Structural and magnetic phase diagram of YMn2−xFex(H,D)y compounds (5 ≤ y ≤ 6) synthesized under high H or D gaseous pressure

Abstract

YMn2−xFexH(D)y compounds with high hydrogen or deuterium content (5 ≤ y ≤ 6) were synthesized under high H or D gaseous pressure (P ≈ 0.8 GPa) at 373 K, in order to determine their structural and magnetic phase diagram. For high Mn content (x < 1) they form complex hydrides (deuterides) with y = 6 and crystallize in a cubic K2PtCl6 structure (Fm-3m space group). For 0.2 ≤ x < 1 the complex hydrides coexist with metal hydrides (y = 5) crystallizing in a cubic MgCu2 type structure (Fd-3m space group). Single phase hydrides with MgCu2 type structure are obtained for 1 ≤ x ≤ 1.5 with interstitial H(D) atoms localized in tetrahedral Y2(Mn,Fe)2 sites (y = 5). The cubic cell volume decreases versus Fe content and is 1.4% larger for the hydride compared to the corresponding deuteride. For x > 1.5 the compounds display an orthorhombic distortion (Pmn21 space group) which is due to H or D ordering in 8 interstitial sites. The magnetic measurements of hydrides and deuterides show a decrease of the magnetization compared to their parent compounds whereas a large irreversibility is observed below the magnetic ordering temperature which depends on the Fe content. Neutron diffraction measurements at 2 and 300 K reveal the existence of only short range order magnetic interactions.