From ordered antiferromagnet to spin glass:: A new phase Mn4Ir7-xMnxGe6

A new ternary phase, Mn4Ir7-xMnxGe6 (0 <= x <= 1.3), was studied by X-ray and neutron powder diffraction and SQUID magnetometry. The crystal structure is cubic, of the U4Re7Si6 type, space group Im3m, Z = 2, with the lattice parameter a((x=0)) = 8.0326(2) angstrom at 295 K. Within the limited range of homogeneity small variations of the composition yield dramatic changes of the magnetic structure. For x = 0 long-range antiferromagnetic order is formed below the transition temperature 228 K, with large magnetic moments on Mn, 4.11(9) mu(B) at 10 K, in a magnetic unit cell a(M) = b(M) = root 2a(C), c(M) = 2a(C). In contrast, for x = 1.3 spin glass behavior is observed below 90 K. The Mn atoms form an ideal cubic framework, on which geometric frustration of competing nearest and next nearest neighbor antiferromagnetic interactions is suggested to explain the composition sensitive magnetic properties. A TiNiSi-type phase, IrMnGe, is found in samples of 1:1:1 composition quenched from the melt. (c) 2005 Elsevier Inc. All rights reserved.