Fe doping effect on EuTiO₃: The magnetic properties and giant magnetocaloric effect

Abstract

The magnetic properties and magnetocaloric effect for EuTi 1-x Fe x O 3 (x = 0.05, 0.1) compounds are investigated. When a part of Ti 4+ ions were substituted by Fe ions, the AFM ordering can be significantly changed to be FM. The EuTi 1-x Fe x O 3 (x = 0.05, 0.1) compounds exhibit a PM to FM transition with decreasing temperature and the Curie temperature is 6 K. Under the field changes of 1 T, ÀΔS M max and RC are valued to be 10.1 J/kg K and 50.2 J/kg for EuTi 0.95 Fe 0.05 O 3 ; 9.6 J/kg K and 47.7 J/kg for EuTi 0.9 Fe 0.1 O 3 , without magnetic and thermal hysteresis. RC is almost twice as much as EuTiO 3 (27 J/kg) as substitution of Fe 3+ ions for Ti 4+ ions, which may be attributed to the magnetic transition (AFM to FM). Therefore, the giant ÀΔS M max and large RC suggest the EuTi 1-x Fe x O 3 compounds are good materials for magnetic refrigerant. K E Y W O R D S magnetic entropy change, magnetic phase transformation, magnetocaloric effect

Cation Valences and Multiferroic Properties of EuTiO3 Co-Doped with Ba and Transition Metals of Co/Ni

“…The cause that turned the Co/Ni co-doped samples from antiferromagnetic to ferromagnetic is not clear. As mentioned in the introduction, doping at the Ti 4+ site with lower-valence cations usually resulted in such a transition [ 19 , 20 , 21 , 22 , 23 , 25 ], which was correlated to the oxygen vacancies or the mixed valences of Eu 2+ /Eu 3+ in some previous works [ 19 , 25 , 45 ]. However, as shown in Section 3.1 , although oxygen vacancies were indeed present in EuTiO 3 and Eu 0.7 Ba 0.3 TiO 3 , the Co/Ni co-doped samples did not seem to contain oxygen vacancies, because other charge compensation mechanisms than the oxygen vacancies—i.e., the increase in Eu 3+ numbers with a decrease in Ti 3+ numbers—were in action for the doping of Co 2+ /Ni 2+ at the Ti 4+ site.…”

“…The dopants at A-site included alkaline-earths, such as Sr, Ba and Ca [ 10 , 13 , 14 , 15 , 16 , 17 ], as well as rare-earths other than Eu (e.g., La, Ce and Sm) [ 17 , 18 ], whereas the dopants at B-site were mainly transition metals (TMs) (e.g., Cr, Ni, Mn, Fe, Co, Nb, Zr, etc.) [ 19 , 20 , 21 , 22 , 23 , 24 ] and a few main group-III elements (e.g., Al and Ga) [ 25 ].…”

“…In contrast to the “inertness” of ferroelectricity to chemical doping, the magnetic properties of EuTiO 3 are affected notably by the chemical doping at either the A or B site. In particular, doping of either TMs or main group elements at the B-site by ions of lower valence than Ti 4+ , such as Cr 3+ , Ni 2+ , Mn 2+ , Fe 3+ , Co 2+ , Al 3+ and Ga 3+ , results in ferromagnetism [ 19 , 20 , 21 , 22 , 23 , 25 ], whereas isovalent doping at the B site by tetravalent ions, such as Zr 4+ , only leads to a decrease in antiferromagnetic ordering temperature (T N ) over the entire substitution range of EuTi 1− x Zr x O 3 , i.e., T N = 5.6 K at x = 0 to T N = 4.1 K at x = 1 [ 24 ]. Furthermore, the effect of doping higher-valence ions at the B site was found to be dependent on the dopant concentration.…”

Viable Materials with a Giant Magnetocaloric Effect

“…A few contain precious Rh (e.g., FeRh [24,222,278,279] and Tb 3 Rh [270]). Many contain critical rare earth, such as Eu in Eu 2 In [140], EuTiO 3 [114,135,156,195] doped with Al [113], Cr [196], Mn [134], Co [151], Ni [119], Ba [157,206], Nb [110,170,195] and Eu in other compounds [133,232,240,251]; Gd in GdAlO 3 [158], GdFeO 3 [138,162], GdCrO 3 [183], GdCrO 4 -ErCrO 4 [202], GdScO 3 [117,124], Gd 2 CoMnO 6 [155], Gd 2 BaNiO 5 [152], GdCrTiO 5 [143], GdCo 2 B 2 [271], GdCoC 2 [171], RuSr 2 GdCu 2 O 8 [208], etc. ; Tb in TbFeO 3 [176], TbMn 2 O 5 [179], Tb 2 CoMnO 6 [132], Tb 5 Ge 2−x Si 2−x Mn 2x [255], Tb 4 Gd 1 Si 2.035 Ge 1.935 Mn 0.03 [197], etc.…”