Magnetocaloric Properties of ${\hbox{La}}({\hbox{Fe}},{\hbox{Co}},{\hbox{Si}})_{13}$ Bulk Material Prepared by Powder Metallurgy

Abstract

Bulk samples of La(Fe,Co,Si) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">13</sub> have been prepared by powder metallurgy starting from elemental powders and cast master alloys. After sintering at about 1400 K for a few hours, the samples achieve densities of about 7.2 g/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> . For ternary La(Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.893</sub> Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.107</sub> ) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">13</sub> the magnetic entropy change for a field variation of 16 kOe and the adiabatic temperature change for a field variation of 17 kOe amounts to 21.9 J/kgK and 4.2 K at a temperature of 193 K, respectively. For this composition, the thermal and the field hysteresis were determined to be 2.5 K and 2.2 kOe, respectively. With increasing Si content the hysteresis as well as the entropy change decreases. By increasing the Co content from La(Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.865</sub> Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.05</sub> Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.085</sub> ) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">13</sub> to La(Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.803</sub> Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.112</sub> Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.085</sub> ) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">13</sub> the peak temperature of the magnetic entropy change was tailored to the commercial relevant range of 254 K-336 K. The Co-containing samples hardly showed any hysteresis at all. Such powders were pressed in a die and sintered to fully dense blocks of about 23times19times12 mm . The blocks can be machined by conventional techniques to the shapes required in magnetic refrigeration prototypes.