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Mathias Kraken

Publications and source records attributed to Mathias Kraken.

2 recordsLinked to original sources

A setup for fast cooling of liquids in sealed containers and at intermediate temperatures

We present a simple layout of a fast cooling system for liquids in sealed containers utilizing the large temperature gradients of cold nitrogen gas. Our system is optimized for about 20 cylindrical containers of 500 cm3 but the setup allows for simple up- and downscaling as well as the use of arbitrary containers. We have characterized the cooling performance of our system experimentally for liquid temperatures in the range from room temperature down to the freezing point at ~ -2 °C. With our system we achieve container cooling times as low as 3 min, a significant reduction if compared to cooling times with common methods in the range of 8 to 40 min. Modeling of the cooling process proves that convection within the liquid is crucial for quick heat transfer and that the most important factor limiting the cooling rate is the thermal conductivity of the container material.

physics.ins-det

Spectroscopic study of the magnetic ground state of Nb$_{1-y}$Fe$_{2+y}$

We have investigated single crystals and polycrystals from the series Nb$_{1-y}$Fe$_{2+y}$, $-0.004 \leq y \leq 0.018$ by electron spin resonance, muon spin relaxation and Mössbauer spectroscopy. Our data establish that at lowest temperatures all samples exhibit bulk magnetic order. Slight Fe-excess induces low-moment ferromagnetism, consistent with bulk magnetometry ($\simeq 0.06 ~μ_B/{\rm Fe}$), Nb--rich and stoichiometric NbFe$_2$ display spin density wave order with small magnetic moment amplitudes of the order $\sim 0.001 - 0.01 ~μ_B/{\rm Fe}$. This provides microscopic evidence for a modulated magnetic state on the border of ferromagnetism in NbFe$_2$.

cond-mat.str-el