Negative pressure driven valence instability of Eu in cubic Eu(0.4)La(0.6)Pd(3).

We report the change in the valency of Eu-ions in the binary intermetallic cubic compound EuPd(3) induced by La doping at rare-earth sites. Doping of La generates negative chemical pressure in the lattice, resulting in a significant increase of the lattice parameter without altering the simple-cubic structure of the compound. Results of dc-magnetic measurements suggest that this increase in the lattice parameter is associated with the valence transition of Eu-ions from Eu(3+) to a mixed-valent state. As Eu(2+)-ions possess a large magnetic moment, this valence transition significantly modifies the magnetic behavior of the compound. In contrast to introducing boron at the vacant body center site of the unit cell to change the valency of Eu-ions, as in the case of EuPd(3)B, our results suggest it can also be altered by doping a rare-earth ion of larger size at the lattice site of Eu in EuPd(3).