• Cardoso, S.
• Lv, Hua
• Wrona, Jerzy
• Fidalgo, Joao
• Freitas, Paulo P.
• Langer, Juergen
• Ocker, Berthold

Abstract

<jats:title>Abstract</jats:title><jats:p>Perpendicular magnetic tunnel junctions (p-MTJs) have attracted great interest due to their excellent performance in spin-transfer-torque magnetic random access memories (STT-MRAMs). Here, the resistance states can be manipulated by an applied current in the order of 10<jats:sup>9</jats:sup>–10<jats:sup>10</jats:sup> A m<jats:sup>−2</jats:sup>, yet the appearance of a heating influence must be understood. In this work, we systematically study the Seebeck effect in nano scale p-MTJs induced due to Joule heating by the tunneling current. The CoFeB/MgO/CoFeB-based p-MTJs were nanofabricated and the current-induced switching was characterized. We find a sign change of the thermovoltage (Δ<jats:italic>V</jats:italic>) between AP (positive) and P (negative) states, indicating a significant dependence of the Seebeck effect on the magnetic state of the p-MTJ. The temperature distribution in the stack was simulated, by which the Seebeck coefficient (<jats:italic>S</jats:italic>) and the tunnel magneto-Seebeck ratio were calculated. Our further study indicates that the thermal STT can reduce the switching currents, showing the possibility to re-use this dissipative heating energy. To improve the efficiency of the energy re-use, a method is proposed through the materials optimization of the non-magnetic layers but still retaining high tunneling magnetoresistance effect. Our study shows that the magneto-Seebeck effect plays an important role in the p-MTJs, which can be crucial and must be considered in the design of the high performance p-STT-MRAMs and thermal-assisted MRAMs.</jats:p>

Topics

• impedance spectroscopy
• random