Abstract
In this investigation, the low-frequency alternate-current (AC) magnetic susceptibility (χac) and hysteresis loop of various MgO thickness in CoFeB/MgO/CoFeB magnetic tunneling junction (MTJ) determined coercivity (Hc) and magnetization (Ms) and correlated that with χac maxima. The multilayer films were sputtered onto glass substrates and the thickness of intermediate barrier MgO layer was varied from 6 to 15 Å. An experiment was also performed to examine the variation of the highest χac and maximum phase angle (θmax) at the optimal resonance frequency (fres), at which the spin sensitivity is maximal. The results reveal that χac falls as the frequency increases due to the relationship between magnetization and thickness of the barrier layer. The maximum χac is at 10 Hz that is related to the maximal spin sensitivity and that this corresponds to a MgO layer of 11 Å. This result also suggests that the spin sensitivity is related to both highest χac and maximum phase angle. The corresponding maximum of χac is related to high exchange coupling. High coercivity and saturation magnetization contribute to high exchange-coupling χac strength.
Highlights
Since 1995, the tunneling magnetoresistance (TMR) effect has been extensively discussed, and it has been exploited in much of our modern technology [1,2]
The low-frequency AC magnetic susceptibility and hysteresis loop of CoFeB/magnesium oxide (MgO)/CoFeB are worthwhile to study. This investigation focuses on the maximum χac, the optimal resonance frequency and maximum phase angle for various MgO
The results suggest that an excitation frequency of 10 to 30 Hz maximizes the χac of the magnetic exchange-coupled signal, and as the frequency increases above 30 Hz, the χac obtained from the signal declines, suggesting that the CoFeB/MgO/CoFeB magnetic tunneling junction (MTJ) is suited to use at low frequencies
Summary
Since 1995, the tunneling magnetoresistance (TMR) effect has been extensively discussed, and it has been exploited in much of our modern technology [1,2]. A magnetic tunneling junction (MTJ) has a trilayer structure that comprises a top free ferromagnetic (FM1) layer, an insulating tunneling barrier layer (spacer), and a bottom pinned ferromagnetic (FM2) layer It has a great potential for use in magnetoresistance random access memory (MRAM). The low-frequency AC magnetic susceptibility (χac) and hysteresis loop of CoFeB/MgO/CoFeB are worthwhile to study. This investigation focuses on the maximum χac, the optimal resonance frequency (fres) and maximum phase angle (θmax) for various MgO barrier thicknesses (6, 8, 11, 13, and 15 Å). The maximum χac is 0.7 at the optimal resonant frequency of Hz and the maximum phase angle is 228° at an MgO thickness of Å These values are larger than compared for Fe40Pd40B20(X Å)/ZnO(500 Å) and suitable for low-frequency magnetic media applications [26]. It means that the optimal fres is associated with maximal spin sensitivity
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