Impact of amorphization on the magnetic properties of EuO-TiO₂ system

Recently, we have reported amorphization-induced ferromagnetism in a magnetic oxide; whereas crystalline EuTiO₃ is an antiferromagnet, its amorphous counterpart shows a ferromagnetic transition. In this paper, we have investigated the magnetic properties of amorphous EuO-TiO₂ system in detail. The present compounds, i.e., amorphous EuTiO₃ and Eu ₂ TiO₄, exhibit a paramagnetic-ferromagnetic transition followed by a spin-glass transition upon cooling down, thereby being characterized as reentrant ferromagnets. Interestingly, the magnetic ordering temperatures of amorphous EuTiO₃ and Eu₂ TiO₄ are comparable to and higher than those of their crystalline counterparts, respectively, indicating the enhancement of ferromagnetic interactions by amorphization. The origin of these features is discussed in terms of both the essential structural difference between amorphous and crystalline oxides and the magnetism unique to the crystalline EuO-TiO₂ compounds. We also find a correlation between the magnitude of ferromagnetic interactions and the covalency of Eu-O bonds.