Magnetic behavior of spin-chain compounds, Sr3ZnRhO6 and Ca3NiMnO6, from heat capacity and AC susceptibility studies

Heat-capacity (C) and ac susceptibility measurements have been performed on the spin-chain compounds, Sr₃ZnRhO₆ and Ca₃NiMnO₆, to establish their magnetic behavior and to explore whether there are magnetic frustration effects due to antiferromagnetic coupling of the chains arranged in a triangular fashion. While the paramagnetic Curie temperatures have been known to be large with a negative sign, as though antiferromagnetic interaction is very strong, the results establish that (i) the former apparently undergoes inhomogeneous magnetic ordering only around 15 K, however without spin-glass anomalies, and (ii) the latter orders antiferromagnetically at a relatively low temperature (17 K). Thus, the magnetic frustration manifests differently in these compounds.     

Paramagnetic state NMR and susceptibility measurements in cobalt based Heusler alloys

Susceptibility of Co₂TAl (T Ti, Zr and Hf) and ⁵⁹Co and ²⁷Al Knight shifts have been measured down to the magnetic ordering temperature of these itinerant ferromagnets. The effective hyperfine fields per Bohr magneton at Co and Al nuclear sites have been derived and for Co these are in very good agreement with the spin echo results in ferromagnetic state of these alloys. The effective fields at Al site are small which is the reason that no spin echo signal due to Al could be observed. The sign of the field at Al site is accounted for in terms of an RKKY model of conduction electron polarization with appropriate preasymptotic correction.     

High-performance ion mobility spectrometry with direct electrospray ionization (ESI-HPIMS) for the detection of additives and contaminants in food

High-performance ion mobility spectrometry (HPIMS) with an electrospray ionization (ESI) source detected a series of food contaminants and additive compounds identified as critical to monitoring the safety of food samples. These compounds included twelve phthalate plasticizers, legal and illegal food and cosmetic dyes, and artificial sweeteners that were all denoted as detection priorities. HPIMS separated and detected the range of compounds with a resolving power better than 60 in both positive and negative ion modes, comparable to the commonly used high-performance liquid chromatography (HPLC) methods, but with most acquisition times under a minute. The reduced mobilities, K₀, have been determined, as have the linear response ranges for ESI-HPIMS, which are 1.5–2 orders of magnitude for concentrations down to sub-ng μL⁻¹ levels. At least one unique mobility peak was seen for two subsets of the phthalates grouped by the country where they were banned. Furthermore, ESI-HPIMS successfully detected low nanogram levels of a phthalate at up to 30 times lower concentration than international detection levels in both a cola matrix and a soy-based bubble tea beverage using only a simplified sample treatment. A newly developed direct ESI source (Directspray) was combined with HPIMS to detect food-grade dyes and industrial dye adulterants, as well as the sweeteners sodium saccharin and sodium cyclamate, with the same good performance as with the phthalates. However, the Directspray method eliminated sources of carryover and decreased the time between sample runs. Limits-of-detection (LOD) for the analyte standards were estimated to be sub-ng μL⁻¹ levels without extensive sample handling or preparation.     

Magnetic anomalies in Gd2PdSi3

The results of ac and dc magnetic susceptibility, thermopower and Hall effect measurements of a compound, Gd₂PdSi₃, establish that this compound orders magnetically below T_n = 20 K. Though the ordering appears to be of an antiferromagnetic-type, the paramagnetic Curie temperature is positive with the magnitude being nearly the same as that of T_N, suggestive of the existence of ferromagnetic correlations. The thermopower at 300 K is large, apparently due to Pd 4d electrons, decreasing monotonically with temperature. There is a change in the sign of Hall constant well below T_N Also considering the observation of Kondo-like characteristics above 21K earlier by us, the overall thermal, transport and magnetic behaviour of this compound is interesting.     

Effects of chemical substitution on the valence of Eu IN EuNi5

The effects of substituting Eu by other rare-earth elements on the valence of Eu in EuNi₅ was studied using the 21.7-keV Mössbauer resonance of¹⁵¹Eu. The experimental results support the view of a dominant influence of the local electronic structure on the valence of Eu as compared to the unit-cell volume.On leave from the Tata Institute of Fundamental Research, Bombay-40005, India