摘要:

The magnetic properties of cobalt complexes of BTCA (BTCA = 1,3,5 benzenetricarboxylic acid) have been investigated. The trianion of the BTCA ligand has the ability to create lattices with competing interactions leading to frustration. A dodecahydrate phase, Co3BTCA2(H2O)12, is obtained from room temperature aqueous solutions and consists of pendant chains with very small interactions. Varying the reaction conditions leads to an amorphous phase which displays many of the features of a spin glass: hysteresis, remanent magnetization, frequency dependent susceptibility, aging effects, and an inverse field dependence of the dc susceptibility. The dehydration state and corresponding magnetic properties are strongly dependent on the temperature of the original reaction. Reaction temperatures below 78 °C lead to the pendant chain while temperatures greater than 78 °C yield more interesting glassy phases. These phases exhibit many properties of reentrant spin glasses.

ISSN:1058-725X    

DOI:10.1080/10587259508031859

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The antiferromagnetic (TN= 2.3 K) compound MnCu(obbz). 5H2O [obbz=oxamido- bisbenzoato was synthesized by Nakatani et al1. It was reported to yield, upon dehydration, a ferromagnetic compound MnCu(obbz).1H2O with Tc= 14 K. The exact crystal structure of both these MnCu-based compounds is not known. The ferromagnetic ordering, however, is suggested to occur when four non-coordinated water molecules leave causing a re-adjustment of the relative positions of ID ferrimagnetic chains comprising Mn(II) and Cu(II) ions. We report on the ac-susceptibility (Xac), dc magnetization (VSM) and TG data on MCu(obbz). nH2O (M=Mn or Co). For vacuum dehydrated MnCu-compound, a large divergence inXac(T) data is observed. FC and ZFC magnetization data and M(H) loops confirm the ferromagnetism with a saturation magnetization of 480 G at 4.5 K. TG data taken on, the precursor MnCu(obbz).nH2O between R.T. and 130°C, however, indicates that 'n' cannot be specified unequivocally for the ferromagnetic compound. A sharp peak is obtained inXacat 27 K for one of the CoCu(obbz).nH2O samples indicating magnetic ordering.

ISSN:1058-725X    

DOI:10.1080/10587259508031860

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

We apply a model recently proposed for the analysis of the spin transitions in molecular crystals of the spin active complexes of Fe(II) to analysis of some experimental data. The molecules undergoing the spin transition are modeled by octahedra of variable size which interact when they are immediate neighbors in the crystal lattice. We show that if the crystal geometry is allowed to relax in the course of the transition the cooperative sign of the effective intermolecular interaction appears and thus the spin transition becomes a first order phase transition with the finite change of the fraction of the high spin molecules as a function of temperature. The magnitude of the effective interaction is estimated from the data on the crystal compressibility and within the assumption of the van der Waals character of the forces responsible for the effective interaction.

ISSN:1058-725X    

DOI:10.1080/10587259508031861

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

New Haldane gap compounds with S=1 have been characterized by single-crystal X-ray analyses and magnetic measurements. From these results, it has been found that the magnitude of the Haldane gaps can be controlled by substituting the bridging groups and in-plane ligands. The magnetic measurements of quasi-one-dimensional halogen-bridged binuclear Ru complexes with S=3/2. Ru2(CH3COO)4X (X=Cl, Br and 1) have revealed that the Br- and I-bridged compounds show one-dimensional antiferromagnetic interactions but no spin-Pelerls transition over the temperature range measured, while the C1-bridged compound shows no magnetic interaction among binuclear RU2units through the bridging Cl−ions along the chain but spin-crossover behavior between S=3/2 and 1/2 in the binuclear Ru2unit. The oxalato-bridged Fe2+compound with S=2, Fe(ox).2Hz0 has no Haldane gap but shows metamagnetism under the high magnetic field.

ISSN:1058-725X    

DOI:10.1080/10587259508031862

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Entirely separate 3D-A.F. magnetic ordering processes are observed for the ionic components of the rock salt like materials [Cr (NH3)6[FeCl6and [RU (NH3)6[FeCl6through high resolution a.c. susceptibility and Mossbauer spectroscopy measurements.

ISSN:1058-725X    

DOI:10.1080/10587259508031863

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

A. C. susceptibility and iron-57 Mossbauer spectroscopy measurements are used to investigate the first examples of cooperative magnetic ordering phenomena for FeCl32-anions and the related methanol and aquo adducts. Depending on the counter cation and/or solvate identity examples of uncanted antiferromagnetic and canted (weakly ferromagnetic) three dimensional order are observed with critical temperatures - 7K.

ISSN:1058-725X    

DOI:10.1080/10587259508031864

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The syntheses, magnetic properties, and reactions with nitrogen donors of a number of related A2[Fe2CI6salts (A = H-TMPP, PPh4, Et4N, AsPh4, ppn) ([H-TMPP Cl = [H-P(C6H2(OMe3)3Cl) as well as the neutral cluster Fe4CI8(THF)6are discussed.

ISSN:1058-725X    

DOI:10.1080/10587259508031865

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The anions and cations of the complex [Fe(cp)2[FeBr4(cp=h5- cylopentadiene) behave as isolated non-interacting Heisenberg and Ising layers respectively. The S =1/2 cations order at ∼ 2.5K while the S =5/2 anions order at ∼ 12.5K. A variety of experimental data confirm independent 3D antiferromagnetic ground states for the component ions as opposed to the usual expectation of ferrimagnetism resulting from the collinear antiferromagnetic interaction of cation and anion sublattices of highly different spin in e.g., a simple two magnetic sublattice system.

ISSN:1058-725X    

DOI:10.1080/10587259508031866

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Copper(II) halides continued to provide examples of interesting low dimensional systems. In the cases discussed, inequivalent Cu-X-Cu linkages are the basis for the novel magnetic behavior. (N-methylphenethylammonium)CuCl3provides an example of chains with alternating FM interactions. The compound (C6N2H8)2Cu3Br8contains chains of Cu3Br82-trimers. Strong AFM coupling in the trimers lead to S=1/2 ground states, which are then coupled together to form FM chains. Cu(cyclam)CuCl4contains chains with alternating FM/AFM interactions, where JFM≫|JAFM| so they should behave as S=l Haldane chains at low T. The compound (Et3MeN)3Cu4Cl11contains FM tetrametric units linked into chains by weak AFM coupling, defining a potential S=2 Haldane chain at low T.

ISSN:1058-725X    

DOI:10.1080/10587259508031867

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Several metal phosphate solids have been prepared from hydrothermal reaction methods that involve vanadium and either alkali metal ions or organic amine templating agents. A variety of magnetic behavior is observed, depending on the structures of the solids that are isolated. Binuclear [(VO)2Cl2(H2O)2(PhAsO3H)2Ph4PCl, trinuclear [(C2H5NH3)2(V0)3H2O- (C2H5PO3)6, hexanuclear [(C2H5)4N2(vO)6(H2O)2(C2H5PO3)6, 16-atom cluster [V16O20(OCH2CCH2O)8(H2O)4and polymeric [AVOPO4, A= Na, NH3materials have been prepared. Some materials exhibit long range antiferromagnetic phase transitions that result from strong lattice interactions between magnetic centers. Ferromagnetic behavior is also observed in [H3N(CH2)3NH3(VO)3(OH)2(H2O)2(PO4)2with a ferromagnetic phase transition at Tc=5K. The magnetic data are interpreted in terms of the molecular and crystallographic data.

ISSN:1058-725X    

DOI:10.1080/10587259508031868

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor