Large room-temperature spin-dependent tunneling magnetoresistance in polycrystalline Fe3O4 films

Abstract

Polycrystalline Fe3O4 films have been prepared by reactive sputtering at room temperature. Transmission electron microscopy images show that the films consist of quite uniform Fe3O4 grains well separated by grain boundaries. It was found that the tunneling of spin-polarized electrons across the antiferromagnetic coupled grain boundaries dominates the transport properties of the films. Magnetoresistance (MR) {=[ρ(H)−ρ(0)]/ρ(0)} shows linear and quadratic magnetic-field dependence in the low-field range when the field is applied parallel and perpendicular to film plane, which is similar to the behaviors observed in the epitaxial Fe3O4 films consisting of a large fraction of antiferromagnetic antiphase domain boundaries. At 300 K, the size of the MR reaches −7.4% under a 50-kOe magnetic field, which is a very large MR for polycrystalline Fe3O4 films.

CVD synthesis of polycrystalline magnetite thin films: structural, magnetic and magnetotransport properties

“…At low field, the MR is linear and parabolic dependent on the angle between the applied field and the sample surface, as typically observed in thin Fe 3 O 4 granular films [7]. This different low-field behaviour is due to the different scattering probability for the tunnelling electrons when the grain magnetizations are parallel or perpendicular to the film plane [41].…”

“…show the sharp change of resistivity typically seen in bulk magnetite at the Vervey transition temperature (120 K). The broadening (sometimes disappearance) of the Verwey transition has been previously observed in polycrystalline magnetite thin films produced by magnetron sputtering [7,15,[34][35][36][37]. The reason for the broadening/disappearance of the Verwey transition is often attributed to cation deficiency (i.e.…”

“…vacancy abundance) [34,35] and/or to the high resistivity at the grains boundaries [7,36,37]. The resistivity of polycrystalline Fe 3 O 4 films is usually higher than the value measured in epitaxial films and single crystals, and the reason is the typical inter-granular tunnelling mechanism that drives the conduction process in polycrystalline magnetite [7,15,36,37].…”

“…Even though very high P values (-80 %) have been observed in epitaxial magnetite films [5], the possibility to obtain full spin polarization in this material is still disputed [4,6]. The large number of recent publications on this topic underlines the high interest in this material [5][6][7][8][9][10][11][12][13][14][15][16], but the practical achievement of (the expected) high performances in functional spintronic devices like magnetic tunnel junctions (MTJ) incorporating Fe 3 O 4 has not been reached yet [9][10][11]13].…”

The investigation of giant magnetic moment in ultrathin Fe3O4 films

“…The 3 nm film shows similar tendencies except for higher resistivity and disappearance of the T v , which implies that the transport property of 3 nm Fe 3 O 4 film is grain-boundary controlled. [26][27][28] We replot the temperature dependence of resistivity as log ρ − T −1/2 , shown in the bottom panel of Fig. 4(c).…”