Exploring the tricritical nature and unconventional magnetoresistance in EuCd2 P2: An in-depth study of complex material characteristics

EuCd2P2, a layered phosphide crystal, exhibits a nonconventional magnetoresistive trend that deviates from typical material behavior. This unique characteristic prompts further intriguing and complex investigation. Herein, we utilize critical exponent analysis, angle-resolved photoemission spectroscopy (ARPES), and density functional theory to uncover physical insights into EuCd2P2. Magnetization analysis reveals a persistent ferromagnetic phase above the antiferromagnetic phase, extending to higher temperatures at high magnetic fields. Critical behavior analysis of H∥ab reveals critical exponents β= 0.2432(2), γ= 0.883(2), and δ= 4.63(1), aligning with a three-dimensional tricritical mean-field model coupled with long-range interaction (σ = 1.53). The H-T phase diagram establishes a tricritical point (H = 620 Oe, T = 18.3 K), signifying diverse spin interactions and magnetic phases. Temperature-dependent ARPES discloses significant modifications in the electronic band spectrum of EuCd2P2 during the spin ordering transitions, characterized by a substantial band gap alteration and valence band splitting. Remarkably, the semiconducting properties of EuCd2P2 remain unaffected throughout these transitions. First-principles simulations unveil a near-degenerate coexistence of layer-antiferromagnetic and -ferromagnetic phases, significant valence band modifications in CdP due to distinct proximity effects induced by the Eu lattice's spin-magnetic moments, and the half-metallic phases in ferromagnetic EuCd2P2 crystals. These findings advance our understanding of magnetic and electronic properties in EuCd2P2.