Signal-to-noise ratios in high-signal-transfer-rate read heads composed of spin-torque oscillators

Abstract

An application of spin-torque oscillators (STOs) to high-signal-transfer-rate read heads beyond 3 Gbits/s is considered and the signal-to-noise ratios (SNRs) of the output signals under the thermal magnetization fluctuations are calculated by using the results of recent nonlinear theories. The STO head senses the media field as a modulation in the oscillation frequency, enabling high signal transfer rates beyond the limit of ferromagnetic relaxation. The output (digital) signal is obtained by frequency modulation (FM) detection, which is commonly used in communication technologies. As the problem of rapid phase diffusion in nonlinear STOs caused by the thermal fluctuations is overcome by employing a delay detection method, the sufficiently large SNRs are obtained even in nonlinear STOs less than 30×30 nm2 in size.

High-data-transfer-rate read heads composed of spin-torque oscillators

“…), dependence on L of the SNR is calculated [4]. The results are shown (in decibels) in figure 5 The decrease of the SNR by electrical noises such as Johnson and shot noises is calculated by adding the electrical noise n (t) = n c (t)cosω 0 t + n s (t)sinω 0 t to s 0 (t) [4].…”

“…The results are shown (in decibels) in figure 5 The decrease of the SNR by electrical noises such as Johnson and shot noises is calculated by adding the electrical noise n (t) = n c (t)cosω 0 t + n s (t)sinω 0 t to s 0 (t) [4]. In the case of the total electrical noise of 100 pW, the output power of STO larger than 10 nW is sufficient to avoid the further degradation of the SNRs by the electrical noises.…”

“…The noise originates from the magnetization fluctuations in the thermal equilibrium and generally exists in the passive MR devices. Here, we consider an application of active devices, that is, spin-torque oscillators (STOs) to read heads [3] [4], and calculate the SNRs of the output signals by using the recent nonlinear theories of STOs [5] [6]. The STO heads are compatible with the high data-transfer rate beyond 3 Gbps (Gbits per second), which are important in large-scale magnetic storage.…”

Frequency-based nanoparticle sensing over large field ranges using the ferromagnetic resonances of a magnetic nanodisc

“…1(b)), even when the underlying magnetic ground state is unchanged. This opens pathways to intrinsically frequency-based detection schemes 28,31 . Potential advantages of a frequencybased, dynamic technique over static magnetoresistive sensing include a larger field range over which the device response is linear 28,39,40 (enabling larger fields to be applied and thus generate higher MNP moments), intrinsically frequency-based operation (typically at GHz frequencies and thus far from low frequency 1/f contributions), the lack of d.c. voltage-level drift (when using direct frequency measurement) and excellent size scalability 28 .…”

“…This translates to a change in the device resistance, enabling electronic nanoparticle detection. However, one may also exploit the magnetic field dependence of ferromagnetic resonance for detection of magnetic fields [28][29][30][31][32] and thus magnetic nanoparticles [32][33][34][35][36][37][38] . Notably, the ferromagnetic resonance frequency within the device will respond directly to the field of the MNP (Fig.…”