High Spin Seebeck and Piezoelectric Responses in 2D RuO2(MgF)2 Ferromagnet with Low Lattice Thermal Conductivity via the Optimized Slack Model

Abstract

We present a comprehensive first-principles investigation into the spin-resolved transport, mechanical, and piezoelectric properties of the two-dimensional (2D) RuO2(MgF)2 ferromagnetic system. The material demonstrates semiconducting behavior with an indirect band gap of 0.99 eV and pronounced spin-polarization along the zigzag (Γ-K) direction. An out-of-plane magnetic anisotropy energy of 0.879 meV/cell ensures magnetic stability and is a prerequisite for robust spintronic functionality. Notably, we uncover a large spin Seebeck coefficient of –1.59 mV/K (1.65 mV/K) under minimal hole (electron) doping, highlighting its potential for efficient spin transport applications. The lattice thermal conductivity was obtained via the optimized Slack model and is 0.81 W/m·K at 700 K. Beyond electronic performance, 2D RuO2(MgF)2 displays low in-plane rigidity and moderate strain tolerance, indicative of superior mechanical flexibility. Meanwhile, a large piezoelectric strain coefficient (d11= –1.65 pm/V) indicates strong electromechanical coupling, suitable for strain-responsive and flexible device applications. Consequently, these attributes, including robust spin-polarization, thermal spin-transport, mechanical adaptability, and enhanced piezoelectric performance, establish 2D RuO2(MgF)2 ferromagnet as a promising candidate for next-generation flexible and energy-efficient technologies in spintronics, spin-caloritronics, and piezotronics.