Alternating linear-chain antiferromagnetism in copper nitrate Cu(NO3)2.2.5

Jill C. Bonner

¹

,

S. A. Friedberg

²

,

Hanako Kobayashi

³

et al.

Abstract

Current interest in the behavior of Heisenberg alternating antiferromagnetic quantum chains has been stimulated by the discovery of an unusual class of magnetoelastic spinPeierls systems. Copper nitrate, Cu(N03}i·2.5H20, does not display a spin-Peierls transition, but its dominant magnetic behavior is that of a strongly alternating antiferromagnetic chain with temperature-independent alternation. A remarkable, simultaneous fit is demonstrated between theoretical studies and a wide variety of zero-(low-) field experimental measurements, including susceptibility, magnetization, and specific heat. The fitting parameters are a (degree of alternation)=0.27, J 1/k=2.58 K, gb =2.31, and g1 =2.11. Slight systematic discrepancies are attributed to weak interchain coupling. Theoretical studies also predict a rich variety of behavior in high fields, particularly in the region involving the lower and upper critical fields, Hc 1 =28 kOe and Hc 2 =44 kOe. Experimental specific-heat measurements at H=28.2 and 35.7 kOe show quantitative agreement with theory in this interesting parameter region. The fitting parameters are the same as for zero field and, again, small discrepancies between theory and experiment may be attributed to interchain coupling. The exceptional magnetic characterization of copper nitrate suggests its use for further experimental study in the vicinity of the high-field ordering region.

Neutron scattering study of two-magnon states in the quantum magnet copper nitrate

“…Using the O(α 9 ) expansions [11] for ∆(α) and e 0 gives J = 0.455 ± .002 meV and α = 0.277 ± .006; in agreement with the results of [19] and [20], J = 0.45 meV and α = 0.27. Our calculated values of the thermodynamic parameters J + u J ′ u = 0.581 meV, ∆ = 0.379 meV and e 0 = −0.172 meV agree within error with the experimental values.…”

Magnetic susceptibility in the spin-Peierls systemCuGeO3

“…The main difference between the Hamiltonian given by Eqs. (1) and (), and the one corresponding to the dimerized or alternating bond chain, [15,16] is that in the former both J 1 and J 2 are temperature dependent because δ = δ(T). We calculate the temperature 3 dependence of these couplings by minimizing at each temperature the free energy F of the total Hamiltonian H = H s + H ph with respect to δ (adiabatic approximation).…”

“…Ref. [16]). The results for the calculated susceptibility and the experimental data are shown in Fig.…”

Synthesis, Crystal Structure, and Magnetic Properties of the Linear-Chain Cobalt Oxide Sr5Pb3CoO12

“…Further investigations, including spectroscopic studies, might help to make clear the issue. Seen in Fig.6, a characteristic maximum expected from 1D antiferromagnetism in T vs χ plot for either BonnerFisher or spin-gap models was not observed at all, although the chains were substantially antiferromagnetic [14,15,16,17]. Below approximately 100 K, the inverse magnetic susceptibility gradually starts to apart from the CW line to go down on cooling, indicative of gradual growth of a ferromagnetic component in short range.…”

“…The c−axis constant (3.56251(9)Å) reflects the average of Co to Co distances in the chains; almost are close to ∼3.56Å, but few parts at ∼2.61Å may be somewhat involved. Since the oxygen-coordination environment of all cobalt atoms is not unique, a degree of magnetic uniformity of the present chain compound might be as low as that of the copper oxide Sr 5 Pb 3 CuO 12 , far rather than other well-studied spin-chain compounds [14,15,16,17].…”