenon called MRAM pentalemma. The main part of the article focuses on the discussion of materials with PMA. The focus is made first on multilayers such as Co/Pd and Co/Pt which have been widely investigated, followed by the recent observation of PMA in FeCoB. In subsequent sections, the progress in future candidates such as FePt is discussed. The article concludes with a summary of the challenges and future directions in this research topic. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) In this Review, the princple of spin-transfer torque magnetic random access memory (STT-MRAM) is explained: The magnetic tunnel junction device is sandwiched between two electrodes (cross-point architecture). The writing is based on spin torque effect and the reading on tunnelling magneto-resistive effect. In contrast to field-based MRAM, STT-MRAM does not require external magnetic field. Since STT-MRAM is scalable, the transistor scales down with the device size. Materials with perpendicular magnetic anisotropy (PMA) are being investigated for their use in STT-MRAM - multilayers such as Co/Pd and Co/Pt as well as FeCoB and future candidates such as FePt.