Spin-Glass Magnetic Properties of A-Site Columnar-Ordered Quadruple Perovskites Y₂MnGa(Mn_4–xGa_x)O₁₂ with 0 ≤ x ≤ 3

Abstract

Y 2 MnGa(Mn 4−x Ga x )O 12 solid solutions were synthesized at high pressure of ∼6 GPa and high temperature of ∼1570 K for the 0 ≤ x ≤ 3 compositional range. Synchrotron X-ray and neutron powder diffraction were used to study the crystal structures and cation distributions. These solutions adopt the parent structure of the A-site columnar-ordered quadruple perovskite family with space group P4 2 /nmc (No. 137). They have lattice parameters of a = 7.36095 Å and c = 7.753 84 Å (x = 0), a = 7.361 68 Å and c = 7.716 16 Å (x = 1), a = 7.360 34 Å and c = 7.67142 Å (x = 2), and a = 7.363 93 Å and c = 7.616 85 Å (x = 3) at room temperature. The x = 0 sample has a cation distribution of [Y 3+ 2 ] A [Mn 3+ ] A′ [Ga 3+ 0.68 Mn 2+ 0.32 ] A″ [Mn 3.68 Ga 0.32 ] B O 12 with a preferred localization of Ga 3+ in the tetrahedral A″ site and with a small amount of Ga 3+ in the octahedral B site. A complete triple A-site order, [Y 3+ 2 ] A [Mn 3+ ] A′ [Ga 3+ ] A″ -[Mn 3+ 4−x Ga 3+x ] B O 12 , is realized for x ≥ 1. All samples demonstrate spin-glass-like magnetic properties, and the absence of a long-range magnetic order at the ground state at 1.5 K was confirmed by neutron diffraction for the x = 1 sample. First-principles calculations indicated the spin-glass-like magnetic ordering is derived from the Ga substitution to the B sites and gave evidence that the ideal cation distribution could produce robust ferromagnetism in this family of perovskites.

Triple A-Site Cation Ordering in the Ferrimagnetic Y2CuGaMn4O12 Perovskite

“…The magnetic properties of Y 2 CuGaMn 4 O 12 are significantly different from those of the "parent" Y 2 MnGaMn 4 O 12 compound. 14 No long-range magnetic ordering was found in Y 2 MnGaMn 3 GaO 12 and Ho 2 MnGaMn 4 O 12 using neutron diffraction, and only diffuse magnetic scattering was observed. 13,14 Magnetic measurements also suggested spinglass-like magnetic properties of Y 2 MnGaMn 4 O 12 .…”

“…14 No long-range magnetic ordering was found in Y 2 MnGaMn 3 GaO 12 and Ho 2 MnGaMn 4 O 12 using neutron diffraction, and only diffuse magnetic scattering was observed. 13,14 Magnetic measurements also suggested spinglass-like magnetic properties of Y 2 MnGaMn 4 O 12 . 14 This behavior was quite unexpected considering the high concentration of magnetic Mn atoms at the B sites.…”

“…Also, the number of examples of the AA′ 3 B 4 O 12 perovskites could even be larger than the number of examples of fully ordered double A 2 BB′O 6 perovskites, even though it is generally believed that B-site ordering is more common in the latter. , The coordination environments of the A 2 A′A″B 4 O 12 perovskites suggest that they have intrinsic triple A-site ordering. However, the triple ordering by different cations has been experimentally realized just in few examples so far, in R 2 MnGa­(Mn 4– x Ga x )­O 12 (R = Ho and Y) solid solutions, , R 2 CuMnMn 4 O 12 (R = Dy and Y), , and Ca­(Mn 0.5 Cu 0.5 )­FeReO 6 . In few cases of Sm 2 MnMn­(Mn 3 Ti)­O 12 and RMn 3 O 6 , , the A′ and A″ sites are occupied by the same element in different oxidation states (e.g., Mn 3+ at A′ and Mn 2+ at A″).…”

“…This was achieved by selecting cations (Y 3+ /Cu 2+ /Ga 3+ ) with different electronic properties (in other words, with different site preferences). Y 2 CuGaMn 4 O 12 demonstrates completely different magnetic properties in comparison with the “parent” Y 2 MnGaMn 4 O 12 , which shows spin-glass magnetic properties . Ferromagnetic (FM) ordering at the B sites and antiparallel ordering at the A′ or A″ sites take place in Y 2 CuGaMn 4 O 12 at T C = 115 K.…”

“…1,12 The coordination environments of the A 2 A′A″B 4 O 12 perovskites suggest that they have intrinsic triple A-site ordering. However, the triple ordering by different cations has been experimentally realized just in few examples so far, in R 2 MnGa(Mn 4−x Ga x )O 12 (R = Ho and Y) solid solutions, 13,14 R 2 CuMnMn 4 O 12 (R = Dy and Y), 13,15 and Ca(Mn 0.5 Cu 0.5 )-FeReO 6 . 16 In few cases of Sm 2 MnMn(Mn 3 Ti)O 12 and RMn 3 O 6 , 17,18 the A′ and A″ sites are occupied by the same element in different oxidation states (e.g., Mn 3+ at A′ and Mn 2+ at A″).…”