High-frequency noise measurements in spin-valve devices (original) (raw)
Related papers
Temperature and field dependence of high-frequency magnetic noise in spin valve devices
Applied Physics Letters, 2003
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.
Thermal magnetization noise in submicrometer spin valve sensors
Journal of Applied Physics, 2003
With decreasing device dimensions thermal fluctuations may ultimately limit the performance of spin valve sensors. Using finite element micromagnetic simulations, we investigate thermal magnetization noise in submicrometer soft magnetic sensor elements within the framework of Langevin simulations. Local random thermal fluctuations lead to a collective motion of the magnetization. The magnetization precesses in the end domains leading to an oscillation of the total magnetization parallel to the long axes with an amplitude in the order of 0.1 M s at 350 K. The noise power increases linearly with temperature. Irrespective of the bias field, the time averaged total magnetization parallel to the long axes decays approximately by 0.01 M s as the temperature is raised by 100 K.
High-frequency measurements of spin-valve films and devices (invited)
Journal of Applied Physics, 2003
High-frequency measurements of spin-valve films and devices, made using several different measurement techniques, are presented and compared. Pulsed inductive measurements were made on sheet films and provide insight into the intrinsic dynamical properties of the component films and multilayer stacks. The damping parameter, in the completed spin-valve stack, is larger than in the constituent films. Direct time and frequency domain measurements of the dynamical response of micrometer-size spin-valve devices, made using high-bandwidth magnetoresistance techniques, showed damping parameters comparable to these measured on spin-valve sheet films. The small-angle magnetization response was also determined by high-frequency magnetic noise measurements. The damping parameters were smaller than those obtained by direct susceptibility measurements. The device-level measurements show a different dependence of the damping parameter on the easy-axis field as compared to sheet-level measurements. In addition to the uniform rotation mode, other peaks can be observed in the noise spectra that correspond to fluctuation modes arising from the micromagnetic structure. Electrical device measurements have much greater sensitivity than other high-frequency magnetic measurement techniques, which allow the direct observation of magnetization motion in submicrometer elements without averaging. This technique is used to directly examine thermally activated events and nonrepetitive dynamical motions.
Intrinsic spin noise in MgO magnetic tunnel junctions
Applied Physics Letters, 2013
We consider two intrinsic sources of noise in ultra-sensitive magnetic field sensors based on MgO magnetic tunnel junctions, coming both from 25 Mg nuclear spins (I = 5/2, 10% natural abundance), and S = 1 Mgvacancies. While nuclear spins induce noise peaked in the MHz frequency range, the vacancies noise peaks in the GHz range. We find that the nuclear noise in submicron devices has a similar magnitude than the 1/f noise, while the vacancy-induced noise dominates in the GHz range. Interestingly, the noise spectrum under a finite magnetic field gradient may provide spatial information about the spins in the MgO layer.
Noise properties of the spin-valve transistor
Sensors and Actuators A: Physical, 2001
Noise measurements have been performed on a spin-valve transistor. This transistor consists of a Pt/NiFe/Au/Co/Au multilayer sandwiched between two semiconductors. For comparison, we also studied metal base transistors with a Pt/Au or Pt/NiFe/Au base. All samples show full shot noise in the collector current. The inclusion of a spin-valve in the base layer decreases the absolute value of the collector current and with it the noise level but it does not change the nature of the noise in this device. Similarly, the collector current, and therefore, the noise changes as a function of magnetic ®eld for the spin-valve transistor, but no additional noise of magnetic origin is observed. #
Dependence of the colored frequency noise in spin torque oscillators on current and magnetic field
Applied Physics Letters, 2014
The nano-scale spin torque oscillator (STO) is a compelling device for on-chip, highly tunable microwave frequency signal generation. Currently, one of the most important challenges for the STO is to increase its longer-time frequency stability by decreasing the 1/f frequency noise, but its high level makes even its measurement impossible using the phase noise mode of spectrum analyzers. Here, we present a custom made time-domain measurement system with 150 MHz measurement bandwidth making possible the investigation of the variation of the 1/f as well as the white frequency noise in a STO over a large set of operating points covering 18-25 GHz. The 1/f level is found to be highly dependent on the oscillation amplitude-frequency non-linearity and the vicinity of unexcited oscillation modes. These findings elucidate the need for a quantitative theoretical treatment of the low-frequency, colored frequency noise in STOs. Based on the results, we suggest that the 1/f frequency noise possibly can be decreased by improving the microstructural quality of the metallic thin films. V C 2014 AIP Publishing LLC.[http://dx.
Physical Review Applied
Magnetoresistive spin valve sensors based on the giant-(GMR) and tunnelling-(TMR) magnetoresisitve effect with a flux-closed vortex state free layer design are compared by means of sensitivity and low frequency noise. The vortex state free layer enables high saturation fields with negligible hysteresis, making it attractive for applications with a high dynamic range. The measured GMR devices comprise lower pink noise and better linearity in resistance but are less sensitive to external magnetic fields than TMR sensors. The results show a comparable detectivity at low frequencies and a better performance of the TMR minimum detectable field at frequencies in the white noise limit.
Time and frequency domain measurements of ferromagnetic resonance in small spin-valve
IEEE Transactions on Magnetics, 2000
Time and frequency domain magnetoresistance measurements of ferromagnetic resonance (FMR) in small spin-valve devices are presented along with comparisons to single-domain simulations. The measurements and simulations give consistent results for rotational motion with angular deviations of less than 30 from the easy axis. While the time and frequency domain measurements produce similar results for ideal devices in the linear regime, each technique provides different information as the devices become nonlinear and less ideal. Both time and frequency domain magnetoresistance measurements allow the study of FMR in considerably smaller magnetic structures than can be done with conventional techniques.