Abstrakt
LuFexAl12-x (4 <= x <= 6) single crystals with the tetragonal structure of the ThMn12-type have been studied in magnetic fields up to 14 T. In this composition range the magnetic exchange interactions are very sensitive to the Fe content.
LuFe4Al8 and LuFe4.5Al7.5 are antiferromagnets with the Neel temperature around T-N = 120 K. Antiferromagnetic exchange interactions weaken with increasing Fe content.
LuFe4.5Al7.5 and LuFe5Al7 display a metamagnetic transition to a non-collinear ferromagnetic state. The transition is not observed in LuFe5.5Al6.5 that displays only some traces of antiferromagnetic exchange interactions at low temperatures.
In the LuFexAl12-x compounds with 5 <= x <= 5.5 antiferromagnetism becomes suppressed at a rather low temperature, above which ferromagnetic exchange interactions dominate. The temperature interval where they are dominant broadens with increasing x as T-N decreases and the Curie temperature T-C increases.
Antiferromagnetism is absent in LuFe6Al6 that displays normal ferromagnetic behavior with T-C = 327 K.