An extremely well isolated 2D-antiferromagnetic layer

Selmani, Veli; Landee, Christopher P.; Turnbull, Mark M.; Wikaira, Jan L.; Fan, Xing

doi:10.1016/j.inoche.2010.07.045

Cited by 20 publications

(22 citation statements)

References 25 publications

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“…In what follows we describe a 35 Cl NMR study aimed at exploring the low-temperature magnetic order in Cu(pz) 2 -(ClO 4 ) 2 . For this purpose a single-crystal specimen was mounted on the sample-holder and aligned with its hard axis a parallel to the externally applied static field µ B H = 7.066 T. From previous investigations it is known that in a field of approximately 0.5 T, Cu(pz) 2 (ClO 4 ) 2 exhibits a spin-flop transition below T N , resulting in a bicritical point in the (H,T ) phase diagram.…”

Section: B Nmr Measurementsmentioning

confidence: 99%

“…For this purpose a single-crystal specimen was mounted on the sample-holder and aligned with its hard axis a parallel to the externally applied static field µ B H = 7.066 T. From previous investigations it is known that in a field of approximately 0.5 T, Cu(pz) 2 (ClO 4 ) 2 exhibits a spin-flop transition below T N , resulting in a bicritical point in the (H,T ) phase diagram. 9 In such a low magnetic field, the S/N ratio of the NMR experiments, however, does not allow for accumulating reliable data in a reasonable amount of time and, therefore, this transition cannot be monitored via 35 Cl NMR. The onset of the AFM order in zero field was first established at T N = 4.21 K via µSR experiments.…”

Section: B Nmr Measurementsmentioning

confidence: 99%

“…For the NMR investigations of Cu(pz) 2 (ClO 4 ) 2 , i.e., line-and spin-lattice relaxation measurements at 7.063 T, the 35 Cl nucleus proved to be the most suitable for our study. Typically, we employed standard spin-echo sequences, consisting in π /2 and π pulses of 2 and 4 µs, respectively, with a recycle delay ranging from 0.2 to 0.6 s, depending on temperature.…”

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confidence: 99%

“…A limited number of scans (from 256 to 1024) was sufficient for acquiring signals with a good S/N ratio. The 35 Cl NMR signal of an aqueous NaCl solution at 29.467 MHz (measured separately at room temperature) served as a frequency reference.…”

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Pressure and magnetic field effects on a quasi-two-dimensional spin-12Heisenberg antiferromagnet

et al. 2016

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Cu(pz) 2 (ClO 4 ) 2 (with pz denoting pyrazine, C 4 H 4 N 2 ) is among the best realizations of a two-dimensional spin-1 /2 square-lattice antiferromagnet. Below T N = 4.21 K, its weak interlayer couplings induce a 3D magnetic order, strongly influenced by external magnetic fields and/or hydrostatic pressure. Previous work, focusing on the [H, T ] phase diagram, identified a spin-flop transition, resulting in a field-tunable bicritical point. However, the influence of external pressure has not been investigated yet. Here we explore the extended [p, H, T ] phase diagram of Cu(pz) 2 (ClO 4 ) 2 under pressures up to 12 kbar and magnetic fields up to 7.1 T, via magnetometry and 35 Cl nuclear magnetic resonance (NMR) measurements. The application of magnetic fields enhances T X Y , the crossover temperature from the Heisenberg to the X Y model, thus pointing to an enhancement of the effective anisotropy. The applied pressure has an opposite effect [dT N /dp = −0.050(8) K/kbar], as it modifies marginally the interlayer couplings, but likely changes more significantly the orbital reorientation and the square-lattice deformation. This results in a remodeling of the effective Hamiltonian, whereby the field and pressure effects compensate each other. Finally, by comparing the experimental data with numerical simulations we estimate T BKT , the temperature of the Berezinskii-Kosterlitz-Thouless topological transition and argue why it is inaccessible in our case.

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Section: B Nmr Measurementsmentioning

confidence: 99%

Section: B Nmr Measurementsmentioning

confidence: 99%

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confidence: 99%

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Pressure and magnetic field effects on a quasi-two-dimensional spin-12Heisenberg antiferromagnet

et al. 2016

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“…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. In this way it has been possible to show evidence of changes in universality class as a function of magnetic field in a molecular SLHAFM 16,17 .…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2016

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Using a mixed-ligand synthetic scheme, we create a family of quasi-two-dimensional antiferromagnets, namely, [Cu(HF2)(pyz)2]ClO4 [pyz = pyrazine], [CuL2(pyz)2](ClO4)2 [L = pyO = pyridine-N-oxide and 4-phpyO = 4-phenylpyridine-N-oxide. These materials are shown to possess equivalent two-dimensional [Cu(pyz)2] 2+ nearly square layers, but exhibit interlayer spacings that vary from 6.5713Å to 16.777Å, as dictated by the axial ligands. We present the structural and magnetic properties of this family as determined via x-ray diffraction, electron-spin resonance, pulsed-and quasistatic-field magnetometry and muon-spin rotation, and compare them to those of the prototypical two-dimensional magnetic polymer Cu(pyz)2(ClO4)2. We find that, within the limits of the experimental error, the two-dimensional, intralayer exchange coupling in our family of materials remains largely unaffected by the axial ligand substitution, while the observed magnetic ordering temperature (1.91 K for the material with the HF2 axial ligand, 1.70 K for the pyO and 1.63 K for the 4-phpyO) decreases slowly with increasing layer separation. Despite the structural motifs common to this family and Cu(pyz)2(ClO4)2, the latter has significantly stronger two-dimensional exchange interactions and hence a higher ordering temperature. We discuss these results, as well as the mechanisms that might drive the long-range order in these materials, in terms of departures from the ideal S = 1/2 two-dimensional square-lattice Heisenberg antiferromagnet. In particular, we find that both spin exchange anisotropy in the intralayer interaction and interlayer couplings (exchange, dipolar, or both) are needed to account for the observed ordering temperatures, with the intralayer anisotropy becoming more important as the layers are pulled further apart.

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