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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) Examples of normalised EHE data from Pt/Co(0.95 nm)/Pt used for finding the anisotropy field Hk. The solid lines show the normalised data with 0 V (black lines) and 150 V (orange lines) applied to the transducer. The dashed lines are extrapolated from fits to the data below 600 Oe. Hk is the applied field at which the extrapolated curves meet the line where the Hall signal is 0. The inset is a schematic of a Hall bar on a transducer showing the measurement geometry. (b) The change in the PMA constant Keff of Pt/Co(t)/Pt (t = 0.85, 0.95, 1.0 nm) due to out-of-plane strain εz induced by piezoelectric transducers. The solid line is a fit of the data to Equation 4. The inset gives the anisotropy constants of the three unstrained films against Co thickness. The error bars in the inset are smaller than the data points.
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f1: (a) Examples of normalised EHE data from Pt/Co(0.95 nm)/Pt used for finding the anisotropy field Hk. The solid lines show the normalised data with 0 V (black lines) and 150 V (orange lines) applied to the transducer. The dashed lines are extrapolated from fits to the data below 600 Oe. Hk is the applied field at which the extrapolated curves meet the line where the Hall signal is 0. The inset is a schematic of a Hall bar on a transducer showing the measurement geometry. (b) The change in the PMA constant Keff of Pt/Co(t)/Pt (t = 0.85, 0.95, 1.0 nm) due to out-of-plane strain εz induced by piezoelectric transducers. The solid line is a fit of the data to Equation 4. The inset gives the anisotropy constants of the three unstrained films against Co thickness. The error bars in the inset are smaller than the data points.

Mentions: A current of 1 mA was passed along the Hall bar (x) and the Hall voltage monitored in an orthogonal in-plane direction (y) via one of the cross structures. A schematic of the measurement geometry is show in the inset to Figure 1a. To make a measurement, the plane of the device was first precisely aligned to an in-plane magnetic field by rotating the sample around the x axis until the Hall signal was as close to zero as possible during a field sweep along the y axis. An out-of-plane field was then applied to saturate the magnetization of the Pt/Co/Pt. Following this, an in-plane field was swept along the y axis from 0 Oe to 7000 Oe and the Hall resistance measured as the magnetization rotated from out-of-plane (maximum Hall signal) to in-plane (zero Hall signal). Figure 1a shows examples of the EHE data obtained. Initially (up to ~600 Oe in the case of Figure 1a), mz follows a parabola as expected if the magnetization were to rotate coherently (see Supplementary Information). As the field increases beyond 600 Oe, mz deviates from the parabola as the magnetization breaks up into domains with a size of ≤2 μm as measured by wide-field Kerr microscopy. The magnetization is eventually saturated in the plane, and the path mz would have followed if the magnetization had continued to rotate coherently is rejoined. The low field regime (up to ~600 Oe) where the moment rotates coherently is extrapolated, following the dashed lines in Figure 1a, to obtain the anisotropy field Hk, which is defined as the point where the extrapolated coherent rotation crosses mz = 0. Proper alignment of the field to the plane of the device ensured that the films were truly saturated along an in-plane axis, allowing for direct comparison of Hk between samples.


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) Examples of normalised EHE data from Pt/Co(0.95 nm)/Pt used for finding the anisotropy field Hk. The solid lines show the normalised data with 0 V (black lines) and 150 V (orange lines) applied to the transducer. The dashed lines are extrapolated from fits to the data below 600 Oe. Hk is the applied field at which the extrapolated curves meet the line where the Hall signal is 0. The inset is a schematic of a Hall bar on a transducer showing the measurement geometry. (b) The change in the PMA constant Keff of Pt/Co(t)/Pt (t = 0.85, 0.95, 1.0 nm) due to out-of-plane strain εz induced by piezoelectric transducers. The solid line is a fit of the data to Equation 4. The inset gives the anisotropy constants of the three unstrained films against Co thickness. The error bars in the inset are smaller than the data points.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f1: (a) Examples of normalised EHE data from Pt/Co(0.95 nm)/Pt used for finding the anisotropy field Hk. The solid lines show the normalised data with 0 V (black lines) and 150 V (orange lines) applied to the transducer. The dashed lines are extrapolated from fits to the data below 600 Oe. Hk is the applied field at which the extrapolated curves meet the line where the Hall signal is 0. The inset is a schematic of a Hall bar on a transducer showing the measurement geometry. (b) The change in the PMA constant Keff of Pt/Co(t)/Pt (t = 0.85, 0.95, 1.0 nm) due to out-of-plane strain εz induced by piezoelectric transducers. The solid line is a fit of the data to Equation 4. The inset gives the anisotropy constants of the three unstrained films against Co thickness. The error bars in the inset are smaller than the data points.
Mentions: A current of 1 mA was passed along the Hall bar (x) and the Hall voltage monitored in an orthogonal in-plane direction (y) via one of the cross structures. A schematic of the measurement geometry is show in the inset to Figure 1a. To make a measurement, the plane of the device was first precisely aligned to an in-plane magnetic field by rotating the sample around the x axis until the Hall signal was as close to zero as possible during a field sweep along the y axis. An out-of-plane field was then applied to saturate the magnetization of the Pt/Co/Pt. Following this, an in-plane field was swept along the y axis from 0 Oe to 7000 Oe and the Hall resistance measured as the magnetization rotated from out-of-plane (maximum Hall signal) to in-plane (zero Hall signal). Figure 1a shows examples of the EHE data obtained. Initially (up to ~600 Oe in the case of Figure 1a), mz follows a parabola as expected if the magnetization were to rotate coherently (see Supplementary Information). As the field increases beyond 600 Oe, mz deviates from the parabola as the magnetization breaks up into domains with a size of ≤2 μm as measured by wide-field Kerr microscopy. The magnetization is eventually saturated in the plane, and the path mz would have followed if the magnetization had continued to rotate coherently is rejoined. The low field regime (up to ~600 Oe) where the moment rotates coherently is extrapolated, following the dashed lines in Figure 1a, to obtain the anisotropy field Hk, which is defined as the point where the extrapolated coherent rotation crosses mz = 0. Proper alignment of the field to the plane of the device ensured that the films were truly saturated along an in-plane axis, allowing for direct comparison of Hk between samples.

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