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

YbRh3Si7 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 prop-erties in this compound, we synthesized Co doped YbRh3Si7, achieving a record-high ferromagnetic ordering temperature TC = 15.6 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 Yb(Rh1-xCox)3Si7 series.