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        2. [煎蛋小學堂]如何讓磁鐵消磁?



          2015-7-8 13:30










          This is a neodymium magnet-it's pretty darn strong.And now,after heating it in a flame...it's no longer magnetic.Well,to build a magnet,all you need to do is find a bunch of magnetic atoms .

          That's easy-they're the ones with half-filled electron shells in the middle of any of the major blocks of the periodic table, and then make a compound where the magnetic fields of the atoms align in the same direction this is Ferromagnetism, named after Iron,which is pretty darn magnetic.


          However,it's not always so easy.Sometimes the atoms actually want to align their magnetic fields in alternating directions.This is called "anti-ferromagnetism,"and it means the bulk material won't have a magnetic field at all.Or,sometimes the tendency of the atomic magnets to align (or anti-align)is just too weak to overcome their intrinsic jiggling.

          That is,their temperature!In which case,even though all the individual atoms in the material are magnetic,the material as a whole isn't.However,in a strong external magnetic field,the atoms do tend to align with each other in the direction parallel to the field.This is called "para-magnetism,"and liquid oxygen is a great example:it's attracted by a magnet,though it doesn't stay magnetized afterwards.
          也就是溫度!此時即使材料內部所有原子都具有磁性,整塊材料卻沒有 但是 在外部強磁場內,原子會沿平行于外部場的方向相互對齊,這就是順磁性,液氧就是個好例子,它會被磁鐵吸引,但之后并不會保持磁性。

          But let's get back to the question-how do you destroy a magnet?Well,a material can only be ferromagnetic it its temperature is low enough:above a certain point,the nicely ordered atomic magnetic fields"melt"into disorder,just as ice crystals melt into water when heated past zero celsius. So to destroy a manget,you just need to heat it up past its "magnetic melting point",called the "Curie Temperature"it probably won't look like much is happening,but once the atoms are jiggling around enough,their magnetic fields will no longer all point in the same direction.

          Magnet destroyed!And just as different elements melt from solid to liquid at different temperatures,They also melt from being ferromagnetic to paramagnetic at different temperatures,which you can explore in this sweet interactive periodic table.Which also plays all of the Periodic Table of Videos.