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We found thal in TmCm the molecular held does not exceed the critical value necessary to induce long-range magnetic order in the CO d-electron subsystem, which is in c n n m t to the other heavy RCoz compounds. Below Tc = 3.8 K a firstader magnetic phase transition at 3.4 K exists, which is due to a r e m g e m e n l of the Tm 4f magnetic moments. When substituting Tm by Gd long-range magnetic order appears in the CO d subsystem. The onset of the magnetic order in the d-electron subsystem can most clearly be seen from thermal expansion measurements. There is an increasing positive volume anomaly with increasing Gd content below Tc.The estimated magnetostriction constant i l I I of TmCoz is -4.1 x io-), in agreement with the single-ion model.Pronounced discontinuities al Tc are characteristic for the transpon properties (resistivity and thermopower) for TmCo2 a well as for the pseudobinary Tmlp,Cd,C% compounds. At elevated temperatures the physical properties of all these compounds are dominated by spin fluctuations.

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