Magnetic phase transitions in La(Fe0.88SixAl0.12−x)13 (x = 0.033 and 0.096) compounds

Magnetic properties, structure parameters, linear thermal expansion, and Mössbauer effect have been measured on intermetallic compounds La(Fe0.88SixAl0.12−x)13 (x = 0.033 and 0.096) with the ground ferromagnetic state. The compound with x = 0.033, on growing temperature, demonstrates a transition to antiferromagnetic state at TF-AF ∼ 140 K and then paramagnetic state at TN = 190 K. The compound with x = 0.096 is a ferromagnet with TC = 190 K, and the transition to paramagnetic state is of the first order. The ferromagnetic ordering is accompanied by the lattice expansion by 0.5% and 1.2% for compositions with x = 0.033 and 0.096, respectively. It is established, based on the results of fitting of Mössbauer spectra, that the antiferromagnetic state is predominantly featured by the subspectrum with a positive quadrupole shift, whereas in the ferromagnetic state approximately equal contributions with the quadrupole shifts of different signs are observed.