Long-range magnetic order in Mn[N(CN)2]2(pyz) (pyz = pyrazine). Susceptibility, magnetization, specific heat, and neutron diffraction measurements and electronic structure calculations

J L Manson; Q Huang; J W Lynn; H J Koo; M H Whangbo; R Bateman; T Otsuka; N Wada; D N Argyriou; J S Miller

doi:10.1021/ja0024791

Long-range magnetic order in Mn[N(CN)2]2(pyz) (pyz = pyrazine). Susceptibility, magnetization, specific heat, and neutron diffraction measurements and electronic structure calculations

J Am Chem Soc. 2001 Jan 10;123(1):162-72. doi: 10.1021/ja0024791.

Authors

J L Manson¹, Q Huang, J W Lynn, H J Koo, M H Whangbo, R Bateman, T Otsuka, N Wada, D N Argyriou, J S Miller

Affiliation

¹ Department of Chemistry, University of Utah, Salt Lake City, Utah 84112-0850, USA. jlmanson@anl.gov

PMID: 11273613
DOI: 10.1021/ja0024791

Abstract

Using dc magnetization, ac susceptibility, specific heat, and neutron diffraction, we have studied the magnetic properties of Mn[N(CN)2]2(pyz) (pyz = pyrazine) in detail. The material crystallizes in the monoclinic space group P2(1)/n with a = 7.3248(2), b = 16.7369(4), and c = 8.7905 (2) A, beta = 89.596 (2) degrees, V = 1077.65(7) A(3), and Z = 4, as determined by Rietveld refinement of neutron powder diffraction data at 1.35 K. The 5 K neutron powder diffraction data reflect very little variation in the crystal structure. Interpenetrating ReO3-like networks are formed from axially elongated Mn(2+) octahedra and edges made up of mu-bonded [N(CN)2](-) anions and neutral pyz ligands. A three-dimensional antiferromagnetic ordering occurs below T(N) = 2.53(2) K. The magnetic unit cell is double the nuclear one along the a- and c-axes, giving the (1/2, 0, 1/2) superstructure. The crystallographic and antiferromagnetic structures are commensurate and consist of collinear Mn(2+) moments, each with a magnitude of 4.15(6) mu(B) aligned parallel to the a-direction (Mn-pyz-Mn chains). Electronic structure calculations indicate that the exchange interaction is much stronger along the Mn-pyz-Mn chain axis than along the Mn-NCNCN-Mn axes by a factor of approximately 40, giving rise to a predominantly one-dimensional magnetic system. Thus, the variable-temperature magnetic susceptibility data are well described by a Heisenberg antiferromagnetic chain model, giving g = 2.01(1) and J/k(B) = -0.27(1) K. Owing to single-ion anisotropy of the Mn(2+) ion, field-induced phenomena ascribed to spin-flop and paramagnetic transitions are observed at 0.43 and 2.83 T, respectively.