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

Composite analysis with Monte Carlo methods: an example with cosmic rays and clouds

The composite (superposed epoch) analysis technique has been frequently employed to examine a hypothesized link between solar activity and the Earth's atmosphere, often through an investigation of Forbush decrease (Fd) events (sudden high-magnitude decreases in the flux cosmic rays impinging on the upper-atmosphere lasting up to several days). This technique is useful for isolating low-amplitude signals within data where background variability would otherwise obscure detection. The application of composite analyses to investigate the possible impacts of Fd events involves a statistical examination of time-dependent atmospheric responses to Fds often from aerosol and/or cloud datasets. Despite the publication of numerous results within this field, clear conclusions have yet to be drawn and much ambiguity and disagreement still remain. In this paper, we argue that the conflicting findings of composite studies within this field relate to methodological differences in the manner in which the composites have been constructed and analyzed. Working from an example, we show how a composite may be objectively constructed to maximize signal detection, robustly identify statistical significance, and quantify the lower-limit uncertainty related to hypothesis testing. Additionally, we also demonstrate how a seemingly significant false positive may be obtained from non-significant data by minor alterations to methodological approaches.Comment: 13 pages, 9 figure

Chemical (Silicate) Garden, One Experiment for Education in STEM Field

Vizualizacija kemijskih procesa iznimno je važna i korisna u edukaciji kemije. Jedan od takvih pokusa je i kemijski vrt koji nastaje dodavanjem topljive soli metala u otopinu natrijeva silikata ili nekog drugog aniona s kojim metalni ion daje koloidni gel koji stvara polupropusnu membranu. Rastom kemijskog vrta nastaju cjevčice različitih veličina i oblika koje podsjećaju na stabalca i biljke u vrtu. U članku se opisuje izrada kemijskog vrta upotrebom lako dostupnih kemikalija. Taj pokus na jednostavan način predočuje precipitaciju povezanu s osmozom i izvrsno je edukativno sredstvo. Ovo djelo je dano na korištenje pod licencom Creative Commons Imenovanje 4.0 međunarodna.Visualization of chemical processes is of primary importance in chemistry education. One of such experiments is the chemical garden, which is formed by addition of soluble metal salts in a solution of sodium silicate, or some other anion that forms a colloid gel with a metal ion. Gel forms tubular semi-permeable membranes, which morphologically resemble garden plants. This paper describes preparation of a chemical garden with easily obtainable chemicals. This simple experiment visualizes osmosis-related precipitation and is a very convenient teaching tool. This work is licensed under a Creative Commons Attribution 4.0 International License