Abstract: A new model is proposed to explain the magnetostriction effects in ferrimagnetic spinels and garnets with Mn(3+), co(2+), and Fe(2+) ions substituted into octahedral sites. Considerable experimental evidence has revealed that small amounts of each of these ions will alter substantially the magnitude of either the lambda 100 or lambda 111 magnetostriction constant, depending on the particular ion. The theory is based on the concept that Jahn-Teller effects produce local site distortions of tetragonal (favoring (100) axes) or trigonal (favoring (111) axes) symmetry which are able to switch among the different axes of the particular family in order to select the axis closest to the direction of the magnetic field. For Mn(3+) ions, the local site distortions are expected to be tetragonal (c/a > 1). With CO(2+) ions, the distortion is also tetragonal, but of the opposite sign (c/a < 1). In the case of Fe(2+) ions, the distortion is trigonal (alpha < 60 deg), as evidenced by its behavior in FeO, and will produce large positive changes in the lambda 111 constant. In each case studied, the theoretical results are in complete accord with the available room temperature magnetostriction constant data on a qualitative basis. An estimate of the magnitude of the elastic energy of the local site distortion suggests that crystal field energy level splittings required to create the observed magnetostrictive effects are only on the order of .01/cm.
| Description: |
Technical rept. |
| Pages: |
28 |
| Report Date: |
29 NOV 1978 |
| Contract Number: |
F1962878C0002 |
| Report Number: |
A052660 |
Report Unavailable |
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