Bulk Spinel Research Articles

Modulation of Co spin state at Co3O4 crystalline-amorphous interfaces for CO oxidation and N2O decomposition

Modulation of electronic spin states in cobalt-based catalysts is an effective strategy for molecule activations. Crystalline-amorphous interfaces often exhibit unique catalytic properties due to disruptions of long-range order and alterations in electronic structure. However, the mechanisms of molecule activation and spin states at interfaces remain elusive. Herein, we present a Co3O4 spinel-based catalyst featuring crystalline-amorphous interfaces. Characterization analyses confirm that tetrahedral Co2+ is selectively etched from bulk spinel, forming amorphous CoO islands on the surface. The resultant symmetry breaking in the coordination field induces a reconstruction of the Co3+3 d orbitals, leading to high-spin states. In CO oxidation, the interface serves as novel active sites with a lower energy barrier, facilitated by lattice oxygen activation. In N2O decomposition, the interface promotes reassociation of dissociated oxygen through quantum spin exchange interactions. This work provides a straightforward approach to modulating the spin state of interfaces and elucidates their role in molecule activations.

Diffusion mechanisms for spinel ferrite NiFe2O4 by using kinetic activation-relaxation technique.

Mass transport in bulk spinel ferrites NiFe2O4 is studied computationally using the kinetic activation-relaxation technique (k-ART), an off-lattice kinetic Monte Carlo algorithm. Diffusion mechanisms-difficult to observe with molecular dynamics-are described by k-ART. Point defects are assumed to be responsible for ionic diffusion; thus, both cation and anion defects are investigated. This work focuses on vacancies and interstitials by comparing their properties with two Buckingham potential parameterizations: one with nominal charges and the other with partial charges. Both potentials are corrected at short distances, thus allowing interstitial diffusion and avoiding the catastrophic infinite energies appearing with Buckingham at short distances. The energy landscape along different pathways is described in detail. Both potentials predict the same mechanisms but different migration energies. Mechanisms by which a normal spinel is transformed to an inverse spinel via cation diffusion are unveiled, and diffusion coefficients are predicted. We find that interstitial Ni diffusion involves the movement of two Ni ions and that O interstitials trigger a collective diffusion of O ions, while an O vacancy diffuses by an O ion moving to the center of a cuboctahedron.

Tuning the magnetic properties of oleic-acid-coated cobalt ferrite nanoparticles by varying the surfactant coverage

Organic coatings on magnetic nanoparticles are extensively used in various applications. As demonstrated recently, these coatings affect the magnetic behavior of the nanoparticles. The modification of the magnetic properties of the nanoparticles and nanoparticle assemblies as the percentage of the oleic acid (OA) coverage of a cobalt ferrite nanoparticle increases, is investigated numerically using a multiscale modeling approach that combines density functional theory (DFT) and Monte Carlo simulations. The DFT calculations show that the increase in OA coverage results in a monotonic decrease of the mean magneto-crystalline anisotropy and in a reduction of the atomic magnetic moments and the exchange coupling constants in the nanoparticle. These effects are attributed to the gradual recovery of the bulk spinel structure at the coated surface, as the OA coverage increases. Input from the DFT calculations is used in the mesoscopic modeling for the study of the magnetic behavior of an assembly of these nanoparticles by employing the Monte Carlo simulations technique. The results demonstrate that despite the decrease of magnetic anisotropy, the coercive field increases with the increase in percentage of OA coverage in the assembly, in agreement with experimental findings. This study suggests the possibility of tailoring the magnetic properties of cobalt ferrite nanoparticles for high-performance applications by varying the organic coating concentration.

X-ray Absorption Near-Edge Structure (XANES) at the O K-Edge of Bulk Co3O4: Experimental and Theoretical Studies.

We combine theoretical and experimental X-ray absorption near-edge spectroscopy (XANES) to probe the local environment around cationic sites of bulk spinel cobalt tetraoxide (CoO). Specifically, we analyse the oxygen K-edge spectrum. We find an excellent agreement between our calculated spectra based on the density functional theory and the projector augmented wave method, previous calculations as well as with the experiment. The oxygen K-edge spectrum shows a strong pre-edge peak which can be ascribed to dipole transitions from O to O states hybridized with the unoccupied states of cobalt atoms. Also, since CoO contains two types of Co atoms, i.e., Co and Co, we find that contribution of Co ions to the pre-edge peak is solely due to single spin-polarized orbitals (, , and ) while that of Co ions is due to spin-up and spin-down polarized orbitals ( and ). Furthermore, we deduce the magnetic moments on the Co and Co to be zero and 3.00 respectively. This is consistent with an earlier experimental study which found that the magnetic structure of CoO consists of antiferromagnetically ordered Co spins, each of which is surrounded by four nearest neighbours of oppositely directed spins.

Investigations on the electronic properties and effect of chitosan capping on the structural and optical properties of zinc aluminate quantum dots

• Low temperature synthesis of zinc aluminate quantum dots. • Evaluation excitonic Bohr radius of zinc aluminate. • Study of chitosan capping on the properties of zin aluminate. Quantum confined uncapped and chitosan capped nanoparticles of ZnAl 2 O 4 synthesized by microwave-assisted sol–gel method were investigated by structural analysis and optical techniques. X-ray diffraction studies confirmed the formation of cubic spinels with crystallite size 4.5 nm and 3.4 nm, respectively for uncapped and chitosan capped ZnAl 2 O 4 nanoparticles. Chitosan capping produced a blue shift in bandgap energy (3.84 to 3.94 eV) agreeing with size effects according to the Brus equation. A blue shift in emission peak and enhancement in photoluminescence intensity was also observed upon chitosan capping. The electronic band structure and the density of states of the bulk spinel were also calculated using density functional theory. The effective masses of electrons and holes estimated based on the band structure were used to extract the excitonic Bohr radius.

Facile synthesis of palladium incorporated NiCo2O4 spinel for low temperature methane combustion: Activate lattice oxygen to promote activity

• Pd-NiCo 2 O 4 with a unique Pd-support structure is obtained via a one-step method. • Majority of Pd incorporated into bulk NiCo 2 O 4 with finite PdO x disperse on surface. • Pd substitute for octahedral Ni 3+ /Co 3+ moves O p -band center closer to Fermi level. • Finite surface Pd at atomic scale reduce aggregation and NiCo 2 O 4 sites blockage. • Deep reduction or oxidation of the active PdO species is inhibited. While palladium-based catalysts are effective in low-temperature methane combustion, their high cost and scarcity render them unsuitable to fulfil the growing demand. The design of improved catalysts which can more efficiently utilize this precious metal is required. Here, by using a facile one-pot thermal decomposition method Pd-NiCo 2 O 4 spinel catalysts with a unique structure are obtained, in which the majority of Pd incorporated into the bulk spinel structure of NiCo 2 O 4 with limited highly dispersed PdO x species on the surface at an atomic scale. The robust 1 %Pd-NiCo 2 O 4 spinel catalyst exhibits comparable activity in methane oxidation to that of the conventional incipient wetness impregnation 2 %Pd/NiCo 2 O 4 . Theoretical calculations and catalyst characterizations (SEM, HRTEM, XRD, XPS, XAS, ICP-OES, etc.) revealed that the enhanced activity is mainly originated from having the O p -band center closer to the Fermi level, with Pd ions incorporated into the bulk NiCo 2 O 4 via substituting for the octahedral coordinated Ni 3+ /Co 3+ .

Binding Li3PO4 to Spinel LiNi0.5Mn1.5O4 via a Surface Co‐Containing Bridging Layer to Improve the Electrochemical Performance

Coating the surface of cathode materials with Li3PO4 to improve the cycling performance is commonly practiced; however, obtaining an effective and uniform coating of Li3PO4 on cathode materials is extremely difficult due to the lack of strong bonds between them. Herein, this issue is solved by coating the surface of LiNi0.5Mn1.5O4 with Li3PO4 via a novel hydrothermal method. It is shown that a uniform Li3PO4 surface coating can only be obtained by introducing a small amount of additional metal ions, such as Co, in the starting solution. X‐ray photoelectron microscopy combined with scanning transmission electron microscopy reveals that the Co ions diffuse into the 16c sites of the surface of the spinel LiNi0.5Mn1.5O4 structure, making the surface layer act as a bridging layer that connects olivine Li3PO4 with bulk spinel LiNi0.5Mn1.5O4. The high‐voltage LiNi0.5Mn1.5O4 half‐cell with the optimal Li3PO4 coating shows a discharge capacity retention of 95.8% after 50 cycles at 55 °C, compared with the only 81.1% discharge capacity retention of the bare counterpart.

Experimental and theoretical investigations of the structural, magnetic and electronic characteristics of copper ferrite nanostructures as potential spin-filtering candidates

• Structural, dielectric, and magnetic attributes CuFe 2 O 4 NPs are analyzed experimentally. • CuFe 2 O 4 NPs are composed of mixture of spinel phases via SEM inspection. • VSM analysis evaluated, the magnetization of saturation and coercivity . • The main peaks of XPS spectra for O 1 s , Cu 2 p and Fe 2 p core levels, are discerned. • Magnetic properties of CuFe 2 O 4 nanostructures are examined with GGA+U. • Spin polarized DOS of CuFe 2 O 4 nanocstructure acquired a magnetic semiconductor character. • Local magnetic moments exhibited a ferrimagnetic spin order in CuFe 2 O 4 nanostructure. • XAS of CuFe 2 O 4 NPs is used to identify the local structure of Cu 2+ , Fe 3+ and O 2- ions. • CuFe 2 O 4 NPs could be useful in the application of energy storage devices. Employing both experimental and first-principle techniques, the structural, dielectric, magnetic, and electronic characteristics of spinel-structured copper ferrite (CuFe 2 O 4 ) nanoparticles (NPs) are examined. The CuFe 2 O 4 NPs are synthesized by a co-precipitation technique (CPT) and characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), vibrating sample magnetometer (VSM), and X-ray photoelectron spectroscopy (XPS). The SEM results display that the CuFe 2 O 4 NPs possess mixed spinel phases. The composition of NP elements is determined via Energy-dispersive X-ray (EDX) spectroscopy. The magnetization and coercivity are evaluated by VSM measurements. The principal peaks of the O 1 s , Cu 2 p , and Fe 2 p states are appeared at peculiar binding energies in XPS spectra. The magnetic features and electronic structures of the CuFe 2 O 4 NPs are examined via density functional theory (DFT) together with on-site correction for Coulomb interaction using the generalized gradient approach (GGA + U) technique for exchange and correlation term. The CuFe 2 O 4 NPs derived from the bulk spinel structure possess a magnetic semiconducting character. The results of density of states (DOSs) reveal an insulating character having an energy band gap of ~1.75 eV for both spin channels. The local magnetic moments display a ferrimagnetic spin arrangement in the CuFe 2 O 4 nanostructure, manifesting through the hybridized d states of Fe/Cu and the p orbitals of O atoms. The K-edge X-ray absorption spectra (XAS) of Cu, Fe, and O ions in the CuFe 2 O 4 nanostructure are also modeled with GGA + U technique and compared with the XPS results. The structural features of the local environment of Cu 2+ , Fe 3+ , and O 2- ions are scrutinized theoretically to discern the ion sites centered at octahedral or tetrahedral lattice voids. The alternating current (AC) conductivity diminishes with the augmentation in frequency, yielding a semiconductive nature. The characterization of CuFe 2 O 4 NPs can provide insights into their preferential magnetic and dielectric behaviors applicable in miniature magnetoelectronic and energy-storage devices.

Origin of the magnetic properties of MnFe2O4 spinel ferrite: Ab initio and Monte Carlo simulation

In this work, the electronic and magnetic properties of bulk spinel ferrite MnFe2O4 were carried out using ab initio calculations and Monte Carlo simulation. The electronic properties as well as, the exchange coupling interactions and the magnetic anisotropy were calculated using Density functional theory. The obtained exchange couplings between nearest n eighbours (JAB = −21.8 K, JBB = 13.7 K and JAA = 8.6 K) and the magnetic anisotropy were used as input parameters in a classical Ising model to study the finite-temperature effects on the magnetic properties of bulk MnFe2O4 with different size. It is shown that MnFe2O4 has a magnetic transition around 559.26 K.

Theoretical investigation of physical properties of the spinel ZnFe2O4 compound: Ab-initio calculation

ABSTRACT The electronic, magnetic, optical and transport properties of ZnFe2O4 compound are calculated using the density functional theory implemented on Wien2k code with GGA + U approximation. The results obtained are in good agreement with the experimental results. In the visible range, ZnFe2O4 has a coefficient of absorption over 104/cm. The first and main critical point calculated with GGA + U appears at 2.10 eV, which is known as optical absorption edge. In addition, the X-ray Magnetic Circular Dichroic (XMCD) spectra exhibit two peaks in L3 edge revealing the existence of Fe3+ and Fe2+ ions, occupying the octahedral sites. Finally, using XMCD and XAS methods, we can calculate the spin and orbital moments of bulk spinel ferrite ZnFe2O4 compound.

Cation Distribution in Spinel Ferrite Nanocrystals: Characterization, Impact on their Physical Properties, and Opportunities for Synthetic Control.

Metal oxide materials that adopt the spinel crystal structure, such as metal ferrites (MFe2O4), present tetrahedral (A) and octahedral [B] sublattice sites surrounded by oxygen anions that provide a relatively weak crystal-field splitting. The formula of a metal ferrite material is most precisely described as (M1-xFex)[MxFe2-x]O4, where the parentheses and square brackets denote the tetrahedral and octahedral sites, respectively, and x is the inversion parameter quantifying the distribution of M2+ and Fe3+ cations among these sites. The electronic, magnetic, and optical properties of spinel ferrites all depend on the magnitude of x, which, in turn, depends on the relative sizes of the cations, their charge, and the relative crystal-field stabilization afforded by tetrahedral or octahedral coordination. Compared to bulk spinel ferrites, the large surface-area-to-volume ratio of spinel ferrite nanocrystals provides additional structural degrees of freedom that enable access to a broader range of x values. Achieving synthetic control over the degree of inversion in addition to the size and shape is critical to tuning the properties of spinel ferrite nanocrystals. In this Forum Article, we review physical inorganic methods used to quantify x in spinel ferrite nanocrystals, describe how the electronic, magnetic, and optical properties of these nanocrystals depend on x, and discuss emerging strategies for achieving synthetic control over this parameter.

Spinel Co3O4 oxides-support synergistic effect on catalytic oxidation of toluene

Abstract Bulk spinel Co3O4 oxide and supported Co3O4 catalysts (Co3O4/YSZ and Co3O4/TiO2) were synthesized by one-step hydrothermal method. Their physicochemical properties were characterized by inductively coupled plasma optical emission spectroscopy, N2-sorption, powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy, hydrogen-temperature programmed reduction and X-ray photoelectron spectroscopy.These characterization strategies were applied to corroborate and better understand the interaction between Co3O4 and the supports induced by the synergistic effect of support and the subsequent catalytic performance in toluene oxidation. The catalytic stability was evaluated by three consecutive runs and a long-term test. A highest toluene catalytic activity was achieved over Co3O4/YSZ supported catalyst comparing to that of the bulk Co3O4 and Co3O4/TiO2 catalysts, which could be attributed to its better low-temperature reducibility, oxygen activation and mobility induced by the intrinsic support properties. Thus, the positive interaction between spinel Co3O4 phase and YSZ support promoted the intrinsic catalytic properties for toluene oxidation, which was verify by testing a dual catalyst bed system consisting of bulk Co3O4 catalyst and YSZ support beds. These results were further confirmed by temperature-programmed oxygen isotopic exchange experiments, which indicated that the activation and diffusion of oxygen species on the YSZ oxygen vacancy sites were promoted by Co3O4, resulting in a significant increase of the reaction rate for toluene oxidation.

Electrical and magnetic properties of ZnCr2S4 – nanoparticles

The results of magnetic and electrical measurements of ZnCr 2 S 4 – nanoparticles (NPs) synthesized by mechanical alloying method showed an almost ideal paramagnetic state with the weak ferromagnetic short-range interactions derived from a small positive paramagnetic Curie-Weiss temperature of θ = 0.9 K and the presence of magnetic NPs confirmed by the significantly lower value of the effective magnetic moment (μ eff = 2.089 μ B /f.u.) compared to the μ eff = 5.215 μ B /f.u. for bulk spinel as well as n -type semiconducting behavior with an extrinsic region not thermally activated and with an intrinsic region with an activation energy of 0.253 eV. Broadband dielectric spectroscopy measurements showed the relaxation processes only in the intrinsic region of the electrical conductivity, i.e. above 170 K, in which the dipole relaxation becomes faster as temperature rise. These results are interpreted in the framework of the Cole-Cole function and a hopping variable range model including structural defects. • The MA method strongly changes the electrical and magnetic properties. • ZnCr 2 S 4 nanospinel is a n -type semiconductor and ideal paramagnet. • Only an intrinsic region is thermally activated of the Arrhenius type. • The spectacular result of this research is the dipole relaxation above 170 K.

Greigite (Fe3S4) is thermodynamically stable: Implications for its terrestrial and planetary occurrence

Iron sulfide minerals are widespread on Earth and likely in planetary bodies in and beyond our solar system. Using measured enthalpies of formation for three magnetic iron sulfide phases: bulk and nanophase Fe3S4 spinel (greigite), and its high-pressure monoclinic phase, we show that greigite is a stable phase in the Fe-S phase diagram at ambient temperature. The thermodynamic stability and low surface energy of greigite supports the common occurrence of fine-grained Fe3S4 in many anoxic terrestrial settings. The high-pressure monoclinic phase, thermodynamically metastable below about 3 GPa, shows a calculated negative P-T slope for its formation from the spinel. The stability of these three phases suggests their potential existence on Mercury and their magnetism may contribute to its present magnetic field.

Ultra-low magnetic damping in epitaxial Li0.5Fe2.5O4 thin films

The realization of more energy efficient nanomagnetic information devices relies on the existence of magnetic insulators capable of supporting pure spin currents in the absence of a dissipative charge current. Currently, there is a limited number of thin-film magnetic insulators with low magnetic damping. Li0.5Fe2.5O4 (LFO) is well known to possess the lowest damping among the bulk spinel structure oxides, but, thus far, LFO thin films have not lived up to these expectations. Here, we demonstrate low magnetic damping (even lower than typical bulk values) and bulk magnetization in 3 nm thick epitaxial LFO thin films. At room temperature, SQUID magnetometry shows a high saturation magnetization of 320 kA/m, and broadband ferromagnetic resonance measurements yield an effective Gilbert damping parameter of 1.3×10−3, which is among the lowest reported for ferro-/ferrimagnetic films of comparable thickness. Our results show the promise of LFO as a candidate material for spin current-based spintronics.

Detailed Mechanism of Ethanol Transformation into Syngas on Catalysts Based on Mesoporous MgAl2O4 Support Loaded with Ru + Ni/(PrCeZrO or MnCr2O4) Active Components

Mechanism of ethanol partial oxidation into syngas over catalysts based on mesoporous MgAl2O4 spinel loaded with fluorite PrCeZrO or spinel MnCr2O4 oxides and promoted by Ru + Ni was studied by in situ FTIRS and 18O SSITKA. Surface species (ethoxy, adsorbed ethanol, acetaldehyde, acetate, etc.) were identified and their thermal stability and reactivity were estimated. Analysis of kinetics of the 18O transfer into reaction products (CO, CO2, CH3CHO) allowed to estimate the rates of steps and present a scheme of the reaction mechanism including (1) fast CH3CHO formation on mixed metal oxide sites; (2) rate-limiting stage of surface oxygen species incorporation into acetaldehyde or ethoxy species with C–C bond rupture yielding CO and CO2 along with H2 and H2O; (3) water gas shift reaction by redox mechanism affecting CO/CO2 ratio and their oxygen isotope fraction. Strong interaction of PrCeZrO or MnCr2O4 oxides with MgAl2O4 support results in decreasing constants of main reaction steps in comparison with those for catalysts based on bulk fluorite and spinel oxides, correlating with a higher surface oxygen bonding strength and its low coverage revealed by pulse microcalorimetry. DFT analysis confirmed a low energy barrier of the step of Ru–O oxygen incorporation into C–C bond of ethoxy species with its rupture explaining a higher syngas selectivity for Ru-doped catalysts.

Porosity characterization of additively manufactured transparent MgAl2O4 spinel by laser direct deposition

Abstract Polycrystalline magnesium aluminate (MgAl2O4) spinel has established itself as one of the leading candidates for use as transparent, high strength ceramics. In this study, additive manufacturing of spinel ceramics by laser direct deposition was investigated with a particular focus on porosity characterization. Residual porosity was the most significant factor hindering transparency of spinel ceramics. Hence, this paper systematically studied how processing conditions and initial powder particle size affected porosity and densification of laser direct deposited spinel samples. Scan speed, laser power, and powder flow rate, along with powder size, were all shown to have substantial influences on density and porosity of produced parts. High density bulk spinel ceramics, with average densities of nearly 98%, were produced at a low powder flow rate of 0.58 g/min. In addition, the pore size distribution was studied under various processing conditions as it was closely related to transmission properties of transparent spinel at different wavelengths. The reduction in average porosity was mainly attributed to a significant reduction in large pores (>30 μm) whereas less obvious effects were found on smaller pores. An increase of scan speed resulted in an initial increase in density, followed by a subsequent decrease at scan speeds higher than 2000 mm/min. No obvious difference in porosity was observed between pulsed mode and continuous mode during laser deposition. The use of nanoparticles in initial MgO–Al2O3 mixtures for deposition also promoted densification of the deposited samples. A systematic understanding of residual porosity in this study can help process optimization to minimize porosity in additively manufactured transparent spinel ceramics, potentially eliminating the needs of time-consuming and expensive post-processing procedures.

Influence of Cr2O3 on the viscosity and crystallization behavior of glass ceramics based on blast furnace slag

Abstract CaO–MgO–Al2O3–SiO2 glass-ceramics with various Cr2O3 contents are successfully prepared from blast furnace slag as the main raw material using a conventional melting method. The influence of Cr2O3 addition on the viscosity, crystallization kinetics, structure, and properties of the obtained materials are systematically determined by viscometry, differential scanning calorimetry, Fourier-transform infrared spectroscopy, X-ray powder diffraction, thermal-field-emission environmental scanning electron microscopy, and corrosion-resistance property tests. The results showed that the obtained glass-ceramics is composed of dendritic diopside (main crystalline phase) and bulk spinel (second crystalline phase). With increasing amount of Cr2O3, the viscosity of the slag glass melt increases. In addition, the samples exhibit crystallization activation energies in the range 378–454 kJ/mol, with slight fluctuations. Moreover, the crystallization index increases from 0.84 to 2.80. The obtained glass-ceramics exhibit a maximum density, bending strength, and acid and alkali resistances of 2.97 g/cm3, 196.69 MPa, 97.61%, and 98.04% respectively, demonstrating their wide application potential for various industrial applications.

Structural and Magnetic Properties of Spinel Ferrite Nanoparticles.

In this paper we review the magnetic properties of spinel ferrite nanoparticles pointing out the primary role of the crystalline structure besides finite size and surface/interface effects. The details of the spinel crystal structure of bulk spinel ferrite materials and their influence on both the magnetization and magnetocrystalline anisotropy are recalled. Moreover, we review some results published in the literature over the last years about how the structure of magnetic nanoparticles influences their magnetic features. Perspectives about the challenges to improve the applications in several fields are finally reported.

Cationic distribution, exchange interactions, and relaxation dynamics in Zn-diluted MnCo2O4 nanostructures

We report an experimental investigation of the electronic structure and magnetic properties of bulk and nanosized MnCo2O4 diluted with Zn. The cationic distribution for tetrahedral A-site dilution is (Co1−yA2+ZnyA2+)A[Mn3+Co3+]BO4±δ, whereas B-site dilution results in (Co2+)A[Mn1−xB3+ZnxB2+Co3+]BO4−δ. The strength of exchange interaction Jij between the magnetic ions in a bulk spinel lattice decreases by ∼15% for A-site dilution relative to the undiluted compound; however, B-site dilution results in an enhancement in Jij by 17%. The frequency and temperature dependence of dynamic-susceptibility [χac(f,T)] studies of nanostructured compounds reveals the existence of spin-glass like behavior below the freezing temperature TF∼125.7K (for xB=0.2) and 154.3 K (yA=0.1). Relaxation time τ follows the Power-Law variation with a dynamical critical exponent zν=6.17 and microscopic spin relaxation time τo=4.4×10−15s for xB=0.2 (for yA=0.1, zν=5.2 and τo=5.4×10−13s). The amplitude and peak position in χac(T) decreases with an increase in the DC bias field, which indicates that the spin-glass phase can survive in the presence of low fields forming a critical line with an exponent 2/3. This behavior is similar to the de Almeida-Thouless (AT-line) analysis in the T-H phase diagram which supports the existence of spin-glass like behavior below TF in these Zn diluted spinels.