Chemical Bonding Governs Complex Magnetism in MnPt₅P

Subtle changes in chemical bonds may result in dramatic revolutions in magnetic properties in solid-state materials. MnPt₅P, a derivative of the rare-earth-free ferromagnetic MnPt₅As, was discovered and is presented in this work. MnPt₅P was synthesized, and its crystal structure and chemical composition were characterized by X-ray diffraction as well as energy-dispersive X-ray spectroscopy. Accordingly, MnPt₅P crystallizes in the layered tetragonal structure with the space group P4/mmm (No. 123), in which the face-shared Mn@Pt₁₂ polyhedral layers are separated by P layers. In contrast to the ferromagnetism observed in MnPt₅As, the magnetic properties measurements on MnPt₅P show antiferromagnetic ordering occurs at ∼188 K with a strong magnetic anisotropy in and out of the ab-plane. Moreover, a spin-flop transition appears when a high magnetic field is applied. An A-type antiferromagnetic structure was obtained from the analysis of powder neutron diffraction (PND) patterns collected at 150 and 9 K. Calculated electronic structures imply that hybridization of Mn-3d and Pt-5d orbitals is critical for both the structural stability and observed magnetic properties. Semiempirical molecular orbitals calculations on both MnPt₅P and MnPt₅As indicate that the lack of 4p character on the P atoms at the highest occupied molecular orbital (HOMO) in MnPt₅P may cause the different magnetic behavior in MnPt₅P compared to MnPt₅As. The discovery of MnPt₅P, along with our previously reported MnPt₅As, parametrizes the end points of a tunable system to study the chemical bonding which tunes the magnetic ordering from ferromagnetism to antiferromagnetism with the strong spin-orbit coupling (SOC) effect.