PhD Defense – Magnetic Memories Optimized for Cryoelectronic Operation

On Monday December 04th, at 14:00, Pedro Brandao Veiga (SPINTEC) will defend his PhD thesis entitled :
Magnetic Memories Optimized for Cryoelectronic Operation


Place : IRIG/SPINTEC, Amphithéâtre Daniel Dautreppe, Bâtiment B, CEA – 17 rue des Martyrs – Grenoble (access needs authorization request it before November 23th to

visio conference :
Pass code: 519490


Abstract : Magnetic Random Access Memories (MRAM) arise as the second main industrial application of spintronics after hard disk drives. They harbor a number of assets to outperform the current state-of-theart devices used in electronics, such as eFLASH and possibly SRAM and DRAM. They still hold many interesting facets that have yet to be fully explored with the advances in Spin Transfer Torque (STT), Spin Orbit Torque and Voltage Controlled Anisotropy (VCMA) driven magnetization reversal. It is a thriving field, and the progress in High Performance Computing and advent of quantum processors are attracting more and more attention, motivating the interest on the subject of this work. To engineer new magnetic memory devices for cryoelectronics, we focused on two different writing mechanisms: STT and VCMA. We studied them under the framework of macrospin numerical simulations to better understand the switching dynamics of our system. For cryo-STT-MRAM, we demonstrated that it is highly beneficial in terms of switching speed and energy consumption to consider a storage layer exhibiting higher order anisotropy terms, resulting in a canted magnetization state called “easy-cone”. Switching simulations revealed that this approach enables very low temperature switching without thermal activation and reduces the switching energy necessary to write the bit. We also demonstrated that the VCMA effect, under certain optimized conditions, yields a novel non-precessional switching regime for temperatures below 50K, enabling deterministic switching of magnetization independently of write pulse duration. To take advantage of the low thermal activation energy at cryogenic temperatures, we fabricated MRAM cells with much lower anisotropy compared to conventional devices. The approach used was to modify the storage layer structure of the magnetic tunnel junctions to either reduce its anisotropy at the interface with the tunnel barrier or increase its demagnetizing energy. The purpose was to lower the energy barrier between the two writeable states. For that, we introduced embedded magnetic layers, such as Co or Permalloy, onto the FeCoB layer and conducted magnetic and electrical characterization at room temperature down to 4K.

Jury :

  • Julie Grollier, DR CNRS, Unité Mixte de Physique CNRS-Thales, Rapporteure
  • Daniel Lacour, DR CNRS, Institut Jean Lamour, Rapporteur
  • Diana Leitao, TU Eindhoven, Examinatrice
  • Martin Kogelschatz, UGA – LTM, Examinateur
  • Matias Urdampilleta, Institut Néel, Examinateur

Thesis supervisor :

  • Ricardo Sousa,  Spintec,Directeur de Thèse

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