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A series of Co/Mn compensated Ca3Co1+xMn1-xO6 compounds were synthesized. The structure and magnetization were characterized, as well as the dielectric properties were studied. In Co/Mn compensated samples, the well-ranked Co/Mn ionic order is destroyed which manifests the suppression of the formation of the short-range magnetic order. As a result, the freezing anomaly around Tf = 150 K diminishes. For the two Co/Mn compensated samples, the critical field HSF that causes magnetic structure change from ↑↑↓↓ state to ↑↑↓↑ state also increases. The appearance of dielectric peak at the antiferromagnetic phase transition temperature clearly indicates the coupling effect between the spin dipole and electric dipole. The temperature corresponding to the dielectric peak increases with the increasing measurement frequency. The frequency dependence of ferroelectric peak identifies relaxor ferroelectric nature. In dielectric measurements associated with magnetic fields, Δε` and Δtanδ have the same sign elucidating intrinsic magnetodielectric effect of Ca3Co1+xMn1-xO6. For the Co/Mn compensated x = ±0.05 two samples, the suppressed magnetic short-range order also leads to a low diffusion exponent γ and the weak relaxor ferroelectric nature. The thermal activation process of the dipole response is characterized by the Vogel–Fulcher equation and the results confirm that the freezing process of Ca3Co1+xMn1-xO6 is mainly dominated by coupling of polar nanodomains. [ABSTRACT FROM AUTHOR]

A series of Ni2+ doped Ca 3 Co 1- x Ni x MnO 6 (0 ≤ x ≤ 0.15) samples were prepared for this study. Their structure, magnetism and electrical properties were investigated. The results show that the spin of Ni2+ is antiferromagnetically coupled to the neighbor Mn4+ cations. In Ni2+ substituted samples, the short-range magnetic correlation is inhibited and the long-range antiferromagnetic structure is strengthened. Due to the random distribution of Ni2+ substitution in Co2+ sites, the macroscopical ferroelectric domains of Ca 3 CoMnO 6 are destroyed and more polar nanoregions form. With the increase of Ni2+ content, the relaxor behavior of the ferroelectric transition becomes stronger and the activation energy E a decreases monotonously. The enhanced antiferromagnetic interaction also reinforces the dipole correlation, leading to the increased static freezing temperature T f in Ni2+ doped samples. Magnetodielectric coupling is significantly improved due to the magnetic structural variation produced by doping of compound with Ni2+ cations. For the x = 0 sample, the maximal deviation of the dielectric permittivity at H = 7 T relative to the value at H = 0 is about 2.25 %. While for the x = 0.1 and 0.15 samples, this value is 7.5 % at H = 7 T. • Doping with Ni2+ could strengthen the antiferromagnetic interaction effectively. • The Ni2+ doped samples present stronger relaxor ferroelectric nature. • The magnetoelectric coupling effect is much improved in Ni2+ doped samples. [ABSTRACT FROM AUTHOR]

The Cr-doped Ca 3 CoMn 1- x Cr x O 6 (x= 0, 0.05, 0.1, 0.15) polycrystalline samples were prepared using a modified sol-gel method. The structural, magnetic and dielectric properties were systemically investigated. With increasing Cr3+-doping level, the partial Co2+ ions change to Co3+, leading to a decreased lattice volume. Correspondingly, the length of the short-range magnetic correlation is inhibited and a faster dynamic behavior in time dependent magnetization is found. At the benefit of the magnetic structural changes with the introduction of Cr3+ ions, the relaxor degree of the ferroelectric transition that induced by the exchange striction becomes lower, while the activation energy of the frozen polar-nanoregions increases. The replacement of Mn4+ by Cr3+ also leads to a reduced intra-chain antiferromagnetic coupling and the emergence of Co3+-Co3+ ferromagnetic interaction. As consequence, the Curie-Weiss temperature (θ) increases monotonously. The variation in dielectric permittivity with magnetic field confirms the existence of large magnetodielectric coupling in the Ca 3 CoMn 1- x Cr x O 6 (0 ​≤ ​ x ​≤ ​0.15) samples. Especially for the x ​= ​0.15 sample, the permittivity changes by about 7% under the magnetic field of H= 4 ​T. Replacement of Mn4+ by Cr3+ in Ca 3 CoMnO 6 makes part of Co2+ change to Co3+ and the magnetic structure can be modified. Thus, the degree of the ferroelectric relaxation becomes lower, implying that introduction of Cr3+ could help to improve the ferroelectricity. Large magnetodielectric coupling is also verified in Cr3+ doped samples. For x ​= ​0.15 sample, the permittivity changes by 7% under H ​= ​4 ​T. [Display omitted] • Replacement of Mn4+ by Cr3+ makes part of Co2+ change to Co3+. • The magnetic structure can be modified by Cr3+-doping. • The degree of the ferroelectric relaxation becomes lower. • The Cr3+-doped could improve the ferroelectricity. • Large magnetodielectric coupling is verified in Cr3+ doped samples. [ABSTRACT FROM AUTHOR]

The typical ↑↑↓↓ spin order of the one-dimensional frustrated Ca 3 CoMnO 6 breaks the inversion symmetry and results in the ferroelectricity. But the previous calculations predict a much larger ferroelectric polarization than the experimental observation. To comprehend the divergence, Ca 3 CoMnO 6 ceramics were prepared and the magnetic, dielectric properties were studied. In accordance with the formation of short range magnetic correlation, around the antiferromagnetic transition temperature T N the Ca 3 CoMnO 6 ceramics present weak relaxor ferroelectric nature. It implies the existence of polar nanoregions. Thus, the destruction of long range ferroelectric order and the formed polar nanoregions should be responsible for the suppressed macroscopic ferroelectric polarization. The activation energy and static freezing temperature of Ca 3 CoMnO 6 are also calculated. The obtained values are E a = 6.31 × 10−3 eV and T f = 1.5 K, respectively. Both of them are lower about two orders of magnitude than the conventional relaxor ferroelectrics. Magnetic field dependent dielectric permittivity manifests the large magnetodielectric coupling of Ca 3 CoMnO 6. Under the application of field of 7 T, the dielectric permittivity reduces by about 10%. • Around the antiferromagnetic transition temperature T N the Ca 3 CoMnO 6 ceramics present weak relaxor ferroelectric nature. • The Ca 3 CoMnO 6 ceramicspresent weak relaxor ferroelectric nature. • Magnetic field dependent dielectric permittivity manifests the largemagnetodielectric coupling. [ABSTRACT FROM AUTHOR]