Temperature and field dependence of high-frequency magnetic noise in spin valve devices

Abstract

The high-frequency noise of micrometer-dimension spin valve devices has been measured as a function of applied field and temperature. The data are well fit with single-domain noise models that predict that the noise power is proportional to the imaginary part of the transverse magnetic susceptibility. The fits to the susceptibility yield the ferromagnetic resonance ͑FMR͒ frequency and the magnetic damping parameter. The resonant frequency increases, from 2.1 to 3.2 GHz, as the longitudinal field varies from Ϫ2 to 4 mT and increases from 2.2 to 3.3 GHz as the temperature decreases from 400 to 100 K. The shift in the FMR frequency with temperature is larger than that expected from the temperature dependence of the saturation magnetization, indicating that other temperature-dependent anisotropy energies are present, in addition to the dominant magnetostatic energies. The measured magnetic damping parameter ␣ decreases from 0.016 to 0.006 as the temperature decreases from 400 to 100 K. The value of the damping parameter shows a peak as a function of longitudinal bias field, indicating that there is no strict correlation between the damping parameter and the resonant frequency.

Spin-Torque Influence on the High-Frequency Magnetization Fluctuations in Magnetic Tunnel Junctions

“…The slope value corresponds to a saturation magnetization of 8950 Oe, that is 27% smaller than the bulk value. This characteristic has been observed in other FMR experiments on nanostructures [12,13]. Concerning the noise amplitude, it decreases with increasing field and fits well a 1=H law derived from Eq.…”

Current-induced magnetization dynamics in current perpendicular to the plane spin valves

“…Hard disk drives currently use GMR read sensors in which current flows in the plane of the thin film multilayer (CIP), but CPP GMR sensors are considered to be a serious alternative for future drives. CPP GMR will encounter the same Johnson noise and thermally activated magnetic noise, or mag-noise [22][23][24], as CIP GMR devices.…”

Magnetic properties of chromium-doped Ni80Fe20 thin films

“…We found for a wide range of Cr up to $15%, the magnetic properties were of sufficient quality that these alloys could be useful in magnetic device technologies. One example is a (Ni 80 Fe 20 ) 85 Cr 15 alloy that has very desirable properties, including at 4 K a reduced M s of %500 emu/cm 3 , an H c of %4 Oe, an H k of %1 Oe, and remanent squareness Sq of %0.8.…”

“…The minimum usable M s is limited by the need to maintain large enough energy barrier to prevent data loss due to thermal fluctuations. [14,15]. Since JMRAM will operate at a temperature of 4 K only, low M s alloys are of particular interest for this application.…”