Cubic NaZn13-type compounds of the form La(FexAl1-x)13 were stabilised with compositions between LaFe6Al7 and LaFe12Al1. For compositions above LaFe11.2Al1.8 (x = 0.861) a low-temperature antiferromagnetic state is present in small external fields. However. upon increasing the field to a few tesla, an exceedingly sharp spin-flip transition with remarkably large hysteresis occurs to the fully saturated ferromagnetic state. The origins of this unusual metamagnetic transition are discussed in terms of the special crystal structure.