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Title: Magnetic order in the S=1/2 two-dimensional molecular antiferromagnet, copper pyrazine perchlorate Cu(Pz){sub 2}(ClO{sub 4}){sub 2}.

Abstract

We present an investigation of magnetic ordering in the two-dimensional S=1/2 quantum magnet Cu(Pz){sub 2}(ClO{sub 4}){sub 2} using specific heat and zero-field muon-spin relaxation ({mu}{sup +}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 T{sub N} = 4.21(1) K using {mu}{sup +} SR even though there is no feature in the specific heat at that temperature. The absence of a specific heat anomaly at T{sub N} is consistent with recent theoretical predictions. The ratio of T{sub N}/J=0.24 corresponds to a ratio of intralayer to interlayer exchange constants of |J{prime}/J| = 6.8 x 10{sup -4}, indicative of excellent two-dimensional isolation. The scaled magnetic specific heat of [Cu(Pz){sub 2}(HF{sub 2})]BF{sub 4}, a compound with an analogous structure, is very similar to that of Cu(Pz){sub 2}(ClO{sub 4}){sub 2} although both differ slightly from the predicted value for an ideal 2D S=1/2 Heisenberg antiferromagnet.

Authors:
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Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org.:
USDOE Office of Science (SC); Engineering and Physical Sciences Research Council (EPSRC); Research Corp.; 1851 Commission; CNPq; CAPES; FAPERJ
OSTI Identifier:
948796
Report Number(s):
ANL/MSD/JA-58565
Journal ID: ISSN 0163-1829; PRBMDO; TRN: US200907%%200
DOE Contract Number:
DE-AC02-06CH11357
Resource Type:
Journal Article
Resource Relation:
Journal Name: Phys. Rev. B; Journal Volume: 75; Journal Issue: 9 ; 2007
Country of Publication:
United States
Language:
ENGLISH
Subject:
36 MATERIALS SCIENCE; COPPER COMPLEXES; MAGNETIC SPECIFIC HEAT; MAGNETS; PERCHLORATES; PYRAZINES; RELAXATION; SPIN; ORDER PARAMETERS; ANTIFERROMAGNETISM

Citation Formats

Lancaster, T., Blundell, S. J., Brooks, M. L., Baker, P. J., Pratt, F. L., Manson, J. L., Connor, M. M., Xiao, F., Landee, C. P., Chaves, F. A., Soriano, S., Novak, M. A., Papageorgiou, T., Bianchi, A., Wosnitza, J., Schlueter, J. A., Materials Science Division, Oxford Univ., Rutherford Appleton Lab., Eastern Washington Univ., Clark Univ., Inst. de Fisica, UFRJ, and Hochfeld-Magnetlabor Dresden. Magnetic order in the S=1/2 two-dimensional molecular antiferromagnet, copper pyrazine perchlorate Cu(Pz){sub 2}(ClO{sub 4}){sub 2}.. United States: N. p., 2007. Web. doi:10.1103/PhysRevB.75.094421.
Lancaster, T., Blundell, S. J., Brooks, M. L., Baker, P. J., Pratt, F. L., Manson, J. L., Connor, M. M., Xiao, F., Landee, C. P., Chaves, F. A., Soriano, S., Novak, M. A., Papageorgiou, T., Bianchi, A., Wosnitza, J., Schlueter, J. A., Materials Science Division, Oxford Univ., Rutherford Appleton Lab., Eastern Washington Univ., Clark Univ., Inst. de Fisica, UFRJ, & Hochfeld-Magnetlabor Dresden. Magnetic order in the S=1/2 two-dimensional molecular antiferromagnet, copper pyrazine perchlorate Cu(Pz){sub 2}(ClO{sub 4}){sub 2}.. United States. doi:10.1103/PhysRevB.75.094421.
Lancaster, T., Blundell, S. J., Brooks, M. L., Baker, P. J., Pratt, F. L., Manson, J. L., Connor, M. M., Xiao, F., Landee, C. P., Chaves, F. A., Soriano, S., Novak, M. A., Papageorgiou, T., Bianchi, A., Wosnitza, J., Schlueter, J. A., Materials Science Division, Oxford Univ., Rutherford Appleton Lab., Eastern Washington Univ., Clark Univ., Inst. de Fisica, UFRJ, and Hochfeld-Magnetlabor Dresden. Mon . "Magnetic order in the S=1/2 two-dimensional molecular antiferromagnet, copper pyrazine perchlorate Cu(Pz){sub 2}(ClO{sub 4}){sub 2}.". United States. doi:10.1103/PhysRevB.75.094421.
@article{osti_948796,
title = {Magnetic order in the S=1/2 two-dimensional molecular antiferromagnet, copper pyrazine perchlorate Cu(Pz){sub 2}(ClO{sub 4}){sub 2}.},
author = {Lancaster, T. and Blundell, S. J. and Brooks, M. L. and Baker, P. J. and Pratt, F. L. and Manson, J. L. and Connor, M. M. and Xiao, F. and Landee, C. P. and Chaves, F. A. and Soriano, S. and Novak, M. A. and Papageorgiou, T. and Bianchi, A. and Wosnitza, J. and Schlueter, J. A. and Materials Science Division and Oxford Univ. and Rutherford Appleton Lab. and Eastern Washington Univ. and Clark Univ. and Inst. de Fisica, UFRJ and Hochfeld-Magnetlabor Dresden},
abstractNote = {We present an investigation of magnetic ordering in the two-dimensional S=1/2 quantum magnet Cu(Pz){sub 2}(ClO{sub 4}){sub 2} using specific heat and zero-field muon-spin relaxation ({mu}{sup +}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 T{sub N} = 4.21(1) K using {mu}{sup +} SR even though there is no feature in the specific heat at that temperature. The absence of a specific heat anomaly at T{sub N} is consistent with recent theoretical predictions. The ratio of T{sub N}/J=0.24 corresponds to a ratio of intralayer to interlayer exchange constants of |J{prime}/J| = 6.8 x 10{sup -4}, indicative of excellent two-dimensional isolation. The scaled magnetic specific heat of [Cu(Pz){sub 2}(HF{sub 2})]BF{sub 4}, a compound with an analogous structure, is very similar to that of Cu(Pz){sub 2}(ClO{sub 4}){sub 2} although both differ slightly from the predicted value for an ideal 2D S=1/2 Heisenberg antiferromagnet.},
doi = {10.1103/PhysRevB.75.094421},
journal = {Phys. Rev. B},
number = 9 ; 2007,
volume = 75,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}
  • Four Cu(II) complexes with the RR,SS-Edds{sup 4-} and SS-HEdds{sup 3-} anions are synthesized, and their crystal structures are studied. In the compounds [Cu2(RR,SS-Edds)] . 6H{sub 2}O (I) and Ba2[Cu(RR,SS-Edds)](ClO{sub 4}){sub 2} . 8H{sub 2}O (II), the ligand forms hexacoordinate chelate [Cu(Edds)]{sup 2-} complexes with the N atoms and O atoms of the propionate groups in the equatorial positions and the O atoms of the acetate groups in the axial vertices. In the compounds Ba[Cu(SS-HEdds)]ClO{sub 4} . 2H{sub 2}O (III) and Ba3[Cu2(RR,SS-Edds){sub 2}](ClO{sub 4}){sub 2} . 6H{sub 2}O (IV), one of the propionate arms, the protonated arm in III and themore » deprotonated arm in IV, does not enter into the coordination sphere of the Cu atom. An acetate arm moves to its position in the equatorial plane, and the free axial vertex is occupied by an O atom of the perchlorate ion. In I-IV, the lengths of the equatorial Cu-N and Cu-O bonds fall in the ranges 1.970-2.014 and 1.921-1.970 A, respectively. The axial Cu-O bonds with the acetate groups and ClO{sub 4}{sup -} anions are elongated to 2.293-2.500 and 2.727-2.992 A, respectively. In structure I, the second Cu atom acts as a counterion forming bonds with the O atoms of two water molecules and three O atoms of the Edds ligands. In II-IV, the Ba{sup 2+} cations are hydrated and bound to the O atoms of the anionic complexes and (except for one of the cations in IV) ClO{sub 4}{sup -} anions. The coordination number of the Ba cations is nine. The structural units in I-IV are connected into layers. In I, an extended system of hydrogen bonds links the layers into a framework. In II and III, the layers are linked only by weak hydrogen bonds, one bond per structural unit. In IV, ClO{sub 4}{sup -} anions are bound to the Ba and Cu atoms of neighboring layers, thus serving as bridges between the layers.« less
  • We report on high-field magnetization, specific heat, and electron-spin-resonance (ESR) studies of the quasi-two-dimensional spin-1/2 Heisenberg antiferromagnet [Cu(pyz){sub 2}(HF{sub 2})]PF{sub 6}. The frequency-field diagram of ESR modes below T{sub N} = 4.38 K is described in the frame of the mean-field theory, confirming a collinear magnetic structure with an easy-plane anisotropy. The obtained results allowed us to determine the anisotropy/exchange interaction ratio, A/J = 0.003, and the upper limit for the interplane/intraplane exchange interaction ratio, J'/J = 1/16. It is argued that despite the onset of three-dimensional long-range magnetic ordering the magnetic properties of this material (including high-magnetic-field magnetization andmore » nonmonotonic field dependence of the Neel temperature) are strongly affected by two-dimensional spin correlations.« less
  • Magnetic properties of quasi-one-dimensional S=1/2 Heisenberg antiferromagnet Sr{sub 2}Cu(PO{sub 4}){sub 2} were investigated by temperature and field dependence of AC susceptibility down to 0.03K. A sharp peak was observed at T{sub N}=0.085K on the temperature dependence of AC susceptibility indicating long-range magnetic ordering. Taking into account the exchange constant, J/k{sub B}=143K (Hamiltonian =J-bar S{sub i}S{sub i+1}), the ratio k{sub B}T{sub N}/J is 0.06%. Sr{sub 2}Cu(PO{sub 4}){sub 2} is, therefore, one of the best one-dimensional Heisenberg antiferromagnet known so far.
  • A competitive solvation study of Al(ClO/sub 4/)/sub 3/, Ga(ClO/sub 4/)/ sub 3/, In(ClO/sub 4/)/sub 3/, r-- acetone-- dimethylsulfoxide (DMSO) and water-- acetone- hexamethylphosphoramide (HMPT) mixtures has been carried out by direct / sup 1/H and sup 31/P nuclear magnetic resonance (NMR) techniques. At low temperature, proton and ligand exchange are slow enough in these systems to permit the observation of signals for bulk and coordinated molecules of water and the organic bases (DMSO and RMPT). Both DMSO and HMPT compete effectively with water for coordination sites in the Al/sup 3+/, Ga/sup 3+/, and In/sup 3+/ systems, with steric effects dominatingmore » t he HMPT results. Both Al/sup 3+/ and In/sup 3+/ are able to bind a maximum of two to three HMPT molecules, for example. In contrast, UO/sup 2+/ is solvated selectively by the organic molecules to the allowed maximuxa of 4 molecules per cation. /sup 1/H and /sup 31/P NMR spectral results support the formation of only the mono-, tri-. and tetra-HMPT solvation complexes. (auth)« less