Torque magnetometry study of magnetically ordered state and spin reorientation in the quasi-one-dimensional S=1/2S=1/2 Heisenberg antiferromagnet CuSb2_2O6_6

We present an experimental study of macroscopic and microscopic magnetic anisotropy of a spin tetramer system \cso using torque magnetometry and ESR spectroscopy. Large rotation of macroscopic magnetic axes with temperature observed from torque magnetometry agrees reasonably well with the rotation of the $\mathbf{g}$ tensor above $T \gtrsim 50$~K. Below 50~K, the $\mathbf{g}$ tensor is temperature independent, while macroscopic magnetic axes continue to rotate. Additionally, the susceptibility anisotropy has a temperature dependence which cannot be reconciled with the isotropic Heisenberg model of interactions between spins. ESR linewidth analysis shows that anisotropic exchange interaction must be present in \csos. These findings strongly support the presence of anisotropic exchange interactions in the Hamiltonian of the studied system. Below $T_N=8$~K, the system enters a long - range antiferromagnetically ordered state with easy axis along the $^*$ direction. Small but significant rotation of magnetic axes is also observed in the antiferromagnetically ordered state suggesting strong spin-lattice coupling in this system.Comment: 10 pages, 10 figure

Study of the local field distribution on a single-molecule magnet-by a single paramagnetic crystal; a DPPH crystal on the surface of an Mn12-acetate crystal

The local magnetic field distribution on the subsurface of a single-molecule magnet crystal, SMM, above blocking temperature (T >> Tb) detected for a very short time interval (~ 10-10 s), has been investigated. Electron Paramagnetic Resonance (EPR) spectroscopy using a local paramagnetic probe was employed as a simple alternative detection method. An SMM crystal of [Mn12O12(CH3COO)16(H2O)4].2CH3COOH.4H2O (Mn12-acetate) and a crystal of 2,2- diphenyl-1-picrylhydrazyl (DPPH) as the paramagnetic probe were chosen for this study. The EPR spectra of DPPH deposited on Mn12-acetate show additional broadening and shifting in the magnetic field in comparison to the spectra of the DPPH in the absence of the SMM crystal. The additional broadening of the DPPH linewidth was considered in terms of the two dominant electron spin interactions (dipolar and exchange) and the local magnetic field distribution on the crystal surface. The temperature dependence of the linewidth of the Gaussian distribution of local fields at the SMM surface was extrapolated for the low temperature interval (70-5 K)

Magnetic anisotropy of spin tetramer system SeCuO3_3 studied by torque magnetometry and ESR spectroscopy

We present an experimental study of macroscopic and microscopic magnetic anisotropy of a spin tetramer system SeCuO$_3$ using torque magnetometry and ESR spectroscopy. Large rotation of macroscopic magnetic axes with temperature observed from torque magnetometry agrees reasonably well with the rotation of the $\textbf{g}$ tensor above $T \gtrsim 50$~K. Below 50~K, the $\textbf{g}$ tensor is temperature independent, while macroscopic magnetic axes continue to rotate. Additionally, the susceptibility anisotropy has a temperature dependence which cannot be reconciled with the isotropic Heisenberg model of interactions between spins. ESR linewidth analysis shows that anisotropic exchange interaction must be present in SeCuO$_3$. These findings strongly support the presence of anisotropic exchange interactions in the Hamiltonian of the studied system. Below $T_N=8$~K, the system enters a long - range antiferromagnetically ordered state with easy axis along the $^*$ direction. Small but significant rotation of magnetic axes is also observed in the antiferromagnetically ordered state suggesting strong spin-lattice coupling in this system.Comment: 14 pages, 13 figure

Ternary Coordination Compounds of Copper(II) with Glycine and 2,2\u27-bipyridine: Synthesis, Structural Characterization, Magnetic and Biological Properties

Three new coordination compounds of copper(II) with glycine (HGly) and 2,2\u27-bipyridine (bipy) were synthesized by solution-based and mechanochemical methods: [Cu(Gly)(H2O)(bipy)][Cu(Gly)(SO4)(bipy)]·6H2O (1a·6H2O), [Cu(Gly)(H2O)(bipy)]2SO4 (1b), [Cu(Gly)(H2O) (bipy)]2SO4·H2O (1b·H2O). The amount of water in the reaction mixture influenced the product of crystallization. All compounds were characterized by X-ray diffraction methods and form 1D infinite chains or 2D sheets of complex ions connected by π-interactions. Compounds 1a·6H2O and 1b were characterized by X-band electron spin resonance (ESR) spectroscopy and the values of g-tensors for Cu(II) ions were determined. Compounds 1a·6H2O and 1b showed pronounced antiproliferative activity toward a panel of six human cell lines. The most impared was HepG2 cell line at 10−5 mol dm−3 concentration (74.5 % reduction of cell growth) followed by moderate activity toward KATO III, Caco-2, MDA-MB-231, PANC-1 and MRC-5 cells at 10−4 mol dm−3 concentration of compounds 1a·6H2O and 1b. Generally, both compounds express similar antiproliferative effect on evaluated cells