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Title: Ferromagnetism in 2D organic iron hemoglobin crystals based on nitrogenated conjugated micropore materials
In this work we study a low-cost two-dimensional ferromagnetic semiconductor with possible applications in biomedicine, solar cells, spintronics, and energy and hydrogen storage. From first principle calculations we describe the unique electronic, transport, optical, and magnetic properties of a π-conjugated micropore polymer (CMP) with three iron atoms placed in the middle of an isolated pore locally resembling heme complexes. This material exhibits strong Fe-localized d z2 bands. The bandgap is direct and equal to 0.28 eV. The valence band is doubly degenerate at the Γ -point and for larger k -wavevectors the HOMO band becomes flat with low contribution to charge mobility. The absorption coefficient is roughly isotropic. The conductivity is also isotropic with the nonzero contribution in the energy range 0.3–8 eV. The xy -component of the imaginary part of the dielectric tensor determines the magneto-optical Faraday and Kerr rotation. Nonvanishing rotation is observed in the interval of 0.5–5.0 eV. This material is found to be a ferromagnet of an Ising type with long-range exchange interactions with a very high magnetic moment per unit cell, m = 6 μ B . The exchange integral is calculated by two independent methods: (a) from the energy difference between ferromagnetic and antiferromagnetic states and (b) from a magnon dispersion curve. In the former case J nn = 27 μeV. In the latter case the magnon dispersion is fitted by the Ising model with the nearest and next-nearest neighbor spin interactions. From these estimations we find that J nn = 19.5 μeV and J nnn = −3 μeV. Despite the different nature of the calculations, the exchange integrals are only within 28% difference.  more » « less
Award ID(s):
1710512
NSF-PAR ID:
10162555
Author(s) / Creator(s):
; ; ;
Date Published:
Journal Name:
Physical Chemistry Chemical Physics
Volume:
21
Issue:
46
ISSN:
1463-9076
Page Range / eLocation ID:
25820 to 25825
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
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Fig. 3(b) shows the tunneling probability T according to the Kane two-band model in the three materials, In0.53Ga0.47As, GaAs, and GaN, following our observation of a similar electroluminescence mechanism in GaN/AlN RTDs (due to strong polarization field of wurtzite structures) [8]. The expression is Tinter = (2/9)∙exp[(-2 ∙Ug 2 ∙me)/(2h∙P∙E)], where Ug is the bandgap energy, P is the valence-to-conduction-band momentum matrix element, and E is the electric field. Values for the highest calculated internal E fields for the InGaAs and GaN are also shown, indicating that Tinter in those structures approaches values of ~10-5. As shown, a GaAs RTD would require an internal field of ~6×105 V/cm, which is rarely realized in standard GaAs RTDs, perhaps explaining why there have been few if any reports of room-temperature electroluminescence in the GaAs devices. [1] E.R. Brown,et al., Appl. Phys. Lett., vol. 58, 2291, 1991. [5] S. Sze, Physics of Semiconductor Devices, 2nd Ed. 12.2.1 (Wiley, 1981). [2] M. Feiginov et al., Appl. Phys. Lett., 99, 233506, 2011. [6] L. Coldren, Diode Lasers and Photonic Integrated Circuits, (Wiley, 1995). [3] Y. Nishida et al., Nature Sci. Reports, 9, 18125, 2019. [7] E.O. Kane, J. of Appl. Phy 32, 83 (1961). [4] P. Fakhimi, et al., 2019 DRC Conference Digest. [8] T. Growden, et al., Nature Light: Science & Applications 7, 17150 (2018). [5] S. Sze, Physics of Semiconductor Devices, 2nd Ed. 12.2.1 (Wiley, 1981). [6] L. Coldren, Diode Lasers and Photonic Integrated Circuits, (Wiley, 1995). [7] E.O. Kane, J. of Appl. Phy 32, 83 (1961). [8] T. Growden, et al., Nature Light: Science & Applications 7, 17150 (2018). 
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