Sputtered magnetite thin films on polymer substrates for flexible spintronics

For flexible and wearable spintronics, it has thus far been a challenge to develop a magnetic material/polymer heterostructure at room temperature due to the thermal sensitivity of polymers. In order to avoid atomic interdiffusion at the interface, reduce deterioration of the films, and prevent the properties of the substrate material from thermal treatment, development of such heterostructures is essential to accomplish at room temperature. Therefore, integration of magnetite (Fe3O4) thin films with the polymer substrates to construct a thermally stable flexible spintronic component is of great demand. The primary objective of this research work was to optimize the parameters for room temperature growth of ~100 nm thick Fe3O4 films through reactive sputtering by flowing oxygen (O2) and argon (Ar) in the ratio of either 2:20, 3.5:20, or 5:20 sccm on flexible substrates of polycarbonate (PC), polystyrene (PS), polymethyl methacrylate (PMMA), polyvinyl chloride (PVC), and polyethylene terephthalate (PET) developed by drop casting method with a thickness of ~250 µm and defect free surfaces. The results showed that the films grown on PC, PMMA, and PET exhibited the pure form of Fe3O4 with O2 flow rate of 3.5 sccm. The Verwey transition (Tv) of ~123 K, ~124 K, and ~126 K; saturation magnetization (Ms) of ~220 emu/cm3, ~235 emu/cm3, and ~261 emu/cm3; and magnetoresistance (MR) of -7.1%, -7.3%, and -7.8% under H∥Film plane below 60 KOe at 300 K for 100-nm-thick Fe3O4 film on PC, PMMA, and PET substrates, respectively were observed. It was found that the antiferromagnetically (AFM) coupled antiphase boundaries (APBs) played a crucial role in these features. Hence, in the second stage of this research work, the finest set of electrical and magnetic properties out of the 50, 100, 200, and 400 nm thick Fe3O4 thin films developed on flexible PC with an increase in the deposition time (td) from 165 to 1335 s were examined. The maximum value of Ms ~317 emu/cm3 and MR -8.3% were obtained for 200 nm thick film for Fe3O4/PC heterostructure. However, a Tv of ~125 K confirmed the presence of AFM coupled APBs in this architecture, but a negligible loss was observed under flexibility tests i.e. resistivity, (M-H and MR under H(∥ and‎⊥)Film plane at 300 K) with 90° and 45° of bent angles and cyclability experiments on 100, 200, and 400 bending cycles. Therefore, in the next stage, Fe3O4 films with the same thicknesses were grown at room temperature on flexible PMMA substrates as a function of td. With a detection of Tv of ~127 K which is again a signature effect of APBs, Fe3O4/PMMA heterostructure with a film thickness of 200 nm showed an Ms value of ~354 emu/cm3 and MR of -8.6%, larger than the Fe3O4/PC heterostructure. Furthermore, the Fe3O4/PMMA heterostructure showed <5% deterioration in the value of Ms and MR under flexibility and cyclability tests. In the final stage of this research work, Fe3O4/PET heterostructures with 50 nm to 400 nm of film thickness were developed by the same procedure and the results showed that the Tv for these systems was ~122 K which is an indication of almost APB free growth of Fe3O4 films on PET. Besides that, Ms of ~361 emu/cm3, MR of -8.9%, and a negligible loss under different bending tests in comparison to Fe3O4/(PC or PMMA) heterostructures with the same film thickness proved that Fe3O4/PET heterostructure can be a potential candidate for flexible and wearable spintronics

Progress in Fe3O4-centered spintronic systems: development, architecture, and features

Spintronics, or spin-based electronics, is a rapidly growing multidisciplinary research area in the development of physical mechanisms based on the spin as well as the charge of an electron. The initial phase of spintronics had a significant influence on the information storage technology sector after the invention of giant magnetoresistance (GMR) in magnetic multilayers of two different transition metals. In contrast, the next phase of spintronics relies on amalgamating magnetic and semiconducting components to improve electronic gadgets. Spin effects have long been studied in traditional ferromagnetic substances, but research into spin production, relaxation, and spin–orbit relationships in non-magnetic materials has only recently started. The introduction of hybrid spintronic materials and design has created exciting possibilities. This article discusses the recent advancements in the research and development of a variety of Fe3O4-based hybrid spintronic structures based on the half-metallicity and other remarkable capabilities of magnetite (Fe3O4), especially thin-film architectures on traditional, two-dimensional (2D) carbon materials, flexible polymer substrates, and nanocomposites. Half-metallic hybrid systems exhibit strong spin polarity at Fermi energies, whereas 2D structures have exceptional electronic band structures such as Dirac cones and the valley degree of freedom. Massive improvements have been attained in synthesizing and unleashing modern patterns and features from atomic configurations and the heterointerfaces of the epitaxially developed hybrid systems for spintronics. Spin-insertion and recognition, including 2D carbon materials such as graphene and transitional-metal dichalcogenides (TMDs), which are potentially leafy due either to the long spin-life, or the strong spin–orbit coupling, are the most recent areas of increased research interest. Semiconducting matter in groups-IV, III-V, and II-VI, and their nanoscale forms, is another area of great interest. In contrast, using the self-template (ST) approach combined with epitaxial growth of Fe3O4 thin films through any of the physical vapor deposition (PVD) techniques on flexible polymer substrates have triggered the field of wearable and implantable spintronics

Large spin-dependent tunneling magnetoresistance in Fe3O4/PET heterostructures developed at room temperature: A promising candidate for flexible and wearable spintronics

Half-metallic nanocrystalline magnetite (Fe3O4) thin films, with different thicknesses were developed on polyethylene-terephthalate (PET) substrates, by reactive sputtering at room temperature. Fe3O4 film (200-nm thick)/PET heterostructures possess superior electrical and magnetic characteristics, with a Verwey transition temperature (Tv) of ~122 K and a saturation magnetization (Ms) ~ 361 emu/cm3. Furthermore, the antiferromagnetic (AFM)-coupled antiphase boundaries (APBs) controlled the transport properties of the Fe3O4 thin films, due to the tunneling of spin-polarized electrons through the films. Very-high magnetoresistance (MR) value (−8.9%) were observed for HFilm plane, constructed from Fe3O4 (200-nm thick)/PET when H values were below 60 kOe at 300 K. In addition, flexibility tests, to examine resistivity, M-H and MR, were performed using with 90° and 45° bent angles and cyclability experiments were implemented to validate the reproducibility of these characteristics. These outcomes demonstrated that Fe3O4/PET heterostructures may represent a promising candidate for flexible/wearable spintronics

Magnetite thin films grown on different flexible polymer substrates at room temperature: Role of antiphase boundaries in electrical and magnetic properties

Currently, there is an enormous need for flexible electronic devices given their astonishing competencies. In this view, we investigated the structural, electrical, and magnetic characterstics of magnetite (Fe3O4) thin films with a thickness of 100 nm prepared using a reactive RF sputtering technique at 300 K on polycarbonate (PC), polymethyl methacrylate (PMMA), and polythene terephthalate (PET) flexible substrates. The structural properties showed that the films grown on PC, PMMA, and PET substrates exhibited the pure form of Fe3O4 nanostructures by flowing oxygen with a flow rate of 3.5 sccm. The Verwey transition temperatures (Tv) of -123 K, -124 K, and -126 K; saturation magnetization (Ms) values of-220 emu/cm(3y),-235 emu/cm(3), and -261 emu/cm(3); and magnetoresistance (MR) values of-7.1%,-7.3%, and-7.8% under the HIIFilm plane below 60 kOe at 300 K for 100-nm-thick Fe3O4 film on PC, PMMA, and PET substrates respectively were observed. These remarkable results were interpreted and the effect of antiferromagnetically (AFM) coupled antiphase boundaries (APBs) was explained, which suggested that Fe3O4/PET heterostructure can be a most promising component for flexible spintronics