def demag(isa, ax=0):
    """plot demag of NC/I7/ISA7 model
    Args:
      isa: Isa7/NC object
    """
    emag = [e for e in isa.elements if e.is_magnet()]
    demag = np.array([e.demagnetization(isa.MAGN_TEMPERATURE) for e in emag])
    _contour(ax, f'Demagnetization at {isa.MAGN_TEMPERATURE} °C',
             emag, demag, '-H / kA/m', isa)
    logger.info("Max demagnetization %f", np.max(demag))