Competition between ferromagnetic and antiferromagnetic interactions in Pr1-xGdxB4

We have prepared single crystals of Pr 1- x R x B 4 (R = La, Ce and Gd) and measured the magnetic susceptibility and specific heat in order to elucidate the origin of the ferromagnetic interaction in PrB 4 and the competition of the ferro- and antiferromagnetic interactions in this system. The ferromagnetic transition temperature decreases with x at nearly the same rate in Pr 1– x La x B 4 and Pr 1– x Gd x B 4 , suggesting that the magnetic moments of Gd do not affect the ferromagnetic order. In Pr 0.82 Gd 0.18 B 4 and Pr 0.8 Gd 0.2 B 4 , ferromagnetic to antiferromagnetic transitions appear with decreasing temperature. The development of antiferromagnetic correlation between Pr and Gd breaks the ferromagnetic order and induces antiferromagnetic correlation among Pr atoms. These results indicate that two types of magnetic interactions with different origin are present in PrB 4 .