Abstract
We have investigated the dependence of magnetic coupling strength on growth direction in superlattices made from alternating layers of Dy and Y metals. Using new molecular-beam epitaxy techniques, we have succeeded in growing high-quality single-crystal materials with structural coherence lengths >500 Å and with the growth direction oriented along a, b, or c crystallographic axes by choice. In earlier work, we showed that, in c-axis samples, Dy layers order coherently via RKKY-like interactions propagated through Y layers up to about 150 Å thick. Here we report neutron scattering data which show that Dy layers in b-axis samples fail to couple coherently even when the Y spacer layers are as thin as 26 Å. This observation can be explained in a semiquantitative way in terms of the anisotropy of the q-dependent susceptibility of Y, which exhibits a peak that is sharp in the c* direction but broad along a* and b*. As a result, the conduction-electron mediated exchange coupling through the Y layer is long ranged along c but short ranged along a and b. An interesting anisotropy of the magnetic coherence in b-axis samples is also observed.
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