Study on the magnetic properties of differently functionalized multilayered Ti3C2Tx MXenes and Ti-Al-C carbides

According to theoretical predictions, the magnetic properties of MXene structures are determined by the properties of the constitutive transition metals, defects in the MXene layers and the surface functional groups. We studied the magnetic properties of differently functionalized multilayered Ti3C2Tx MXenes and compared them with those of Ti3AlC2 and Ti2AlC MAX phases, as well as titanium carbide (TiC). The influence of the type and concentration of functional groups on MXene's magnetic properties was investigated by studying Ti3C2Tx samples obtained by etching the aluminum layer from the Ti3AlC2 MAX phase using (1) hydrofluoric acid, (2) chlorosulfonic acid and (3) hydrofluoric acid followed by chlorosulfonic acid. The samples prepared by hydrofluoric or chlorosulfonic acid only showed paramagnetic behavior, while MXenes prepared with an assistance of both acids were found to exhibit two different types of radicals and/or defects in the electron paramagnetic spectrum and mixed antiferromagnetic/paramagnetic behavior under external magnetic field of 100 Oe. The appearance of magnetic ordering was assigned to sulfur-based functional groups (-S-2 and -SO3H) introduced by chlorosulfonic acid. The obtained results confirm that the magnetic properties of Ti3C2Tx MXenes may depend on the type and concentration of terminal functionalities.