High sensitivity of magnetism of the “114” ferrimagnet CaBaCo4O7 to stoichiometry deviation (original) (raw)
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Spin-assisted ferroelectricity in ferrimagnetic CaBaCo 4 O 7
Dielectric and polarization measurements of the noncentrosymmetric "114" cobaltite CaBaCo 4 O 7 were carried out on polycrystalline pellets. Our results show that this material exhibits a clear dielectric peak at T C and polarization in the ferrimagnetic state below T C = 70 K. The ferroelectric nature of this phase is supported by pyroelectric measurements. It is shown that this multiferroic material exhibits a magnetodielectric effect of 16% under 14 T just below T C . In the absence of any structural transition in the whole temperature range (300-4 K), the emergence of polarization at T C suggests that the ferrimagnetic ordering induces or assists the ferroelectricity. The symmetry analysis shows that in the magnetic phase the Heesch-Schubnikov point group is m m2 , which offers a unique potential for the possible coexistence of ferroelectricity, ferromagnetism, and ferrotoroidicity in this compound along three directions oriented at 90 • .
Complex magnetic phase separation induced by Li-doping in multiferroic CaBaCo4O7
Journal of Applied Physics, 2013
Electron and hole doping at the cobalt sites of CaBaCo 4 O 7 has been successfully realized by heterovalent substitution on A sites (Ln at Ca sites and K at Ba sites) with a narrow range. Both electron and hole doping have a dramatic impact upon the structure and magnetism, decreasing the orthorhombic distortion and weakening considerably the ferrimagnetism at the benefit of magnetic frustration. The hole doping very drastically kills the ferrimagnetism of the parent phase leading to a cluster-glass phase at lower temperatures, whereas the electron doping with a smaller cation like yttrium leads to an admixture of cluster and spin glass along with the preservation of weak ferrimagnetism. The frequency dependence of the peak position in χ (T ) curves was quantitatively analyzed using the power law, τ = τ 0 (T f /T g − 1) −zν . Moreover, the electron doping with larger lanthanides (Pr and Nd) leads to spin-glass states, which are manifested at two temperatures vis-à-vis ∼60 K and ∼110-115 K. The appearance of magnetic frustration at the expense of ferrimagnetism in both cases is interpreted as the result of deviation of the Co 2+ /Co 3+ ratio from unity and cationic disordering on cobalt sites, even if the crystal remains orthorhombic.
MAGNETIC PROPERTIES OF Co X Fe 3-X O 4 AND PRECURSOR INFLUENCE ON THESE PROPERTIES
Cobalt ferrite is characterized by a partial inverse spinellic structure, which makes it a material with special magnetic properties that vary as a function of the cobalt concentration. The special magnetic properties represent one of the parameters due to which cobalt ferrite is of a great interest. In the present paper, we studied these properties from the perspective of the effect produced by the precursors of Co x Fe 3-x O 4 nanomaterial synthesis on magnetic properties , shape, and morphology characteristics to these nanomaterials. Magnetic measurements were achieved with a SQUID magnetometer, while the structural and morphological characterization was achieved by X-ray diffraction (XRD), SEM-EDAX and AFM.
Physical Review B, 2012
Electron and hole doping at the cobalt sites of CaBaCo 4 O 7 has been successfully realized by heterovalent substitution on A sites (Ln at Ca sites and K at Ba sites) with a narrow range. Both electron and hole doping have a dramatic impact upon the structure and magnetism, decreasing the orthorhombic distortion and weakening considerably the ferrimagnetism at the benefit of magnetic frustration. The hole doping very drastically kills the ferrimagnetism of the parent phase leading to a cluster-glass phase at lower temperatures, whereas the electron doping with a smaller cation like yttrium leads to an admixture of cluster and spin glass along with the preservation of weak ferrimagnetism. The frequency dependence of the peak position in χ (T) curves was quantitatively analyzed using the power law, τ = τ 0 (T f /T g − 1) −zν. Moreover, the electron doping with larger lanthanides (Pr and Nd) leads to spin-glass states, which are manifested at two temperatures vis-à-vis ∼60 K and ∼110-115 K. The appearance of magnetic frustration at the expense of ferrimagnetism in both cases is interpreted as the result of deviation of the Co 2+ /Co 3+ ratio from unity and cationic disordering on cobalt sites, even if the crystal remains orthorhombic.
Room-temperature ferromagnetism in the mixtures of the TiO_ {2} and Co_ {3} O_ {4} powders
Physical Review B, 2009
We report here the observation of ferromagnetism (FM) at 300 K in mixtures of TiO 2 and Co 3 O 4 powders despite the antiferromagnetic and diamagnetic character of both oxides respectively. The ferromagnetic behavior is found in the early stages of reaction and only for TiO 2 in anatase structure; no FM is found for identical samples prepared with rutile-TiO 2 . Optical spectroscopy and X-ray absorption spectra confirm a surface reduction of octahedral Co +3 →Co +2 in the mixtures which is in the origin of the observed magnetism.
Room temperature ferrimagnetism, magnetodielectric and exchange bias effect in CoFeRhO4
Physical Review Materials
Geometrically frustrated structures, combined with competing exchange interactions that have different magnitudes, are known ingredients for achieving exotic properties. Herein, we studied detailed structural, magnetic, thermal (specific heat), magnetodielectric, and magnetic exchange bias properties of a mixed 3d-4d spinel oxide with composition CoFeRhO 4. Detailed magnetization, heat capacity, and neutron powder diffraction studies highlight long-range ferrimagnetic ordering with an onset at 355 K. The magnetic structure is established using a ferrimagnetic model (collinear type) that has a propagation vector k = 0, 0, and 0. The magnetodielectric effect appears below the magnetic ordering temperature, and the exchange bias (EB) effect is observed in fieldcooled conditions below 355 K. The magnetodielectric coupling in CoFeRhO 4 originates due to the frustration in the structure, collinear ferrimagnetic ordering, and uncompensated magnetic moments. The unidirectional anisotropy resulting from the uncompensated magnetic moments causes the room-temperature exchange bias effect. Remarkably, the appearance of technologically important properties (ferromagnetism, magnetodielectric effect, and EB) at room temperature in CoFeRhO 4 indicates its potential use in sensors or spintronics.
Magnetoelectric coupling in ceramic of the Zn-doped CaBaCo4O7 pyroelectric ferrimagnet
Ceramics International, 2017
Electric and magnetic properties of the CaBaCo 3.97 Zn 0.03 O 7 ferrimagnet ceramic have been studied. For this magnetoelectric compound, thermally assisted transitions in the pyroelectric current, at different temperatures characteristic of the magnetic transitions, are evidenced even in the absence of electrical poling. This result, interpreted by taking into account the magnetostrictive nature of this cobaltite, is supported by P(H) magnetoelectric coupling measurements performed in the 48K to 70K interval. The change of polarization sign induced by changing the polarity of the poling electrical field, not observed in crystals but in 114 ferrimagnetic ceramics, is explained by symmetry arguments related to the tetrahedral coordination of the cobalt cations. Thus, this new type of pyroelectric ferrimagnetic ceramics might offer novel ways to exploit the magnetoelectric coupling of these oxides.
Inorganic Chemistry, 2010
The synthesis and nuclear and magnetic structures from the powder diffraction of Co II 5 (OH) 6 (SeO 4 ) 2 (H 2 O) 4 and its deuterated analogues as well as their infrared spectral, thermal, and magnetic properties are reported. The nuclear structure consists of brucite-like cobalt hydroxide layers connected by ...OSeO 3 -Co(H 2 O) 4 -O 3 SeO... bridges. The two independent cobalt atoms within the layer are arranged in chains along the b axis creating an anisotropy within each layer. The interlayer distance (10.718 A ˚) is the only parameter to increase compared to the sulfate analogue (10.273 A ˚). The infrared spectra and thermal properties are similar to those reported for the sulfate analogue. Due to the ferromagnetic exchange between the nearest-neighbor cobalt atoms within the layer, satisfying the Goodenough-Kanamori rule, and the weak interlayer exchange, an overall ferromagnet is obtained. The ferromagnetic order at 9 K was confirmed by the ac susceptibilities, the saturation magnetization, and most importantly the enhancement of some Bragg diffraction peaks below the Curie temperature. The moments of all the cobalt atoms were found to be aligned along the b axis with a moment of 3.25(8) μ B each giving the best fit. The increase in layer distance and the electron density by replacing sulfur by selenium lowers the Curie temperature.