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Hydrogen can be absorbed into various metals, but generally causes the metals to expand. Here the authors show that when hydrogen is dynamically bound to the lattice, as in dilute Au:H solutions, the gold contracts accordingly.

The La-excess alloys La1+δ(Fe0.85Si0.15)13 (d=0.06 and 0.09) exhibit large magnetocaloric effect which has been attributed to the occurrence of itinerant-electron metamagnetic transition near the Curie temperature TC. The maximum entropy change -ΔSm was shown to be from 4.5 to 11.5 J/kg K for the applied field variation ΔH from 20 to 70 kOe, respectively. The estimated relative cooling power for ΔH=70 kOe was 418 J/kg. The alloys show a typical NaZn13-type cubic structure, featuring a doping-induced magnetovolume effect with the increase in TC. Under the applied pressure up to 2 GPa, the TC as deduced from resistance measurements decreased linearly, ΔTC=113 (for δ=0.06) and 111K (for δ=0.09), together with a corresponding decrease of resistivity, Δp=6.1 µΩ m at room temperature for both samples. At a low pressure, the effect of spontaneous magnetostriction on TC caused by applying the pressure appeared to have a similar magnitude to that of the negative magnetovolume effect caused by La-excess doping. In comparison with other stoichiometric La(Fe1-xSix)13 compounds, the pressure in our case was shown to have a smaller influence on TC. [ABSTRACT FROM AUTHOR]