Magnetic anisotropy in doped and undoped LiFePO4 single crystals

Abstract

We report on the magnetic anisotropic properties of pure and

Heat capacity (C) and entropy of olivine-type LiFePO4 in the temperature range (2 to 773) K

“…The found transition peak in the heat capacity at about T = 49 K can be attributed to an antiferromagnetic transition already described in literature [7][8][9]. Certainly, this effect is of magnetic nature and is not considered in the first-principles phonon calculations.…”

“…The antiferromagnetic transition of LFP at T = $49 K has been described and studied in detail by various groups [7][8][9]. This transition is not only interesting from a theoretical point of view but also crucial for the precise determination of the standard entropy of LFP.…”

“…The experimental heat capacity data as a function of temperature allow the calculation of molar standard entropies for LFP according to equation (8) as well as the molar enthalpy difference D T 0 H m using equation (9). Table 9 presents a summary of the thermodynamic functions at selected temperatures from (5 to 760) K.…”

“…On the other hand, Shang et al [6] reported theoretical heat capacity data starting between T = (0 and 1200) K as well as Gibbs free energy, enthalpy, and entropy functions derived from firstprinciples phonon calculations. However, the theoretical results only represent the vibrational energy/entropy contribution, hence, expected electronic and especially magnetic contributions from the known antiferromagnetic transition of LFP near T = 50 K [7][8][9] were not taken into account. The magnetic transition should add a considerable amount to the thermodynamic functions as had been demonstrated by Shi et al for different iron phosphates using low temperature heat capacity measurements [10][11][12].…”

Anomalous magnetic structure and spin dynamics in magnetoelectricLiFePO4

“…The susceptibilities χ(T ) for fields along a and b are taken from Ref. 42 and multiplied a proportionality factor d∆θ/dM calculated from figure 6 and 7 assuming the same moment S 2 for all 4 ions. We use a scaling parameter C i ∝ λ DM i /k for both α xy and α yx to fit the low temperature response and these are the only free parameters used.…”