Synthesis,Nuclear,and Magnetic Structures and Magnetic Properties ofMn_3(OH)_2(SO_4)_2(H_O)_2

摘要

Mn_3(OH)_2(SO_4)_2(H_2O)_2and its deuterated anlaogue were synthesized by a hydrothermal technique and characterized by differential thermal analysis,thermogravimetric analysis,and IR spectroscopy.Its nuclear structure,determined by single-crystal X-ray analysis and Rietveld analysis of neutron powder-diffraction data,consists of a 3D network of chains of edge-sharing Mn(1)O_6,running along the c axis,connected by the apices of Mn(2)O_6 and SO_4 units.It is isostruc-tural to the nickel analogue.Determi-nation of the magnetic structure and measurements of magnetization and heat capacity indicate the coexistence of both magnetic long-range ordering(LRO)and short-range ordering(SRO)below a Neel temperature of 26 K,while the SRO is retained at higher temperatures.The moments of the two independent Mn atoms lie in the bc plane,and that of Mn(l)rotates continuously by 54 deg towards the c axis on decreasing the temperature from 25 to 1.4 K.While the SRO may be associated with frustration of the moments within a Mn_3 trimer,the LRO is achieved by antiparallel alignment of the four symmetry-related trimers within the magnetic unit cell.A spin-flop field,measured by dc and ac magnetization on a SQUID,is observed at 15 kOe.