The nature of magneto-elastic coupling with the isovalent substitution at the B-site in LaCo$_{1-y}$B$_{y}$O$_{3}$

The influence of magnetic ion doping on the interplay of the lattice~with magnetism in LaCo$_{1-y}$B$_{y}$O$_{3}$ (B = Ni or Fe, y= 0.1, 0.4) has been investigated via neutron scattering techniques. The substitution of~either Ni$^{3+}$ (3d$^{7})$ or Fe$^{3+}$ (3d$^{5})$ does not alter the crystal symmetry~which remains rhombohedral (R-3c) at all temperatures. With doping, the~degree of cooperative octahedral rotations about the (111) axis~increases, but it is only with Ni that such a rotation is accompanied by~a compression along the trigonal axis. The observed crystal distortion~is invoked to break the degeneracy of the magnetic Co$^{3+}$ ions, while maintaining the Co-O bonds at a constant length. The absence of two~distinct types of Co-O bond lengths in the local structure with the~substitution of Fe$^{3+}$ or Ni$^{3+}$ for Co$^{3+}$ (3d$^{6})$ is indicative that, unlike~in the hole doped cobaltites with Ba$^{2+}$ or Sr$^{2+}$ previously studied, the~intermediate spin state of Co is either absent or suppressed. This~leaves us to question the origin of the magnetic interactions, which~most likely arises from a high-spin state of the Co ion.