*3.2.2 Lattice constant, grains size and magnetism in pure NFO, CFO and MFO thin films*

**Table 1** shows the experimental results of lattice constant (*a*), grain's size [*x* (SEM) & *x***′** (AFM)], Ms, Mr and Hc measured at room temperature (300 K) and 10 K, and magnetic phase transition temperature (Tpm) of NiFe2O4 (NFO),

**Figure 5.**

*(a) XRD patterns and SEM image (inset) of Co0.65Zn0.35Fe2O4 (CZFO). (b) CZFO unit cell with a spinel structure. AFM of (c) NFO, (d) CFO (e) MFO thin films. Adopted from Refs. [9, 32].*

**101**

**Sample**

NFO CFO MFO *Adopted from Verma et al. [9].*

**Table 1.**

8.425

74

75

5.40

13.35

1.10 *Values of lattice constant (a), grain's size (x) (SEM), grain's size (x*′*) (AFM), Ms, Mr and Hc at 300 K and 10 K, and magnetic phase transition (Tpm) of pure NFO, CFO and MFO thin films.*

7.20

113.30

39.28

8.312

60

61

33.50

54.57

15.50

8.90

1292.00

69.33

8.161

44

46

50.60

76.42

14.33

63.31

265.33

73.90

687

693

581

*a* **(Å)**

*x* **(nm)**

*x***′ (nm)**

*Ms* **(emu cc−1**

**300 K**

**10 K**

**300 K**

**10 K**

**300 K**

**10 K**

**)**

*Mr* **(emu cc−1**

**)**

*Hc* **(Oe)**

*Ferromagnetism in Multiferroic BaTiO3, Spinel MFe2O4 (M = Mn, Co, Ni, Zn) Ferrite…*

*DOI: http://dx.doi.org/10.5772/intechopen.82437*

*Tpm* **(K)**

#### *Ferromagnetism in Multiferroic BaTiO3, Spinel MFe2O4 (M = Mn, Co, Ni, Zn) Ferrite… DOI: http://dx.doi.org/10.5772/intechopen.82437*


*Values of lattice constant (a), grain's size (x) (SEM), grain's size (x*′*) (AFM), Ms, Mr and Hc at 300 K and 10 K, and magnetic phase transition (Tpm) of pure NFO, CFO and MFO thin films.*

*Electromagnetic Materials and Devices*

= \_1 *t* \_\_\_ ∂*V* ∂*H* = \_\_\_\_\_\_ *<sup>V</sup>*out

*3.1.5 ME coupling in Ce, La-substituted BFTO*

respectively, for BFTO:Ce and BFTO:La.

*3.2.1 Structural studies of Co0.65Zn0.35Fe2O4*

*thin films*

An upward curvature observed in M-T curve suggests a Curie-Weiss like behavior. It is attributed with short-range ferromagnetism, or a spin-cluster within a matrix of spin disorder [30]. Li et al*.* [31] suggested that the oxygen vacancy might be medi-

The longitudinal ME coupling coefficient, αME is measured for Ce and La-doped

*<sup>t</sup>* <sup>×</sup> *<sup>H</sup>*ac. In **Figure 4(c)**, the value of αME increases rapidly to a maximal value (due to an enhancement of elastic interactions) and then slowly decreasing in the

parameter of CZFO is found to be 8.4183 Å. A three-dimensional sketch of CZFO unit cell projected along the *c*-axis (**Figure 5(b)**). The inset of **Figure 5(a)** shows the SEM image of a CZFO pellet sample to displays densely packed grains with few scattered pores and voids. It is also reported in Ref. [32] that the high dielectric permittivity value is obtained. The ferrimagnetic-paramagnetic phase transition is ~640 K.

*3.2.2 Lattice constant, grains size and magnetism in pure NFO, CFO and MFO* 

**Table 1** shows the experimental results of lattice constant (*a*), grain's size [*x* (SEM) & *x***′** (AFM)], Ms, Mr and Hc measured at room temperature (300 K) and 10 K, and magnetic phase transition temperature (Tpm) of NiFe2O4 (NFO),

Oe<sup>−</sup><sup>1</sup>

∂*H*

) is 62.65 and 49.79,

<sup>3</sup>*m*) of Co0.65Zn0.35Fe2O4

is 1.648. The lattice

BFTO and shown in **Figure 4(c)**. The samples are biased with *ac* magnetizing field, Hac = 10 Oe at 1093 Hz, and a *dc* magnetic field, Hdc is applied collinear to it. The value of αME was determined as a function of *dc* magnetic field using: αME = \_\_\_ <sup>∂</sup>*<sup>E</sup>*

ate antiferromagnetic-ferromagnetic interactions in multiferroics.

higher region of Hdc. The maximum value of αME (mV cm<sup>−</sup><sup>1</sup>

**3.2 Spinel ferrites MFe2O4 (M = Mn, Co, Ni, Zn, Cu, etc.)**

**Figure 5 (a)** shows the Rietveld refinement (space group: *Fd*¯

(CZFO) ferrite, which indicate spinel phase [32]. The value of χ<sup>2</sup>

**100**

**Figure 5.**

*(a) XRD patterns and SEM image (inset) of Co0.65Zn0.35Fe2O4 (CZFO). (b) CZFO unit cell with a spinel* 

*structure. AFM of (c) NFO, (d) CFO (e) MFO thin films. Adopted from Refs. [9, 32].*

CoFe2O4 (CFO) and MnFe2O4 (MFO) thin films [9]. These ferrites were prepared by a MOD method using spin coating. The thickness of all the film is ~700 nm. It is also reported that the miller indices of cubic spinel ferrites structure are (2 2 0), (3 1 1), (2 2 2), (4 0 0), (3 3 1), (4 2 2) and (5 1 1), respectively, detected with diffraction angle 2θ = 30.48, 34.99, 37.48, 42.58, 48.02, 51.23 and 55.85° for NFO, for CFO, 2θ = 30.25, 34.87, 37.36, 42.58, 47.20, 51.23 and 55.84° and 2θ = 29.77, 34.64, 37.36, 41.75, 47.08, 51.23 and 57.04° for MFO. The higher coercivity value of CFO than NFO and MFO is the effect of higher magneto-crystalline anisotropy of Co cations than Ni and Mn. The observed values of Ms, Mr and Hc of the NFO, CFO and MFO films are quite smaller than bulk form [9]. For this, the decrease in Ms in ferrite nanoparticles is the canted spins in the surface layers [33]. Also, it observed very smaller values of Mr, Ms and Hc of MFO because lowering number of magnetic domains and the rate of alignment of the spins with the applied field [34, 35].
