Antiferromagnet to ferromagnet crossover driven by nonmagnetic Co doping in heavy-fermion YbRh3Si7

${\mathrm{YbRh}}_{3}{\mathrm{Si}}_{7}$ is a heavy fermion compound that stands out among Yb-based heavy fermions, with its relatively high magnetic ordering temperature and large Yb-Yb distance. To investigate the origin of the magnetic properties in this compound, we synthesized Co doped ${\mathrm{YbRh}}_{3}{\mathrm{Si}}_{7}$, achieving a record-high ferromagnetic ordering temperature ${T}_{\mathrm{C}}=15.6\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, only limited by the Co solubility of 20%. Furthermore, we find a crossover from antiferromagnetic to ferromagnetic order with Co doping. The specific heat and magnetotransport measurements show heavy fermion behavior and the persistence of Kondo latticelike behavior in the $\mathrm{Yb}{({\mathrm{Rh}}_{1\ensuremath{-}x}{\mathrm{Co}}_{x})}_{3}{\mathrm{Si}}_{7}$ series.