Abstract
Pliable and lightweight thin-film magnets performing at room temperature are indispensable ingredients of the next-generation flexible electronics. However, conventional inorganic magnets based on f-block metals are rigid and heavy, whereas the emerging organic/molecular magnets are inferior regarding their magnetic characteristics. Here we fuse the best features of the two worlds, by tailoring ε-Fe2O3-terephthalate superlattice thin films with inbuilt flexibility due to the thin organic layers intimately embedded within the ferrimagnetic ε-Fe2O3 matrix; these films are also sustainable as they do not contain rare heavy metals. The films are grown with sub-nanometer-scale accuracy from gaseous precursors using the atomic/molecular layer deposition (ALD/MLD) technique. Tensile tests confirm the expected increased flexibility with increasing organic content reaching a 3-fold decrease in critical bending radius (2.4 ± 0.3 mm) as compared to ε-Fe2O3 thin film (7.7 ± 0.3 mm). Most remarkably, these hybrid ε-Fe2O3-terephthalate films do not compromise the exceptional intrinsic magnetic characteristics of the ε-Fe2O3 phase, in particular the ultrahigh coercive force (∼2 kOe) even at room temperature.
Highlights
Research on flexible magnets is inspired by the strong drive to make consumer electronics thin, lightweight, and wearable; such next-generation flexible electronics should be shapeable into any arbitrary configuration depending on the intended use.[1−3] Progress in the flexible electronics has already opened the door to plethora of advanced applications such as wearable solar cells,[4] flexible transparent electrodes,[2] biocompatible electronic devices,[1,4] stretchable energy harvesters,[1,4] full color displays,[3] and flexible optoelectronic devices.[1]
The multistep and often harsh solution-based reaction pathways used in the first approach are not optimal for the fabrication of conformal, homogeneous, and solvent-free magnetic thin films required in practical applications
The second approach, on the other hand, is more likely to yield high-quality homogeneous thin films, but the organic/molecular magnets based on s- or porbital spins typically suffer from weak magnetization/low coercivity field,[7,10,11,16] low magnetic transition temperature,[8,9,17] structural disorder,[18] and/or instability.[7,11,19]
Summary
Research on flexible magnets is inspired by the strong drive to make consumer electronics thin, lightweight, and wearable; such next-generation flexible electronics should be shapeable into any arbitrary configuration depending on the intended use.[1−3] Progress in the flexible electronics has already opened the door to plethora of advanced applications such as wearable solar cells,[4] flexible transparent electrodes,[2] biocompatible electronic devices,[1,4] stretchable energy harvesters,[1,4] full color displays,[3] and flexible optoelectronic devices.[1]. We present a novel approach to the flexible roomtemperature magnets; we fabricate inorganic−organic superlattice (SL) thin-film structures using the currently strongly emerging atomic/molecular layer deposition (ALD/MLD) technique,[20−25] which combines the leading ALD (atomic layer deposition)[26−28] technology of advanced inorganic thin films and its less exploited MLD (molecular layer deposition)[29,30] counterpart for purely organic films. It should be emphasized that to the parent ALD technology, the combined ALD/MLD method yields high-quality ultrathin films with atomic-level thickness control, large-area homogeneity, and conformality. These superior features derive from the way of introducing the gaseous/evaporated precursors one after another into the reactor in sequential pulses to achieve the desired surface reactions. The well-controlled surface reactions make the ALD/MLD method uniquely suited to the engineering of inorganic−organic SL structures with the required atomic/molecular level accuracy for the individual layer thicknesses.[36−40]
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