Volume 91, Issue 10, 15 May 2002
Index of content:
- THERMAL MAGNETIC STABILITY OF NANO-SIZED MAGNETIC DEVICES
91(2002); http://dx.doi.org/10.1063/1.1452685View Description Hide Description
Thermally induced magnetization fluctuations in the free (sense) layer of micron-sized, photolithographically defined giant magetoresistive spin-valve devices are measured electrically, by passing a dccurrent through the devices and measuring the current-dependent part of the voltage noise power spectrum. Using fluctuation–dissipation relations, the effective Gilbert damping parameter α for 1.2, 1.8, and 2.4 nm thick free layers is estimated from either the low-frequency white-noise tail, or independently from the observed thermally excited ferromagnetic resonance peaks in the noise power spectrum, as a function of applied field. The geometry, field, and frequency dependence of the measurednoise are found to be reasonably consistent with fluctuation–dissipation predictions based on a quasianalytical eigenmode model to describe the spatial dependence for the magnetization fluctuations. The extracted effective damping constant found for the 1.2 nm free layer was close to 3× larger than that measured in either the 1.8 or 2.4 films, which has potentially serious implications for the future scaling down of spin-valve read heads.
91(2002); http://dx.doi.org/10.1063/1.1452686View Description Hide Description
We have studied quasistatic magnetic switching of electron-beam patterned (NiFe) elements over a wide range of temperatures. Switching properties depend on both lateral and thickness dimensions of the patterned structures. In large aspect-ratio elements, the switching between the two bistable states occurs through thermally activated nucleation and the switching field depends linearly on temperature. As the aspect ratio decreases, a third stable remanent state-trapped vortex state develops, but the switching fields between different states also linearly depend on temperature. As the film thickness decreases, the trapped vortex population clearly becomes thermally activated.