Large, Negative Magnetoresistance in an Oleic Acid-Coated Fe₃O₄ Nanocrystal Self-Assembled Film

Abstract

An oleic acid-coated Fe3O4 nanocrystal self-assembled film was fabricated via drop casting of colloidal particles on a SiO2/Si substrate. The film exhibited bifurcation of the zero-field-cooled and field-cooled magnetizations around 250 K. The nonlinear current-voltage (I-V) characteristics between the source and drain electrodes in both zero and non-zero magnetic fields (H) were observed above and below the bifurcation temperature. A large negative magnetoresistance (MR ≈ -60%) was achieved at 200 K and H = 1 T. Even at 295 K and 0.2 T, the negative MR (∼ -50%) persisted. A Fowler-Nordheim plot and power-law scaling of the I-V characteristics revealed that the current flows through two-dimensional (2D) percolated electron tunneling paths. The enlargement of MR can be attributed to spin-dependent electron tunneling between magnetically coupled Fe3O4 nanocrystals self-assembled in 2D ordered arrays.

Large tunneling magnetoresistance in octahedral Fe3O4 nanoparticles

“…7 Substituting the maximum achievable value of P and m, a 50% TMR is foreseen using equation (1). However, similar to our results, an enhanced TMR (>50%) is reported for intergranular tunneling in literature.…”

“…2(b) and S6 a-b in supplementary material 15 depict the current versus voltage plots in different fields at the temperature of 273 K, 200 K and 180 K. The calculated MR values are 40% at 273 K, 49% at 200 K and 69% at 180 K. As the degree of spin polarization near the Fermi level enhances with the decreasing temperature, the TMR value increases at low temperature. 7 For spherical particles of 8 nm, 24% TMR is observed at room temperature (Fig. 2(c)).…”

“…5,6 Exploiting this surface monolayer as the insulating barrier, nanoparticle based MR devices could be designed. 4,7,8 Researchers have also synthesized magnetic core-shell nanoparticles whose core material has very high spin polarization and the shell material acts as an insulator. 9 There are a few reports in literature where a TMR has been observed in multiple tunnel junctions.…”

“…The straight line fit indicates that the tunnelling dominates the electron conduction between the adjacent Fe 3 O 4 nanoparticles. 4,7 Fig . 2(a) shows the electrical transport measurement curves of 8 nm sized octahedral particles under magnetic field of 0, 0.2, 0.5 and 1.0 T at room temperature.…”

“…However, similar to our results, an enhanced TMR (>50%) is reported for intergranular tunneling in literature. 7,24 Inter-granular tunneling is a complex phenomenon and several deviations occur from theoretical calculation because of spin independent conduction between the nanoparticles via hopping and scattering of electrons. 4 Ziese et al 25 had developed an equation for MR in intergranular tunneling using a modified spin hopping model in discontinuous manganite (La 0.7 Ca 0.3 MnO 3 ) films.…”