Crystal structure and magnetic properties of the solid-solution phase Ca3Co2-vMnvO6

The homogeneity range of the Ca₃Co_2-vMn_vO₆ solid-solution phase covers the entire composition interval from v=0 to 1. A systematic powder X-ray and neutron diffraction, magnetic susceptibility, and magnetization study has been carried out to investigate effects of the Mn-for-Co substitution on structural and magnetic properties. The Mn substitution concerns primarily only the octahedral Co1 site of the Ca₃Co1Co2O₆ crystal structure, whereas the trigonal-prismatic Co2 site structurally is left essentially unaffected. The Ca₃Co_2-vMn_vO₆ crystal structure belongs to space group with unit-cell dimensions (in hexagonal setting) 9.084?a?9.134 Å and 10.448?c?10.583 Å. A cut through the magnetic phase diagram at 10 K shows a ferrimagnetic domain for 0?v<∼0.3 and an antiferromagnetic domain for ∼0.50<v<∼1. The magnetic ordering temperatures are quite low (<∼25/18 K), and even so further magnetic transitions appear to take place at still lower temperature. The legitimity and reliability of the different indicators used to establish the magnetic transitions, their individual accuracy, and mutual consistency are briefly discussed. Variable parameters of the crystal and magnetic structures of Ca₃Co1_1-vMn_vCo2O₆ are determined and their variation with v is briefly discussed in relation to chemical bonding. The magnetic structure in the ferrimagnetic region is essentially the same as that of the pristine v=0 phase, but since the moments at the Co2 site decrease and those at the (Co1,Mn) site increase with increasing v; characteristic traits of ferrimagnetism in magnetic susceptibility and magnetization gradually disappear. The magnetic arrangement in the antiferromagnetic region is characterized by differently sized moments at the (Co1,Mn) and Co2 sites, moments at adjacent sites in each of these sublattices being oppositely oriented along [001].