Colossal magnetoresistance - a huge decrease in resistance in response to a magnetic field - has recently been observed in manganese oxides with perovskite structure. This effect is attracting considerable interest from both fundamental and practical points of view. In the context of using this effect in practical devices, a noteworthy feature of these materials is the high degree of spin polarization of the charge carriers, caused by half metallic nature of these materials. In principle, this allows spin dependent carrier scattering processes, and hence the resistance to be strongly influenced by low magnetic fields. This field control has been demonstrated for low-field intergrain magnetoresistance(MR)
low-field intergrain magnetoresistance(MR) at room temperature has been reported for sintered polycrystalline samples of $Sr_2FeMoO_6$(SFMO). This compound has a structure with a NaCl-type ordering of B sites cations in cubic $ABO_3$ perovskite and this compound are expected to be highly spin polarized even at room temperature. This feature makes SFMO a most prospective candidate for magnetic sensors in a form of tunnel junction devices.
In this study, We have studied SFMO compound that has been not known until now. The phase formation condition, magnetization and M-H curves of bulk SFMO fabricated by standard solid-state reaction was investigated. Also the magnetoresistance of bulk SFMO was measured in order to confirm colossal magnetoresistance effect. Double-ordered perovskite SFMO with a single phase was formed at such sintering condition as 5%$H_2$/Ar reductive ambients, 1200℃, and 3hrs. Bulk SFMO has the high ferromagnetic transition temperature(TC∼420K) and has ferromagnetic characteristics from 8K to room temperature and has about 8% magnetoresistance(MR).
Because SFMO thin films were deposited using sputtering method for commercial application, amorphous SFMO thin films were deposited on LAO, STO substrate using bulk SFMO target and then SFMO thin films were obtained by annealing at 5%$H_2$/Ar reductive ambients. We measured the M-H curve and magnetores istance of SFMO thin films. SFMO thin films show weaker ferromagnetic characteristics than bulk SFMO. Also, SFMO thin films have very low magnetoresis tance at low temperature and increasing temperature, SFMO thin films have not colossal magnetoresistance. We think this reason is that SFMO thin films have not dense thin films and have a second phase.
