Enhancement of ferromagnetism by nickel doping in the ‘112’ cobaltite EuBaCo₂O_5.50

Abstract

The study of the ordered oxygen deficient perovskite EuBaCo 2-x Ni x O 5.50 shows that the doping of cobalt sites by nickel induces a strong ferromagnetic component at low temperature in the antiferromagnetic matrix of EuBaCo 2 O 5.50 . This system exhibits indeed phase separation, i.e. consists of ferromagnetic domains embedded in the antiferromagnetic matrix of EuBaCo 2 O 5.50 . Besides, a magnetic transition is observed for the first time at 40K in the undoped and nickel doped phases, which can be attributed to the ferromagnetic ordering of the Eu 3+ moments below this temperature. Moreover sharp ultra magnetization multisteps are observed below 5K, characteristic of motion of domain walls in a "strong pinning" system and very different from any metamagnetic transition.

Switching from unusual to usual ferromagnetism in “112” LnBaCo2O5.50±δ: By calcium doping

“…1c) could be related to the ordering of the Sm 3+ moments. Similar type of ordering in the Eu sample has been reported by Raveau et al [30]. However, such ordering has disappeared in the Ca-doped samples, which could be related to the destruction of the magnetic ordering by substitution with non-magnetic calcium ions.…”

Synthesis and structural and magnetic characterization of the frustrated magnetic system La2Ni4/3−Co Sb2/3O6

“…Phenomena like double hysteresis and multiple steps in M vs. H curves were found in doped cobaltites Ga 1 À x Ca x BaCo 2 O 5.5 [28] and EuBaCo 2 À x M x O 5.5 with M 2 þ ¼ Zn 2 þ , Cu 2 þ [29] and M 2 þ ¼Ni 2 þ [30]. In undoped samples all cobalt ions are Co 3 þ , and the replacement of Ga 3 þ for Ca 2 þ in the first case and Co 3 þ for Zn 2 þ , Cu 2 þ or Ni 2 þ in the second case produce the oxidation of some amount of Co 3 þ to Co 4 þ .…”

Ordered oxygen deficient ‘112’ perovskites, LnBaCo2O5·50+δ : complex magnetism and transport properties

“…They suggest the formation of superparamagnetic clusters within the antiferromagnetic matrix below 40 K, which are associated with the IS Co 3+ species. Moreover, it was reported that the substitution of Ni for Co enhances significantly the ferromagnetism in the Eu-phase (Raveau et al 2006b). More interestingly, ultrasharp magnetization multisteps were observed in these doped systems (figure 11), which were explained by the pinning effect of the Zn 2+ and Cu 2+ cations at the narrow domain walls of the ferromagnetic phase (Raveau et al 2006a).…”

“…Such multisteps, observed in EuBaCo 1⋅85 Ni 0⋅15 O 5⋅57 below 5 K, were attributed to the domain-wall motion in a 'strong pinning' ferromagnetic system, which is very different from any metamagnetic transition previously observed in manganites. The Ni 2+ species change the local crystal field dramatically and induce a very effective pinning of the narrow domain walls at low temperature, responsible for the very sharp and large steps observed for the oxide EuBaCo 1⋅85 Ni 0⋅15 O 5⋅57 (Raveau et al 2006b).…”