Two-dimensional hybrid nanosheets towards room-temperature organic ferrimagnetic semiconductor

Abstract

Organic magnetic semiconductors have aroused much attention for spintronic applications. However, it remains challenging to achieve organic semiconductors with strong room-temperature ferromagnetism. Here, we report a two-dimensional (2D) tetragonal organic-inorganic ferrimagnetic (FIM) semiconductor of Fe₁₄Se₁₆(peha)_0.7 (peha = pentaethylenehexamine) with excellent thermal stability and a Curie temperature (T_C) higher than 519 K. Magnetic and Mössbauer measurements reveal a long-range magnetic ordering in single crystalline Fe₁₄Se₁₆(peha)_0.7 nanosheets. The saturation magnetization and coercivity are 5.9 emu g⁻¹ and 0.42 kOe at 5 K, which slightly reduces to 4.6 emu g⁻¹ and ∼0 Oe at 300 K. A direct optical bandgap of 2.22 eV is obtained by tuning electronic structure of β-Fe₃Se₄ host layers through spacer layers consisting of Fe³⁺ and peha. Electrical and Seebeck coefficient data indicate that the n-type semiconductor follows the thermally-activated conduction mechanism (lnρ $\propto$$\propto$ T⁻¹) in a range of 130–300 K with an activation energy (E_a) of 62.69 meV. Thermal conductivity is 2.5 W m⁻¹ K⁻¹ at 300 K, while the Wiedemann-Franz law is strongly violated according to electrical-thermal transport data due to weak incorporation of organic spacer layers and host layers. This study sets the stage for exploiting new room-temperature organic magnetic semiconductor systems for spintronic materials.