The coupling relationships among the crystal structure, electronic structure, and physical properties of PrMn₂Ge₂ during its magnetic transition

Abstract

Magnetic phase transitions govern the performance frontier of spintronic technologies, yet their microscopic origins in complex intermetallics remain elusive. Here, we resolve this challenge through a combined Physical Property Measurement System (PPMS), in situ X-ray diffraction (XRD), and Maximum Entropy Method (MEM) study of PrMn₂Ge₂, revealing that thermally driven electron transfer from Ge-4^p to Mn-3^d orbitals serves as the dominant mechanism for its sequential transitions: canted ferromagnetic (Fmc, 330 K) → conical magnetic order (Fmi_ab). Crucially, this directional charge migration first enhances Mn-Ge covalency, thereby driving lattice contraction; this amplified covalency subsequently strengthens Mn-Mn exchange interactions, inducing magnetic reorganization; finally, the resultant electron depletion at Pr sites weakens 4^f spin chirality, consequently suppressing topological transport. We thereby propose an electron-lattice-magnetism triple-coupling theory. Building directly on our discovery of electron-transfer-driven phase transitions, this framework establishes orbital-resolved electron dynamics as the central control mechanism - replacing thermal disorder - and enables two practical engineering strategies: Ge-site substitution to modulate charge transfer intensity, alongside epitaxial strain for precise control of magnetoelectric coupling via bond-length tuning. Collectively, this demonstrates electron-transfer engineering as a directly implementable strategy for manipulating topological states in functional magnets.

Keywords

PrMn₂Ge₂ / magnetic transitions / topological Hall effect / crystal structure / electron density

References

[1] Pielichowska K.Phase change materials for thermal energy storage.Prog Mater Sci2014;65:67-123

[2] Wuttig M.Phase-change materials for rewriteable data storage.Nat Mater2007;6:824-32

[3] Jr. K, Pecharsky V, Pecharsky A, Zimm C. Recent developments in magnetic refrigeration.Mater Sci Forum1999;315-317:69-76

[4] Franco V,Ipus J,Moreno-ramírez L.Magnetocaloric effect: from materials research to refrigeration devices.Prog Mater Sci2018;93:112-232

[5] Franco V,Ingale B.ChemInform abstract: the magnetocaloric effect and magnetic refrigeration near room temperature: materials and models.ChemInform2013;44:chin.201324197

[6] Sun Y,Ren Y.Structure, magnetism and low thermal expansion in Tb_1-xEr_xCo₂Mn_y intermetallic compounds.Microstructures2023;3:2023028

[7] Zhao X,Qi J.Low-pressure-driven barocaloric effects at colinear-to-triangular antiferromagnetic transitions in Mn_3-xPt_1+x.Microstructures2023;3:2023022

[8] Napoli S, Llois AM, Bihlmayer G, Blügel S. Magnetic order in RMn₂Ge₂(R=Y,Ca) compounds and their solid solutions with LaMn₂Ge₂.Phys Rev B2007;75:104406

[9] Wang S,He L.Research on the structural and magnetic phase transitions of CeMn₂Ge₂ Alloy.Inorg Chem2024;63:24834-43

[10] Md Din MF,Cheng ZX.Tuneable magnetic phase transitions in layered CeMn₂Ge_2-xSi_x compounds.Sci Rep2015;5:11288 PMCID:PMC4650650

[11] Welter R,Ressouche E.Neutron diffraction study of CeMn₂Ge₂, PrMn₂Ge₂ and NdMn₂Ge₂: evidence of dominant antiferromagnetic components within the (001) Mn planes in ferromagnetic ThCr₂Si₂-type manganese ternary compounds.J Alloys Compd1995;218:204-15

[12] Wang S,Liu D.Giant topological Hall effect and superstable spontaneous skyrmions below 330 K in a centrosymmetric complex noncollinear ferromagnet NdMn₂Ge₂.ACS Appl Mater Interfaces2020;12:24125-32

[13] Kılıç A,Özcan Ş.Magnetic properties of Pr_1-xGd_xMn₂Ge₂ compounds.J Alloys Compd2004;370:47-52

[14] Kennedy S,Campbell S,Dou S.Pressure induced magneto-structural phase transitions in layered RMn₂X₂ compounds (invited).J Appl Phys2014;115:172617

[15] Kervan S,Gencer A.Magnetic characterization of intermetallic PrMn₂Ge_2-xSi_x compounds by AC susceptibility, X-ray diffraction and differential scanning calorimetry studies.J Phys Condens Matter2004;16:4955-62

[16] Bosch-santos B,Saxena RN,Carbonari AW.Characterization of magnetic phase transitions in PrMn₂Ge₂ compound investigated by magnetization and hyperfine field measurements.AIP Adv2017;7:056211

[17] Hou Z,Liu C.Emergence of room temperature stable skyrmionic bubbles in the rare earth based REMn₂Ge₂ (RE= Ce, Pr, and Nd) magnets.Mater Today Phys2021;17:100341

[18] Nagaosa N.Topological properties and dynamics of magnetic skyrmions.Nat Nanotechnol2013;8:899-911

[19] Li S,Zhang X.Magnetic skyrmions for unconventional computing.Mater Horiz2021;8:854-68

[20] Fert A,Sampaio J.Skyrmions on the track.Nat Nanotechnol2013;8:152-6

[21] Granovsky S,Doerr M,Markosyan A.The magnetic structures and the magnetic phase diagram of the TbMn₂(Ge,Si)₂ system.Phys B Condens Matter2007;391:79-87

[22] Nowik I,Felner I.New multiple magnetic phase transitions and structures in RMn₂X₂, X = Si or Ge, R = rare earth.J Magn Magn Mater1995;147:373-84

[23] Ye-qing C,Jing-kui L,Guang-hui R.Crystal structure and magnetic properties of Nd(Mn_1-xFe_x)₂Si₂ compounds.Chin Phys B2009;18:4944-8

[24] Pandey S,Rawat R.Effect of Tb substitution in naturally layered LaMn₂Si₂: magnetic, magnetocaloric, magnetoresistance and neutron diffraction study.J Phys Condens Matter2020;32:035807

[25] Shein I.Structural, elastic, electronic and magnetic properties of ThCr₂Si₂ from first-principles calculations.Solid State Commun2011;151:1165-8

[26] Pavithra N.Structure, electron density distribution using maximum entropy method, optical and magnetic characteristics of Fe doped SnS₂.Cryst Res Technol2024;59:2300145

[27] Li Q,Lou Y,Jin S.Experimental electron density distribution of KZnB₃O₆ constructed by maximum-entropy method.Powder Diffr2023;38:233-9

[28] Kuroiwa Y,Sawada A.Evidence for Pb-O covalency in tetragonal PbTiO₃.Phys Rev Lett2001;87:217601

[29] Huang SX.Extended skyrmion phase in epitaxial FeGe(111) thin films.Phys Rev Lett2012;108:267201

[30] Tokunaga Y,White JS.A new class of chiral materials hosting magnetic skyrmions beyond room temperature.Nat Commun2015;6:7638 PMCID:PMC4506512

[31] Karube K,Reynolds N.Robust metastable skyrmions and their triangular-square lattice structural transition in a high-temperature chiral magnet.Nat Mater2016;15:1237-42

[32] Hou Z,Ding B.Observation of various and spontaneous magnetic skyrmionic bubbles at room temperature in a frustrated kagome magnet with uniaxial magnetic anisotropy.Adv Mater2018;30