Magnetic behavior of Ni substituted LiCoO2, magnetization and electron paramagnetic resonance studies
Magnetic behavior of Ni substituted LiCoO2, magnetization and electron paramagnetic resonance studies
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DOI：
10.1016/j.matchemphys.2017.06.019
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发表时间：
2016-11
期刊：
影响因子：
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通讯作者：
Mofasser Mallick;S. Vitta
中科院分区：
文献类型：
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作者：
Mofasser Mallick;S. Vitta
合成了单相Ni取代的LiCo 1-xNixO 2固溶体，研究了取代对磁性的影响。两种不同的技术，磁化率和电子顺磁共振（EPR）提供的信息，在两个不同的时间窗口已被使用。发现固溶体为单相，具有符合R3 m菱面体结构的大晶粒。晶格常数c和a随Ni取代量的增加而增加，但c/a比值几乎不变，为1.499，表明CoO 6和LiO 6八面体没有发生Jahn-Teller畸变.室温EPR吸收光谱清楚地显示了所有化合物在314 mT的场处的峰，对应于2.14的g因子。然而，发现峰宽是Ni取代的强函数;随着Ni从3.6 mT增加到6.5 mT（x= 0.08）而增加。磁化强度随着温度的降低而增加，这是一种顺磁行为，不像缺乏Li的化合物表现出泡利顺磁磁化率。此外，磁化强度表现出热不可逆性，在所有化合物的大磁场消失。未取代的化合物在200 K和50 K时出现不连续性，对应于2%Ni取代Co时消失的磁跃迁。当取代量增加到0.15时，有效磁矩μ eff从0.32 μ B增加到0.66 μ B。然而，其独特之处在于，所有化合物在室温下均表现出明显的磁滞现象，并具有有限的矫顽力。当x= 0.04时，矫顽力从31 Oe增加到168 Oe，然后随着x的进一步增加而减小。磁滞回线的去卷积清楚地显示出随着取代而增加的顺磁分量。
Abstract Single phase Ni substituted LiCo 1-x Ni x O 2 solid solutions with x≤ 0.15 have been synthesized to study the effect of substitution on the magnetic behavior. Two different techniques, magnetic susceptibility and electron paramagnetic resonance (EPR) which provide information in two different time windows have been used. The solid solutions have been found to be single phase with large grains conforming to R 3¯ m rhombohedral structure. The lattice parameters ‘c’and ‘a’increase with increasing Ni substitution but with a nearly constant c/a ratio of≈ 4.99 in all the cases indicating that the CoO 6 and LiO 6 octahedra do not undergo any Jahn-Teller distortions. The room temperature EPR absorption spectra clearly shows a peak in all the compounds at a field of 314 mT corresponding to a g-factor of 2.14. The peak width however is found to be a strong function of Ni substitution; increasing with increasing Ni from 3.6 mT to 6.5 mT for x= 0.08. The magnetization increases with decreasing temperature in all the compounds, a paramagnetic behavior, unlike Li-deficient compounds which show a Pauli paramagnetic susceptibility. Also, the magnetization exhibits thermal irreversibility which vanishes at large magnetic fields in all the compounds. The unsubstituted compound has discontinuities at 200 K and 50 K corresponding to magnetic transitions which disappear on substitution with 2% Ni for Co. The effective magnetic moment μ eff is found to increase from 0.32 μ B to 0.66 μ B on increasing the substitution to 0.15. The unique feature however is that all the compounds exhibit a clear magnetic hysteresis at room temperature with a finite coercivity. The coercivity increases from 31 Oe to 168 Oe for x= 0.04 and then decreases on further increasing of x. A deconvolution of the hysteresis loops clearly shows an increasing paramagnetic component with substitution.