The experimentally known d E effect of polycrystalline ferromagnets is classified into three types. The third-type
ΔE effect, in which Young's modulus,
E, shows a maximum and then a minimum, is observed with cobalt and h.c.p. Ni-Co alloys and may be interpreted as associated with the process of reversible rotation of magnetization vectors. The first type in which
E increases monotonously with magnetization and the second type in which E decreases at first and then increases to a value larger than that in unmagnetized state are observed with cubic metals and alloys. The second-type dE effect is especially conspicuous in f. c. c. Ni-Co alloys. It is shown that the initial decrease of
E in the second-type JE effect is associated with the fact the non-180° domain wall displacements due to stress occurs more and more easily as the specimen is magnetized, and that the first-tpye
ΔE effect is merely an extreme case in which non-180° domain wall displacements occur very easily at weak fields. Internal stress or inclusions distributed randomly in the specimen may certainly be a cause of the second-type
ΔE effect, but such a cause can not explain remarakble extreme values of the
ΔE effect and their composition dependence observed with Ni-Co alloys. It is, than, shown, based on the calculation of
ΔE effect due to the displacements of (100) 90° domain walls in an ideal simple cubic solid solution, that the stabilization of domain walls by the induced uniaxial ferromagnetic anisotropy is the primary cause of the second-type
ΔE effect observed with Ni-Co and other cubic sold solution alloys.
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