William E. Estes

The magnetic properties of several quasi two‐dimensional Heisenberg layer compounds: A new class of ferromagnetic insulators involving halocuprates

Magnetic susceptibility measurements on powdered samples of bis(benzylammonium) tetrachlorocuprate (II), bis(phenethylammonium) tetrachlorocuprate(II), bis(3‐phenyl‐1‐propylammonium) tetrachlorocuprate(II), and bis(benzylammonium) tetrabromocuprate(II) have shown that these four substances order ferromagnetically with Curie temperatures of 8.0±0.5, 9.0±0.2, 7.0±0.5, and 12.3±1.0 K, respectively. Fits of a series expansion for a two‐dimensional lattice to the magnetic susceptibility data obtained from powdered samples in the paramagnetic region yielded exchange constants J for the chloride compounds in the range 16.7–18.8 K, and a value of 25.3 K for the bromide compound. For these fits the <g≳ value of 2.14±0.01 determined from EPR measurements was used. Magnetic susceptibility measurements made at 10 Oe on a single crystal of bis(phenethylammonium) CuCl4 at temperatures just below Tc revealed ratios of susceptibilities of 30:7:1 along the c, a, and b axes, respectively, where the b axis is perpendicular ...

The Synthesis and Static Magnetic Properties of First-Row Transition-Metal Compounds with Chain Structures

The most authoritative reviews of exchange coupling in one-dimensional linear chain systems of transition-metal ions are now several years old.1–4 Recent advances are largely a result of systematic studies of magnetic properties in conjunction with structural determinations. Since a large number of systems have been investigated, we will discuss only one example of each type of behavior that has been found for each of the first-row transition-metal ions, and tabulate data for other systems which have figured prominently in the development of the field. For the most part, only those chain compounds for which rather complete structural and magnetic data are available will be considered here.

Unusual magnetic properties in two copper(II) chelates of Schiff bases derived from .alpha.-amino acids: a dimeric interaction in a structural linear chain

Abstract : Ordinarily one expects the structural and magnetic properties of a given substance to be intimately related, with the dimensionality of the magnetic or electrical interactions that are present reflecting the lattice dimensionality. For example, a cluster of two interacting magnetic ions should obey a theoretical model whose statistics treat only the pair of interacting spins. Systems in which there are interactions between a small number of spins in a definable cluster within a macroscopic crystal are considered to be zero-dimensional (O-D) from a lattice viewpoint. Each cluster is assumed to be isolated from neighboring clusters in the crystal structure, and interactions of spins of the individual clusters with the spins on neighboring clusters are assumed to be absent. This basic idea may be generalized to include one dimensional chains (1-D) and two-dimensional layers (2-D). Eventually such a process leads to the ultimate reality of a three-dimensional (3-D) crystal structure in which there are more or less equally interacting near neighbors. (Author)

Spectral and magnetic properties of linear-chain aminoacid complexes of copper(II), bis(d,l-α-aminobutyrato)- and bis(1-asparaginato)copper(II)

Abstract The electronic structures of the linear-chain aminoacid complexes, bis(l-asparaginato)copper(II), Cu(aspg)2, and bis(d,l-α-aminobutyrato)copper(II), Cu(aba)2, have been elucidated using variable temperature magnetic susceptibility measurements and electronic and electron paramagnetic resonance (EPR) spectroscopy. Despite established linear chain structures, no evidence was found for metal-metal spin exchange coupling to 1.8 °K. EPR spectra demonstrated that metal-ligand covalency is minimal. The g- and hyperfine anisotropy of copper(II)-doped Cd(aspg)2 were completely resolved.

Magnetic properties and superexchange in single chloride-bridged copper(II) chain compounds

Magnetic susceptibility data have been measured in the temperature range 1.75 to 60 K for the following structurally characterized, single chloride-bridged copper(II) chain compounds: dichlorobis(dimethyl sulphoxide)copper(II), dichlorobis(imidazole)copper(II), aquo(caffeine)dichlorocopper(II), and dichloro[2-(2′-methylaminoethyl)pyridine]copper(II). The first two compounds exhibit antiferromagnetic intrachain interactions with exchange coupling constants of –6.1 and –2.1 cm–1, respectively, while the second two compounds exhibit ferromagnetic interactions with J values of 0.48 and 1.58 cm–1 respectively. Except for dichlorobis(imidazole)copper(II), which undergoes long-range magnetic ordering below 7.7 K, the exchange coupling constants become more negative as the angle at the chloride bridge increases from 113.6° in dichloro[2-(2′-methylaminoethyl)pyridine]copper(II) to 144.6° in dichlorobis(dimethyl sulphoxide)copper(II).

Evidence for photoactivated defect induced dielectric anomalies in CuCL

Dielectric measurements of optically irradiated single crystal and composite samples of CuCl prepared and stored under carefully controlled conditions have revealed anomalies in both the capacitance and tan δ at 220 K. At low temperature the capacitance shows a peak versus increasing integrated photon flux which is interpreted as increasing photoinduced Cu° defect precipitate. The results are reproducible and correlate with earlier reports of anomalous diamagnetism (high temperature superconductivity precursor) in CuCl. The observation of a large low frequency dielectric constant in CuCl supports the existence of a low frequency (soft) phonon mode in the CuCl-Cu precipitate composite which could provide a mechanism for high temperature superconductivity.