title: High-throughput Designing of Magnetic Antiperovskites for Multifunctional Applications
Creators: name: Singh, Harish Kumar
Publisher: name: UNSPECIFIED
Year: 2024

description: Antiperovskite (AP) materials exhibit various interesting physical properties and have been investigated for various technological applications, including spintronics, superconductivity, and energy storage. Antiperovskites (APs) have a cubic structure that is similar to perovskites, but with an inverted arrangement of anions and cations. Despite their potential, the AP family is not as robust as perovskites, and there is still much to be understood about their stability and magnetic properties. Motivated by the intriguing magnetic properties of AP compounds, the main objective of this thesis was to explore these magnetic multifunctional phenomena in existing AP compounds and in newly predicted AP compounds.

First objective of our study was to predict new magnetic APs with magnetic elements (Cr, Mn, Fe, Co, and Ni) as M in the chemical formula M₃XZ, where X is C and N, and Z are elements from Li to Bi except noble gases and 4f rare-earth metals. To achieve this, we considered three stability criteria: thermodynamic, mechanical, and dynamical. We conducted a high-throughput screening for 630 APs and evaluated their stabilities using density functional theory (DFT) calculations. Our analysis resulted in the prediction of 11
new magnetic APs that fulfilled all three stability criteria. Additionally, we verified the stabilities of 76 experimentally known APs.

AP compounds have been reported to display various magnetic structures such as non- collinear (Γ4g and Γ5g configurations, represented by irreducible notations) antiferromagnetic (AFM), collinear AFM, and ferromagnetic (FM) structures. Therefore, it is necessary to know their magnetic ground state before determining their magnetic properties. We analyzed the magnetic ground state for 54 APs, consisting of 11 newly predicted and 43 experimentally known magnetic APs, by considering seven magnetic configurations. Our analysis revealed that 15 AP compounds have either Γ4g or Γ5g non-collinear AFM as the lowest energy state. While a non-collinear structure was previously reported for Mn-based APs, our study found that Cr-based APs (Cr₃IrN and Cr₃PtN) also stabilized in the Γ4g non-collinear AFM state. We also found that 6 APs exhibit a collinear AFM structure, and 33 APs stabilize in the FM ground state.

Next, we focused on non-collinear magnetic properties that are influenced by strong magnetostructural coupling, negative thermal expansion (NTE), and the piezomagnetic effect (PME). We investigated NTE phenomenon by analyzing the relative change in lattice constant (Δa/a₀ ) between the paramagnetic state and ordered AFM state. To obtain better agreement with experimentally observed (Δa/a₀), we propose the use of the PM state obtained based on the disordered local moment (DLM) approach, rather than using a non-magnetic state as a substitute for the PM state. We studied the PME of non-collinear AFM APs under compressive and tensile biaxial strains. In a few AP compounds, PME induces a phase transition between two non-collinear states Γ4g ⇔ Γ5g states.

At last, we analyzed the topological transport properties, including the anomalous Hall conductivity (AHC) and anomalous Nernst conductivity (ANC), for non-collinear AFM and
FM APs. For the FM APs, the largest AHC and ANC of 1128 S/cm and 6.31 A/mK are obtained in Co₃LiN and Co₃PtN, respectively. In general, FM compounds exhibits a larger AHC and ANC than non-collinear AFM compounds. The large AHC and ANC originate due to the presence of Weyl points near the Fermi energy, as illustrated for Co₃PtN. Moreover, AHC can also be fine-tuned by tuning the energies of Weyl nodes by applying biaxial strain, as demonstrated in the case of Mn₃PdN.

Overall, this study sheds light on the validation of stability for experimentally known AP compounds and the prediction of new AP compounds. Furthermore, it investigates the
magnetic properties of the stable magnetic APs, thus offering new insights for potential technological applications.