Effect of Ho³⁺ substitution on the cation distribution, crystal structure and magnetocrystalline anisotropy of nanocrystalline cobalt ferrite

Figures & data

Figure 1. XRD patterns of the sample CoFe_1.9Ho_0.1O₄ annealed at 200°C.

Figure 2. XRD patterns of the samples CoFe_{2− x} Ho _x O₄ (x = 0.0, 0.025, 0.05, 0.075 and 0.1) annealed at 600°C.

Figure 3. Rietveld refined XRD pattern for the sample CoFe_1.95Ho_0.05O₄ annealed at 600°C. The circles represent experimental points and the solid line represents Rietveld refined data. The bottom line shows the difference between the experimental and refined data. The marked 2θ positions are the allowed Bragg peaks.

Table 1. Atomic coordinates and isothermal parameters for CoFe_1.95Ho_0.05O₄ composition.

Atoms	x	y	z	B iso
Co/Fe/Ho	0.1250	0.1250	0.1250	0.1199
Fe/Co/Ho	0.5000	0.5000	0.5000	0.8292
O	0.2442	0.2442	0.2442	1.0000

Table 2. Parameters obtained from Rietveld analysis of XRD patterns for the sample CoFe_{2− x} Ho _x O₄ (x = 0.0, 0.025, 0.05, 0.075 and 0.1) annealed at 600°C. Errors of the lattice parameters are shown in brackets.

Sample	R p	Χ ^2	a = b = c (Å)	D (nm)
CoFe2O4	16.6	0.79	8.378(22)	35.12
CoFe1.975Ho0.025O4	19.3	0.67	8.370(12)	15.37
CoFe1.95Ho0.05O4	19.1	0.75	8.365(14)	13.41
CoFe1.925Ho0.075O4	19.5	0.68	8.375(16)	11.16
CoFe1.9Ho0.1O4	20.1	0.84	8.374(18)	9.89
Notes: R p = profile factor, χ^2= goodness fit factor, a = lattice parameter (Å), D = average crystallite size in nm.

Table 3. Site occupancies of cations for the samples CoFe_{2− x} Ho _x O₄ (x = 0.0, 0.025, 0.05, 0.075 and 0.1) annealed at 600°C.

Sample	A-site	B-site
CoFe2O4	Co0.110Fe0.890	Co0.890Fe1.100
CoFe1.975Ho0.025O4	Co0.175Fe0.824Ho0.001	Co0.825Fe1.151Ho0.024
CoFe1.95Ho0.05O4	Co0.187Fe0.810Ho0.003	Co0.813Fe1.140Ho0.047
CoFe1.925Ho0.075O4	Co0.219Fe0.780Ho0.001	Co0.781Fe1.145Ho0.074
CoFe1.9Ho0.1O4	Co0.299Fe0.699Ho0.002	Co0.701Fe1.201Ho0.098

Figure 4. FT-IR spectra of the samples CoFe_{2− x} Ho _x O₄ with x = 0.0 and 0.025 annealed at 600°C.

Figure 5. FE-SEM image of the sample CoFe_1.975Ho_0.025O₄ annealed at 600°C.

Figure 6. The EDS pattern of the sample CoFe_1.975Ho_0.025O₄ annealed at 600°C. Au (gold) peaks are due to thin coating on the sample.

Figure 7. Hysteresis loops for the samples CoFe_{2− x} Ho _x O₄ (x = 0.0, 0.025, 0.05, 0.075 and 0.1) annealed at 600°C.

Table 4. Coercivity, saturation magnetisation (M _S), and anisotropic constant (K ₁) of the samples CoFe_{2− x} Ho _x O₄ (x = 0, 0.025, 0.05, 0.075 and 0.1) annealed at 600°C.

Sample	Coercivity (kOe)	M S (emu g^−1)	K 1 (erg cm^−3)
CoFe2O4	1.394	50.00	2.27 × 10^6
CoFe1.975Ho0.025O4	1.347	12.21	0.77 × 10^6
CoFe1.95Ho0.05O4	1.158	07.62	0.40 × 10^6
CoFe1.925Ho0.075O4	1.096	36.64	2.75 × 10^6
CoFe1.9Ho0.1O4	0.847	17.02	1.42 × 10^6

Figure 8. Fit to LA for the sample CoFe_1.95Ho_0.05O₄ annealed at 600°C.