Electrical, Magnetic, and Thermal Properties of XMnPn2 (X = Ba, Eu, and Pn = Sb, Bi)

Author

Silu Huang, Louisiana State University and Agricultural and Mechanical CollegeFollow

Degree

Doctor of Philosophy (PhD)

Department

Physics and Astronomy

Document Type

Dissertation

Abstract

Abstract

Layered manganese pnictides with the general formula XMnPn₂ (X = Ca, Sr, Ba, Eu, or Yb, Pn = Sb, or Bi) are reported as 3D Dirac/Weyl semimetals. Although any magnetic ordering breaks the time-reversal symmetry, the specific spin structure, such as the canted antiferromagnetic structure, is required to realize the Weyl state. This dissertation is designed to investigate magnetic structures and physical properties of topological materials with the general formula XMnPn₂. The compounds we have studied are BaMnSb₂, EuMnSb₂, and BaMnBi₂.

BaMnSb₂ undergoes three magnetic phase transitions at T_C = 690 K, T_N,2 = 450 K and T_N,1 = 286 K. Below T_N,1 = 286 K, Mn moments form the caned antiferromagnetic structure with spin canting angle is about 50° with respect to the c axis. The analysis of Shubnikov-de Haas oscillations reveals the low effective mass and nontrivial Berry phase. The evidence of the Zeeman splitting is also observed near n = 1. Thermal property measurements reveal the low phonon thermal conductivity and the moderate thermopower, which are important for understanding the underlying physics of BaMnSb₂.

EuMnSb₂ undergoes three magnetic phase transitions at T_C = 700 K, T_N,Mn = 346 K, and T_N,Eu = 21 K. Below, Mn moments form the ferromagnetic structure below T_C = 700 K and the C-type antiferromagnetic structure below T_N,Mn = 346 K. Below T_N,Eu = 21 K, Eu Moments form the canted A-type antiferromagnetic structure, with the spin canting angle is about 41° with respect to the a axis at 7 K. Both Mn and Eu sublattices, we obtain that the spin-spin correlation length along the a axis is much shorter than that along the b and c axes, indicating the anisotropic magnetic coupling. The analysis of the longitudinal and transverse magnetoresistance of EuMnSb₂ indicates the magnetoresistance is dominated by spin scattering.

The temperature dependence of the susceptibility reversals that BaMnBi₂ exhibits the antiferromagnetic transition at T_N = 345 K. The temperature dependence of the in-plane resistivity shows semiconductor-like behavior with the activation energy 2.6 meV. Both MR_ab(H)and MR_c(H)show positive magnetoresistance.

Date

7-3-2020

Recommended Citation

Huang, Silu, "Electrical, Magnetic, and Thermal Properties of XMnPn2 (X = Ba, Eu, and Pn = Sb, Bi)" (2020). LSU Doctoral Dissertations. 5318.
https://repository.lsu.edu/gradschool_dissertations/5318

Committee Chair

Jin, Rongying

DOI

10.31390/gradschool_dissertations.5318