The magnetic properties of two similar Er3+ complexes have been investigated. [Er(tpm)3(bipy)] (Htpm = 1,1,1-trifluoro-5,5-dimethyl-2,4-hexanedione and bipy = 2,2′-bipyridine) displays thermally activated slow relaxation of magnetisation under a zero direct-current (DC) field. Under an applied HDC field of 1000 G, [Er(tpm)3(bipy)] exhibits two thermally activated processes with energy barriers of 9 and 40 K, while [Er(tfa)3(bipy)] (Htfa = 4,4,4-trifluoro-1-(2-furyl)-1,3-butanedione) shows only one activated process with a barrier of 15 K. Both compounds are luminescent in the solid state, emitting in the near IR region.