Mössbauer studies of the states of Fe atoms in the antiferromagnetic Fe–Mn Invar alloys

• The component of HFD having anomalous large value of isomer shift were identified.
• The temperature dependence of the isomer shifts for LF component was observed.
• We argue that the observed behavior of the isomer shift due to a local volume effect.
• The observed peculiarities strongly correlate to the Invar properties of the alloys.

A study of the magnetic hyperfine field distribution (HFD) for 57Fe in the antiferromagnetic Fe–Mn Invar alloys have been performed by Mössbauer spectroscopy technique. The component of HFD having anomalous large value of isomer shift was observed. The component is localized in the low-field part of HFD and its intensity is equal to 12(3)%. We argue that the observed anomalous isomer shift value due to a local volume effect. The observation of the pronounced temperature dependence of the isomer shift for the low-field component strongly supports a relationship between the appearance of the component and the Invar effect. Analogous features were found previously in the Fe–Ni and Fe–Al Invar alloys. On the basis of the results, we have reason to believe that the existence of the Fe sites having anomalous isomer shift values (and, as we suggest, the anomalous large local volume) is a common characteristic for Fe-based Invar alloys with the competing exchange interactions. In such systems, the radial dependences of the competing exchange interactions are the key factors in the determination of the ground-state properties of the different atomic configurations.