magnetic dipole(磁偶极子)： Magnetic moment(磁矩) Pu NIS M=D xB (1)p=0°M=0。The loop is in state of stable equilibrium (2)p-90°，M=Mma=NBIS (3)p=180°M=0。The loop is in state of unstable equilibrium magnetic dipole（磁偶极子）： p NIS m    M pm B      （1）=0 M=0 。The loop is in state of stable equilibrium （2） =90 ，M = Mmax= NBIS （3）=180 M=0 。The loop is in state of unstable equilibrium m p  I S Magnetic moment（磁矩）