Spin dynamics in brownmillerite Ca2Fe1.2Al0.8O5: A temperature dependent neutron diffraction study. Issue 16 (November 2018) - Sharma, Gaurav
Abstract: The crystal and magnetic structure of brownmillerite Ca2 Fe2-x Alx O5 ; x = 0.8 has been refined against the powder neutron diffraction data collected as a function of temperature from 3 K to 350 K. Ca2 Fe2-x Alx O5 is a G-type antiferromagnet with Ibm 2 symmetry, the magnetic ion Fe occupies both tetrahedral and octahedral sites and both the sites are antiferromagnetically coupled individually. In this report, the mechanism of spin reorientation transition shown by these compounds is elucidated. The moment direction is found to be directed preferably along the crystallographic c -axis at low temperatures along with a small fraction of domains that are aligned along the a -axis. As the temperature is increased the domain with a -axis aligned moment inflates at the expense of domains with the moment directed along c -axis. However, at all temperatures both types of domains are found to be coexisting. The results suggest phase coexistence of the two magnetic structures with temperature dependent dynamics.