Magnetic order in theS=1∕2two-dimensional molecular antiferromagnet copper pyrazine perchlorateCu(Pz)2

Abstract

We present an investigation of magnetic ordering in the two-dimensional S = 1/2 quantum magnet Cu(Pz)2(ClO4)2 using specific heat and zero field muon-spin relaxation (µ + SR). The magnetic contribution to the specific heat is consistent with an exchange strength of 17.7(3) K. We find unambiguous evidence for a transition to a state of three-dimensional long range order below a critical temperature TN = 4.21(1) K using µ + SR even though there is no feature in the specific heat at that temperature. The absence of a specific heat anomaly at TN is consistent with recent theoretical predictions. The ratio of TN/J = 0.24 corresponds to a ratio of intralayer to interlayer exchange constants of |J ′ /J| = 6.8 × 10 −4 , indicative of excellent two-dimensional isolation. The scaled magnetic specific heat of [Cu(Pz)2(HF2)]BF4, a compound with an analogous structure, is essentially identical to that of Cu(Pz)2(ClO4)2 although both differ slightly from the predicted value for an ideal 2D S=1/2 Heisenberg antiferromagnet.

Control of the third dimension in copper-based square-lattice antiferromagnets

“…According to this calculation all four compounds can be considered to be highly two-dimensional with spatial-exchange anisotropies ≤ 10 −3 (although it should be noted that this requires extrapolation of Equation 8 somewhat beyond the range for which it was originally derived 48 ). By this estimate 2 and 3 are among the closest approximations to an ideal SLHAFM of any copper-pyrazine system realised so far, having a spatial exchange ratio (0.03%) slightly lower than that of the related compound [Cu(2-pyridone) 2 (pyz) 2 ](ClO 4 ) 2 (0.05%) 15 , but not as low as the inorganic SLHAFM Sr 2 CuO 2 Cl 2 (0.003%) 12 , or the S = 1/2 coordination polymer Ag(pyz) 2 (S 2 O 8 ) (0.0002%) 13 . The estimated interlayer couplings are similar for 1 and 4, which have comparable interlayer spacings (see Table II); this implies that the difference in ordering temperatures in these two materials arises predominantly from the variation in their intralayer exchange strength described in the previous section.…”

“…The asymmetry spectra for 3 at T ≤ 1.6 K were fitted to the same functional form but with A b = A 0 exp(−Γt) instead of a constant. The fits to the low-temperature spectra for 1 and 4 also use Equation 7 (with the addition of a third precession frequency for 4) and have been previously described elsewhere 12,14 .…”

“…Reducing the interlayer coupling may allow the above effects to come to the fore, permitting the associated theoretical predictions to be investigated in the laboratory. In this context, the closest experimental approximations to ideal 2D magnets have typically made use of copper-oxygen superexchange bonds 12 . However, crystal-engineering efforts have given rise to a number of reduced-dimensionality molecular candidates [13][14][15] in which the interlayer coupling is reduced to levels seen in the best inorganic materials.…”

“…These materials have interlayer spacings that range from 6.5713 to 16.777Å at low temperatures. 4 is the prototypical example of a molecular SL-HAFM 12,19,24 and is used here as a yardstick by which to judge the other compounds.…”

Persistent dynamics in theS=1/2quasi-one-dimensional chain compound Rb4Cu(MoO4Lancaster1, Baker2, Pratt3 et al. 2012Phys. Rev. BSelf Cite141100View full textAdd to dashboardCite

“…12 These factors often make the identification of magnetic ordering difficult using thermodynamic probes. We have shown previously 6,10,11 that muons are often sensitive to LRO that can be very difficult to detect with conventional probes. At temperatures above T N muon-spin relaxation (μ + SR) may also be used to probe the nature of the spin excitations and their transport.…”