Magnetostriction Constants of Rare Earth Iron Garnets

Magnetostriction constants, λ 111 and λ 100 , were measured for rare earth iron garnet single crystals M 3 Fe 5 O 12 (M=Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Y) at 78°K, 196°K and room temperature. They are classified into two groups: A (Y, Gd, Eu), B (Sm, Tb, Dy, Ho, Er, Tm, Yb). Group A has smaller magnetostriction constants than other groups and has a tendency to almost saturate at 78°K. Absolute values of the magnetostriction constants for group B increase steeply when temperature is lowered. An exceptionally large λ 111 (+560×10 -6 at 78°K) and considerably small λ 100 is observed for TbIG. For group B and for EuIG the absolute magnitudes of the striction constants are in parallel with the contribution of the rare earth ions to the total magnetization, and the classical model of the presence of induced strain from the deformed electron orbits of 4f electrons seems plousible. For GdIG a new explanation is given which neglects entirely the contribution from the S state 4f orbits.