Enhancement of ferromagnetism by nickel doping in the ‘112’ cobaltite EuBaCo2O5.50

Study of the ordered oxygen deficient perovskite EuBaCo2−xNixO5.50 shows that the doping of cobalt sites by nickel induces a strong ferromagnetic component at low temperature in the antiferromagnetic matrix of EuBaCo2O5.50. This system indeed exhibits phase separation, i.e. it consists of ferromagnetic domains embedded in the antiferromagnetic matrix of EuBaCo2O5.50. Besides, a magnetic transition is observed for the first time at 40 K in the undoped and nickel-doped phases, which can be attributed to the ferromagnetic ordering of the Eu3+ moments below this temperature. Moreover sharp ultra magnetization multisteps are observed below 5 K, characteristic of the motion of domain walls in a ‘strong pinning’ system and very different from any metamagnetic transition.