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Article

Interrelation between the Solid-State Synthesis Conditions and Magnetic Properties of the NiCr2O4 Spinel

by
Mikhail Cherosov
,
Ruslan Batulin
*,
Airat Kiiamov
,
Alexey Rogov
,
Iskander Vakhitov
,
Damir Gabadullin
,
Dmitrii Tayurskii
and
Roman Yusupov
Institute of Physics, Kazan Federal University, Kremlyovskaya Str., 18, 420008 Kazan, Russia
*
Author to whom correspondence should be addressed.
Magnetochemistry 2023, 9(1), 13; https://doi.org/10.3390/magnetochemistry9010013
Submission received: 11 November 2022 / Revised: 23 December 2022 / Accepted: 26 December 2022 / Published: 30 December 2022
(This article belongs to the Special Issue Editorial Board Members’ Collection Series: Magnetic and Magnetoelectric Materials)
Browse Figures
Versions Notes

Abstract

:
The synthesis of the NiCr2O4 compound with the spinel structure via the high-temperature solid-state reaction leads to different deviations of the cationic composition from the nominal depending on the atmosphere in the furnace chamber. The samples prepared from the same starting NiO and Cr2O3 compounds but in different atmospheres differ in phase composition and orbital and spin ordering temperatures. We find that a common route of synthesis in the air and a possible presence of the Ni2O3 in initial NiO lead to the incorporation of the Ni3+ ions into the octahedral sites regularly occupied by the Cr3+ ions. This results in a decrease in the orbital ordering and an increase in the Nèel temperatures. We propose that the Nèel temperature value serves as a measure of a departure of a composition from the nominal NiCr2O4. The lowest Nèel temperature among our series was TN = 63 K which we consider the closest to the intrinsic quantity of the NiCr2O4 compound.

1. Introduction

Crystalline materials with the spinel structure and a general chemical formula MM’2X4 are studied for several decades due to a broad range of magnetic, structural, and dielectric properties [1,2,3,4,5,6,7,8,9]. Typically, M and M’ are metal ions or a combination of them, and X represents oxygen or some chalcogen divalent anion (S2−, Se2−, Te2−). Among spinels, oxide compounds reveal outstanding mechanical properties (hardness) and high-temperature stability. Two types of cationic positions are present in spinels: tetrahedrally coordinated A-sites and octahedrally coordinated B-sites. Cations in the B-sites form a network of corner-sharing tetrahedra, typical for pyrochlores. Each face of a regular tetrahedron represents an equilateral triangle. If the B-sites are occupied by the magnetic ions with an antiferromagnetic coupling in each pair, B-sublattice is the subject of magnetic frustration. When Cr3+ ions reside at the B site, the material is known as chromite. ZnCr2O4 [10] and MgCr2O4 [11] chromites are prominent representatives of frustrated magnets.
In recent decades, much attention has been paid to transition metal chromites, when both A and B sites are occupied by magnetic ions [12,13]. In these compounds, a sequence of magnetic phase transitions takes place. In some cases, spontaneous polarization development accompanies these transitions, and a multiferroic state is formed. Thus, in CoCr2O4 a polar state appears with an onset of a spiral modulation of ferrimagnetic structure [14]. Multiferroics are promising in practical applications for the creation of magnetic non-volatile memory elements where the information is written by an electric field.
For FeCr2O4, electric polarization is induced by an applied electric field above the Nèel temperature TN and is metastable [15]. Among transition metal chromites, nickel chromite NiCr2O4 attracts much attention due to manifestations of multiferroicity, pronounced magnetodielectric, and magnetostrictive phenomena. Moreover, NiCr2O4 has diverse promising applications such as catalyst materials [16,17], electrodes in supercapacitors [18], sensitive gas sensors [19], etc.
Nickel chromite NiCr2O4 is a normal spinel with a cubic structure slightly above room temperature [20]. The ground state of the Ni2+ ions in a regular tetrahedral surrounding is the orbital triplet. Consequently, at TOO ≈ 310 K the nickel chromite spinel experiences the second-order phase transition to an orbitally ordered state. Orbital ordering occurs in the Ni-ion A-site sublattice, and crystal structure symmetry is lowered to tetragonal. On cooling to ~ 70 K, the symmetry of the NiCr2O4 crystal structure is further lowered to orthorhombic, almost simultaneously with an onset of the ferrimagnetic order at TN ~ 65 K [21,22]. On cooling below 40 K, the magnetic order develops further which is manifested in a jump of magnetization at Ts ~ 31 K [23,24]. The magnetic structure of NiCr2O4 is considered a superposition of ferrimagnetic (longitudinal) and antiferromagnetic (transverse) counterparts, and the latter sets in at Ts [23,24,25,26,27].
However, the complex magnetic structure of chromite spinels is still under debate. NiCr2O4 spinels require careful verification that the samples under study correspond to the declared stoichiometry. It is expected and verified experimentally that a dilution of the chromium sublattice with guest ions disturbs the magnetic frustration and thus leads to an increase in the Nèel temperature [28,29,30,31]. Our recent studies show that the substitution of the chromium sublattice of FeCr2O4 spinel can also occur in an uncontrolled manner due to the oxidation of Fe2+ ions to the Fe3+ state [32].
Summarizing, one can generally state that deviations of complex magnetic spinels, and transition metal chromites in particular, from their nominal compositions, can easily lead to wrong and misleading interpretations of the obtained experimental data. For practical applications, it is highly desirable to have an easily controlled criterion that would indicate a deviation from the nominal composition of a compound. In the case of iron chromite, Mössbauer spectroscopy of iron nuclei has shown itself a powerful experimental approach sensitive both to iron-ions coordination and oxidation state [33]. In the case of nickel chromite, the use of the Mössbauer effect is in principle possible (for 61Ni nuclei with a natural abundance of 1.1%). However, this requires experiments with synchrotron radiation, which limits its use as an express method.
In this paper, the studies of NiCr2O4 polycrystalline powder samples with spinel structure are presented. We show that the atmosphere in a furnace chamber in the course of a conventional high-temperature solid-state synthesis affects notably the resulting composition of an output product. We analyze the output phase composition as well as the elemental composition of the spinel fraction, its magnetic properties, and critical temperatures of the spin and orbital orderings. It will be shown that all three critical temperatures TOO, TN and Ts vary with changing the synthesis atmosphere. We suggest that the value of the Nèel temperature can serve a criterion for a departure of a nickel chromite spinel from the nominal NiCr2O4.

2. Sample Preparation and Experimental Details

A series of seven polycrystalline NiCr2O4 samples (Table 1) was synthesized by the high-temperature solid-state reaction procedure using the nickel (II) oxide NiO (99.95% from Lanhit Ltd., Moscow, Russia) and chromium (III) oxide Cr2O3 (99.5% from Alfa Aesar, Haverhill, MA, USA). The reagents were dried at the temperature of 250 °C for 12 h in the air, mixed in a target ratio (in the majority of cases, stoichiometric), and thoroughly ground in an agate mortar for 3 h. The synthesis was performed in the vertical tube furnace (GSL1700X, MTI, Richmond, VA, USA) with the mixture kept in an alumina crucible. Several syntheses were carried out with various atmospheres in the furnace chamber—in the air (samples I and II), in an argon flow (sample III), in a steady mixture of 90% of Ar and 10% of air (sample IV) or in the steady nitrogen (samples V–VII). In a case of an argon or nitrogen atmosphere, the chamber was evacuated to 10−2 mbar and purged with the pure Ar/N2 gas (99.9998%) several times. Then the synthesis took place in either a weak flow of argon (~0.01 L/min) or a sealed chamber with a slight overpressure (~0.02–0.03 bar) of Ar, Ar/air mixture or N2-gas at a temperature of 1200 °C or 1300 °C for 24 h. The synthesis was supposed to follow the reaction of
NiO + Cr2O3 → NiCr2O4
Note that the synthesis in a nitrogen atmosphere demanded an elevated temperature of 1300 °C (samples VII and VIII) as its performance at 1200 °C left a significant part of an initial mixture unreacted (sample VI).
The resulting product in all cases was examined for a formation of the desired phase as well as the impurity phases with the powder XRD analysi. XRD measurements were carried out with the Bruker D8 Advance diffractometer (Bruker AXS GmbH, Karlsruhe, Federal Republic of Germany) equipped with the Cu-Kα source. Due to imperfect spectral filtering of the X-rays, each diffraction maximum has a doublet structure originating from the Kα1 and Kα2 components. Prior to measurements, samples were carefully ground in an agate mortar to a fine powder state. The temperature of a sample was stabilized with the nitrogen vapor flow system (Anton Paar, Graz, Austria).
The morphology of the obtained samples was studied with scanning electron microscopy (SEM). The images were taken with the Merlin (Carl Zeiss, Oberkochen, Federal Republic of Germany) high-resolution self-emission microscope at a low acceleration voltage of 5 kV in the secondary electron detection mode. A sample was dispersed over a carbon tape and covered with 10 nm of AuPd 80/20 alloy using the Q150T ES (Quorum Technologies, Lewes, UK) sample preparation system. Elemental analysis was performed by means of energy-dispersive spectrometry (EDX) with the X-Max setup (Oxford Instruments, Abingdon-on-Thames, UK) combined with SEM, at an accelerating voltage of 20 kV.
Magnetization measurements of the samples were performed with vibrating sample magnetometry (VSM) option of the Physical Property Measurement System PPMS-9 (Quantum Design, San Diego, CA, USA) in a temperature range of 5–300 K and the magnetic fields within ± 9 T. Temperature dependences of the susceptibility were studied under an applied field of 10 mT.
Further, the results for the four characteristic representatives of the series, namely, samples I, II, III, and VI, will be presented and discussed.

3. X-ray Diffraction Analysis

Powder XRD patterns of the synthesized NiCr2O4 samples I, II, III, and VI at room temperature (RT) are presented in Figure 1. Diffractograms of samples I and II produced in the air reveal an occurrence of two crystalline phases—a dominant cubic-symmetry spinel and a residual α-Cr2O3. For sample I, the phase’s contents were 92% and 8%, and for sample II, these were 99.8% and 0.2%, respectively. A modification of the NiO/Cr2O3 mixture composition from stoichiometric (see Table 1) by an excessive 10 mol.% of NiO was done intentionally to compensate for an assumed loss of NiO in the course of a synthesis. This trick has indeed led to essentially a single-phase spinel-structure product. However, the masses of an initial NiO/Cr2O3 mixture and of a product were identical indicating no loss of NiO. It means that nickel ions somehow substitute partially for Cr3+-ions in the B-sites of the spinel.
The diffractogram of sample III (Figure 1c) synthesized in a flow of argon, at room temperature, reveals four crystalline phases: two spinel phases—one with the cubic and another with the tetragonal symmetry (in total 65%), metallic nickel (27%), and a residue of α-Cr2O3 (8%). Evidently, an exposure of NiO to the high temperature of 1200 °C results in a chemical reduction of nickel to the metallic state that cannot participate in the reaction with Cr2O3. A presence of the tetragonal-structure spinel fraction is expected as at ~ 310 K an orbital ordering in the Ni-ion sublattice sets in.
Sample VI was synthesized with the oven chamber filled with nitrogen without its flow. Its diffractogram contains the patterns of three crystalline phases: two spinel-structure ones similar to sample III (in total 99.5%), and a vanishingly small amount of α-Cr2O3 (0.5%).
Temperature transformation of the XRD pattern of sample VI was studied in a limited 2θ-range from 61 to 66 degrees (Figure 2). In this range, the (440) diffraction maximum of the cubic NiCr2O4 phase is located, which splits into the (224) and (400) peaks below the structural phase transition temperature. The symmetry lowering is due to the cooperative Jahn-Teller effect within the A-ion (Ni2+) sublattice. At T = 323 K and above, a single (404) diffraction maximum is observed which corresponds to the cubic Fd 3 ¯ m phase of NiCr2O4. On cooling (Figure 2), new components start to manifest themselves on the left and right wings of the cubic-phase (404) peak while the last gradually vanishes. The development of the diffraction pattern indicates a coexistence of the cubic and tetragonal phases in the temperature range of 288–313 K; below 288 K, the sample reveals only the tetragonal I41/amd phase. Such an observation shows that the actual sample is not perfectly homogeneous and is characterized by a distribution of the critical orbital ordering temperatures.
The patterns in the 2θ-range of 61–66 degrees measured at T = 295 K for samples I, II, III, and VI are shown in the insets to panels (a)–(d) of Figure 1, respectively. Clearly, samples I and II are found fully within the whole volume in the cubic phase while samples III and VI represent the mixtures of the cubic and tetragonal-symmetry phases. Thus, we can conclude that samples I and II have TOO < 295 K. This indicates that samples I and II, on one hand, and III and VI, on the other, are different.

4. Morphology and Chemical Composition

In Figure 3a–d, the SEM images of the NiCr2O4 powder samples I, II, III, and VI are presented. Samples I and II synthesized in the air evidently have larger mean grain size than samples III and VI obtained in a flow of argon and in a steady N2 atmosphere, respectively. Most of the grains in the obtained powders have a characteristic for spinels octahedron-like shape. Grain images for samples I, II, and VI are very clear and high-contrast, however, an image of sample III is notably worse. This is a consequence of a multi-phase composition of sample III with comparable fractions of a spinel, Cr2O3, and metallic nickel (Table 1). Definitely, the grains of sample III have a developed surface and probably are covered with the impurity phases.
A typical EDX spectrum (sample II) of the obtained materials is shown in Figure 3e. We have extracted from these spectra a ratio of Ni:Cr concentrations (Table 2). For samples, I, II, and VI, these ratios are well-defined regardless of a chosen grain/spot. The concentration of chromium in all three samples is less than twice the concentration of nickel. The Ni:Cr ratio of sample III varies in a broad range from 1:2.2 to 1:9 depending on a spot. This shows that the Cr2O3 dominates at the surface of the spinel grains in this multi-phase sample. The knowledge of the Ni:Cr ratio allows us to calculate the substitution degree x of the Cr3+-sites by nickel-ions assuming the composition of the spinel phase as Ni(Cr1-xNix)2O4.

5. Magnetic Properties of NiCr2O4 Powder Samples

Figure 4 shows the temperature dependences of the magnetization of samples I, II, III, and VI measured on cooling in the field of 10 mT. For sample III, ferromagnetic nickel particles have been extracted from the powder with the permanent NdFeB magnet prior to measurements. M(T) curves of every sample reveal two anomalies. The first anomaly corresponds to the transition from the paramagnetic to the ferrimagnetic state at TN. Nèel temperature for samples I, II, III, and VI has the value of 68.5 K, 73.1 K, 63.0 K, and 67.7 K, respectively (Table 2). On further cooling, a rise of magnetization is observed at Ts associated with the antiferromagnetic counterpart of the magnetic structure due to a long-range ordering in the transverse spin arrangement [23,24,25,26,27]. This anomaly takes place at 25.7 K, 22.3 K, 27.2 K, and 25.8 K for samples I, II, III, and VI, respectively. Note an obvious correlation between the trends for two magnetic transitions: the lower the Nèel temperature the higher the Ts. Thus, we find that the magnetic ordering in the four representatives of our series that differ in the synthesis conditions takes place at different temperatures again indicating some differences in these samples.
Magnetization curves were also studied to compare the coercivities and saturation magnetizations of NiCr2O4 powders. Figure 5 shows hysteresis loops measured at 40 K (Ts < T < TN) and at 10 K (T < Ts) for samples II, III, and VI. For each sample, the coercive field value is ~0.25 T at 40 K and ~0.54 T at 10 K. The loops of all samples are near identical, only the saturated magnetic moment for sample II is ~ 10% less than that of samples III and VI. Moreover, a non-monotonous variation of the magnetization is found for sample II on changing the sign of an applied field revealing the presence of another magnetic fraction.

6. Discussion

Four representatives of a series of nominal NiCr2O4 powders with the spinel structure that were produced by the high-temperature solid-state synthesis from the same NiO and Cr2O3 oxides differ in values of three critical temperatures characteristic for the target compound. What can serve as a source for these differences? A clue, in our opinion, lies in (i) a need for an extra 10 mol.% of NiO to obtain a phase-pure spinel-structure product (sample II, Table 1) and (ii) a non-stoichiometric ratio of Cr:Ni < 2 for samples I, II, and VI (Table 2). This clearly indicates a partial substitution of the octahedral Cr3+-sites by nickel ions.
To our knowledge, no cationic disorder was reported for the NiCr2O4 compound. Such substitution could happen if NiO contains Ni3+ ions. An easy transformation of NiO to Ni2O3 is well known and manifests itself in the color change of naturally green NiO to black “nickel oxide”. Indeed, the starting NiO that we used for the synthesis had a greyish-greenish color. Though the XRD test had not revealed any crystalline constituent apart from the cubic NiO in it, X-ray photoemission indicates only Ni3+ ions at the surface of the particles. Thus, at least a presence of Ni3+ ions has been established in the NiO reagent. On the other hand, oxidation of NiO to Ni2O3 is not inhibited if the synthesis is performed in the air, and the common high-temperature solid-state route in the air may cause a departure of the nominal NiCr2O4 composition. The substitution of the Cr3+ sites by Ni3+ ions looks favorable due to identical charges and similar ionic radii of these ions (0.615 Å for Cr3+ and 0.600 Å for Ni3+ in six-fold coordination [34]).
The electronic configuration of Ni3+ ions (3d8, t 2 g 5 e g 2 in the cubic-symmetry crystal field) is different from that of the substituted Cr3+ ions (3d8, t 2 g 3 ). Anyway, the incorporation of the Ni3+ ions to the Cr3+ sites creates the local lattice distortions and therefore can easily affect the temperature of the orbital ordering, most probably decreasing its value. The pyrochlore-like structure of the B-site sublattice is the subject to magnetic frustration [35], which undoubtedly is a part of the story of why the temperature of magnetic ordering in NiCr2O4 is as low as ~65 K. A difference in electronic configurations between the Cr3+ and Ni3+ ions disturbs the fine balance of exchange interactions within the B-sublattice which will lead to an increase of the long-range spin ordering temperature. This indeed is the case in our study: the lower the value of the cationic substitution degree x, the lower the Nèel temperature (Table 2, Figure 6). It is not so easy to discuss in simple terms the trend for the transverse antiferromagnetic transition temperature Ts. As a matter of fact, the lower the x value, the higher the Ts (Table 2, Figure 6).
For sample III, which was obtained in a flow of argon, a significant part of the product was the metallic nickel (Table 1), and we expect a minimum of Ni3+ ions in its spinel fraction. This sample reveals the lowest Nèel temperature among our series and, probably, it is the lowest reported for this compound in the literature. Therefore, we suggest that the value of TN = 63.0 K is most close to the intrinsic characteristic of the true NiCr2O4. We also propose that the Nèel temperature can serve as an easily accessible measure of departure of the composition of a compound obtained by whatever synthesis procedure from its nominal NiCr2O4.

7. Conclusions

To summarize, a series of seven NiCr2O4 powder samples have been produced following a conventional high-temperature solid-state synthesis route from the same NiO and Cr2O3 compounds. The influence of synthesis conditions, in particular the atmosphere in an oven chamber, on the phase composition of a product and magnetic and structural properties of the spinel fraction was studied. We find that all three critical temperatures corresponding to the orbital ordering (TOO), onsets of the ferrimagnetic state (TN), and transverse spin arrangement (Ts) vary with the changing atmosphere. We propose that Ni3+ ions that either occur in initial NiO or form during synthesis substitute for the Cr3+ ions in the octahedral B-sites of the spinel. Such substitution disturbs crystal lattice and dilutes the pyrochlore-like B-site magnetic sublattice and causes thus the shifts of the critical temperatures. The sample produced under an inert flowing Ar-gas atmosphere reveals the lowest Nèel temperature TN = 63.0 K and the highest Ts = 27.2 K. In our opinion, the value of the Nèel temperature can serve as a measure of a departure of a sample composition from the nominal NiCr2O4. A study of the structural phase transition associated with an orbital ordering in the A-site Ni2+-ion sublattice revealed the coexistence of cubic and tetragonal symmetry phases in the temperature range of 288–313 K, indicating a distribution of the orbital ordering temperature over a sample volume.

Author Contributions

Conceptualization, R.B. and R.Y.; methodology, I.V., A.K. and M.C.; formal analysis, A.R., D.G., A.K. and M.C.; investigation, M.C, A.R., D.G. and A.K.; resources, D.T. and R.Y.; writing—original draft preparation, R.B. and R.Y.; writing—review and editing, R.Y., R.B. and M.C.; visualization, R.B. and M.C.; supervision, R.Y., D.T. and R.B. All authors have read and agreed to the published version of the manuscript.

Funding

The reported studies were performed with support from the Russian Science Foundation, project No. 19-12-00244.

Data Availability Statement

Raw data are available on a reasonable request to the corresponding author.

Acknowledgments

Electron microscopy studies were performed at the Interdisciplinary Centre for Analytical Microscopy of Kazan Federal University.

Conflicts of Interest

The authors declare no conflict of interest.

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Magnetochemistry 09 00013 g001 550
Figure 1. Powder XRD patterns of samples I (a), II (b), III (c), and VI (d) measured at T = 295 K. Vertical tick patterns represent Bragg peak positions of the NiCr2O4 (green), Cr2O3 (blue), and nickel (purple) constituents. Insets show the XRD pattern in the 2θ angle range corresponding to the (440) maximum of the cubic spinel phase (see text).
Figure 1. Powder XRD patterns of samples I (a), II (b), III (c), and VI (d) measured at T = 295 K. Vertical tick patterns represent Bragg peak positions of the NiCr2O4 (green), Cr2O3 (blue), and nickel (purple) constituents. Insets show the XRD pattern in the 2θ angle range corresponding to the (440) maximum of the cubic spinel phase (see text).
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Figure 2. (a) Temperature dependence XRD pattern of the powder NiCr2O4 sample VI in the course of the structural phase transition associated with an orbital ordering within the Ni2+ A-site sublattice, (b) Temperature dependence of the cubic- (squares) and tetragonal-symmetry (triangles) phase fractions.
Figure 2. (a) Temperature dependence XRD pattern of the powder NiCr2O4 sample VI in the course of the structural phase transition associated with an orbital ordering within the Ni2+ A-site sublattice, (b) Temperature dependence of the cubic- (squares) and tetragonal-symmetry (triangles) phase fractions.
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Figure 3. Scanning electron microscopy images of NiCr2O4 powder samples I (a), II (b), III (c), and VI (d). Energy dispersion spectrum of sample II (e).
Figure 3. Scanning electron microscopy images of NiCr2O4 powder samples I (a), II (b), III (c), and VI (d). Energy dispersion spectrum of sample II (e).
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Figure 4. Temperature dependences of the magnetization of samples I, II, III, and VI of the NiCr2O4 powders measured with an applied magnetic field of 10 mT on cooling.
Figure 4. Temperature dependences of the magnetization of samples I, II, III, and VI of the NiCr2O4 powders measured with an applied magnetic field of 10 mT on cooling.
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Figure 5. Magnetic hysteresis loops of samples II, III, and VI measured at T = 10 K and at T = 40 K.
Figure 5. Magnetic hysteresis loops of samples II, III, and VI measured at T = 10 K and at T = 40 K.
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Figure 6. Dependence of the critical temperatures of magnetic orderings in powder samples of NiCr2O4 on the degree of Ni3+-ion substitution for Cr3+ sites.
Figure 6. Dependence of the critical temperatures of magnetic orderings in powder samples of NiCr2O4 on the degree of Ni3+-ion substitution for Cr3+ sites.
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Table
Table 1. A list of the NiCr2O4 powder samples obtained by the solid-state synthesis procedure, conditions of the synthesis, products of the reaction according to XRD data, and temperature of the orbital ordering TOO.
Table 1. A list of the NiCr2O4 powder samples obtained by the solid-state synthesis procedure, conditions of the synthesis, products of the reaction according to XRD data, and temperature of the orbital ordering TOO.
SampleAtmosphereSynthesis Temperature, Deg. CMolar Ratio Cr2O3/NiO in Initial Mixture ProductsTOO, K
IAir12001:1spinel (92%), Cr2O3 (8%)<295
IIAir12001:1.1spinel (99.8%), Cr2O3 (0.2%)<295
IIIAr flow12001:1spinel (65%), Cr2O3 (8%),
Ni (27%)		>295
IVAir (10%)+ Ar (90%) closed12001:1spinel (99.3%), Cr2O3 (~0.7%)<295
VN2 closed12001:1spinel (67%), Cr2O3 (22%), NiO (11%)>295
VIN2 closed13001:1spinel (99.6%), Cr2O3 (0.4%)313
VIIN2 closed13001:1spinel (99.6%), Cr2O3 (0.4%)>295
Table
Table 2. Cationic composition Ni:Cr and a substitution degree x of the Cr3+ sites by nickel ions in Ni(Cr1-xNix)2O4 and magnetic critical temperatures TN and Ts determined from VSM data.
Table 2. Cationic composition Ni:Cr and a substitution degree x of the Cr3+ sites by nickel ions in Ni(Cr1-xNix)2O4 and magnetic critical temperatures TN and Ts determined from VSM data.
SampleNi:Cr Ratiox, at.%TN, KTS, K
I1:1.980.368.525.7
II1:1.852.673.122.3
III1:(2.18 to 9)0 *63.027.2
VI1:1.970.567.725.8
* an assumed value, see the text.
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Cherosov, M.; Batulin, R.; Kiiamov, A.; Rogov, A.; Vakhitov, I.; Gabadullin, D.; Tayurskii, D.; Yusupov, R. Interrelation between the Solid-State Synthesis Conditions and Magnetic Properties of the NiCr2O4 Spinel. Magnetochemistry 2023, 9, 13. https://doi.org/10.3390/magnetochemistry9010013

AMA Style

Cherosov M, Batulin R, Kiiamov A, Rogov A, Vakhitov I, Gabadullin D, Tayurskii D, Yusupov R. Interrelation between the Solid-State Synthesis Conditions and Magnetic Properties of the NiCr2O4 Spinel. Magnetochemistry. 2023; 9(1):13. https://doi.org/10.3390/magnetochemistry9010013

Chicago/Turabian Style

Cherosov, Mikhail, Ruslan Batulin, Airat Kiiamov, Alexey Rogov, Iskander Vakhitov, Damir Gabadullin, Dmitrii Tayurskii, and Roman Yusupov. 2023. "Interrelation between the Solid-State Synthesis Conditions and Magnetic Properties of the NiCr2O4 Spinel" Magnetochemistry 9, no. 1: 13. https://doi.org/10.3390/magnetochemistry9010013

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