Field induced single ion magnet based on a quasi octahedral Co ii complex with mixed sulfur oxygen coordination environment

Synthesis and characterization of structure and magnetic properties of the quasi octahedral complex pipH2 [Co TDA 2] 2H2O I , pipH22 piperazine dication, TDA2 amp; 8722; thiodiacetic anion are described. X ray diffraction studies reveal the first coordination sphere of the Co II ion, consisting of two chelating tridentate TDA ligands with a mixed sulfur oxygen strongly elongated octahedral coordination environment. SQUID magnetometry, frequency domain Fourier transform FD FT THz EPR spectroscopy, and high level ab initio SA CASSCF NEVPT2 quantum chemical calculations reveal a strong easy plane type magnetic anisotropy D amp; 8776; 54 cm amp; 8722;1 of complex I. The complex shows field induced slow relaxation of magnetization at an applied DC field of 1000 O

Spin gap behavior and charge ordering in \alpha^{\prime}-NaV_2O_5 probed by light scattering

We present a detailed analysis of light scattering experiments performed on the quarter-filled spin ladder compound $\alpha^\prime$-NaV$_{2}$O$_{5}$ for the temperature range 5 K$\le$T$\le$300 K. This system undergoes a phase transition into a singlet ground state at T=34 K accompanied by the formation of a super structure. For T$\leq$34 K several new modes were detected. Three of these modes are identified as magnetic bound states. Experimental evidence for charge ordering on the V sites is detected as an anomalous shift and splitting of a V-O vibration at 422 cm$^{-1}$ for temperatures above 34 K. The smooth and crossover-like onset of this ordering at T$_{\rm CO}$= 80 K is accompanied by pretransitional fluctuations both in magnetic and phononic Raman scattering. It resembles the effect of stripe order on the super structure intensities in La$_2$NiO$_{4+\delta}$.Comment: 36 pages, 11 figures, accepted for publication in PRB (sept.99

EPR spectra of deuterated methyl radicals trapped in low temperature matrices

EPR spectra of CHD₂, and CD₃ radicals have been investigated in low-temperature matrices of H₂, D₂, and Ne at temperatures 1.6–4.2 K. A method of condensation from the gas phase on a cold substrate has been used. With decreasing sample temperature, a transformation of the shape of the CD₃ spectrum in H₂, D₂, and Ne matrices and CHD₂ spectrum in H₂ and Ne was observed. This transformation was reversible in the above temperature range. The temperature effects are explained as reflecting a change in the populations of the lowest rotational states of the radicals. Based on the present data and known results for deuterated methyl radicals in Ar obtained in photolytic experiments, we compare the temperature behavior of the EPR spectra for the radicals trapped in various matrices. As a result an existence of a hindering barrier for the radical rotation is suggested