Chemical Manipulation of Magnetic Ordering in Mn_1–<i>x</i>Sn_<i>x</i>Bi₂Se₄ Solid–Solutions

Abstract

Several compositions of manganese–tin–bismuth selenide solid–solution series, Mn_1–<i>x</i>Sn_<i>x</i>Bi₂Se₄ (<i>x</i> = 0, 0.3, 0.75), were synthesized by combining high purity elements in the desired ratio at moderate temperatures. X-ray single crystal studies of a Mn-rich composition (<i>x</i> = 0) and a Mn-poor phase (<i>x</i> = 0.75) at 100 and 300 K revealed that the compounds crystallize isostructurally in the monoclinic space group <i>C</i>2/<i>m</i> (no.12) and adopt the MnSb₂Se₄ structure type. Direct current (DC) magnetic susceptibility measurements in the temperature range from 2 to 300 K indicated that the dominant magnetic ordering within the Mn_1–<i>x</i>Sn_<i>x</i>Bi₂Se₄ solid–solutions below 50 K switches from antiferromagnetic (AFM) for MnBi₂Se₄ (<i>x</i> = 0), to ferromagnetic (FM) for Mn_0.7Sn_0.3Bi₂Se₄ (<i>x</i> = 0.3), and finally to paramagnetic (PM) for Mn_0.25Sn_0.75Bi₂Se₄ (<i>x</i> = 0.75). We show that this striking variation in the nature of magnetic ordering within the Mn_1–<i>x</i>Sn_<i>x</i>Bi₂Se₄ solid–solution series can be rationalized by taking into account: (1) changes in the distribution of magnetic centers within the structure arising from the Mn to Sn substitutions, (2) the contributions of spin-polarized free charge carriers resulting from the intermixing of Mn and Sn within the same crystallographic site, and (3) a possible long-range ordering of Mn and Sn atoms within individual {M}_<i>n</i>Se_4<i>n</i>+2 single chain leading to quasi isolated {MnSe₆} octahedra spaced by nonmagnetic {SnSe₆} octahedra