镍基磷化物新型纳米结构的合成、组装和磁性质
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摘要
新型纳米结构如中空纳米颗粒和核壳纳米颗粒,因其独特的化学和物理功能以及巨大的应用前景而倍受化学、物理学和材料学等领域的科学家所广泛关注。在目前所发现纳米磁现象的基础之上,通过设计和制备各种磁性新型纳米结构,并探索其可能具有的纳米磁效应与功能,将可能利用所发现的新纳米磁效应来进一步提高磁信息容量。本论文围绕镍基磷化物新型纳米结构的制备、组装和磁性质进行了以下几个方面的研究：
1.采用有机液相化学反应法,以乙酰丙酮镍为镍源和三苯基膦为磷源,利用纳米Kirkendall效应成功一步合成出Ni2P中空纳米颗粒。并发现：Ni2P中空纳米颗粒是通过前期形成的颗粒Ni与三苯基膦反应并沿纳米Kirkendall桥不断向外扩散而形成。而且改变三苯基膦的浓度获得了中空直径从5nm到60nm的中空纳米颗,证实了三苯基膦可以作为一种表面活性剂以及新的廉价的磷源,来调控和提高Ni2P中空纳米颗粒的中空尺寸。
2.利用三苯基膦表面磷化镍纳米颗粒的工艺成功地合成出Ni/Ni2P核壳纳米颗粒。并发现：通过反应时间可以调控核壳比例,随着磷化时间的延长,Ni2P壳逐渐增厚,而Ni核不断减小,最终转变成Ni2P纳米颗粒。并且,将调整核壳比例后的Ni/Ni2P核壳纳米颗粒于氩气中退火,可以利用Ni核与Ni2P壳的化合反应合成出新型镍磷化物Ni3P。
3.对所合成纳米颗粒的室温磁性和磁热稳定性进行了深入研究。并发现：Ni/Ni2P核壳纳米颗粒存在铁磁-超顺磁转变,而Ni2P纳米颗粒为顺磁性。随着Ni2P壳的引入,表面磁性质的改性更加显著。磁表面改性后,颗粒的磁表面各向异性增强了,以致尺寸减小的同时磁热稳定性还可以提高,使利用尺寸来进一步提高磁信息容量成为可能。
4.通过选用铁磁-超顺磁转变温度更高的Ni/Ni2P核壳纳米颗粒进行自组装形成致密块材,获得了直到室温的记忆效应。并发现：采用平均转变温度更高的分散纳米颗粒进行自组装可以获得更高的记忆温区,并且减小组装间距可以进一步提升记忆温区；同时,增加测量磁场将导致记忆温区不断向低温移动；另外,利用磁-温记忆效应,实现了基于温度的磁信息读写新方式,使利用温度来进一步提高磁信息读写容量成为可能。
Increasing attention had been paid to the new styles of nanoscale structures with various application in the field of chemistry, physics and material, due to the unique properties and considerable potencial of the hollow nanostructures and core-shell nanostructures. On the basis of current nanoscale magnetic phenomena, the design and preparation of various new-style magnetic nanostructures with potential new nanomagnetic effect and properties would make it possible to further improve the capacity of magnetic information. In this thesis, the synthesis, assembly, and magnetic properties of the nickel-based phosphide nanoparticles with hollow and core-shell nanostructures were investigated.
Ni2P hollow nanoparticles with tunable void sizes were obtained by one-pot synthetic technique using triphenylphosphine as a lower-price phosphorus source in a mild temperature organic solution. It was found that the Ni2P hollow nanoparticles were formed by the reaction of as-formed Ni nanoparticles with the surface triphenylphosphine and the outward-diffusion of Ni core via Kirkendall bridges. Varied triphenylphosphine concentrations were used to prepare nanoparticles with void sizes tunable from about 5 to 60 nm in diameter, showing that the lower-price phosphorus source triphenylphosphine can serve a reactive surfactant to tune and heighten the void capacity for potentia applications.
Ni/Ni2P core-shell nanoparticles with tunable core-shell sizes were synthesized through surface phosphatizing Ni nanoparticles using triphenylphosphine as phosphorus source in a mild temperature organic solution. It was found that increasing phosphatizing time would lead to thickening of the Ni2P shell, with the Ni core diminishing. Overphosphatizing the particles would make Ni2P nanoparticles form with almost no Ni remaining. And after adjusting the core-shell proportion by reaction time, annealing the Ni/Ni2P core-shell nanoparticles would lead the formation of new-style phosphide Ni3P, through the chemical combination of Ni2P shell with inner Ni during annealing.
The magnetic properties of as-synthesized nickel-based phosphide nanoparticles were studied at and below the room temperature. It was found that the Ni/Ni2P core-shell nanoparticles have a magnetic transforming from ferromagnetism to superparamagnetism as warming from 10 K to the room temperature. However, the Ni2P nanoparticles are paramagnetic. As a result, the surface magnetic modification of Ni core by the Ni2P shell was enhanced as the increase of phosphatizing time. And the magnetic thermal stability of the nanoparticles with redued ferromagnetic Ni core was inproved through the enhanced influence of magnetic surface anisotropy after surface magnetic modification, which makes it possible to further improve the information capacity via size.
The magnetization-temperature memory effect up to room-temperature was observed in the self-assembly of Ni/Ni2P core-shell nanomagnetic particles under low-filed direct-current magnetization process. It was found that the self-assembly of nanoparticels with higher magnetic thermal stability can highen the temperature-rang for memory effect, and lowering interparticle spacing can further improve the temperature-rang. However, heightening applied magnetic field can suppress the memory effect with decreasing temperature-range. Moreover, a new mode to read-write magnetic coding was realized based on temperature using the memory effect, indicating a new way to further heighten the information capacity via temperature.
1.采用有机液相化学反应法,以乙酰丙酮镍为镍源和三苯基膦为磷源,利用纳米Kirkendall效应成功一步合成出Ni2P中空纳米颗粒。并发现：Ni2P中空纳米颗粒是通过前期形成的颗粒Ni与三苯基膦反应并沿纳米Kirkendall桥不断向外扩散而形成。而且改变三苯基膦的浓度获得了中空直径从5nm到60nm的中空纳米颗,证实了三苯基膦可以作为一种表面活性剂以及新的廉价的磷源,来调控和提高Ni2P中空纳米颗粒的中空尺寸。
2.利用三苯基膦表面磷化镍纳米颗粒的工艺成功地合成出Ni/Ni2P核壳纳米颗粒。并发现：通过反应时间可以调控核壳比例,随着磷化时间的延长,Ni2P壳逐渐增厚,而Ni核不断减小,最终转变成Ni2P纳米颗粒。并且,将调整核壳比例后的Ni/Ni2P核壳纳米颗粒于氩气中退火,可以利用Ni核与Ni2P壳的化合反应合成出新型镍磷化物Ni3P。
3.对所合成纳米颗粒的室温磁性和磁热稳定性进行了深入研究。并发现：Ni/Ni2P核壳纳米颗粒存在铁磁-超顺磁转变,而Ni2P纳米颗粒为顺磁性。随着Ni2P壳的引入,表面磁性质的改性更加显著。磁表面改性后,颗粒的磁表面各向异性增强了,以致尺寸减小的同时磁热稳定性还可以提高,使利用尺寸来进一步提高磁信息容量成为可能。
4.通过选用铁磁-超顺磁转变温度更高的Ni/Ni2P核壳纳米颗粒进行自组装形成致密块材,获得了直到室温的记忆效应。并发现：采用平均转变温度更高的分散纳米颗粒进行自组装可以获得更高的记忆温区,并且减小组装间距可以进一步提升记忆温区；同时,增加测量磁场将导致记忆温区不断向低温移动；另外,利用磁-温记忆效应,实现了基于温度的磁信息读写新方式,使利用温度来进一步提高磁信息读写容量成为可能。
Increasing attention had been paid to the new styles of nanoscale structures with various application in the field of chemistry, physics and material, due to the unique properties and considerable potencial of the hollow nanostructures and core-shell nanostructures. On the basis of current nanoscale magnetic phenomena, the design and preparation of various new-style magnetic nanostructures with potential new nanomagnetic effect and properties would make it possible to further improve the capacity of magnetic information. In this thesis, the synthesis, assembly, and magnetic properties of the nickel-based phosphide nanoparticles with hollow and core-shell nanostructures were investigated.
Ni2P hollow nanoparticles with tunable void sizes were obtained by one-pot synthetic technique using triphenylphosphine as a lower-price phosphorus source in a mild temperature organic solution. It was found that the Ni2P hollow nanoparticles were formed by the reaction of as-formed Ni nanoparticles with the surface triphenylphosphine and the outward-diffusion of Ni core via Kirkendall bridges. Varied triphenylphosphine concentrations were used to prepare nanoparticles with void sizes tunable from about 5 to 60 nm in diameter, showing that the lower-price phosphorus source triphenylphosphine can serve a reactive surfactant to tune and heighten the void capacity for potentia applications.
Ni/Ni2P core-shell nanoparticles with tunable core-shell sizes were synthesized through surface phosphatizing Ni nanoparticles using triphenylphosphine as phosphorus source in a mild temperature organic solution. It was found that increasing phosphatizing time would lead to thickening of the Ni2P shell, with the Ni core diminishing. Overphosphatizing the particles would make Ni2P nanoparticles form with almost no Ni remaining. And after adjusting the core-shell proportion by reaction time, annealing the Ni/Ni2P core-shell nanoparticles would lead the formation of new-style phosphide Ni3P, through the chemical combination of Ni2P shell with inner Ni during annealing.
The magnetic properties of as-synthesized nickel-based phosphide nanoparticles were studied at and below the room temperature. It was found that the Ni/Ni2P core-shell nanoparticles have a magnetic transforming from ferromagnetism to superparamagnetism as warming from 10 K to the room temperature. However, the Ni2P nanoparticles are paramagnetic. As a result, the surface magnetic modification of Ni core by the Ni2P shell was enhanced as the increase of phosphatizing time. And the magnetic thermal stability of the nanoparticles with redued ferromagnetic Ni core was inproved through the enhanced influence of magnetic surface anisotropy after surface magnetic modification, which makes it possible to further improve the information capacity via size.
The magnetization-temperature memory effect up to room-temperature was observed in the self-assembly of Ni/Ni2P core-shell nanomagnetic particles under low-filed direct-current magnetization process. It was found that the self-assembly of nanoparticels with higher magnetic thermal stability can highen the temperature-rang for memory effect, and lowering interparticle spacing can further improve the temperature-rang. However, heightening applied magnetic field can suppress the memory effect with decreasing temperature-range. Moreover, a new mode to read-write magnetic coding was realized based on temperature using the memory effect, indicating a new way to further heighten the information capacity via temperature.
引文
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