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首页> 外文期刊>RSC Advances >Effect of size reduction on cation distribution and magnetic transitions in CoCr2O4 multiferroic: EXAFS, magnetic and diffused neutron scattering measurements
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Effect of size reduction on cation distribution and magnetic transitions in CoCr2O4 multiferroic: EXAFS, magnetic and diffused neutron scattering measurements

机译：尺寸降低对COCR2O4多二二二二异种的阳离子分布和磁化转变的影响：exafs，磁性和扩散中子散射测量

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摘要

A rich sequence of magnetic transitions such as para to long-range ferrimagnetic transition at Curie temperature, T-C, to a short range non-collinear spiral ordering at spiral ordering temperature, T-S, and finally to a lock in transition, T-L, are examined in similar to 10 and similar to 50 nm samples of CoCr2O4 multiferroic through dc, ac magnetic measurements and diffused neutron scattering using polarized neutrons. Analysis of extended X-ray absorption fine structure (EXAFS) spectra and Fourier transforms of Co and Cr edges in real (r) and momentum (k) space show no change in cation distribution among A and B sites even after reducing the size to the nanometer range due to the high crystal field stabilisation energy of Cr3+ towards the B site. While T-S remains independent, T-C increases from 97.2 to 100.1 K and T-L increases from 5 to 8.5 K with varying size from 10 to 50 nm. Temperature dependent ac susceptibility (chi) measurements demonstrate that chi' and chi" do not show any dispersion behaviour in the 10 nm sample. However, we observe splitting of chi" into two peaks and one of them shows dispersion behaviour in the 50 nm sample, indicating a core-shell structure. Magnetization vs. magnetic field measurement show hysteresis behaviour with unsaturated magnetization at high magnetic field indicating a ferrimagnetic core surrounded by disordered surface spins. Fitting of chi" with an empirical relation Phi = Delta T-B/T-B Delta log(10) omega, and memory effect measurement, further confirm the spin-glass behaviour of the shell in the 50 nm sample. Magnetic ordering temperatures are examined through neutron scattering using a polarized neutron beam, and reveal that while the para- to ferrimagnetic transition, T-C, is continuous and long-range in both nanocrystalline particles, T-S is found to be sharp, short-range, and commensurate in 50 nm sample.
机译：在诸如居里温度，TC的诸如Para到远程铁磁性过渡的诸如Para的磁性过渡序列，以在螺旋排序温度下，TS和最后在转换中锁定TL的短程非共线螺旋排序使用偏振中子，类似于10且类似于CoCr2O4多体的COCR2O4多样性的50nm样品，并使用偏振中子散射。延长X射线吸收精细结构（EXAFS）光谱和傅立叶变换的实际（R）和CR边缘（k）空间显示出A和B位点的阳离子分布没有变化，即使在减小到尺寸纳米范围由于CR3 +向B网站的高晶体场稳定能量。虽然T-S保持独立，但T-C从97.2增加到100.1 k，T-L从5到8.5 k增加，不同尺寸为10至50nm。温度依赖性AC敏感性（CHI）测量表明，CHI'和CHI“在10nm样本中不显示任何色散行为。然而，我们观察CHI”分成两个峰值，其中一个在50nm样本中显示分散行为，表示核心壳结构。磁化率与磁场测量显示在高磁场下具有不饱和磁化的滞后行为，指示由无序表面旋转围绕的亚铁磁芯。 Chi“用经验关系PHI = Delta TB / Tb Delta log（10）ω和记忆效应测量，进一步证实了50 nm样品中壳的旋转玻璃行为。通过中子散射检查磁性有序温度使用偏振中子束，并揭示虽然纳米晶体颗粒中的与亚铁磁性过渡的Tc是连续和长距离的同时，发现TS是尖锐的，短的范围和在50nm样品中的相称。

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  • 来源
    《RSC Advances》 |2016年第68期|共11页
  • 作者

    Galivarapu Jagadish K.; Kumar D.; Banerjee A.; Sathe V.; Aquilanti Giuliana; Rath Chandana;

  • 作者单位

    Indian Inst Technol BHU Sch Mat Sci &

    Technol Varanasi 221005 Uttar Pradesh India;

    Indian Inst Technol BHU Sch Mat Sci &

    Technol Varanasi 221005 Uttar Pradesh India;

    UGC DAE Consortium Sci Res Univ Campus Khandwa Rd Indore 452001 India;

    UGC DAE Consortium Sci Res Univ Campus Khandwa Rd Indore 452001 India;

    Elettra Sincrotrone XAFS Beamline Trieste Italy;

    Indian Inst Technol BHU Sch Mat Sci &

    Technol Varanasi 221005 Uttar Pradesh India;

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