The structure, magnetic and dielectric properties of the CaBaCo4-xNixO7 (0 <= x <= 0.1) compounds

We report the structure, magnetic and dielectric behaviors of the polar magnet CaBaCo4-xNixO7 (0 <= x <= 0.1). The Rietveld refinements results for polycrystalline samples shows that the orthorhombic distortion gradually decreases with the increase of Ni2+ content. Different from the undoped sample, two antiferromagnetic phases and a ferrimagnetic phase can be observed in M -T curves for Ni-doped samples. For x = 0.06, the antiferro-magnetic phase around 79K competes with another antiferromagnetic phase that appears around 62K, giving a magnetic plateau between 62K and 79K. With increasing Ni-doping, the ferrimagnetic phase transition peak moves to lower temperature and it fades gradually, while the antiferromagnetic phase transition peak around 79K shifts to higher temperature. The magnetization behaviors could be attributed to the enhanced antiferro-magnetic interactions and the reorientation of the adjacent spins of cobalt ions due to the introduction of Ni2+ doping. As a result, the Ni-doped samples present stronger magnetoelectric coupling than the undoped sample, as well as an enhanced polarization.