The magnetic, magnetic entropy and critical behavior studies in La0.8Ba0.2MnO3 around magnetic phase transition temperature.

doi:10.21203/rs.3.rs-25917/v1

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The magnetic, magnetic entropy and critical behavior studies in La0.8Ba0.2MnO3 around magnetic phase transition temperature.

https://doi.org/10.21203/rs.3.rs-25917/v1

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Magnetocaloric and critical phenomenon investigations were carried out in the crystalline La_0.8Ba_0.2MnO₃ samples prepared through solid state reaction technique. X-ray diffraction (XRD) pattern and its Rietveld refinement using Rietica software confirmed the crystalline phase purity of rhombohedral structure with space group \(R\bar{3}c\). From magnetic measurements, the Ferromagnetic to paramagnetic (FM-PM) phase transition was observed at T_C ~ 285K. The maximum change in magnetic entropy (\(Delta{S}^{max}_M\)) and relative cooling power (RCP) extracted from magnetic measurements were 3.02 J/kg K and 142.00 J/kg at an applied magnetic field (m_oH) of 4T. Griffiths phase (GP) with a susceptibility exponent λ = 0.44 was also detected in temperature range of T_C < T < T_G. Critical exponential analysis indicated the 3D-Ising model like magnetic phase transition at T_C. Critical exponent’s reliability was confirmed using models such as universal scaling equations of state and Widom scaling relation. Magnetic entropy change follows the law ΔS_M = (m_oH)ⁿ for n = 0.46.

Ceramics

Manganites

Reliability

Phase transition

Magnetic Entropy

Magnetocaloric

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Table 1 : Structural parameters found from the refinement of XRD pattern. The refinement confirms the single phase rhombohedral crystalline structure of La_0.8Ba_0.2MnO₃sample with space group R.

La_0.8Ba_0.2MnO₃ a=5.55039(23)Å, c=13.47702(97)Å, Rp=15.29, Rwp=24.95, Rexp=17.91, GOF=1.94 and R_BRAGG=2.49
	La	Ba	Mn	O
x	0	0	0	0.5411
y	0	0	0	0
z	0.25	0.25	0	0.25
B	0.64	0.64	0.41	2.95
n	0.800	0.212	1.000	3.730
La/Ba-O	3.0034(1) Å ×3	2.5470(1) Å ×3	2.7685(1) Å ×6
O-Mn-O	90.27^o ×6	89.73^o ×6	180^o ×3
Mn-O-Mn	175.27^o
Mn-O	1.96993(6) Å×6
Note: Here B is isotropic temperature factors (Å²) and n represents the concentration of different elements in sample.

Table 2 : Relative variations in δT_FWHM, ∆S_M and RCP under different magnetic fields for La_0.8Ba_0.2MnO₃ sample.

H(T)	Area(Jkg^-1K^-1)	δT_FWHM(K^-1)	∆S_M(Jkg^-1K^-1)	RCP(Jkg^-1)
0.5T	11.84	20.64	0.81	16.71
1.0T	21.66	26.63	1.37	36.4
1.5T	28.56	32.92	1.74	57.28
2.0T	34.72	36.12	2.10	75.85
2.5T	40.34	38.60	2.38	91.86
3.0T	48.23	41.32	2.52	104.13
3.5T	55.70	44.05	2.79	122.89
4.0T	61.42	47.01	3.02	142.00

Table 3 : Experimentally found values of T_C and critical exponent’s b, g and d.

SAMPLE	Technique	β	γ	δ	Curie temperature (T_C) (K)
La_0.8Ba_0.2MnO₃	MAP	0.29	1.20	4.82	285
	KF	0.29	1.21	4.83	285
	From fitting of M (µ_oH) isotherm at T_C	-	-	4.80	-

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The magnetic, magnetic entropy and critical behavior studies in La0.8Ba0.2MnO3 around magnetic phase transition temperature.

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