Crystal Structure and Magnetic and Magnetocaloric Properties of Cobalt Hydroxychlorides Co-2(OH)(4-x)Cl-x

Abstract

A series of isostructural cobalt hydroxychloride salts with the formula Co-2(OH)(4-x)Cl-x were fabricated by using a precipitation method from aqueous solutions of CoCl2 and NaOH with different mixing ratios. The crystal structure was resolved from neutron powder diffraction data, including the location of H atoms of the hydroxide groups. The structure (space group R (3) over barm) consists of an open network of edge-sharing CoO6 and CoO6-2xCl2x octahedra, forming intercrossed 1D channels where the hydrogen atoms reside. Unusually high values of the magnetic entropy change were observed for all samples, probably due to the geometrically frustrated magnetic structure; for example, the magnetic entropy change was 8.3 J/kg K for the sample with Co/Cl > 2.5 at 10 K in a magnetic field change of 20 kOe.