High-temperature ferromagnetism in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mrow><mml:mi>Cr</mml:mi></mml:mrow><mml:mrow><mml:mn>1</mml:mn><mml:mo>+</mml:mo><mml:mi>x</mml:mi></mml:mrow></mml:msub><mml:msub><mml:mrow><mml:mi>Pt</mml:mi></mml:mrow><mml:mrow><mml:mn>5</mml:mn><mml:mo>−</mml:mo><mml:mi>x</mml:mi></mml:mrow></mml:msub><mml:mi mathvariant="normal">P</mml:mi></mml:math>

Identification of ambient-temperature ferromagnets is crucial for advancing established and emerging technologies including energy production, memory storage, spintronics. The authors outline the discovery basic properties compound Cr${}_{1+x}$Pt${}_{5\ensuremath{-}x}$P, first ternary material in Cr-Pt-P phase space. Sizable single crystals Cr${}_{1+x}$Pt${}_{5\ensuremath{-}x}$P are grown from solution by adding Cr into Pt-P based melts. adopts a tetragonal $P$4/$m\phantom{\rule{0}{0ex}}m\phantom{\rule{0}{0ex}}m$ crystal structure composed CrPt${}_{3}$ slabs that span $a\phantom{\rule{0}{0ex}}b$-plane separated sheets P atoms along $c$-axis. ferromagnetic metal with high Curie temperature T${}_{C}$ = 464.5(5) K extremely strong planar anisotropy estimated fields H${}_{A}$ 345 kOe 220 at 1.8 300 respectively.