You might want to use multi atlas to specify different thickness regions and their properties. An example is below

Specify Oxs_ImageAtlas:AnotherAtlas {

xrange {0.000E-6 1.000E-6}

yrange {0.000E-6 1.000E-6}

zrange {0.00E-6 0.025E-6}

image xx.bmp

viewplane xy

colormap {

white nonmagnetic

black magnetic }

}

Specify Oxs_ImageAtlas:AnotherAtlas {

xrange {0.000E-6 1.000E-6}

yrange {0.000E-6 1.000E-6}

zrange {0.000E-6 0.050E-6}

image xx2.bmp

viewplane xy

colormap {

white nonmagnetic

black magnetic }

}

Specify Oxs_MultiAtlas:globalatlas {

atlas :Mbuffer

atlas :AnotherAtlas

}

# Create a mesh

Specify Oxs_RectangularMesh:mesh {

cellsize {10e-9 10e-9 5e-9}

atlas :globalatlas

}