Magnetic Properties of Phospho-Olivine Li(Fe$_{1-x}$Mn$_{x}$)PO$_{4}$ Investigated With Mössbauer Spectroscopy

The crystalline structure of the Li(Fe
_1-x
Mn
_x
)PO
₄
(x = 0.0, 0.2) samples was determined to be olivine-type orthorhombic with Pnma space group. The contraction ofunit cell volume from LiFe
_0.8
Mn
_0.2
PO
₄
(V = 293.296 Å
³
) to LiFePO
₄
(V = 291.445 Å
³
) can be explained by the different ionic radii of high-spin Fe
²⁺
and Mn
²⁺
. The temperature-dependent magnetic susceptibility and Curie-Weiss fitted reciprocal susceptibility curves of Li(Fe
_1-x
Mn
_x
)PO
₄
indicates that there are antiferromagnetic ordering with different values of magnetic Neel temperature and effective moment between LiFe
_0.8
Mn
_0.2
PO
₄
(T
_N
= 49 K, μ
_eff
= 5.66μ
_B
) and LiFePO
₄
(T
_N
= 51 K, μ
_eff
= 5.37 μ
_B
). From the Mossbauer analysis, The distribution of the Mn
²⁺
(3d
₅
) ions in M
₂
magnetic sites can lead to the reduction of magnetic hyperfine field (H
_hf
) of LiFe
_0.8
Mn
_0.2
PO
₄
in Fe
²⁺
(3d
₆
) sites. Also, the isomer shift (δ) and electric quadrupole splitting (ΔE
_Q
) values, increasing with Mn
²⁺
substitution, can be attributed to the decrease of charge density at Fe nucleus ρ
_A
(0) due to the 3d-electron penetrating closer to the Fe nucleus with asymmetric charge distribution by the presence of Mn
²⁺
ions on the FeO
₆
octahedral sites.