Magnetism in EuAlSi and the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>Eu</mml:mi><mml:mrow><mml:mn>1</mml:mn><mml:mo>−</mml:mo><mml:mi>x</mml:mi></mml:mrow></mml:msub><mml:msub><mml:mi>Sr</mml:mi><mml:mi>x</

The magnetic properties of EuAlSi, a compound comprising a honeycomb lattice of Al/Si atoms and a triangular lattice of Eu atoms, are presented. By means of single-crystal x-ray diffraction, we find that EuAlSi crystallizes in an <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"><a:msub><a:mi>AlB</a:mi><a:mn>2</a:mn></a:msub></a:math>-type structure with space group <b:math xmlns:b="http://www.w3.org/1998/Math/MathML"><b:mrow><b:mi>P</b:mi></b:mrow><b:mn>6</b:mn></b:math>/ and unit cell parameters <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"><c:mrow><c:mi>a</c:mi><c:mo>=</c:mo><c:mn>4.2229</c:mn><c:mo>(</c:mo><c:mn>10</c:mn><c:mo>)</c:mo><c:mspace width="0.16em"/><c:mo>Å</c:mo></c:mrow></c:math> and <e:math xmlns:e="http://www.w3.org/1998/Math/MathML"><e:mrow><e:mi>c</e:mi><e:mo>=</e:mo><e:mn>4.5268</e:mn><e:mo>(</e:mo><e:mn>12</e:mn><e:mo>)</e:mo><e:mspace width="0.16em"/><e:mo>Å</e:mo></e:mrow></e:math>. Our magnetic measurements indicate that EuAlSi is a soft ferromagnetic material with <g:math xmlns:g="http://www.w3.org/1998/Math/MathML"><g:mrow><g:msub><g:mi>T</g:mi><g:mi>Curie</g:mi></g:msub><g:mo>=</g:mo><g:mn>25.8</g:mn><g:mspace width="0.16em"/><g:mi mathvariant="normal">K</g:mi></g:mrow></g:math>. The susceptibility follows the Curie-Weiss law at high temperatures, which allowed us to determine the paramagnetic Curie temperature <j:math xmlns:j="http://www.w3.org/1998/Math/MathML"><j:mrow><j:msub><j:mi>θ</j:mi><j:mi>P</j:mi></j:msub><j:mo>=</j:mo><j:mn>36.2</j:mn><j:mrow><j:mo>(</j:mo><j:mn>1</j:mn><j:mo>)</j:mo></j:mrow><j:mspace width="0.16em"/><j:mi mathvariant="normal">K</j:mi></j:mrow></j:math> and an effective magnetic moment <m:math xmlns:m="http://www.w3.org/1998/Math/MathML"><m:mrow><m:msub><m:mi>μ</m:mi><m:mtext>eff</m:mtext></m:msub><m:mo>=</m:mo><m:mn>8.07</m:mn><m:mrow><m:mo>(</m:mo><m:mn>1</m:mn><m:mo>)</m:mo></m:mrow><m:mspace width="0.16em"/><m:msub><m:mi>µ</m:mi><m:mi>B</m:mi></m:msub><m:mo>/</m:mo><m:mi>Eu</m:mi></m:mrow></m:math>. This value is in agreement with the theoretical value of <o:math xmlns:o="http://www.w3.org/1998/Math/MathML"><o:mrow><o:mn>7.9</o:mn><o:mspace width="0.16em"/><o:msub><o:mi>µ</o:mi><o:mi>B</o:mi></o:msub></o:mrow></o:math> for <q:math xmlns:q="http://www.w3.org/1998/Math/MathML"><q:msup><q:mrow><q:mi>Eu</q:mi></q:mrow><q:mrow><q:mn>2</q:mn><q:mo>+</q:mo></q:mrow></q:msup></q:math> free ion. Moreover, we have prepared the <r:math xmlns:r="http://www.w3.org/1998/Math/MathML"><r:mrow><r:msub><r:mi>Eu</r:mi><r:mrow><r:mn>1</r:mn><r:mo>−</r:mo><r:mi>x</r:mi></r:mrow></r:msub><r:msub><r:mi>Sr</r:mi><r:mi>x</r:mi></r:msub><r:mi>AlSi</r:mi></r:mrow></r:math> solid solution, where the atoms in the triangular lattice were systematically exchanged, in order to study the evolution of the collective quantum properties from the ferromagnetic EuAlSi toward the superconducting SrAlSi. Across the <s:math xmlns:s="http://www.w3.org/1998/Math/MathML"><s:mrow><s:msub><s:mi>Eu</s:mi><s:mrow><s:mn>1</s:mn><s:mo>−</s:mo><s:mi>x</s:mi></s:mrow></s:msub><s:msub><s:mi>Sr</s:mi><s:mi>x</s:mi></s:msub><s:mi>AlSi</s:mi></s:mrow></s:math> solid solution, the unit cell parameters change linearly, following Vegard’s law, and making the system reliable for studying composition dependence of the interplay between the crystal structure and physical properties. As the Sr content increases, i.e., <t:math xmlns:t="http://www.w3.org/1998/Math/MathML"><t:mi>x</t:mi></t:math> increases, we note a consistent reduction of <u:math xmlns:u="http://www.w3.org/1998/Math/MathML"><u:msub><u:mi>μ</u:mi><u:mi>eff</u:mi></u:msub></u:math> and <v:math xmlns:v="http://www.w3.org/1998/Math/MathML"><v:msub><v:mi>T</v:mi><v:mi>Curie</v:mi></v:msub></v:math>. Long-range magnetic order in <w:math xmlns:w="http://www.w3.org/1998/Math/MathML"><w:mrow><w:msub><w:mi>Eu</w:mi><w:mrow><w:mn>1</w:mn><w:mo>−</w:mo><w:mi>x</w:mi></w:mrow></w:msub><w:msub><w:mi>Sr</w:mi><w:mi>x</w:mi></w:msub><w:mi>AlSi</w:mi></w:mrow></w:math> persists up to <x:math xmlns:x="http://www.w3.org/1998/Math/MathML"><x:mrow><x:mi>x</x:mi><x:mo>=</x:mo><x:mn>0.95</x:mn></x:mrow></x:math>, whereas superconductivity is only observed for samples with <y:math xmlns:y="http://www.w3.org/1998/Math/MathML"><y:mrow><y:mi>x</y:mi><y:mspace width="4pt"/><y:mo>&gt;</y:mo><y:mn>0.97</y:mn></y:mrow></y:math>.