Abstract
Recently, perpendicular magnetic anisotropy (PMA) and its voltage control (VC) was demonstrated for Cr/Fe/MgO. In this study, we shed light on the origin of large voltage-induced anisotropy change in Cr/Fe/MgO. Analysis of the chemical structure of Cr/Fe/MgO revealed the existence of Cr atoms in the proximity of the Fe/MgO interface, which can affect both magnetic anisotropy (MA) and its VC. We showed that PMA and its VC can be enhanced by controlled Cr doping at the Fe/MgO interface. For Cr/Fe (5.9 Å)/Cr (0.7 Å)/MgO with an effective PMA of 0.8 MJ/m3, a maximum value of the voltage-controlled magnetic anisotropy (VCMA) effect of 370 fJ/Vm was demonstrated due to Cr insertion.
Highlights
Development of high density non-volatile memories that provide fast access and low energy consumption is crucial for generation spintronics
Theoretical studies attributed the origin of the voltage-controlled magnetic anisotropy (VCMA) effect to the spin-dependent screening of the electric field in FM layers[21] or the change in the relative occupancy of the orbitals of atoms at the interface related to the accumulation/depletion of electrons[22,23,24]
The spectra were deconvoluted into two groups of magnetic sub-spectra that are distinct by isomer shifts (IS) and their correlations with the hyperfine magnetic field (Bhf) distributions
Summary
Epitaxial MgO (30 Å)/Cr (300 Å)/Fe (tFe)/Cr (dCr)/MgO (25 Å)/Fe (100 Å)/Ta (50 Å)/Ru (70 Å) multilayers (where the order is given from the bottom to the top of the sample) were grown on polished MgO(001) substrates under ultrahigh vacuum conditions (sample A). A wedge-shaped Fe layer with a thickness tFe ranging from 3 Å to 7 Å was grown at 150 °C and annealed at 250 °C for 20 minutes. The Fe wedge was capped with a wedge-shaped Cr layer was prepared at room temperature with a thickness dCr ranging from 0 Å to 2 Å and with the Cr wedge gradient perpendicular to that of Fe (see Fig. 1). The tunneling magnetoresistance (TMR) was measured in the current-perpendicular-to-plane geometry (CPP) using the standard two-probe method under an in-plane external magnetic field on junctions with different Fe and Cr thicknesses. Note that in the studied Fe thickness regime (tFe = (3–7) Å), the magnetization of the bottom Fe free (switchable) layer was aligned along the surface normal, while a direction of magnetization of the top reference (fixed) Fe layer was aligned in-plane along the easy-axis Fe [001] direction. A Voight-line based method was applied to fit the spectra, in which the distribution of the hyperfine parameters is represented by the sum of the Gaussian components[38]
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