First-principles study on Hf doped LaMnO<sub>3</sub>

LaMnO₃ is an insulator with perovskite structure, which attracts the intense attention due to its promising properties. However, the previous studies mainly focused on the p-type doping of LaMnO₃, while the n-type doping is under investigated. The effects of doping with various concentrations on the lattice structure, energy band and optical absorption of La_1-x Hf _x MnO₃, as well as the spin valve device consisted of La_1-x Hf _x MnO₃ scattering region sandwiched by two Ba doped LaMnO₃ probes, are studied by the first-principles calculations based on the density functional theory. The results show that the antiferromagnetic or ferrimagnetic structure rather than the ferromagnetic structure is the ground state for La_1-x Hf _x MnO₃. Hf elements exist in La_1-x Hf _x MnO₃ as stable Hf ⁴⁺ ions, showing the properties of n-type doping. When the HF doping concentration x is small (i.e. x ≤ 0.031), the bandgap of La_1-x Hf _x MnO₃ is close to that of the undoped intrinsic phase LaMnO₃, and an isolated impurity level due to Hf doping is formed in the bandgap. The optical absorption spectrum of La_1-x Hf _x MnO₃ shows that its optical absorption edge appears a red shift and the optical bandgap decreases with the increase of x. Meanwhile, the spin valve device composed of La_3/4Ba_1/4MnO₃ as the left and right electrodes and La_3/4Hf_1/4MnO₃ as the center layers is calculated, and the magnetoresistance near the Fermi level reaches about ~ (2.8 × 10⁵)%. Through the gate voltage manipulation, the magnetoresistance can reach up to ~ (5.1 × 10⁵)%. Our work provides a theoretical guideline for design of novel spintronic devices.