Stability Of Magnetic Tunnel Junctions Research Articles

Enhancement of the thermal stability of magnetic tunnel junctions employing artificial ferrimagnets

We have fabricated magnetic tunnel junctions that use Co/Ru/Co and Co/Ru/Co50Fe50 artificial ferrimagnet (AFi) systems as hard magnetic electrodes and AlOx as tunnel barrier. The thermal behavior of the two AFis, incorporated in tunnel junctions, presents dramatic differences, the most remarkable being the much greater thermal stability of the Co/Ru/CoFe system. This stems from the improvement of the interfaces the CoFe alloy forms with its adjacent Ru and AlOx layers. After successive annealing steps up to 400 °C, junctions incorporating the Co/Ru/CoFe system still present a significant tunnel magnetoresistance signal of nearly 20%, and most importantly, an almost intact magnetic rigidity of the hard magnetic system, being very promising for spin-electronic devices.

Switching stability of magnetic tunnel junctions with an artificial antiferromagnet

Avoiding fatigue in the switching of magnetic tunnel junctions is crucial for their long-term use in nonvolatile magnetic memories. We compare the switching stability of two types of junctions with different soft layers: Fe or Ni81Fe19, both with Co dusting at the barrier interface. The magnetically hard electrode is a Co/Cu/Co artificial antiferromagnet. While the tunneling magnetoresistance (TMR) remains unchanged after 104 cycles in a 4 kA/m rotating field, it decreases by more than 45% due to uniaxial switching. Fringing fields of domain walls in the soft layer and an intrinsic instability of Co/Cu/Co are identified as the main reasons. Magnetization reversal by two perpendicular switching pulses avoids this magnetic degradation and maintains a full TMR signal.

Temperature stability of Co/Al2O3/Co junctions

The temperature stability of magnetic tunnel junctions is an important requirement for the fabrication of magnetic memory devices and the integration in the semiconductor process technology. We have investigated the temperature evolution of the tunneling magnetoresistance (TMR) and the structural properties by isochronal annealing experiments up to 750 K. The magnetically hard electrode of the junction consists of an artificial antiferromagnet Co/Cu/Co, the soft electrode of a Co/Fe bilayer. The tunnel barriers are formed by plasma oxidized Al. The tunnel junctions have TMR signals up to 22% at room temperature. Besides a small increase of the TMR signal after annealing up to 480 K, a first decrease at 530 K and a breakdown beyond 600 K are found. This behavior can be attributed to structural changes of the junctions. Auger depth profiles show an unaltered Al2O3 barrier up to 600 K, but the beginning of interdiffusion processes within the magnetic electrodes already at 540 K and above.