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• The crystal structure, optical, magnetic and dielectric properties of the GdCr 1- x Ga x O 3 (0 ≤ x ≤ 0.3) polycrystalline samples were investigated in detail. • The UV–vis measurement shows that the band gap raises from 2.76 eV to 2.99 eV of × = 0.2 sample due to the decrease of vacancy defect concentration, and then the decrease of band gap is related to the increase of particle size. • The magnetic properties show that negative magnetization and spin-reorientation is restrained and vanished when x ≥ 0.2, because the change of Gd3+-Cr3+ interaction. • The positive and decreasing MD coefficient indicates that the sample is in the antiferromagnetic state, and the antiferromagnetic interaction is gradually weakened. The structural, optical, magnetic, and dielectric properties of GdCr 1- x Ga x O 3 (0 ≤ x ≤ 0.3) polycrystalline samples were explored in this research. The lattice parameters, bond length, and bond angle are altered by Ga3+ doping. An evident transition point exists at x = 0.2. The UV–vis measurement shows that the band gap raises from 2.76 eV to 2.99 eV of × = 0.2 sample due to the decrease of vacancy defect concentration, and then the decrease of the band gap is related to the increase of particle size. The dilution of Ga3+ leads to a decrease in the antiferromagnetic transition temperature. Temperature dependent magnetization manifests that the negative magnetization and spin reorientation are inhibited and vanished when x ≥ 0.2. Importantly, the dielectric permittivity is consistent with the variation of the magnetic properties, proving the existence of magnetoelectric coupling in Ga-doped samples. Simultaneously, the weakened antiferromagnetic interaction also lessens the positive MD coefficient, which correspondingly correlates with the variation in magnetic properties. This study can serve as a guide for comprehending the evolution of microstructure, magnetic and dielectric properties of RCrO 3 materials. [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]

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 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 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]

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]

For the spin-chain compound Ca 3 CoMnO 6 , the perfect Co/Mn ionic order causes the lost of ↑↑↓↓ long-range antiferromagnetic order. The lost long-range magnetic order results in the emergence of short range magnetic correlation interaction, forming the so called "order by disorder" phenomenon. In present paper, nonmagnetic Ga3+-doped Ca 3 CoMn 1- x Ga x O 6 compounds were prepared. The influence of Ga3+ substitution on the structure and magnetic order of Ca 3 CoMn 1- x Ga x O 6 were investigated. It is found that the solid solubility of Ga3+ cation in Ca 3 CoMn 1- x Ga x O 6 is 0.2 < x < 0.3. With introducing of Ga3+ cation, the oxidation state of some Co cations changes from Co2+ to Co3+. Magnetization measurements reveal that doped with nonmagnetic Ga3+ weakens the formation of short range magnetic order and enhances the antiferromagnetic transition temperature. As a result, more robust long rang antiferromagnetic order is established and the transition field that causes the ↑↑↓↓ spin state of Co–Mn–Co–Mn chain to ↑↑↓↑ state increases obviously. Meanwhile, the shortened short range magnetic correlation in Ga3+ doped Ca 3 CoMn 1- x Ga x O 6 can be driven more easily by the thermal activation energy and a quicker dynamic behavior was observed in time windows. • A series of Ga3+-doped Ca 3 CoMn 1- x Ga x O 6 compounds were synthesized. Our result reveals that the solid solubility of Ga3+ cation in Ca 3 CoMnO 6 is between x= 0.2 and x= 0.3. • Magnetization measurements indicate that doping with nonmagnetic Ga3+ could weak the formation of short range magnetic order and increase the antiferromagnetic transition temperature. • With introducing of Ga3+ cations, more robust long rang antiferromagnetic order is established and the transition field that causes the ↑↑↓↓ spin state of Co–Mn–Co–Mn chain to ↑↑↓↑ state enhances obviously. • In Ga3+ doped Ca 3 CoMn 1- x Ga x O 6 , the short range magnetic order is suppressed and more robust long rang antiferromagnetic order is established. [ABSTRACT FROM AUTHOR]