Abstract
We report neutron di®raction studies of TbCo2Zn20 and TbFe2Zn20, two isostructural compounds
which exhibit dramatically di®erent magnetic behavior. In the case of TbCo2Zn20, magnetic Bragg
peaks corresponding to antiferromagnetic order are observed below TN ¼ 2.5 K with a propagation
vector of (0.5 0.5 0.5). On the other hand, TbFe2Zn20 undergoes a ferromagnetic transition at
temperatures as high as 66 K which shows a high sensitivity to sample-to-sample variations. Two
samples of TbFe2Zn20 with the same nominal compositions but with substantially di®erent mag-
netic ordering temperatures (Tc ¼ 51 and 66 K) were measured by single crystal neutron di®raction.
Structural re¯nements of the neutron di®raction data ¯nd no direct signature of atomic site disorder
between the two TbFe2Zn20 samples except for subtle di®erences in the anisotropic thermal param-
eters. The di®erences in the anisotropic thermal parameters between the two samples is likely due
to very small amounts of disorder. This provides further evidence for the extreme sensitivity of the
magnetic properties of TbFe2Zn20 to small sample variations, even small amounts of disorder.
