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This paper reports the synthesis, microstructure and electrical properties of a new Ba4SrBiTi3Nb7O30 ceramic. X-ray diffraction analysis shows that the sample crystallizes into tungsten bronze structure, and the space group is P4bm. The electrical measurement results show that Ba4SrBiTi3Nb7O30 exhibits good dielectric and ferroelectric properties. The temperature-dependent dielectric permittivity indicates that the transition temperature of the prepared Ba4SrBiTi3Nb7O30 sample is around Tm ≈ 250K. With increasing the frequency, the dielectric peak moves to a lower temperature. Below 250 K, obvious polarization current can be detected, corresponding to the formation of spontaneous ferroelectric polarization. These results indicate the relaxor ferroelectric behavior of Ba4SrBiTi3Nb7O30 ceramic. [ABSTRACT FROM AUTHOR]

The incompatibility between the antiferromagnetic exchange interaction and the triangular lattice makes Ca 3 Co 2 O 6 become a frustrated system. It leads to the existence of disordered magnetic structure in the frustrated spin chains. At low temperature, the disordered spins are frozen. In this study, the Ca 3 Co 2 O 6 was prepared and its low temperature dynamic behaviors were characterized. The spin freezing peak and the decay of magnetization with time well confirm the thermally assisted magnetization. Since that the flip of the spins can result in the conservation of the total angular momentum and the conserved angular momentum can make the adjacent lattice feel a transfer torque. In response to variation of magnetization, the dielectric permittivity of Ca 3 Co 2 O 6 also presents relaxation feature. For the isothermal dielectric permittivity, it not only depends greatly on the sweep rates of magnetic field but also decays with time. This detectable variation of the dielectric property in Ca 3 Co 2 O 6 suggests that the thermally assisted dielectric relaxation is an alternative method for characterizing the dynamic behaviors of the frustrated system. • Spin-freezing peaks and magnetization intensity decay with time. • The presence of thermally assisted magnetization intensity is well confirmed. • The dielectric permittivity of Ca 3 Co 2 O 6 also presents relaxation feature. • The isothermal dielectric constant depends on the sweep of the magnetic field and decays with time. • The thermally assisted dielectric relaxation is alternative way for characterizing dynamic behavior of frustrated system. [ABSTRACT FROM AUTHOR]

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]

In one dimensional Ca 3 Co 2 O 6 , the magnetic frustration could result in partially disordered antiferromagnetic state. The Ca 3 Co 2 O 6 thus presents spin freezing and slow relaxation at low temperature. In this investigation, magnetic Cr3+-dopants were chosen to substitute the Co3+ cations and a series of Ca 3 Co 2- x Cr x O 6 ceramics were synthesized. Their magnetoelectric properties were characterized. The results manifest that the introduced Cr3+ cations situate in the CoO 6 octahedral centers and they could increase the lattice volume slightly. The antiferromagnetic coupling between Cr3+ and the adjacent Co3+ could reduce the frustration. The doped-Ca 3 Co 2- x Cr x O 6 compounds display a slower magnetic dynamic behavior. The Cr3+ substitution also has great impact on the dielectric properties of Ca 3 Co 2 O 6. The slower response of the freezing spin in Cr3+ doped-Ca 3 Co 2 O 6 makes the dielectric anomaly (anomaly Ⅰ) around the freezing temperature weakens with increasing Cr3+. Additionally, the introduced Cr3+ dopant not only increases the dielectric permittivity but also decreases the dielectric loss greatly. Cr3+ cation is a good candidate for improving the dielectric properties of Ca 3 Co 2 O 6. Magnetodielectric measurement reflects the effectiveness of magnetic field on manipulating the electric dipole of Ca 3 Co 2 O 6. For spin frustrated materials, electric measurement is proved to be an effective method on characterizing the subtle variation of the magnetic structure. [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]

We report the structure, magnetic and dielectric behaviors of the polar magnet CaBaCo 4- x Ni x O 7 (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 antiferromagnetic 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 antiferromagnetic 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. [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]

A series of the polar magnets CaBaCo 4- x Al x O 7 (x = 0, 0.15, 0.3, 0.4, 0.5) were synthesized by the Al element doping strategy. Their structure, magnetism, dielectric and magnetodielectric properties were characterized and analyzed. XRD patterns show that the prepared polycrystalline samples (x ≤ 0.5) feature good crystallinity and a small amount of secondary phase can be detected. The magnetic transition temperature (T C) decreases from 60 K to 30 K when the x value increases from 0 to 1.0, due to the diluted effect of Al3+ to the magnetic interaction. The Al3+ doping also results in an antiferromagnetic transition above T C Correspondingly, the dielectric peak around the magnetic transition moves to lower temperature gradually (x ≥ 0.15). Al3+ doping could well suppress the short-range magnetic order. It causes a new dielectric peak near 70 K, suggesting that the magnetism has a great influence on the dielectric property. With increasing doping concentration, the dielectric peak around the magnetic transition temperature merges with the new dielectric peak near 70 K. Finally, only a broad peak was observed. [ABSTRACT FROM AUTHOR]

• At present, there are no papers about Mn doping CaBaCo 4 O 7. • Mn-doping weakened the FIM interaction. • Few reports focused on the effects of valence states on properties of Ni-doped. • Ni-doping enhances the antiferromagnetic interaction. • Ni-doping induces an additional antiferromagnetic phase. • Both Mn doping and Ni doping enhance the magnetodielectric effect of the sample. We reported the magnetic and dielectric properties of the polar magnet CaBaCo 4- x Mn x O 7 and CaBaCo 4- x Ni x O 7 (x = 0.04, 0.08). The result shows that Mn ions exist in the sample in + 2 and + 3 valence, replacing both Co2+ and Co3+, and the Ni ions exist in + 2 valence, only replacing Co2+. Mn ion doping does not change the ratio of Co2+ to Co3+ in the crystal, leading to similar magnetic behavior to CaBaCo 4 O 7. Ni ions increase the relative content of Co3+, which has a greater damage to the ferromagnetic interaction. Meanwhile, Mn-doping can partially release the magnetic frustration and cause the spin freezing temperature shifting to high temperature. It also slightly weakened the FIM interaction in the sample. While Ni-doping enhances the antiferromagnetic interaction and induces an additional antiferromagnetic phase at 82 K in the sample. The dielectric behavior of all samples is obviously abnormal at magnetic phase transitions, which proves the magnetodielectric effect of the samples. After Mn and Ni ions doping, the magnetodielectric properties of the samples are improved. Compared with Mn ions, Ni ions have a greater effect on the dielectric properties of CaBaCo 4 O 7. [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]