Effect of Size on the Structural Transition and Magnetic Properties of Nano-CuFe₂O₄

Abstract

Advances in the field of chemistry often involve nanoparticles, in which the structural transition is surprisingly different from the bulk material, and the difference between them is mainly attributed to the size of the nanoparticles. In this paper, tetragonal nano-CuFe 2 O 4 (t-CuFe 2 O 4 ) with different sizes ranging from 32 to 79 nm was prepared using the high temperature solid phase method. The structural transition of nano-CuFe 2 O 4 from tetragonal to cubic was determined by differential scanning calorimetry (DSC). The theoretical derivations and experimental tests indicate that, as the size decreases, the temperature, the enthalpy, and the entropy of the structural transition of nano-CuFe 2 O 4 decrease accordingly and present linear variation with the reciprocal of size, respectively. Furthermore, the effect of particle sizes on the magnetic properties of nano-CuFe 2 O 4 was investigated. The results show that the size of nano-CuFe 2 O 4 can obviously affect the magnetic properties: with the particle size of nano-CuFe 2 O 4 decreasing, the saturated magnetic induction decreases, the coercivity increases, while the remanence decreases.

Size-Dependent Thermodynamics of Structural Transition and Magnetic Properties of Nano-Fe2O3

“…Furthermore, the qualitative change regularity of the temperature of structural transition with particle size agrees with previous reports. 19,20,35 Because of the larger surface energy of nanocrystals with smaller sizes participating in the phase transition process, the energy needed for this transition is reduced, allowing the phase transition to occur at a lower temperature.…”

“…Our results on the influence regularity of particle size on the enthalpy of structural transition coincide with the above theoretical analysis of eq 13 and previous reports. 19,20,36 To explore the effect of particle size on the entropy of structural transition of nano-γ-Fe 2 O 3 , the relationship between the transition entropy of nano-γ-Fe 2 O 3 and the inverse particle size was evaluated, as shown in Figure 9.…”

“…Our results on the influence regularity of particle size on the entropy of structural transition agree with the above theoretical analysis of eq 14 and previous reports. 19,20,36 Figure 10 illustrates the magnetization (M) of nano-γ-Fe 2 O 3 of various sizes, measured on the applied magnetic field (H) at room temperature. The magnetizations increase with increasing magnetic field and are basically saturated when the magnetic field exceeds 10,000 Oe for samples with diameters of 19.3, 39.9, 60.3, and 140.5 nm.…”

“…Our group recently derived approximate expressions of integral enthalpy and entropy of structural transitions of nanocrystals without considering any change in temperature during the transition process 19 and assuming equality of crystal density between the two transition phases. 20 Overall, current theories fail to accurately describe the structural transition process of nanocrystals. Experimentally, Gnanaprakash et al 10 found that the transition temperature from γto α-Fe 2 O 3 decreases with decreasing particle size with diameters ranging from 2.3 to 6.5 nm.…”

The Study of the Influence of Matrix, Size, Rotation Angle, and Magnetic Field on the Isothermal Entropy, and the Néel Phase Transition Temperature of Fe2O3 Nanocomposite Thin Films by the Monte-Carlo Simulation Method

“…Cui et al [43] demonstrated that the crystallinity densities of the two transitions are equal. Zhang et al [44] successfully determined the Néel phase transition temperature of Fe 2 O 3 when considered system transitioned from the maghemite phase to the α hematite phase, namely T Ntot = 623 K at D = 4 nm and T Ntot = 723 K at D = 24 nm. Mendili et al [45], Wenger et al [46] have successfully determined that the magnetization (M) of γ-Fe 2 O 3 nanoparticles increases when D increases (from D = 2 nm to D = 4 nm).…”