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Unusual magnetic properties of Mn-doped ThO_2 nanoparticles

机译：Mn掺杂ThO_2纳米粒子的异常磁性能

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摘要

We report the synthesis of Th_(1-x)Mn_xO_2 (x = 0, 0.001, 0.002, 0.004, and 0.01 wt%) nanoparticles by the urea combustion method using thorium nitrate gel followed by heat treatment at a higher temperature (T). The obtained Th_(1_x)Mn_xO_2 nanocrystals were characterized by x-ray diffraction (XRD), direct-current magnetization (M) measurements and electron paramagnetic resonance (EPR). XRD analysis revealed that Th_(1-x)Mn_xO_2 crystallizes in the cubic structure (Fm3m). M measurements showed ferromagnetic ordering at room temperature for Th_(0.99)Mn_(0.01)O_2 samples annealed at 775 K. An intense and broad ferromagnetic resonance (FMR) having linewidth of ～1200 G, was observed at relatively lower fields in the EPR spectra of Th_(0.99)Mn_(0.01)O_2 samples annealed at 775 K, indicating the presence of a ferromagnetic phase at room temperature. EPR measurements were used to estimate the number of spins involved in the ferromagnetic ordering. Out of the total Mn present in Th_(0.99)Mn_(0.01)O_2 samples, about 25% of the Mn~(2+) ions were found to be responsible for the ferromagnetic ordering. In addition to the FMR signal, a weak hyperfine sextet was observed at g = 2.0048 (~(55)Mn, I = 5/2), which corresponds to the -1/2 ←→ +1/2 transition of Mn~(2+) ions, suggesting its presence at thorium sites (uncoupled spins). X-ray photoelectron spectra indicated that the manganese ions exist mainly as Mn~(2+), Mn~(3+), and Mn~(4+). The room-temperature ferromagnetism may be attributed to the coupling between these Mn~(2+) ions at thorium sites in ThO_2 rather than due to the formation of any metastable secondary phases.
机译：我们报道了通过尿素燃烧法使用硝酸or凝胶，然后在较高的温度（T）下进行热处理，合成了Th_（1-x）Mn_xO_2（x = 0、0.001、0.002、0.004和0.01 wt％）纳米粒子。通过X射线衍射（XRD），直流磁化（M）测量和电子顺磁共振（EPR）表征获得的Th_（1_x）Mn_xO_2纳米晶体。 XRD分析表明，Th_（1-x）Mn_xO_2在立方结构（Fm3m）中结晶。 M测量显示，在775 K下退火的Th_（0.99）Mn_（0.01）O_2样品在室温下铁磁有序。在EPR光谱中相对较低的场处观察到线宽为1200 G的强而宽的铁磁共振（FMR） Th_（0.99）Mn_（0.01）O_2样品在775 K退火，表明在室温下存在铁磁相。 EPR测量用于估计铁磁排序中涉及的自旋数。在Th_（0.99）Mn_（0.01）O_2样品中存在的总Mn中，发现约25％的Mn〜（2+）离子与铁磁有序有关。除FMR信号外，在g = 2.0048（〜（55）Mn，I = 5/2）处观察到微弱的超细六重音，对应于Mn〜（-1/2←→+1/2跃迁2+）离子，表明其存在于th位点（未耦合的自旋）。 X射线光电子能谱表明锰离子主要以Mn〜（2 +），Mn〜（3+）和Mn〜（4+）的形式存在。室温铁磁性可能归因于ThO_2中th位置的这些Mn〜（2+）离子之间的耦合，而不是归因于任何亚稳次级相的形成。

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