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Ca 3 Co 2- x Al x O 6 (x = 0, 0.02, 0.04, 0.06, 0.08 and 0.1) were prepared via the conventional sol-gel method. The structure, magnetic, dielectric and magnetodielectric properties were investigated. The Rietveld structural refinement confirms the rhombohedral structure of the samples. The positive Curie-Weiss temperature θ and magnetic coupling exchange constants J indicate the dominant intrachain ferromagnetic interactions in the spin chains. The obvious inhibition effect to equally spaced magnetization steps demonstrates that Al3+ could release the magnetic frustration. With Al3+ substitution, both the magnetization intensity and the critical field of the ferrimagnetism to ferromagnetism transition decrease. The samples present obvious dielectric anomalies around the Curie temperature T c and the freezing temperature T f. Meanwhile, the magnetic field dependence of dielectric permittivity decreases suddenly at critical magnetic fields. These results reveal strong magnetodielectric coupling effect in Ca 3 Co 2- x Al x O 6. The same sign of Δε r and Δtanδ suggests that the magnetodielectric coupling effect is intrinsic. [ABSTRACT FROM AUTHOR]

The introduction of defects is the key method to control the multiferroic properties of one-dimensional frustration Ca 3 CoMnO 6. In this work, we synthesized a series of Ga3+ doped Ca 3 CoMn 1- x Ga x O 6 (x = 0, 0.05, 0.1, 0.2) compounds. Their crystallographic structure, magnetism as well as the dielectric properties were characterized. The XRD patterns verify the rhombohedral structure of all the samples. The Ga3+ ions have obvious inhibitory effect on the magnetic short-range order. With the substitution of Mn4+ by Ga3+, the polar nanodomains are inhibited and the diffusion index γ becomes lower. The same sign of Δε' and Δtanδ in magnetic field dependent permittivity suggests that the magnetoelectric coupling effect in Ca 3 CoMn 1- x Ga x O 6 is intrinsic. For the Ca 3 CoMn 1- x Ga x O 6 system, the freezing process is primarily dominated by the coupling of the polar nanodomains. • Ga3+ ions play a significant role in suppressing the short-range magnetic correlation. • The same sign of Δε' and Δtanδ in magnetic dependent permittivity shows magnetoelectric coupling effect is intrinsic. • The introduction of Ga3+ could inhibit the formation of polar nanodomains. [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]

• The introduction of defects could directly reflect the influence and contribution of ions to the properties of materials. • The Co defects destroy the Co-Co exchange interactions, it has an obvious dilution effect on the FM interaction. • The weakened ferromagnetic interaction results in that disordered magnetic correlations become long-range FM order. • The Co-defective Ca 3 Co 2 O 6 compound has a strong magnetodielectric coupling effect. The Ca 3 Co 2 -x O 6 (x = 0, 0.02, 0.04, 0.06, 0.08, 0.1) samples were prepared by reducing the stoichiometric ratio of Co atoms. Their structure, magnetic properties, dielectric and magnetodielectric properties were investigated. XRD results show that the presence of a small number of vacancies does not change the crystalline structure. The positive Curie-Weiss temperature θ and interchain exchange constants J indicate that ferromagnetic interactions are stronger than the antiferromagnetic interactions in Co-defective Ca 3 Co 2 -x O 6. The Co-vacancies could weaken the Co-Co exchange interactions, it has an obvious dilution effect on the ferromagnetic interactions within the chain. The magnetization steps move to low field accompanying the defects increase. Simultaneously, Co defects could also release part of the magnetic frustration. The competition of the released magnetic frustration and the dilution effect of the vacancies to the ferromagnetic chains and low doping concentration make the Co-defective Ca 3 Co 2 -x O 6 present similar magnetic property with the parent Ca 3 Co 2 O 6. At the positions of magnetic phase transition and the critical magnetic field of magnetization steps, clear dielectric anomalies can be detected. This result suggests the strong magnetodielectric coupling effect in Ca 3 Co 2 -x O 6 (x = 0, 0.02, 0.04, 0.06, 0.08, 0.1) samples. [ABSTRACT FROM AUTHOR]

We report a detailed study of the influence of non-magnetic Al3+ doping on the microstructure, magnetic, and dielectric characteristics Ca 3 CoMnO 6. The introduction of Al3+ leads to the suppression of competing short-range magnetic orders, a gradual disappearance of the spin freezing peak in Ca 3 CoMn 1- x Al x O 6 was observed, accompanied by the release of magnetic frustration. Moreover, a weakening of the antiferromagnetic order in Ca 3 CoMnO 6 was attributed to the dilution effect induced by non-magnetic Al3+ within the Co-Mn-Co-Mn spin chains. The dielectric measurements exhibit excellent agreement with the magnetic measurements. The substitution of Mn4+ with Al3+ results in the attenuation of relaxor ferroelectric behavior, accompanied by a decrease in the static freezing temperature T f and an increase in the activation energy E a. It indicates that Al3+ substitution could well suppress the formation of polar nanoregions. With introducing Al3+ the magnetodielectric effect of Ca 3 CoMnO 6 is also significantly enhanced. For the x = 0.15 sample, the magnetodielectric effect undergoes a notable variation of approximately 10 % under a magnetic field of H = 4 T. • A weakening of the antiferromagnetic order in Ca 3 CoMnO 6 is induced by the increase in the Al3+ doping level. • The substitution of Mn4+ with Al3+ results in the attenuation of relaxor ferroelectric behavior. • The magnetodielectric effect of Ca 3 CoMnO 6 is significantly enhanced by Al3+ doping. [ABSTRACT FROM AUTHOR]