Tunable Curie temperature of Mn0.6Zn0.4Fe2O4 nanoparticles

Accepted Manuscript Tunable Curie Temperature of Mn0.6Zn0.4Fe2O4 Nanoparticles Navjot Kaur, Bhupendra Chudasama PII: DOI: Reference:

S0304-8853(18)30804-7 https://doi.org/10.1016/j.jmmm.2018.05.103 MAGMA 64015

To appear in:

Journal of Magnetism and Magnetic Materials

Received Date: Revised Date: Accepted Date:

18 March 2018 29 May 2018 30 May 2018

Please cite this article as: N. Kaur, B. Chudasama, Tunable Curie Temperature of Mn0.6Zn0.4Fe2O4 Nanoparticles, Journal of Magnetism and Magnetic Materials (2018), doi: https://doi.org/10.1016/j.jmmm.2018.05.103

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Tunable Curie Temperature of Mn0.6Zn0.4Fe2O4 Nanoparticles Navjot Kaur and Bhupendra Chudasama School of Physics and Materials Science, Thapar Institute of Engineering & Technology, Patiala-147004, India

Email: [email protected]

*Corresponding Author contact details Bhupendra Chudasama Laboratory of Nanomedicine School of Physics & Materials Science Thapar Institute of Engineering & Technology, Patiala – 147004 INDIA E-mail: [email protected] Phone: +91-175-2393893 FAX: +91-175-2393020

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Tunable Curie Temperature of Mn0.6Zn0.4Fe2O4 Nanoparticles Navjot Kaur and Bhupendra Chudasama School of Physics and Materials Science, Thapar Institute of Engineering & Technology, Patiala-147004, India

Email: [email protected]

ABSTRACT Synthesis of stable temperature sensitive magnetic fluids that can be used in heat exchange devices having desired magnetic properties and tunable Curie temperature is quite challenging as their performance parameters are strongly correlated with preparation conditions of magnetic nanoparticles. In this article, we report size dependence of Curie temperature and saturation magnetization of Mn0.6Zn0.4Fe2O4 (MZ4) nanoparticles synthesized by co-precipitation method by controlling the pH, reaction temperature and reaction time. As-synthesized MZ4 nanoparticles have tunable Curie temperature that ranges between 392 K to 665 K. These magnetic nanoparticles are well suited for cooling applications in energy conversion electronic devices as their Curie temperatures are close to the working temperature of these devices. The observed tunability of Curie temperature and magnetization of MZ4 nanoparticles are analysed in terms of the corresponding changes in the magnetic particle size and distribution of Mn ions between tetrahedral (A-site) and octahedral (B-site) in an inverse spinel structure. Keywords: Magnetic nanoparticles; Curie temperature; transformer cooling; magnetic particle size, Inverse spinel structure

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1. Introduction Magnetic fluids have promising applications as liquid heat carriers in heat exchange and magnetocaloric energy conversion devices [1, 2]. Magnetization of magnetic fluid is temperature-dependent, decreasing steadily until the fluid reaches a characteristic “Curie temperature” at which, it loses all its magnetic strength [3, 4]. This property of temperature sensitive magnetic fluids can be exploit to design a smart coolant that can tune its cooling efficiency according to the operating temperature of the transformer by adjusting its magnetic field induced convective flow [5]. These characteristic of magnetic fluids can be utilized to design smaller, more efficient transformers, or to extend the life and loading capacity of the existing units [5, 6]. In order to use magnetic fluid for transformer cooling applications, magnetic fluid may require large pyromagnetic coefficient i.e. fluid with a high saturation magnetization and low Curie temperature. Therefore synthesis of temperature sensitive magnetic fluids with tunable magnetization and Curie temperature which matches with the operating temperature of transformers is of great interest. In general, temperature sensitive magnetic fluids suitable for cooling applications in high power transformers should have Curie temperatures ranging between 70 °C to 300 °C [7]. Most substituted ferrites used in the preparation of magnetic fluids tend to have Curie temperatures that are too high (> 500 °C) for practical use in transformers. Curie temperature of mixed metal ferrites lie between 100 °C to 300 °C. Amongst them Mn-Zn ferrites are well suited for thermo-magnetic cooling, because of their sufficiently high saturation magnetization and large pyromagnetic coefficient [8, 9]. Mn-Zn ferrite is of great interest because Curie temperature of MnFe2O4 can be lowered by replacing Mn ions at tetrahedral A-site with nonmagnetic ions like Zn. The substitution of Zn ions may alter the saturation magnetization and reduce the Curie temperature if the cation distribution is not altered [10]. 3

Jeyadevan et al. has reported the use of Mn-Zn ferrite for the preparation of temperature sensitive magnetic fluids by co-precipitation method. It was observed that magnetization of Mn-Zn ferrite nanoparticles depends on the reaction temperature, pH of the solvent, initial molar concentration, etc. The average particle diameter and magnetization of the particles increased from 9 to 12 nm and 37 to 50 emu/g, respectively [11]. But no change in Curie temperature was observed. Arulmurugan et al. have reported synthesis of Mn1-xZnxFe2O4 (x = 0.1 - 0.5) nanoparticles having Curie temperatures of 160 °C to 360 °C. They have observed that Curie temperature of Mn1-xZnxFe2O4 nanoparticles decreases with increasing Zn content [12]. Desai et al. have reported synthesis of Mn0.5Zn0.5Fe2O4 nanoparticles having Curie temperature ranging between 400K to 449K and saturation magnetization between 55emu/g to 78 emu/g by using hydrothermal method [13]. In our recent work we have prepared a series of Mn1-xZnxFe2O4 nanoparticles and determined their magnetic properties [14]. Amongst them x = 0.4, i.e. Mn0.6Zn0.4Fe2O4 (MZ4) nanoparticles have good crystallinity, high saturation magnetization and moderate Curie temperature that is close to the operating temperature of transformers [14]. Therefore we have chosen MZ4 nanoparticles for further investigation. In this article we report synthesis of series of MZ4 nanoparticles under different conditions of reaction pH, temperature and time. Tunability of Curie temperature MZ4 nanoparticles has been demonstrated and its correlation with the magnetic particle size and cation (Mn) distribution at A and B sites in inverse spinel structure have been established. 2. Materials and methods AR grade FeCl3 was obtained from S.D. fine-chem Ltd., MnCl2.4H2O was purchased from LOBA chemicals. ZnSO4.7H2O, NaOH and acetone were purchased from Merck, India. All chemicals were used as-received without any purification. Aqueous solutions were prepared in Milli-Q ultrapure water (ρ = 18.2 MΩ). 4

A series of Mn0.6Zn0.4Fe2O4 (MZ4) nanoparticles were prepared by co-precipitation method at varying conditions of pH (10-13), reaction temperature (80 -100 oC) and reaction time (1-4h) [15, 16]. MnCl2.4H2O, ZnSO4.7H2O and FeCl3 were used as precursors and sodium hydroxide was used as precipitating agent. Aqueous solutions of MnCl2.4H2O, ZnSO4.H2O and FeCl3 were prepared by dissolving appropriate quantities of reactants in 300 mL distilled water. The pH of the solution was adjusted to < 2 with dilute HCl. It was added to 100 mL NaOH solution under continuous stirring. The molar ratio of (MnCl2.4H2O + ZnSO4.7H2O) : FeCl3 : NaOH was kept at 1 : 2 : 8. The solution pH was adjusted between 10 to13 by adding desired quantity of 1 M NaOH solution. Within 20 min of stirring, metal salts were converted into their hydroxides. Metal hydroxides were then subjected to heating at 80 100 oC for 1

4h. During this heating cycle, metal hydroxides transform themselves to metal

oxide nanoparticles [17]. Magnetic nanoparticles were then cooled to room temperature and decanted with permanent magnet. They were washed multiple times with copious amount of warm distilled water followed by an acetone wash and dried overnight at 100 oC. Sample codes along with the preparation conditions of nanoparticles are summarized in Table 1.

As-synthesized MZ4 nanoparticles were characterized by X-ray diffraction. Structural investigation of nanoparticles was carried out on PAN analytical X’pert PRO powder X-ray diffractometer. X-ray diffraction patterns were recorded at room temperature by using monochromatic CuKα radiation (λ = 1.5405 nm) in the 2 range of 28° to 70°. X-ray diffraction patterns were refined by Rietveld refinement technique using “Fullprof suite” program. Magnetization and Curie temperature measurements of MZ4 nanoparticles were carried out on Lake Shore 7404 vibrating sample magnetometer (VSM). M-H loops were measured at 25 оC for magnetic field strength (H) of 0 to 5 KOe. High temperature M-T measurements were also carried on Lake Shore 7404 VSM with 74035 single stage cryostat oven assembly from 300K to 700K. 5

3. Results and discussion X-ray diffraction patterns of MZ4 nanoparticles prepared by coprecipitation method at different reaction pH, time and temperatures are shown in supporting information Fig. S1, S2 and S3, respectively. In each diffractogram six peaks were observed, which are indexed well with the ABO4 type spinel structure. Small sizes of nanoparticles lead to the peak broadening in the X-ray diffraction. We have adopted Williamson-Hall approach to estimate the crystallite size of MZ4 nanoparticles [14]. Crystallite sizes of MZ4 nanoparticles prepared as a function of pH, reaction time and reaction temperature are reported in Table 2. Crystallite size of MZ4 nanoparticles increases with increase in the co-precipitation pH, reaction time and reaction temperature. A similar observation was also reported by Desai et al. [18]. Diffraction patterns (Fig. S1, S2 and S3) were refined by Rietveld method by assuming Fd3m space group [19, 20]. Obtained best fit values of various structure factors and goodness of fit parameters (2, Rp, Rwp) are reported in supporting information (Table S1, S2 and S3) section. Cation (Mn) between tetrahedral A-site and octahedral B-site shows strong dependence on the parameters of coprecipitation reaction.

Magnetization curves of as-synthesized MZ4 nanoparticles prepared as a function of co-precipitation pH, reaction time and reaction temperature are shown in Fig. 1 (a-c) and S4 (a-c). With increase in magnetic field, the magnetization of MZ4 nanoparticles increases because of progressive alignment of ensemble of magnetic particles along the external field. All samples exhibit superparamagnetism as evidence from the near zero remanence and coercivity values (Table 2). Magnetization data of MZ4 nanoparticles is fitted modified Langevin equation [21] + χH

M = Ms

6

(1)

Here Ms is the saturation magnetization of nanoparticles and L(α) = cothα−1/α is the Langevin function. The Langevin parameter, α = µ(H +Hint)/kBT. µ is the magnetic moment of individual spin clusters, H is the applied external magnetic field, Hint=λM1; λ is the mean field constant (dimensionless) and M1 is the internal field acting on each particle/cluster, f(D)d(D) is the log-normal cluster diameter distribution function with mean cluster diameter Dm and width σ and χ is the susceptibility of nanoparticles having mean particle size above superparamagnetic limit. From the fit, magnetic particle diameter (Dm), saturation magnetization (Ms), polydispersity (), mean field constant () and ferrimagnetic susceptibility () have been determined, which are reported in Table 3. It has been observed that the magnetic diameter increases with increase in pH, reaction time and reaction temperature (Table 3). Mean field constant (λ) and mean internal field (M1) decreases with increase in magnetic particle size (Table 3). Saturation magnetization (Ms) increases with increase in the particle size. Highest saturation magnetization (28.7 emu/g) was observed when magnetic particle size was ~13 nm. Beyond 13 nm, magnetization of MZ4 nanoparticles decreases with increase in the particle size [22]. This variation in magnetization can be explained in terms of site occupancy of cations (Mn) at A-sites and B-sites. MZ4 nanoparticles possess mixed spinel structure (Zn2+0.4 Mn2+0.4 Fe3+0.2 [Mn2+0.2 Fe3+0.8 Fe3+] O2-4). AA interactions in mixed spinel are extremely weak as compared to AB or BB interactions [14]. Thus changes in the occupancy of Mn2+ ions at A-site (Table S1) are responsible for the observed trend of saturation magnetization. Occupancy of Mn2+ ions at B- site increases with increase in synthesis pH (upto 11) and then decreases with further increase in pH. Accordingly, saturation magnetization of MZ4 nanoparticles increases with the pH (upto 11) and with further increase in the pH; saturation magnetization of nanoparticles decreases. This may be because of decrease in occupancy of Mn2+ ions at B-site (supporting information Table S1 and Table 3). Similarly with the increase in reaction time and reaction temperature

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upto 3h and 90 оC respectively, the saturation magnetization increases with increase in occupancy of Mn2+ ions at B-site. Further increase in reaction time or reaction temperature lead to the decrease in saturation magnetization of nanoparticles. This is because of decrease in the occupancy of Mn2+ ions at the B-site (supporting information - Table S2, S3 and Table 3). Saturation magnetization of nanoparticles can be described as, Ms(D)=Ms(∞)(1-

(2)

where Ms(D) represents the saturation magnetization of D-sized particle, Ms(∞) is the saturation magnetization of bulk sample and t is the thickness of magnetic dead layer [23]. Bulk saturation magnetization (Ms (∞)) is calculated from the cation distribution obtained from the Rietveld refinement of MZ4 nanoparticles. The changes in the thickness of the magnetic dead layer of MZ4 nanoparticles observed under different preparation conditions of pH, reaction temperature and reaction time is shown in Table 3. As evident from table 3, particle size of MZ4 nanoparticles decrease leading to an increase in the surface to volume ratio of nanoparticles is responsible for the observed increase in the thickness of magnetic dead layer. Saturation magnetization of MZ4 nanoparticles is also well correlated to changes in the thickness of magnetic dead layer. With the increase in dead layer thickness, the saturation magnetization of small sized (d < 13 nm) MZ4 nanoparticles also decreases. Curie temperature of MZ4 nanoparticles has been determined from high temperature VSM measurements. The M  T curves of MZ4 nanoparticles prepared as a function of pH, reaction time and reaction temperature are shown in Fig. S5, S6 and S7, respectively in supporting information section. The linear region of M  T curves have been extrapolated and intercept of each of this extrapolation on x-axis provides an estimation of the Curie temperature of nanoparticles. They are reported in table 2. Curie temperature of MZ4 nanoparticles increase with increase in the pH from 10 to 11 and then decreases with further 8

increase in the pH (Table 2). For larger size nanoparticles (d > 13), the demagnetization effect appears at higher temperature and this effect disappears for size d < 13 nm because of lower saturation magnetization of these nanoparticles (Fig. 2) [24]. This size dependence of Curie temperature of MZ4 nanoparticles can be explained in terms of site occupancy of cations (Mn) ions in the spinel lattice [25]. As-synthesized MZ4 nanoparticles having mixed spinel structure (Zn2+0.4 Mn2+0.4 Fe3+0.2 [Mn2+0.2 Fe3+0.8 Fe3+] O2-4), have Curie temperatures that ranges between 392 K to 665 K. As the AA interactions are 10 times weaker than the AB and BB interactions in these ferrites, Tc depends on the respective exchange integrals J [25]

(3)

Here k Boltzmann’s constant, and │S│is absolute spin value, J is exchange integral, nij is number of nearest exchange coupled neighbours. In MZ4 nanoparticles it is assumed that Mn2+ occupies the A- site. Partial presence of Mn2+ at B-site may change the Tc from its original value. The highest value of Tc for sample S3 (at pH 11) can be explained in terms of site occupancy of Mn2+. For higher pH values (pH >11), Curie temperature decreases with increase in the particle size due to the decrease in occupancy of Mn2+ ions at B-site (Fig 2). For lower pH values (pH <11), Curie temperature increases with increase in magnetic particle size or magnetization. Effect of reaction time on the Curie temperature of MZ4 nanoparticles can be seen in Fig. S6 and Table 2. It has been observed that Curie temperature of MZ4 nanoparticles increases with increase in the reaction time of MZ4 nanoparticles from 1h to 3h. This is because of the increase in the particle size and saturation magnetization of MZ4 nanoparticles. A sharp decrease in TC was observed for MZ4 nanoparticles prepared at 4h reaction time. The observed variation in the Curie temperature of MZ4 nanoparticles has 9

similar dependency on magnetic particle size and ratio of occupancy of Mn ions at A-site and B-site in inverse spinel structure (Fig. 3). Curie temperature of MZ4 nanoparticles increases with increase in magnetization of nanoparticles which was caused by increase in their magnetic particle size. These changes are in correlation with the changes in site occupancy of Mn ions at A-site and B-site in inverse spinel structure. Effect of reaction temperature on the Curie temperature of MZ4 nanoparticles are shown in Fig S7 and table 2. It has been observed that Curie temperature of MZ4 nanoparticles increases with increase in the reaction temperature from 80 оC to 90 оC and with further increase in temperature Tc decreases. This decrease in Tc at higher reaction temperature was caused by sharp changes in the occupancy of cations (Mn) at A-site and at B-site leading to decrease in the saturation magnetization of nanoparticles. 4. Conclusion Curie temperature of MZ4 nanoparticles has been tuned between 392 K to 665 K. Particle size dependence of Curie temperature of MZ4 nanoparticles have also been investigated. It has been observed that magnetization and Curie temperature increases with increase in the particle size upto 13 nm. For larger particles (d > 13 nm), magnetization and Curie temperature decreases with increase in the particle size. These changes in the magnetization and Curie temperatures are in correlation with changes in magnetic particle size and magnetic cation (Mn) ions distribution between the tetrahedral (A-site) and the octahedral (B-site) in inverse spinel structure.

Acknowledgements

Authors are thankful to UGC-MANF (F1-17.1/2015-16/MANF-2015-17-PUN-53556), Council of Scientific and Industrial Research, New Delhi (scheme No. 03(1226)/12/ERM-II) and DST-FIST (SR/FST/PSI-176/2012) for the financial support. 10

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[10] T. Upadhyay, R. V. Upadhyay, R.V. Mehta, Phys Rev B, 55(1997) 5585. [11] B. Jeyadevan, C.N. Chinnasamy, K. shinoda, K. Tohji, J.Appl. Phys. 93(2003) 8450. [12] R. Arulmurugan, G. Vaidyanathan, S. Sendhilnathan, B. Jeyadevan, J. Magn. Magn. Mater. 298 (2006) 83. [13] R. Desai, V. Davariya, K. Parekh, R. V. Upadhyay, Pramana – J. Phys. 73 (2009) 765. [14] N. Kaur, B. Chudasama, Micro & Nano Letters 12 (2017)151. [15] K. Mazz, A. Mumtaz, S. K. Hasanin, A. Ceylan, J. Magn. Magn. Mater. 308 (2007) 289. [16] N. T. Lan, T. D. Hien, N. P. Duong, D. V. Truong, J. Korean Phys. Soc. 52 (2008) 1522. [17] R. Arulmurugan, G. Vaidyanathan, S. Sendhilnathan, B. Jeyadevan, J. Magn. Magn. Mater, 298 (2006) 83.

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[18] R Desai, V Davariya1, K Parekh, R V Upadhyay, PRAMANA Journal of physics 73(2009)765. [19] J. A Gomes, M. H. Sousa, F. A. Tourinho, J. Mestnik-Filho, R. Itri, J. Depeyrot, J. Magn. Magn. Mater. 289 (2005) 184. [20] J. Kim, J. Seo, J. Cheon, Y Kim, Bull. Korean Chem. Soc. 30(2009) 183. [21] N. Kaur, B. Chudasama, J. Magn. Magn. Mater. 451 (2018) 647. [22] M. Yokoyarna, E. Ohta, T. Sato, T. Komaba, T. Sato, J. Phys IV France 7 (1997) C1521. [23] J. P. Chen, C. M. Sorensen, K J Klabunde, G C Hadjipanayis, E Delvin and A Kostikas, Phys. Rev. B 54 (1996) 9288. [24] Z. X. Tang, C. M. Sorensen, and K. J. Klabunde, Phys Rev Lett. 67 (1991) 3602. [25] P. J van der Zaag, A. Noordermeer, M.T. Johnson, P.F. Bongers, Phys Rev Lett. 68 (1992) 3112.

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Fig. 1a. M-H curves of MZ4 nanoparticles (prepared at different pH) and fitted with modified Langevin equation.

13

Fig. 1b. M-H curves of MZ4 nanoparticles (prepared at different reaction time) and fitted with modified Langevin equation.

14

Fig. 1 c. M-H curves of MZ4 nanoparticles (prepared at different reaction temperature) and fitted with modified Langevin equation.

15

Fig. 2. Curie temperature (Tc of MZ4 nanoparticles (prepared at different pH)as function of (a) magnetic diameter of nanoparticles and (b) ratio of occupancy of Mn at A – site and Mn at B – site in inverse spinel structure. 

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Fig. 3. Curie temperature (Tc of MZ4 nanoparticles (prepared at different reaction time)as function of (a) magnetic diameter of nanoparticles and (b) ratio of occupancy of Mn at A – site and Mn at B – site in inverse spinel structure.

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Fig. 4. Curie temperature (Tc of MZ4 nanoparticles (prepared at different reaction temperature)as a function of (a) magnetic diameter of nanoparticles and (b) ratio of occupancy of Mn at A – site and Mn at B – site in inverse spinel structure.

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Table 1. Sample codes along with preparation conditions of MZ nanoparticles. Preparation conditions Sample code pH

Reaction time (h)

S1

10.0

3

Reaction temperature (оC) 90

S2

10.5

3

90

S3

11.0

3

90

S4

11.5

3

90

S5

12.0

3

90

S6

12.5

3

90

S7

13.0

3

90

S8

11.0

1

90

S9

11.0

2

90

S10

11.0

3

90

S11

11.0

4

90

S12

11.0

3

80

S13

11.0

3

90

S14

11.0

3

100

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Table 2. Effect of pH, reaction time and reaction temperature on structural (crystallite size) and magnetic properties (Corecivity Hc, Retentivity (Mr), Curie temperature (Tc)) of MZ4 nanoparticles. Sample

Crystallite Size (nm)

Hc ( Oe)

Mr (emu/g)

Tc (K)

S1

8.4

0.6

0.002

392

S2

9.8

0.4

0.002

547

S3

13.3

2.0

0.14

665

S4

14.9

2.2

0.13

611

S5

18.1

4.7

0.3

589

S6

18.3

0.3

0.01

574

S7

19.4

0.2

0.3

557

S8

6.7

1.39

0.016

428

S9

10.2

0.75

0.077

543

S10

13.3

2.17

0.196

665

S11

14.9

0.51

0.007

573

S12

10.2

0.2

0.018

464

S13

13.3

2

0.014

665

S14

14.9

1.16

0.09

566

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Table 3. Magnetic parameters (magnetic particle diameter (Dm), saturation magnetization (Ms), polydispersity (), mean field constant () and ferrimagnetic susceptibility (), thickness of magnetic dead layer (t)) derived from the modified Langevin theory of MZ4 nanoparticles prepared under different pH, reaction time and reaction temperature. Sample

Ms (emu/g)

??

Dm (nm)

λ

M1

χ (x10-4)

t (nm)

S1

3.7

0.30

4.4

33

1.8

5.38

0.69

S2

16.6

0.32

7.7

29.7

1.48

11.6

0.94

S3

28.7

0.29

11.7

22.0

1.33

10.5

0.92

S4

24.8

0.26

12.3

22.0

1.3

10.4

1.39

S5

24.5

0.27

15.0

20.2

1.2

7.7

1.49

S6

18.8

0.29

17.2

20.0

1.2

10.3

1.96

S7

17.0

0.30

17.8

19

1.1

7.9

2.16

S8

3.7

0.25

4.4

32.5

1.86

3.9

0.69

S9

22.4

0.29

8.6

25.1

1.43

12.3

0.96

S10

28.7

0.29

11.7

22.0

1.33

10.5

0.92

S11

18.5

0.26

12.2

21.2

1.3

11.2

1.46

S12

10.6

0.31

9.3

24.0

1.6

10.3

1.29

S13

28.7

0.29

11.7

22.0

1.33

10.5

0.92

S14

25.7

0.26

12.2

20.8

1.3

11.1

1.21

21

Supporting Information Tunable Curie Temperature of Mn0.6Zn0.4Fe2O4 Nanoparticles Navjot Kaur and Bhupendra Chudasama* School of Physics and Materials Science, Thapar Institute of Engineering and Technology, Patiala-147004, India

Fig. S1. Rietveld refined X-ray diffraction patterns of MZ4 nanoparticles prepared at pH 1013 by coprecipitation method.

22

Fig. S2. Rietveld refined X-ray diffraction patterns of MZ4 nanoparticles prepared at 1- 4h reaction time by coprecipitation method.

23

Fig. S3. Rietveld refined X-ray diffraction patterns of MZ4 nanoparticles prepared at 80 -100 ˚C by coprecipitation method.

24

Fig. S4.  M-H curves of MZ4 nanoparticles prepared at different (a) pH, (b) reaction time and (c) reaction temperature.

25

Fig. S5. Temperature dependence of magnetization of MZ4 nanoparticles prepared at different reaction pH by coprecipitation method. Each Mvs T curve is linearly extrapolated on temperature axis to obtain the Curie temperature of magnetic nanoparticles.

26

Fig. S6. Temperature dependence of magnetization of MZ4 nanoparticles prepared at different reaction time by coprecipitation method. Each Mvs T curve is linearly extrapolated on temperature axis to obtain the Curie temperature of magnetic nanoparticles.

27

Fig. S7. Plot of magnetization as a function of temperature for MZ4 nanoparticles prepared at different reaction temperatures. Each Mvs T curve is linearly extrapolated to obtain the Curie temperature of magnetic nanoparticles

28

Table S1. Structural parameters of MZ4 nanoparticles obtained from Rietveld refinement of X-ray diffraction patterns of nanoparticles synthesized at pH 10-13 (Here Rp, RBrag are structure factors and 2 is goodness of fit)

Sample/pH

Lattice parameter

Atom

Atomic positons

x

y

z

RBrag

2

Rf

Occ.

S1 (pH- 10)

8.313(10)

Mn Mn Zn Fe Fe Fe O

0.62500(0) 0.00000(0) 0.62500(0) 0.62500(0) 0.00000(0) 0.00000(0) 0.2783(10)

0.62500(0) 0.00000(0) 0.62500(0) 0.62500(0) 0.00000(0) 0.00000(0) 0.2783(10)

0.62500(0) 0.00000(0) 0.62500(0) 0.62500(0) 0.00000(0) 0.00000(0) 0.2783(10)

0.27014 0.14701 0.43861 0.29125 0.35319 0.49980 1.00000

23.4

19.6

1.21

S2 (pH- 10.5)

8.358(7)

Mn Mn Zn Fe Fe Fe O

0.62500(0) 0.00000(0) 0.62500(0) 0.62500(0) 0.00000(0) 0.00000(0) 0.247(5)

0.62500(0) 0.00000(0) 0.62500(0) 0.62500(0) 0.00000(0) 0.00000(0) 0.247(5)

0.62500(0) 0.00000(0) 0.62500(0) 0.62500(0) 0.00000(0) 0.00000(0) 0.247(5)

0.33240 0.17067 0.38692 0.28068 0.32953 0.49980 0.89435

3.70

3.44

1.11

S3 (pH- 11)

8.386(4)

Mn Mn Zn Fe Fe Fe O

0.62500(0) 0.00000(0) 0.62500(0) 0.62500(0) 0.00000(0) 0.00000(0) 0.242(3)

0.62500(0) 0.00000(0) 0.62500(0) 0.62500(0) 0.00000(0) 0.00000(0) 0.242(3)

0.62500(0) 0.00000(0) 0.62500(0) 0.62500(0) 0.00000(0) 0.00000(0) 0.242(3)

0.38987 0.18949 0.32895 0.28118 0.30999 0.50052 1.20145

6.15

1.15

S4

8.364(4)

Mn Mn Zn Fe Fe Fe O

0.62500(0) 0.00000(0) 0.62500(0) 0.62500(0) 0.00000(0) 0.00000(0) 0.2270(13)

0.62500(0) 0.00000(0) 0.62500(0) 0.62500(0) 0.00000(0) 0.00000(0) 0.2270(13)

0.62500(0) 0.00000(0) 0.62500(0) 0.62500(0) 0.00000(0) 0.00000(0) 0.2270(13)

0.31005 0.12206 0.40803 0.28192 0.34490 0.49996 1.00000

9.13

11.4

1.19

8.333(3)

Mn Mn Zn Fe Fe Fe O

0.62500(0) 0.00000(0) 0.62500(0) 0.62500(0) 0.00000(0) 0.00000(0) 0.250(4)

0.62500(0) 0.00000(0) 0.62500(0) 0.62500(0) 0.00000(0) 0.00000(0) 0.250(4)

0.62500(0) 0.00000(0) 0.62500(0) 0.62500(0) 0.00000(0) 0.00000(0) 0.250(4)

0.35332 0.12601 0.36554 0.28114 0.37408 0.49991 1.00000

7.50

5.66

1.64

8.377(4)

Mn Mn Zn Fe Fe Fe O

0.62500(0) 0.00000(0) 0.62500(0) 0.62500(0) 0.00000(0) 0.00000(0) 0.238(3)

0.62500(0) 0.00000(0) 0.62500(0) 0.62500(0) 0.00000(0) 0.00000(0) 0.238(3)

0.62500(0) 0.00000(0) 0.62500(0) 0.62500(0) 0.00000(0) 0.00000(0) 0.238(3)

0.34996 0.11743 0.36785 0.28219 0.31647 0.49972 1.08934

9.32

20.6

1.19

8.373(4)

Mn Mn Zn Fe Fe Fe O

0.62500(0) 0.00000(0) 0.62500(0) 0.62500(0) 0.00000(0) 0.00000(0) 0.245(2)

0.62500(0) 0.00000(0) 0.62500(0) 0.62500(0) 0.00000(0) 0.00000(0) 0.245(2)

0.62500(0) 0.00000(0) 0.62500(0) 0.62500(0) 0.00000(0) 0.00000(0) 0.245(2)

0.34620 0.11217 0.39145 0.28235 0.34354 0.49429 0.97655

12.5

11.4

1.20

(pH- 11.5)

S5 (pH- 12)

S6 (pH- 12.5)

S7 (pH- 13)

29

5.17

Table S2. Structural parameters of MZ4 nanoparticles obtained from Rietveld refinement of X-ray diffraction patterns of nanoparticles synthesized at reaction time of 1-4 h (Here Rp, RBrag are structure factors and 2 is goodness of fit) Sample/ Reaction time (h)

Lattice parameter

Atom

Atomic positons

x S8 / (1h)

8.344(14)

y

z

RBragg

Rf

2

Occ.

Mn Mn Zn Fe Fe Fe O

0.62500(0) 0.00000(0) 0.62500(0) 0.62500(0) 0.00000(0) 0.00000(0) 0.275(4)

0.62500(0) 0.00000(0) 0.62500(0) 0.62500(0) 0.00000(0) 0.00000(0) 0.275(4)

0.62500(0) 0.00000(0) 0.62500(0) 0.62500(0) 0.00000(0) 0.00000(0) 0.275(4)

0.27014 0.14701

13.3

21.0

1.08

10.9

21.1

1.07

0.39321 0.20523 0.40255 0.49979 1.00000

S9 / (2h)

8.358(7)

Mn Mn Zn Fe Fe Fe O

0.62500(0) 0.00000(0) 0.62500(0) 0.62500(0) 0.00000(0) 0.00000(0) 0.238(7)

0.62500(0) 0.00000(0) 0.62500(0) 0.62500(0) 0.00000(0) 0.00000(0) 0.238(7)

0.62500(0) 0.00000(0) 0.62500(0) 0.62500(0) 0.00000(0) 0.00000(0) 0.238(7)

0.30639 0.15427 0.38082 0.20236 0.40393 0.49996 1.00000

S10 / (3h)

8.386(4)

Mn Mn Zn Fe Fe Fe O

0.62500(0) 0.00000(0) 0.62500(0) 0.62500(0) 0.00000(0) 0.00000(0) 0.242(3)

0.62500(0) 0.00000(0) 0.62500(0) 0.62500(0) 0.00000(0) 0.00000(0) 0.242(3)

0.62500(0) 0.00000(0) 0.62500(0) 0.62500(0) 0.00000(0) 0.00000(0) 0.242(3)

0.38987 0.18949 0.32895 0.28118 0.30999 0.50052 1.20145

5.17

6.15

1.15

S11 / (4h)

8.502(9)

Mn Mn Zn Fe Fe Fe O

0.62500(0) 0.00000(0) 0.62500(0) 0.62500(0) 0.00000(0) 0.00000(0) 0.2354(0)

0.62500(0) 0.00000(0) 0.62500(0) 0.62500(0) 0.00000(0) 0.00000(0) 0.2354(0)

0.62500(0) 0.00000(0) 0.62500(0) 0.62500(0) 0.00000(0) 0.00000(0) 0.2354(0)

0.41682 0.09711 0.40456 0.28529 0.34701 0.50102 1.00000

3.91

3.67

1.04

30

Table S3. Structural parameters of MZ4 nanoparticles obtained from Rietveld refinement of X-ray diffraction pattern of nanoparticles synthesized at 80-100 °C reaction temperature (Here Rp, RBrag are structure factors and 2 is goodness of fit) Sample/

Reaction temperature (˚C)

Lattice parameter

Atom

Atomic positons

x

y

z

RBragg

Rf

2

Occ.

S12 (80 ˚C)

8.343(9)

Mn Mn Zn Fe Fe Fe O

0.62500(0) 0.00000(0) 0.62500(0) 0.62500(0) 0.00000(0) 0.00000(0) 0.2299(14)

0.62500(0) 0.00000(0) 0.62500(0) 0.62500(0) 0.00000(0) 0.00000(0) 0.2299(14)

0.62500(0) 0.00000(0) 0.62500(0) 0.62500(0) 0.00000(0) 0.00000(0) 0.2299(14)

0.30149 0.16769 0.41620 0.28231 0.33224 0.50007 0.90240

1.93

0.895

1.11

S13 (90 ˚C)

8.358(7)

Mn Mn Zn Fe Fe Fe O

0.62500(0) 0.00000(0) 0.62500(0) 0.62500(0) 0.00000(0) 0.00000(0) 0.242(3)

0.62500(0) 0.00000(0) 0.62500(0) 0.62500(0) 0.00000(0) 0.00000(0) 0.242(3)

0.62500(0) 0.00000(0) 0.62500(0) 0.62500(0) 0.00000(0) 0.00000(0) 0.242(3)

0.38987 0.18949 0.32895 0.28118 0.30999 0.50052 1.20145

10.9

21.1

1.07

S14 (100 ˚C)

8.355(6)

Mn Mn Zn Fe Fe Fe O

0.62500(0) 0.00000(0) 0.62500(0) 0.62500(0) 0.00000(0) 0.00000(0) 0.2680(9)

0.62500(0) 0.00000(0) 0.62500(0) 0.62500(0) 0.00000(0) 0.00000(0) 0.2680(9)

0.62500(0) 0.00000(0) 0.62500(0) 0.62500(0) 0.00000(0) 0.00000(0) 0.2680(9)

0.40156 0.09666 0.40263 0.29098 0.35025 0.49548 1.00000

0.680

0.424

1.26

31

Tunable Curie Temperature of Mn0.6Zn0.4Fe2O4 Nanoparticles Navjot Kaur and Bhupendra Chudasama* School of Physics and Materials Science, Thapar Institute of Engineering & Technology, Patiala-147004, India

*Email: [email protected]

HIGHLIGHTS

1. Curie temperature of MZ4 (Mn0.6Zn0.4Fe2O4) nanoparticles synthesized by coprecipitation method has been tuned from 392 K to 665K by controlling the pH, temperature and time of reaction. 2. Particle size dependence of Curie temperature of MZ4 nanoparticles has been established. 3. Curie temperature and magnetization of MZ4 nanoparticles strongly correlated with the cation (Mn) distribution between tetrahedral (A-site) and octahedral (B-site) in inverse spinel structure.

32