The Effect of Thickness-Tunable ZrO2 Shell on Enhancing the Tunneling Magnetoresistance of Fe3O4 Supraparticles

The core-shell Fe3O4@ZrO2 nanoparticles with controllable shell thickness and core dimensions are synthesized using solvothermal approaches. The introduction of the insulator ZrO2 shell allows realizing the enhancement of tunneling magnetoresistance (TMR) effect of the functional nanomaterials. The influences of temperature, magnetic field, and shell thickness on the TMR are explored. With the shell thickness approximate to 3 nm TMR ratio of 10% is obtained, which improves the MR compared to the pure Fe3O4 counterpart of 5.7%. Furthermore, the MR is increased first and then decreases with increase of the shell thickness, which suggests that the addition of insulated shell-layer promotes the electron tunneling among the supraparticles and thereby increases the MR. The fault-cutting data indicate that the tunneling mechanism occurs mainly through the magnetic-insulator interfaces rather than the interior nanoparticle interfaces. In addition, the MR with different core-size presents a monotonic increase with decrease of the size of core.