any material which is thin, can insulate the magnetic field?
Lines of magnetism pass through every substance known to man. Lead will not stop magnetism, but it can channel it. Lines of magnetism pass more easily through lead than any other substance (or lack thereof). If you surround something with a lead shield, lines of magnetism will curve to flow through the lead shield rather than cross it. Lead is the only substance which effectively exhibits this property. However. Just about any conductive material can be used to shield from RF induction (which differs from true magnetism). Which is why most data cables hace a thins metal foil around them as a shield to RF.
Not directly and not if static. A changing magnetic field generates electrical currents in metal circuits and if these circuits have resistance (and most do) then heat is generated.
