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

Abstract

Abstract. Magnetite (Fe 3 O 4 ) is predicted to be half metallic at room temperature and it shows the highest Curie temperature among oxides. The use of Fe 3 O 4 thin films is therefore promising for spintronic devices such as magnetic tunnel junctions and magnetoresistive sensors. The structural, magnetic, and magnetotransport properties of magnetite are reported to be strongly dependent on the growth conditions. We have developed a very simple deposition chamber for growing thin magnetite films via a chemical vapor deposition process based on the Fe 3 (CO) 12 carbonyl precursor. The structural, morphological and magnetic properties of the as deposited Fe 3 O 4 films have been investigated by means of time of flight secondary ion mass spectrometry, grazing incidence X-ray diffraction, X-ray reflectivity, atomic force microscopy, conversion electron Mössbauer spectroscopy, and superconducting quantum interference device magnetometry. Magnetotransport measurements show magnetoresistance up to -2.4% at room temperature at the maximum applied field of 1.1 T.Resistivity measurements in the 100-300 K temperature range reveal that the magnetotransport properties of the Fe 3 O 4 films are governed by inter-granular tunneling of the spin polarized electrons.The spin polarization is estimated to be around -16%. A possible route for increasing the spinpolarized performances of our magnetite films is proposed. We have also deposited Fe 3 O 4 /MgO/Co stacks by using a combined chemical vapor-and atomic layer-deposition process. The trilayer's hysteresis curve evidences the presence of two distinct switching fields making it promising for magnetite-based magnetic tunnel junction applications.

Synthesis of phase pure iron oxide polymorphs thin films and their enhanced magnetic properties

“…as well as Fe 2? state [7]. From technological importance, the Fe 3 O 4 showing ferrimagnetic nature is highly used in electro-optical industry also due to its high Curie temperature (T c = 585°C) and 100 % spin polarization the thin films of Fe 3 O 4 have wide applications in spintronics [3,7].…”

Influence of the Substrate and Precursor on the Magnetic and Magneto-transport Properties in Magnetite Films

“…These two distinct thermal behaviours observed for the ln(ρ(T)) curves of our films indicate a difference in the fundamental mechanism of the charge transport in these systems. In a polycrystalline film, the thermal dependence of the resistivity with 1/T 1/2 is expected, since the charge transport is dominated by the scattering of grain boundaries [6,18]. In this case, the resistivity depends majority from the grains size, which is associated preferentially to the synthesis conditions and not with the thickness of the film.…”

“…These considerations have been the basis of one of the key concepts to understand the magnetotransport properties of Fe 3 O 4 epitaxial films through the antiphase boundary (APB). The APB is a natural growth defect in epitaxial films, whose origin is associated to discontinuities stoichiometry and structure of the film [9,18]. Resistivity is higher than the bulk one, as consequence of the scattering in the grain boundaries [9,18].…”

“…For example, Bohra et al [19] have observed significant improves in the crystallinity and in the magnetic properties of annealed polycrystalline films, while Mantovan et al [18] correlate the number of vacancies and the stoichiometric characteristics with the magnetic and transport properties of the system.…”

Tailoring the Interface Properties of Magnetite for Spintronics

“…(bottom) Anti-parallel alignment leads to high resistance since there are no matching states available at E F The considerations described above led to a surge of interest in half-metallic ferromagnets, including Fe 3 O 4 , which exhibits nearly 100% spin polarization at the Fermi level [32][33][34][35]. However in magnetite, which is particularly attractive to industry due to its ubiquity and inexpensive production, the expected benefits of 100% spin polarization have never been realized in prototype devices [36][37][38][39][40][41]. In fact, the highest magnetoresistance reported to date for a Fe 3 O 4 based device is a mere 16 %.…”