Spin Selectivity of Chiral Mesostructured Iron Oxides with Different Magnetisms

Abstract

The spin-polarized electrons are of particular interest, which make it highly desirable for transferring and manipulating information when combining spin properties with electronics. [3] The spin of charged particles is the intrinsic magnetic moment and is the essential feature underlying the magnetic properties of matter. Thus, these spinpolarized electrons transfer or transport is usually associated with magnetic materials or depends on the presence of strong magnetic fields. Recently, spin-selective transport in the systems that lack inversion symmetry with a large spin-orbit coupling (SOC) has been proposed. [4,5] As an intrinsic property in all matter, the SOC is remarkably enhanced in inorganic crystals with heavy atoms or in organic compounds with curved carbon systems. [6] The chirality-dependent SOC that acts on the propagating electrons in symmetry-breaking potentials is referred to as Dresselhaus or Rashba effect, [7] and chirality induced spin selectivity (CISS), [4,5,8,9] which could affect the spin current, enantiomeric discrimination, electronic memory, spintronic-based magnetic memory devices, etc. [9,10] In a symmetrybreaking matter, the intrinsic magnetic field that is contributed by the self-magnetization due to the spin alignment acting on the magnetic moment of the electron could produce a magnetization-dependent SOC, which might be a key factor for tuning spin selectivity in addition to the chiral parameter and electron motion. [4,5] However, the effect of intrinsic spin alignment on the spin selectivity of chiral matter has not been understood.Here, iron oxides were chosen as the target materials due to their abundant crystal phases with various magnetisms. [11,12] Among them, highly crystalline Fe 3 O 4 , α-Fe 2 O 3 , and γ-Fe 2 O 3 are known to be stable and have been well studied. Hematite (α-Fe 2 O 3 ) is an antiferromagnetic n-type semiconductor with a bandgap of 2.2 eV. [13] All energy bands in α-Fe 2 O 3 are degenerate because of the spatial inversion symmetry. [14] Magnetite (Fe 3 O 4 ) is a ferrimagnetic half-metallic material [15] and maghemite (γ-Fe 2 O 3 ) is a ferrimagnetic n-type semiconductor with bandgap of 2.2 eV. [16] Both the conduction band and valence band in Fe 3 O 4 and γ-Fe 2 O 3 are nondegenerate because of the exchange interaction. [17] All three iron oxides could be obtained by a controllable calcination process. Thus, various chiral mesostructured iron oxides with identical chiral mesostructures but different magnetisms (see below) were obtained from the same precursor, here, which was chosen for investigating the effect of intrinsic spin alignment on the spin selectivity of chiral matter.

Spin-Polarized Photoemission from Chiral CuO Catalyst Thin Films

“…The copper atoms in the oxide form one-dimensional antiferromagnetic chains along the [10] direction. , Since k = 0, this orientation cannot be exactly perpendicular to any chiral plane. We argue that the atomic lattice of the CuO films is chirally distorted, consistent with findings by Widmer et al using XPD and by Bai et al. , using a TEM analysis. The observed monotonous increase of the CD magnitude with the film thickness (Figure b) supports this argument.…”

“…17 Recent transmission electron microscopy (TEM) studies of similar compounds by Bai et al furthermore indicate that the bulk crystal structure of the investigated nickel and iron oxide films is chirally distorted. 28,29 To confirm that the films investigated in this study are chiral as expected, transmission circular dichroism (CD) spectra were acquired from each sample prior to the photoemission measurements. Figure 2a shows representative CD spectra measured on 40 nm CuO thin films of both L and D chirality.…”

“…Switzer et al also demonstrated that the chiral films can act as enantioselective catalysts . Recent transmission electron microscopy (TEM) studies of similar compounds by Bai et al furthermore indicate that the bulk crystal structure of the investigated nickel and iron oxide films is chirally distorted. , …”

Block Copolymer Enabled Synthesis and Assembly of Chiral Metal Oxide Nanoparticle

“…When the direction of the applied magnetic field was changed, the sign of the total CD signals corresponding to the MLCT and LMCT transitions were completely switched, accompanied by a sign reversal in the MCD spectra (Figure a,b). These results are consistent with the magnetic field-dependent MCD behaviors of chiral Fe 3 O 4 films in the previous study . In the total CD spectra (Figure S22c,d) of the chiral Co 3 O 4 NPs array, the CD signals arising from the LMCT and d–d transitions were strongly influenced by the applied magnetic field.…”

“…These results are consistent with the magnetic field-dependent MCD behaviors of chiral Fe 3 O 4 films in the previous study. 79 In the total CD spectra (Figure S22c,d) of the chiral Co 3 O 4 NPs array, the CD signals arising from the LMCT and d−d transitions were strongly influenced by the applied magnetic field. The MCD spectra showed two peaks at around 550 and 690 nm, which were vertically reversed upon changing the direction of the applied magnetic field (Figure 6c,d), which is in good agreement with the MCD response of chiral Co 3 O 4 NPs in the previous literature.…”