Abstract. Detailed optical metallographic studies at room temperature on polycrystalline Gd₅Ge₄ are presented for two cases: (a) a sample in the as-cast condition and (b) the same sample subjected to a known number of temperature and magnetic field cycles. A herringbone- (criss-cross-) like pattern whose characteristic feature size extends to 20 µm is observed in the as-cast sample. The herringbone pattern at room temperature is interpreted as arising due to a long-lived (kinetically arrested) metastable phase. This herringbone pattern can be trained to form a pattern having a different morphology by cycling the sample through the low-temperature field induced magneto-structural transition. Training effects are also observed in magneto-transport and magnetization measurements as the sample is subjected to temperature and field cycles. Based on heuristic arguments, a model is proposed which self-consistently explains anomalies in transport and magnetization properties in terms of changes occurring in the microstructure of the sample. These results highlight the need for analysing the interesting properties of Gd₅Ge₄ and its family of alloys with microstructure as an important component.

Print publication: Issue 26 (5 July 2006)
Received 18 January 2006, in final form 27 April 2006
Published 19 June 2006