MOKE Microscopy and low field domain magneteroresistance ofpatterned La0.7Sr0.3MnO3 thin films

International audienceThe magnetization reversal in 16 nm and 70 nm thick La0.7Sr0.3MnO3 (LSMO) patterned films deposited on 10° vicinal SrTiO3 substrates were studied by longitudinal magneto-optical Kerr (MOKE) microscopy. MOKE microscopy showed that the vicinal substrate induces uniaxial anisotropy and that both domain arrangement and magnetization reversal process depend on this substrate induced anisotropy as well as on the shape induced anisotropy. This is consistent with recently published papers [1, 2].Based both on local magnetization loops and on the observed magnetic microstructure, we showed that the low field magnetoresistance originates from anisotropic magnetoresistance within domain walls during magnetization reversal that proceeds by nucleation and propagation when H was applied parallel to the step edge direction and from bulk anisotropic magnetoresistance during magnetization reversal that proceeds by coherent rotation of the magnetization when H was applied perpendicular to the step edge direction. It is proposed that magnetization reversal as sharp as possible occurring by nucleation/propagation of vortex type domain walls is favourable in order to induce high low field sensitivity.The resulting equivalent magnetic noise spectral density level was finally found minimum, about 1 - 2 nT·Hz-1/2 at 1 Hz and 0.3 - 0.4 nT·Hz-1/2 in the white noise frequency range, in the 100 μm wide strip patterned in the 16 nm thick LSMO film with H parallel to the step edge direction, whatever the orientation of H with I. These measured bn values of the order of few nT·Hz-1/2 at room temperature are very promising for future room temperature low field magnetic sensors based on LSMO thin films. Comparable to usual AMR sensors, the low frequency excess noise occurs at a much mower frequency which is also to be pointed out [3].[1] J. Heidler et al J. Appl. Phys. 112, 103921 (2012)[2] P. Wohlhüter et al J. Phys.: Condens. Matter. 25 176004 (2013)[3] Stutzke et al, Journal of Applied Physics 97, 10Q107 (2005