size(3cm,3cm);

pair origin = (0,0), xhat = (1,0), zhat = (0,1);

path current = ellipse(origin, 1, 2/5);

fill(current, lightgray);
draw(current, Arrow); //major axis = 2, minor axis = 4/5
draw(origin--zhat, Arrow);

label("$I$",xhat,E);
label("$\vec{\mu}$",zhat,N);
label("$S$",-0.5*xhat);