Experimental observations of thermally excited ferromagnetic resonance and mag-noise spectra in spin valve heads

Abstract

Thermally excited ferromagnetic resonance (FMR) gives rise to so-called mag-noise in the spin valve read heads used in disk drives. In this article, an experimental method of measuring the mag-noise power spectrum density (PSD) in a frequency range of 2.5–6 GHz is presented. The thermally excited FMR modes in the spin valve and the corresponding resonant frequencies have been observed. It is found that the resonance frequencies occur in the range from 3 to 5 GHz in today’s spin valve heads at the quiescent state. Multiple resonance peaks were observed for some spin valve read heads while others only show a single resonance peak. An external field was applied to the spin valve heads to study the field dependence of the FMR spectrum. The mag-noise level at low frequencies is at the similar level of the head’s Johnson noise for heads of track width W=0.3 μm and 50 Ω resistance. It is suggested that the thermally excited FMR PSD could be used as a rapid diagnostic tool for spin valve heads.

Spin-wave excitations in finite rectangular elements ofNi80Fe20

“…If this element is used as a part of a magnetic reading head, or as a memory element at microwave frequencies ͑and a typical speed of a modern computer processor is around 3 -4 GHz͒ it is the thermal magnetic noise that limits the figures of merit of those devices. [12][13][14] Recently, the pronounced maxima in the thermal noise spectrum of small magnetic elements has been observed experimentally in the microwave frequency range as well as addressed theoretically. [12][13][14] Thus, to understand this effect and to be able to control the high-frequency properties of small magnetic elements it is necessary to study the properties of thermally excited spin-wave modes in laterally confined magnetic elements.…”

Dipolar localization of quantized spin-wave modes in thin rectangular magnetic elements

“…In order to avoid unwanted ''ringing'' in the re-magnetization process of a pattern element, the duration of the ''writing'' pulse should be equal to the half period of the lowest spin-wave eigenmode of the element. 12,13 Also, one of the most important limitations in operation of magnetic sensors and recording heads ͑that, essentially, are small magnetic elements͒ working in the microwave frequency range is the magnetic noise 14,15 that has spectral maxima near the frequencies of SW eigenmodes in these elements.…”

Frequency conversion of microwave signal without direct bias current using nanoscale magnetic tunnel junctions

“…3(a) shows that frequency conversion happens at any external magnetic field. A second explanation comes from Zhou work 19 . This work shows thermally excited ferromagnetic resonance, also called mag-noise, that produces resistance oscillations even without input DC current.…”