Electric-field effects on magnetic anisotropy and damping constant in Ta/CoFeB/MgO investigated by ferromagnetic resonance

Abstract

We investigate electric-field effects on the effective magnetic anisotropy energy density Keff and the Gilbert damping constant α in Ta/CoFeB/MgO structures with CoFeB thickness t ranging from 1.4 to 1.8 nm by ferromagnetic resonance. The electric field-induced modulation ratio of the areal energy density Kefft does not depend on the CoFeB thickness, indicating that the electric-field effect on the magnetic anisotropy originates from the modulation of CoFeB/MgO-interfacial magnetic anisotropy. A clear electric-field modulation of α is observed for the structure with t = 1.4 nm, and almost no modulation for the structures with t ≥ 1.5 nm.

Effect of electric-field modulation of magnetic parameters on domain structure in MgO/CoFeB

“…7,11 The H R at θ H = 0 o (90 o ) decreases (increases) under a positive (negative) electric field, which indicates that the perpendicular anisotropy increases under positive electric fields. By fitting the resonance condition to the dependence as shown by solid lines, 8 we determine the effective magnetic anisotropy energy density K eff at E = 0 to be 6.3 × 10 4 J/m 3 , and its areal modulation per electric field to be dK eff t/dE = 55 fJ/Vm, where t = 1.5 nm is the thickness of the CoFeB layer. These values are in line with previous reports.…”

“…We measure ferromagnetic resonance (FMR) spectra to determine the effective perpendicular magnetic field and its electric-field modulation. 8 Figure 1 shows the magnetic-field angle θ H dependence of resonance fields H R , where θ H is measured from the device normal. The lowest H R at θ H = 0 o indicates that the CoFeB layer has a perpendicular magnetic easy axis due to the interfacial magnetic anisotropy at MgO/CoFeB.…”

“…C Capability of mutual control between magnetic and electrical properties in magnetic materials is essential for the study on spintronics. So far, it was reported that by applying an external electric field E, one can modulate various magnetic parameters such as the Curie temperature, 1,2 coercive force, 3,4 magnetic anisotropy, [5][6][7] and damping constant 8,9 in both ferromagnetic semiconductors and metals. 10 These magnetic parameters determine the performance of the spintronics devices.…”

“…These values are in line with previous reports. 7,8 Next, we observe magnetic domain structures at demagnetized state by a polar magnetooptical Kerr effect (MOKE) microscope. [28][29][30] We demagnetize the CoFeB by applying an alternative perpendicular magnetic field with exponentially decaying amplitude starting from 20 mT.…”

Role of CoFeB thickness in electric field controlled sub-100 nm sized magnetic tunnel junctions

“…We determine that VCMA is, surprisingly, strongest near the higher end of the thickness spectrum which is quite unexpected for an interfacial phenomenon. 30 …”