EMS172L_Lab05_MagneticProperties

EMS172L_Lab05_MagneticProperties - UC Davis EMS 107L...

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UC Davis – EMS 107L Electronic, Magnetic, and Optical Properties Laboratory – Prof. Ricardo Castro 1 UNIVERSITY OF CALIFORNIA, DAVIS Department of Chemical Engineering and Materials Science EMS 172L: Electronic, Magnetic, and Optical Properties Laboratory Laboratory Class V – Magnetic Properties The magnetic properties of materials are dependent mainly on the electronic distribution. For instance, the electronic distribution of Fe atoms is 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 6 . The orbital d is completed with 6 electrons. Remembering that this orbital has 5 sub-orbitals (with different shapes) and in each sub-orbital we can put 2 electrons with opposite spins, this means that we will have 4 unpaired electrons for the Fe case. Since the unpaired electrons will have to have the same spin due to the exclusion principle, this will generate a high magnetic moment in Fe atoms. This theory is applicable for all atoms and one may expect that the magnetism of a material will depend on the number of unpaired electrons. Other property that will define the magnetic property of a material is the relative position of these unpaired electrons. That is, depending of the crystal structure the alignment of spins can be beneficiated or not. For instance, ferrite and austenite are different phases of metallic iron. Ferrite is ferromagnetic and austenite is non-magnetic. Macroscopically, the magnetic behavior of a material can be defined by five different classifications: para-, dia-, ferro-, ferri- and anti- ferromagnetic. We may differ one from the other by simple experiments, as the one that Faraday did in the past. Faraday placed the material to be evaluated in a scale with one of the arms holding the material in a magnetic field (as shown in the cartoon). Diamagnetic materials are expelled from the field, but para-, ferro-,
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EMS172L_Lab05_MagneticProperties - UC Davis EMS 107L...

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