State diagram of nanopillar spin valves with perpendicular magnetic anisotropy

Abstract

The spin-torque switching of metallic nanopillar spin-valves showing strong perpendicular anisotropy are studied. The magnetic states of the layers depend on extrinsic parameters such as the magnetic field and the DC current applied to the device. A state diagram presents a comprehensive graph the role of those parameters on the spin-valve magnetic response. After explaining how state diagrams can be built and the different possible representation, experimental state diagram are studied for perpendicular devices and the influence of lateral size, temperature and field orientation are shown. An analytical model of a purely uniaxial system is presented. It is shown that this simple model does not properly reflect the experimental results whereas if the symmetry is broken a qualitative agreement is obtained. Finally the possible origins of the symmetry break are discussed in the light of analytical model and numerical simulations.2

Optimization of top-pinned perpendicular anisotropy tunnel junctions through Ta insertion

“…Anyhow, whatever the physical origin the anisotropy terms, the sum H eff k1 þ H k2 is large and increases with the Ta thickness, which warrants the stability of the reference layer in MRAM applications. 25) In contrast for the Ta 3 Å sample, the fits can converge to degenerate sets of H eff k1 and H k2 pairs that yield matching with our measurements with comparable qualities. We shall see that this is because in the Ta 3 Å case, the (strong) interlayer exchange field acting on the Co=Pt layer can not be neglected against its (sub-optimal) anisotropy fields.…”

Switching field distributions with spin transfer torques in perpendicularly magnetized spin-valve nanopillars

“…Nevertheless, the switching appears well described by thermally overcoming a single energy barrier, whose height is related to an excited magnetic subvolume in the free layer element [16]. Standard measurements probing the effects of spin torques on switching-current-field state diagrams and measurements of the Stoner-Wohlfarth astroid-also appear to agree with the simple effective barrier model [6,[17][18][19].…”

“…The sudden increase in slope dI c /dH for fields |μ 0 H | 100 mT cannot be understood by a modified Néel-Brown law, but tilts of the applied field relative to the uniaxial axis and higher-order terms in the uniaxial potential energy landscape (e.g., sin 2n θ,n 2) may be important for the origin of the deviations from the predicted linear dependence [17].…”

Effect of spin transfer torque on domain wall motion regimes in [Co/Ni] superlattice wires

“…For instance, current-induced domain wall motion [3] may be implemented to increase the density, performance and endurance of non-volatile storage devices [4]. Materials with out-of-plane anisotropy are promising candidates [5][6][7], as they can host narrow domain walls (DW), which are attractive for maximizing storage density and improving current-induced domain wall displacement efficiency. [Co/Ni] superlattices are often considered as an promising material for nanostructured spintronic devices because of their tunable magnetic and spinelectronic properties [5,8,9], especially for domain wall motion by STT [10][11][12].…”