FIG 1 - uploaded by Alorika Chatterjee
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(a) Connecting Cr octahedron and Cu tetrahedron within the unit cell. (b) Distortion of CuO 4 tetrahedra driven by the J-T effect. (c) Lifting of orbital degeneracy of d orbitals in the tetrahedral coordination due to J-T effect.
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We observe a ferroelectric (FE) order in an unexplored CuCr2O4 with a reasonably high value of the FE Curie temperature (TFE) at 170 K, which is also much higher than the magnetic ordering temperature. The systematic substitution of Jahn-Teller (J-T) active divalent Cu ion by a non-Jahn-Teller active divalent Co ion causes a systematic shift of TFE...
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Citations
... It will enhance the compounds' qualities. For instance, improved multiferroicity is demonstrated by CuCr 2 O 4 doped with Co, [13][14][15]. Additionally, CuCr 2 O 4 substituted with rare-earth ions yields positive findings for structural and vibrational [16]. The influence of Jahn-Teller and structural frustration effects is examined on the structural and magnetic ground states of substituted spinels (Cu, A)Cr 2 O 4 , (A = Mn/Ni) [17][18][19][20][21]. ...
... Ye et al. [7] studied different properties of CCO single crystals. The effects of Co doping on the MF order in CCO is reported recently by Chatterjee et al. [8]. Structure and vibrational studies of La doped CCO are performed recently by Rajeswari et al. [9]. ...
... Firstly, we will substitute Cu 2+ ions with ferromagnetic transition metal Co 2+ ions. Thus, we can compare our results with those of Ref. [8] and check our model. By doping with Co 2+ ions (0.65Ȧ [30]), which radius is smaller than that of the Cu 2+ ion (0.73Ȧ [31]), there appears a compressive strain. ...
... Thus the magnetization M s increases with increasing Co doping concentration up to x = 0.6. After x > 0.6, where appears a secondary phase we use the relation J d1 < J b1 and the magnetization M s (see Figure 2, curve 1) begins to decrease, in accordance with the experimental data of Chatterjee et al. [8]. T N decreases with increasing the Co dopants. ...
The magnetic, electric, and optical properties of pure and ion-doped CuCr2O4 bulk and nanoparticles are investigated theoretically. The magnetization Ms and the band gap Eg decrease with increasing particle size. By Co ion doping, Ms and the polarization P show a maximum, whereas by Pr ion doping, they decrease when increasing the doping concentration. The dielectric constant increases with decreasing Pr dopants. It is shown that the difference between the doping and host ions’ radii leads to the appearance of a compressive or tensile strain and different exchange interaction constants in the doped state. Eg decreases by Co doping, whereas it increases by Pr doping.
... Notably, an absence of external E during the signalmeasurements helps in avoiding possible spurious contributions due to free-carrier currents. This linear T -ramp method or Byer-Roundy method [21], has been widely adopted in many studies [16,18,[22][23][24][25][26][27][28][29][30][31] in the past. In addition, laser assisted heating techniques are also an alternative for I P vs. T measurements. ...
The rare-earth chromates (RECrO$_3$) and manganites (REMnO$_3$) where, RE = Eu, Y, Dy, Ho, Gd are constantly under scrutiny in search of room temperature magnetoelectric multiferroics. However, the artefacts and undesirable signal in some of the measurements pose a severe challenge in confirming the ferroelectric (FE) phase, especially in reference to pyroelectric current measurement technique. In this regard, we propose a simple modified approach to pyroelectric current measurement named as 4-segment thermal cycling protocol. This protocol assists in isolating the elusive, irreversible thermally stimulated current from the currents associated with spontaneous and reversible nature of the electric polarization in FE phase. In order to explain working principle of the protocol, we have compared simulated response of two hypothetical materials; an FE material free of space charges and a paraelectric material possessing only space charges. Further, we experimentally verify these new protocols in a single crystal of prototype ferroelectric material, Glycine Phosphite. This report primarily focuses on detailed investigation of ferroelectricity using the proposed protocol in two polycrystalline materials, HoCrO$_3$ and DyFe$_{0.5}$Mn$_{0.5}$O$_3$ where, the former has been reported to be multiferroic earlier. Our elaborative and careful approach to pyroelectric studies expound on the absence of reversible spontaneous electric polarization at temperature ranges tested in both, HoCrO$_3$ and DyFe$_{0.5}$Mn$_{0.5}$O$_3$.
... The structural study attempts to extract knowledge from the crystallography and understanding origins of the different multifunctional properties of the system. The structural correlation to the electrical and magnetic properties has been recently found crucial in few systems, which provides rich consequences in solid state such as colossal magnetoresistance [1], giant magnetocaloric effect [2], Griffiths phase (GP) singularities [3], spontaneous ferroelectric order [4,5], multiferroic order [6]. In the current observation we report important structural correlations to the various unexplored multifunctional properties of YbCrO 4 . ...
We report a ferroelectric order around ~ 99 K (T FE ), which is considerably above the long range ferrimagnetic order at 25 K (T N ). The value of saturation electric polarization is considerable as ~ 570 μC/m ² for a poling field of 5 kV/cm. The ferroelectric order is associated with a significant magnetoelectric coupling below ~ 90 K. A weak signature of T FE is observed in the dielectric constant, which is associated with a linear magnetodielectric response at 18 K (< T N ). A transition to a polar structure has been correlated with the occurrence of ferroelectric order. A non-Griffiths like phase is observed around $\sim$ 48 K, which is also linked with the structural distortion. A reasonable value of the magnetic entropy change of 5.07 JKg ⁻¹ K ⁻¹ is noted at T N for a change in field of 50 kOe, which involves a strong magnetoelastic coupling. The results indicate considerable structural instabilities, which is linked with the observed multifunctional properties of YbCrO 4 .
... Control of CoCr 2 O 4 magnetic properties through site-selective doping i.e., doping in either tetrahedral or octahedral sites from the point of view of technological applications is currently an active area of research [5,9,[21][22][23][24][25][26][27][28][29][30][31]. We have recently studied the effects of the Bi-and Sc-doping in CoCr 2 O 4 NPs, providing compelling evidence that tetrahedral site doping modifies exchange coupling strength between Co-Co, Co-Cr, and Cr-Cr resulting in singular magneto-structural behavior [32,33]. ...
In this study CoCr 2-y Sc y O 4 (y = 0, 0.01, 0.02, and 0.03) nanoparticles (NPs) have been synthesized following the solution combustion method and characterized by combining experimental techniques with high-throughput Density Functional Theory calculations. The structural analysis confirmed the crystalline nature with spinel cubic structure exhibiting an average particle size between 7 and 10 nm. The morphological analysis confirmed the exposure of the (2 2 0), (3 1 1), (4 0 0), and (4 2 2) planes in agreement with theoretical results based on Wulff Construction. Magnetic analysis indicated the existence of paramagnetic to ferrimagnetic phase transition at the critical temperature (T c) and a conical spiral spin phase was found at the spiral transition temperature (T s). In both the cases, the transition temperature was seen to decrease with increase in the Sc content in agreement with the exchange-coupling constants calculated by DFT, where a singular magneto-structural behavior was observed. Theoretical results for shape-oriented magnetic properties indicate the anisotropic spin density distribution and surface exposure, providing a general picture of shape-selective control of nanomagnetism.
... Spinel (AB 2 O 4 ) compounds whose crystal symmetry departs from the cubic to other Bravais lattices due to the Jahn-Teller (JT) distortion in the AO 4 tetrahedron have gained considerable interest because of their remarkable magnetic properties [1][2][3]. Novel magnetic phenomena such as multiferroic, exchange-bias, low-T spin liquid ground states, re-entrant glassy behaviour driven by geometric/orbital magnetic frustration and spontaneous dimerization are some of the key features that are observed in systems having JT active elements [1,[3][4][5]. Spinels such as Mn 3 O 4 , CuFe 2 O 4 , NiCr 2 O 4 , CuCr 2 O 4 and ZnMn 2 O 4 exhibit distortion in the crystal structure as a consequence of JT effect [1,[6][7][8][9]. ...
... Spinel (AB 2 O 4 ) compounds whose crystal symmetry departs from the cubic to other Bravais lattices due to the Jahn-Teller (JT) distortion in the AO 4 tetrahedron have gained considerable interest because of their remarkable magnetic properties [1][2][3]. Novel magnetic phenomena such as multiferroic, exchange-bias, low-T spin liquid ground states, re-entrant glassy behaviour driven by geometric/orbital magnetic frustration and spontaneous dimerization are some of the key features that are observed in systems having JT active elements [1,[3][4][5]. Spinels such as Mn 3 O 4 , CuFe 2 O 4 , NiCr 2 O 4 , CuCr 2 O 4 and ZnMn 2 O 4 exhibit distortion in the crystal structure as a consequence of JT effect [1,[6][7][8][9]. Tuning such structural distortion by site specific substitution with either magnetic or nonmagnetic elements in the spinel lattice is a well-known strategy to probe the cooperative phenomena like orbital, charge, spin, and lattice degrees of freedom in strongly correlated electron systems [7,[10][11][12][13]. ...
... Novel magnetic phenomena such as multiferroic, exchange-bias, low-T spin liquid ground states, re-entrant glassy behaviour driven by geometric/orbital magnetic frustration and spontaneous dimerization are some of the key features that are observed in systems having JT active elements [1,[3][4][5]. Spinels such as Mn 3 O 4 , CuFe 2 O 4 , NiCr 2 O 4 , CuCr 2 O 4 and ZnMn 2 O 4 exhibit distortion in the crystal structure as a consequence of JT effect [1,[6][7][8][9]. Tuning such structural distortion by site specific substitution with either magnetic or nonmagnetic elements in the spinel lattice is a well-known strategy to probe the cooperative phenomena like orbital, charge, spin, and lattice degrees of freedom in strongly correlated electron systems [7,[10][11][12][13]. ...
We report a detailed study on the dynamical response of localized electron hopping and dipole
relaxation in bulk polycrystals of Zn diluted Cuprospinel (Cu1−xZnxFe2O4). The variations in
the dielectric dispersion and ac-resistivity (ρac) were analyzed over a wide temperature (77 K
≤T ≤ 823 K) and frequency (20 Hz ≤ f ≤ 20 MHz) window for a critical composition xc = 0.4.
The variation of ϵR( f, T) followed the Maxwell–Wagner type polarization mechanism in-line
with the Koops phenomenological theory. Our analysis of ρac(T, f ) provide strong evidence to
the Mott’s variable range hopping of charge transport between the localized states at low
temperatures, however, thermally-activated Arrhenius like behaviour was noticed at high
temperatures with EA = 656 meV for xc = 0.4. Moreover, electric modulus spectroscopic
studies (M
∗
( f, T)) reveals two distinct types of relaxation phenomena: (i) the short-range
oscillations of the charge carriers within the potential well of grains and (ii) the long-range
movement of charge carriers across the grain boundaries. The depressed semi-circles of the
Nyquist plots and lower values of non-exponential parameter extracted from M
∗
( f, T) suggest
the non-Debye type relaxation process present in the system with a widespread distribution of
relaxation times. The frequency exponent (s(x, T)) study of Jonscher’s power law reveals that
the ac-conductivity follows small-polaron tunneling followed by the correlated-barrier-hopping
mechanism for x < 0.1. However, for x ≥ xc reorientational hopping mechanism is
predominant, except for T > 400 K, where thermally activated Arrhenius-type conduction of
charge carriers is prevalent in this spinel system. Furthermore, the tetragonally (I41/amd)
distorted systems (x ≤ 0.05) exhibit less activation energy (EA−VRH ) values as compared to
those of cubic-spinel symmetry (Fd-3m) which saturates at 130 meV for 0.1 ≤ x ≤ 0.6.
Compositional dependent tunability of the above discussed parameters may open a constructive
approach to design low energy-loss and high-resistive electromagnetic elements for microwave
devices which is the key significance of the present study.
... For example, the solely Asite magnetic atom in the spinel structure gives rise to exotic effects such as spin dimerization [1], spin liquid ground states [2][3][4], and suppressed antiferromagnetic order [5], which are often regulated by either orbital ordering or geometric magnetic frustrations, or both. Transition elements in both the Aand B-sites reduce the magnetic frustration, but this produces interesting consequences such as structural instabilities [6][7][8], intricate magnetic structures [9,10], ferroelectricity [11][12][13][14], etc. The solely B-site magnetic atom in AB 2 X 4 is found to have potential for the pyrochlore structure, producing strong geometric magnetic frustration [15,16]. ...
... In the figure, T pole (1), T pole (2), T pole (3), and T pole (4) represent the poling temperatures at 150, 95, 20, and 8 K, respectively. In all the cases, a peak at 110 K is always observed, pointing to a genuine occurrence of the peak [7,58,59], which is shown in the figure. For T pole (1) another high-temperature peak is observed, which disappears with T pole close to or below the polar order. ...
... For T pole (1) another high-temperature peak is observed, which disappears with T pole close to or below the polar order. The high-T peak appears due to the extrinsic thermally stimulated depolarization currents (TSDC) [7,[58][59][60]. For the poling at 95 K, an additional peak close to 95 K appears below the peak at 110 K. ...
The rhombohedral distortion-driven occurrence of the spontaneous electric polarization at a reasonably high temperature (T) and an exchange bias (EB) effect below the antiferromagnetic (AFM) Néel temperature (TN) are revealed in ZnFe2O4. We observe the magnetic memory effect, suggesting a cooperative glassy magnetic state below TN. The phase separation between the long-range AFM and the glassy magnetic component leads to the EB effect below TN. The synchrotron diffraction studies confirm a structural transition to a polar R3m structure from the cubic spinel structure, involving a strong rhombohedral distortion. This distortion correlates with the occurrence of the spontaneous electric polarization (P) below ∼110 K (TFE1), which is accompanied by a short-range order (SRO). The P-value enhances further due to an additional rhombohedral distortion below TN. A considerable magnetoelectric (ME) coupling is detected below TFE1. The increase of P is ∼7.2% for 5 T at the liquid nitrogen temperature. There has been a fundamental interest among the community in the unique result of the occurrence of ferroelectric (FE) order coexisting with SRO and having a significant ME coupling, which is accompanied by a strong rhombohedral structural distortion analogous to that observed in BiFeO3.
... Particularly, spinels have demonstrated various magnetic properties [1]. This diversity is associated with the wide variety of cation substitutions that can be made in tetrahedral (A) and octahedral (B) sites leading to a number of interesting magnetic properties such as ferrimagnetic [5], ferromagnetic [6], antiferomagnetic [7], magnetic frustration [8], and/or multiferroicity [9]. These compounds continue to interest scientists, for example, spinel ferrites doped with rare earths have been the subject of great attention in recent years. ...
... Consequently, Al 1.5 Mn 1.5 O 4 adopts a mixed spinel structure. The cell parameter a = 8.28269(3) Å and the oxygen position u = 0.26390 (9) are in agreement with the previously reported studies [28,29]. However, the occupancy rate of Al 3+ ions in the A sites is lower compared with that reported in the literature, which can be attributed to the different synthesis methods. ...
The polycrystalline samples of Al1.5Mn1.5O4, MgAl0.5Mn1.5O4 and MgGa0.5Mn1.5O4 were prepared using a standard ceramic method and characterized by X-ray diffraction and magnetic measurements. The cationic distributions were determined by the combination of the Rietveld refinement and the tabulated cation-oxygen distances in spinel compounds. The results obtained were compared with those calculated using a thermodynamic calculation according to the O’Neill model. The Al1.5Mn1.5O4 compound is characterized by its cationic distribution with a high occupancy rate of the magnetic ions Mn2+ in the A sites, in agreement with the experimental magnetic moment. This compound presents a ferrimagnetic behavior at T < 23.5 K. The MgAl0.5Mn1.5O4 and MgGa0.5Mn1.5O4 compounds have almost the same distribution of magnetic manganese cations in both A and B sites, with a weak presence of the magnetic ions Mn2+ in the A sites, justified by the refinement Rietveld, thermodynamic calculation and the hyperbolic form of the inverse magnetic susceptibility above 23.2 K. Both compounds have almost the same magnetic behavior at low temperature T < 23.2 K, typical of a spin glass. This behavior is attributed to the strong presence of diamagnetic ions on the A sites and the magnetic disorder in B sites.
... Indeed, several authors reported the existence of CoCr2O4 nanoparticles doped with Cd, Mn, Fe, Cu, Bi, Zn, and Mg cations, showing that both magnetic and ferroelectric orders are affected, resulting in superior multiferroic properties for doped Cobalt chromates. 5,[11][12][13][14][15][16][17][18][19][20][21][22] Based on these facts, our focus was addressed to the synthesis, characterization, and simulation of the Sc 3+ doped Cobalt chromate material obtained by solution combustion method. Such method is timeless consuming, requires low temperature and has a low-cost in comparison to other preparation methods, such as facile and fast sonochemical assisted route, 6 co-precipitations, 13 Sol-gel auto-combustion, 23, 24 chemical sol-gel reaction, 25 and solution combustion synthesis. ...
The control over spin distribution to simulate magnetic properties in crystalline structures is crucial for materials design. The clear understanding between structure and properties is essential for the development of magnetic materials. Herein, we investigate the effect of Sc doping on structural, electronic, and magnetic properties of solution combustion method to synthesis Co1-xScxCr2O4 (x = 0.0 and 0.05) nanoparticles and in-depth DFT calculations to clarify the spin distribution and magnetic states. The synthesized samples showed a single phase in the spinel cubic structure. Structural distortions associated with the creation of A-site vacancies originate overall deformations on tetrahedral [CoO4] and octahedral [CrO6] clusters. Aiming to understand the magnetic behavior of the sintered samples, temperature-dependent susceptibility, and field-dependent magnetizations were conducted, revealing two magnetic transitions defined as paramagnetic collinear ferrimagnetic (FIM) (TC) and non-collinear spiral FIM (TS) state. Further, from Sc-doping on [CoO4] cluster, the TC and TS decreased because of structural defects acting directly on the exchange coupling constants. The modification resulted in an enhancement of A-B and B-B antiferromagnetic (AFM) interactions, deeply clarified by DFT calculations. Hence, our experimental and theoretical approach shows a Sc-doping mechanism to control the CoCr2O4 magnetic properties of the matrix from structural distortions and long-range spin ordering.
The magnetic order and phase transitions in the normal spinel system Ni1−xCuxCr2O4 are studied by powder-neutron and x-ray diffraction, as well as by magnetization measurements to get a complete magnetic phase diagram. For chromites with x(Cu) > 0.5 a canted antiferromagnetic phase of Cr appears first, followed by the onset of ferromagnetism in the Cu sublattice at lower temperature forming a ferrimagnetic lattice. Conversely, with x(Cu) < 0.5 the ferrimagnetic order between the Cr and Cu spins occurs at the higher ordering temperature followed by the onset of antiferromagnetic order in the Cr sublattice. Apart from the crossing of the two boundary lines of the transition temperatures at x(Cu) = 0.50 a compensation point of the ferrimagnetic moments is determined at x(Cu) = 0.60, where the spontaneous magnetization has almost completely vanished. Most remarkable is the antiferromagnetic Cr ordering on the orthorhombic distorted pyrochlore lattice for samples in the x(Cu) range from 0 to 0.12 due to the large variety of coexisting magnetic phases. In the magnetic ground state of NiCr2O4 two commensurate antiferromagnetic structures with the propagation vectors k = (0,0,1) and (½,½,½) coexist. With increasing Cu content from x(Cu) = 0 to 0.09 these phases undergo a transition to another commensurate structure with k = 0 via two coexisting incommensurate magnetic phases with the vectors k = (0,0,kz) and k = (0,ky,kz). The different magnetic phases are discussed qualitatively based on the lattice dimensions depending on the concentration ratio of two Jahn-Teller ions at the tetrahedral A site, where Ni2+ causes elongated and Cu2+ compressed tetragonal lattice distortions. Further, magnetoelasticity studies on selected samples indicate that the magnetically induced lattice strains follow the symmetry of the underlying Jahn-Teller distorted lattices.
