The effect of Co doping on the magnetic, hyperfine and transport properties of the metamagnetic LaFe11.44Al1.56 intermetallic compound

Abstract

The influence of Co doping on the hyperfine, structural, magnetic and transport properties of La(Fe1−xCox)11.44Al1.56 (x = 0, 0.04, 0.08 and 0.12) compounds was investigated by Mössbauer spectroscopy, x-ray diffraction, magnetization and electric resistivity measurements. Stabilization of the NaZn13 structure by Al atoms was also investigated in Co undoped samples and a relatively large amount of α -Fe segregated phase was observed for Al content lower than 0.10, which indicate a solubility limit for Al substitution. The Mössbauer spectra indicate that Fe atoms see a chemically disordered environment, which is related to the presence of substitutional Al and/or Co atoms. The electric field gradient value at the Fe sites of the compounds is not affected by the Al substitution, with a quadrupole splitting value of 0.44 mm s−1. The compound magnetic ordering temperature varies from 195 to 360 K and can be set according to the Co content. An enhancement of the Fe effective magnetic moment with increasing Co doping has also been observed. The applied magnetic field induces antiferromagnetic (AFM) to ferromagnetic (FM) phase transition, with a field value depending on the Co concentration, and is about 5 T for x = 0 and about 0.5 T for x = 0.04. A second magnetic phase transition occurs on cooling to low temperatures from an AFM to a spin-glass-like (SGL) state for x = 0. A possibly reentrant SGL state may occur from the FM state for x = 0.04. For x > 0.04, the compounds behave as FM for measuring field of 0.04 T.