Magnetic noise in MgO-based magnetic tunnel junction rings

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confidence: 99%

Yoke-shaped MgO-barrier magnetic tunnel junction sensors

Chen

Carroll

Feng

et al. 2012

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“…3,4 Normally, thermal domain hoppings are connected with the magnetization rotations or fluctuations in a complicated internal anisotropic field due to shape, stress, impurity, displacement, nonuniformity, and other factors. 3,5 In theory, magnetic hysteresis and 1/f resistance noise can be suppressed by meliorating the internal anisotropic field of ferromagnetic layers in MR sensors. It was recently demonstrated that the magnetic hysteresis and 1/f resistance noise of MgO tunneling MR sensors was improved by properly thinning their ferromagnetic layers with the enhancement of perpendicular anisotropic field but the expense of large sensitivity drop.…”

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confidence: 99%

Remedying magnetic hysteresis and 1/f noise for magnetoresistive sensors

Zhao

Pan

et al. 2013

Thermal domain hoppings cause magnetic hysteresis and 1/f resistance noise in magnetoresistive sensors, which largely degrades their response linearity and low-frequency detection ability. In this Letter, the method of constant magnetic excitation integrated with vertical motion flux modulation was proposed to remedy magnetic hysteresis and 1/f resistance noise together. As demonstrated in experiments, the response linearity of the prototype sensor is promoted by about 10 times. Its noise level is reduced to near Johnson-Nyquist noise level, and, therefore, the low-frequency detection ability is approximately enhanced with a factor of 100.

“…Further details on the sample growth process and measurement can be found in Refs. [20][21][22]. Figure 1 shows MR curves for an EB-MTJ and a rf-MTJ.…”

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confidence: 99%

Reduced low frequency noise in electron beam evaporated MgO magnetic tunnel junctions

Diao

Feng

et al. 2010

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We compare low frequency noise in magnetic tunnel junctions with MgO barriers prepared by electron-beam evaporation with those prepared by radiofrequency sputtering, both showing a high tunneling magnetoresistance. The normalized noise parameter in the parallel state of junctions with evaporated barriers is at least one order of magnitude lower than that in junctions with sputtered barriers, and exhibits a weaker bias dependence. The lowest normalized noise is in the 10 −11 m 2 range. A lower density of oxygen vacancies acting as charge trap states in the evaporated MgO is responsible for the lower noise. © 2010 American Institute of Physics. ͓doi:10.1063/1.3431620͔Magnetic tunnel junctions ͑MTJs͒ have attracted a great deal of attention since the demonstration of the tunneling magnetoresistance ͑TMR͒ effect at room temperature. 1,2 Following theoretical predictions, 3,4 a large TMR ratio of up to 200% at room temperature in MTJs with CoFeB electrodes and MgO tunnel barriers was achieved. 5,6 A record room temperature TMR of 604% has since been reported in a pseudospin valve stack, 7 which is close to the theoretical maximum. 3,4 Major advances in MTJs have led to important applications in hard-disk read heads, 8 sensors, 9 and magnetic random access memory. 10 For magnetic field sensing applications, both signal and noise in the MTJ are of equal significance. It has been found previously that 1 / f noise usually dominates other kinds of noise, e.g., thermal noise and shot noise, at frequencies up to a few kilohertz in an MTJ device, and it limits the low-frequency sensitivity. [11][12][13][14][15][16] The 1 / f noise in these devices is normally quantified by the Hooge parameter ␣, defined as AfS V / V 2 , in which A is the junction area, f the frequency, S V the noise power spectrum density, and V the voltage applied to the MTJ. 12,17 In conventional radio frequency ͑rf͒ sputtered MTJs with CoFeB electrodes and MgO tunnel barriers, ␣ was reported to decrease as a function of annealing time and reach a minimum value of 2 ϫ 10 −10 m 2 . 18 The lowest ␣ value ever observed in MTJs, between ͑1-5͒ ϫ 10 −11 m 2 , was achieved in fully epitaxial Fe͑100͒/MgO͑100͒/Fe͑100͒ junctions grown by molecular beam epitaxy ͑MBE͒. 19 Recently, some of us suggested electron-beam evaporation as an alternative to MBE or rf-sputtering for growing high quality MgO tunnel barriers. The junctions fabricated in this way have been shown to possess high TMR ratios of ϳ240% at room temperature and a reduced density of oxygen vacancies, compared to counterparts grown entirely by rf-sputtering. 20 In this work, we report on low frequency noise in the MTJs with electron-beam evaporated MgO barriers of different thicknesses ͑EB-MTJs͒, comparing it to that measured in our MTJs with rf-sputtered MgO tunnel barriers ͑rf-MTJs͒. We show that the Hooge parameter ␣ in the EB-MTJs in their parallel state is at least one order of magnitude lower than that in the rf-MTJs, across a large range of resistance-area ͑RA͒ product 5 ϫ 10 2 Ͻ RAϽ 1 ϫ 10 6 ⍀ m 2 ...