Epitaxial Patterning of Bi₂FeCrO₆ Double Perovskite Nanostructures: Multiferroic at Room Temperature

Abstract

There is an increasing interest in developing and characterizing multifunctional materials, as they exhibit rich physical and chemical properties and offer exciting opportunities, for example, to miniaturize integrated devices and extend the potential of establishing nanoarchitecture concepts. [ 1 , 2 ] In this context, multiferroic materials [ 3 ] which combine two or more ferroic functionalities are promising for applications in fi elds such as spintronics and non-volatile data storage. [ 4 ] As recently demonstrated [ 5 ] ferromagnetic-ferroelectric multiferroics can be advantageously used to encode the information in electric polarization and magnetization giving rise to a four logic state memory. The coupling between magnetic and electrical properties leads to additional versatility for related devices, such as electric fi eld-controlled magnetic data storage. [ 6 ] The recent emergence of Bi-based double perovskite thin fi lms, such as Bi 2 FeCrO 6 (BFCO) [7][8][9] and Bi 2 CoMnO 6 , [ 10 ] with strong magnetic behavior at room temperature, create opportunities to practically apply multiferroics. In competition with rival technologies, downscaling the feature size of multifunctional materials is an important step to achieve very high-density memory devices. [ 11 , 12 ] However, conventional patterning and lithography techniques applied to these materials with complex multiphase structure often damage or induce changes in stoichiometry, affecting the quality (and thus the properties) of the as-grown fi lm.Non-conventional patterning techniques, such as microcontact printing, [ 13 ] nanoimprint, [ 14 ] and nanostencil patterning, [ 15 , 16 ] are being increasingly explored. Compared to traditional methods (e.g., electron-beam lithography and focused ion beam lithography), they are simpler, faster and even cheaper. In addition, they offer a better process fl exibility and compatibility with several applications, [ 13 ] as they do not require post-deposition etching processes.Here we demonstrate the controlled epitaxial growth by pulsed laser deposition (PLD) of ordered arrays of sub-micrometer BFCO multiferroic structures on niobium-doped SrTiO 3 (Nb-STO) substrates, through a nanostencil, i.e., a shadow mask with nanometer-scale features. We show that the asgrown structures retain their room temperature multifunctional (ferroelectric and magnetic) character even at submicrometer dimensions. Our work represents an important step towards the successful integration of nanometer-scale multiferroic elements in current microelectronics and future nanoelectronics.Growth through a nanostencil allows a simpler parallel and resist-free patterning of complex oxides (as opposed to resistbased methods; see Experimental Section). To obtain large arrays (square millimeters) of multiferroic BFCO nano structures we fi rst optimized the PLD parameters to obtain stoichiometric, epitaxial BFCO multiferroic thin fi lms on single crystal STO substrates, [ 7 , 17 ] and under conditions compatible with stencil technology (e.g....

Combined magnetron sputtering and pulsed laser deposition of TiO 2 and BFCO thin films

“…In Figure S5, we also show the in-plane hysteresis loop recorded on the same area. The existence of hysteresis loops confirm the presence of a switchable ferroelectric polarization, hence confirming the ferroelectric character of the BFCO film produced by the hybrid technique 36, 38 . We carried out a similar investigation on films grown by PLD and MS alone but no piezoresponse was observed (Figure S6), confirming that the hybrid technique was the only deposition approach capable of synthesizing a functional BFCO film.

Figure 8AFM/PFM measurements of BFCO produced with the MS/PLD technique.

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“…5) exhibits additional reflections that can be attributed to the presence of Bi-rich phases 36–38 . The film also has a higher RMS roughness value (~12 nm), and AFM shows large particles 196 ± 50 nm in lateral size and 48 ± 19 nm in height uniformly covering the surface (Fig.…”

Domain rotation induced strain effect on the magnetic and magneto-electric response in CoFe2O4/Pb(Mg,Nb)O3-PbTiO3 heterostructures

“…Although room temperature magnetoelectric effect has been found in a series of single phase materials, such as bulk Ba 3 Co 2 Fe 24 O 41 (Ref. 6) and Bi-based double perovskite thin films, 7 they all have relative complex crystal structure and both FM and FE properties are much weaker than the single functional FE and FM materials. Thus, engineered composite ME materials still promise highest ME coupling effect.…”

Fabrication of complex oxide microstructures by combinatorial chemical beam vapour deposition through stencil masks

“…room temperature PLD [12], high temperature PLD [13,14], non reactive magnetron sputtering [15]). In the present work, we combine it with a Chemical Vapour Deposition (CVD) technique, namely Chemical Beam Vapour Deposition (CBVD).…”