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Modification of perpendicular magnetic anisotropy and domain wall velocity in Pt/Co/Pt by voltage-induced strain.

Shepley PM, Rushforth AW, Wang M, Burnell G, Moore TA - Sci Rep (2015)

Bottom Line: K(eff), measured by the extraordinary Hall effect, is reduced by 10 kJ/m(3) by tensile strain out-of-plane ε(z) = 9 × 10(-4), independently of the film thickness, indicating a dominant volume contribution to the magnetostriction.The same strain reduces the coercive field by 2-4 Oe, and increases the domain wall velocity measured by wide-field Kerr microscopy by 30-100%, with larger changes observed for thicker Co layers.We consider how strain-induced changes in the perpendicular magnetic anisotropy can modify the coercive field and domain wall velocity.

View Article: PubMed Central - PubMed

Affiliation: School of Physics and Astronomy, University of Leeds, Leeds, LS2 9JT, United Kingdom.

ABSTRACT
The perpendicular magnetic anisotropy K(eff), magnetization reversal, and field-driven domain wall velocity in the creep regime are modified in Pt/Co(0.85-1.0 nm)/Pt thin films by strain applied via piezoelectric transducers. K(eff), measured by the extraordinary Hall effect, is reduced by 10 kJ/m(3) by tensile strain out-of-plane ε(z) = 9 × 10(-4), independently of the film thickness, indicating a dominant volume contribution to the magnetostriction. The same strain reduces the coercive field by 2-4 Oe, and increases the domain wall velocity measured by wide-field Kerr microscopy by 30-100%, with larger changes observed for thicker Co layers. We consider how strain-induced changes in the perpendicular magnetic anisotropy can modify the coercive field and domain wall velocity.

No MeSH data available.


Related in: MedlinePlus

(a) The values of the intercepts with the ln v axis extracted from fits of the creep law (Equation 1) to the data in Figures 3b and 3c plotted against the voltage applied to the transducers. (b) Gradients of the fits of the creep law to data in Figure 3b and 3c plotted against the voltage applied to the transducers. (c) Ratio of the pinning energy to thermal energy kT obtained by assuming Hdep = Hc. Red triangles represent Pt/Co(t)/Pt t = 1 nm, green squares are t = 0.95 nm and blue circles are t = 0.85 nm.
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f5: (a) The values of the intercepts with the ln v axis extracted from fits of the creep law (Equation 1) to the data in Figures 3b and 3c plotted against the voltage applied to the transducers. (b) Gradients of the fits of the creep law to data in Figure 3b and 3c plotted against the voltage applied to the transducers. (c) Ratio of the pinning energy to thermal energy kT obtained by assuming Hdep = Hc. Red triangles represent Pt/Co(t)/Pt t = 1 nm, green squares are t = 0.95 nm and blue circles are t = 0.85 nm.

Mentions: The creep law (Equation 1) was fitted with a least squares method to the data in Figures 3b and 3c. The intercept of the fit with the vertical axis is lnvo and the gradient of the line is the product Hdep1/4Uc/kT. Figures 5a and 5b show how lnvo and Hdep1/4Uc/kT vary with Co thickness in the strained and unstrained Pt/Co/Pt. Since we do not have a direct measure of Hdep, Uc/kT is extracted by assuming that Hdep = Hc, which is reasonable because it accommodates the change with strain of Hdep (proportional to the change in Hc). A comparison of the values of Hc (Figure 2b) to the range of applied fields driving domain wall velocity (Figure 3a) shows this estimate of Hdep to be too low; Hc is within the range of fields that drive creep motion. The estimate of Hdep produces an increased Uc/kT, but allows for a shift in Hdep under strain equal to the shift in Hc. Figure 5c shows the measured values of Uc/kT. At 0 V it is found to be 69 ± 2 for 0.85 nm, 87 ± 2 for 0.95 nm and 87 ± 1 for 1.0 nm. As these values are artificially inflated by the estimate of Hdep, they are somewhat larger than values found in similar polycrystalline Pt/Co/Pt films26, and to epitaxial Pt/Co/Pt films27.


Modification of perpendicular magnetic anisotropy and domain wall velocity in Pt/Co/Pt by voltage-induced strain.

Shepley PM, Rushforth AW, Wang M, Burnell G, Moore TA - Sci Rep (2015)

(a) The values of the intercepts with the ln v axis extracted from fits of the creep law (Equation 1) to the data in Figures 3b and 3c plotted against the voltage applied to the transducers. (b) Gradients of the fits of the creep law to data in Figure 3b and 3c plotted against the voltage applied to the transducers. (c) Ratio of the pinning energy to thermal energy kT obtained by assuming Hdep = Hc. Red triangles represent Pt/Co(t)/Pt t = 1 nm, green squares are t = 0.95 nm and blue circles are t = 0.85 nm.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4300497&req=5

f5: (a) The values of the intercepts with the ln v axis extracted from fits of the creep law (Equation 1) to the data in Figures 3b and 3c plotted against the voltage applied to the transducers. (b) Gradients of the fits of the creep law to data in Figure 3b and 3c plotted against the voltage applied to the transducers. (c) Ratio of the pinning energy to thermal energy kT obtained by assuming Hdep = Hc. Red triangles represent Pt/Co(t)/Pt t = 1 nm, green squares are t = 0.95 nm and blue circles are t = 0.85 nm.
Mentions: The creep law (Equation 1) was fitted with a least squares method to the data in Figures 3b and 3c. The intercept of the fit with the vertical axis is lnvo and the gradient of the line is the product Hdep1/4Uc/kT. Figures 5a and 5b show how lnvo and Hdep1/4Uc/kT vary with Co thickness in the strained and unstrained Pt/Co/Pt. Since we do not have a direct measure of Hdep, Uc/kT is extracted by assuming that Hdep = Hc, which is reasonable because it accommodates the change with strain of Hdep (proportional to the change in Hc). A comparison of the values of Hc (Figure 2b) to the range of applied fields driving domain wall velocity (Figure 3a) shows this estimate of Hdep to be too low; Hc is within the range of fields that drive creep motion. The estimate of Hdep produces an increased Uc/kT, but allows for a shift in Hdep under strain equal to the shift in Hc. Figure 5c shows the measured values of Uc/kT. At 0 V it is found to be 69 ± 2 for 0.85 nm, 87 ± 2 for 0.95 nm and 87 ± 1 for 1.0 nm. As these values are artificially inflated by the estimate of Hdep, they are somewhat larger than values found in similar polycrystalline Pt/Co/Pt films26, and to epitaxial Pt/Co/Pt films27.

Bottom Line: K(eff), measured by the extraordinary Hall effect, is reduced by 10 kJ/m(3) by tensile strain out-of-plane ε(z) = 9 × 10(-4), independently of the film thickness, indicating a dominant volume contribution to the magnetostriction.The same strain reduces the coercive field by 2-4 Oe, and increases the domain wall velocity measured by wide-field Kerr microscopy by 30-100%, with larger changes observed for thicker Co layers.We consider how strain-induced changes in the perpendicular magnetic anisotropy can modify the coercive field and domain wall velocity.

View Article: PubMed Central - PubMed

Affiliation: School of Physics and Astronomy, University of Leeds, Leeds, LS2 9JT, United Kingdom.

ABSTRACT
The perpendicular magnetic anisotropy K(eff), magnetization reversal, and field-driven domain wall velocity in the creep regime are modified in Pt/Co(0.85-1.0 nm)/Pt thin films by strain applied via piezoelectric transducers. K(eff), measured by the extraordinary Hall effect, is reduced by 10 kJ/m(3) by tensile strain out-of-plane ε(z) = 9 × 10(-4), independently of the film thickness, indicating a dominant volume contribution to the magnetostriction. The same strain reduces the coercive field by 2-4 Oe, and increases the domain wall velocity measured by wide-field Kerr microscopy by 30-100%, with larger changes observed for thicker Co layers. We consider how strain-induced changes in the perpendicular magnetic anisotropy can modify the coercive field and domain wall velocity.

No MeSH data available.


Related in: MedlinePlus