Strain-mediated photomagnetic effects in heterostructured nanoparticles of Prussian blue analogues
Strain-mediated photomagnetic effects in heterostructured nanoparticles of Prussian blue analogues
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普鲁士蓝类似物异质结构纳米粒子中应变介导的光磁效应
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发表时间：
2013
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通讯作者：
E. S. Knowles
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作者：
E. S. Knowles
报道了普鲁士蓝类似物立方异质纳米粒子(PBAs)在宽的温度(2K)和磁场(µ0H<；10T)范围内的光磁性质。这些结果集中在压敏NiCr-PBA(A)和光磁CoFe-PBA(B)的异质结构上，用来解释非光活性A组分在其铁磁有序温度(T_c~70K)范围内所产生的应变效应。电荷转移诱导的自旋跃迁(CTIST)在慢冷过程中在B中产生晶格收缩，在白光照射后，所产生的应力通过B组分在低温(T<；150K)下的光致膨胀而释放。这项工作的核心是解决异质结构中A组分应变的机制和程度。以此为目标，研究了一系列具有相同B核和不同A壳层厚度的BA核@壳纳米粒子。此外，该系列立方体纳米粒子允许直接计算A壳层中的高场磁化强度。因此，通过采用磁性降低的猜想机制，从高场数据中提取了感应应变的深度，揭示了名义上为20 nm的应变深度，这是对于PBAs出现的递归长度和尺度。伴随着高场分析，对低场磁化率数据进行数值区分这一看似简单的步骤进一步阐明了应变效应。具体地说，这些衍生物暴露了核@壳纳米粒子在光态下A有序温度的锐化，这一效应被发现在所有含A的异质结构中都是普遍存在的。这一发现证实了这样一种理解，即B核的光致膨胀缓解了暗状态下施加在A壳上的应力。这些核心@壳研究最初是以先前的核心@壳@壳研究结果为指导的，这些发现表明，虽然不需要A的自由表面，但必须通过在具有甚至微妙不同的骨架的底层相上生长A材料来建立应力敏感性。最后，寻求在更实际的温度下实现光效的研究在新型BC、CB和CAB异质结中引入了具有高T_c(220K)的CrCr-PBA(C)。为了补充块体磁性的结果，电子磁共振(EMR)研究表明，以前在A膜中观察到的来自磁畴的退磁效应在THEBA粒子的A壳层中的光致应变中起着核心作用。此外，虽然EMR结果证实了异质结构中A组分的高场磁性总体上的降低，但这一研究也揭示了光效应的历史依赖性，其中系统必须循环通过B核的有序化温度来允许A磁区完全松弛。除了对异质结构聚对苯二甲酸的研究外，…
The photomagnetic properties of cubic heterostructured nanoparticles of Prussian blue analogues (PBAs) are reported for various morphologies (with length scales of 100 nm < l < 1 µm) studied over a wide range of temperature (2 K < T < 300 K) and magnetic field (µ0H < 10 T). These results focus on heterostructures of a pressure-sensitive NiCr-PBA (A) and a photomagnetic CoFe-PBA (B) to illuminate the strain effects that are induced in the nonphotoactive A component up to its ferromagnetic ordering temperature (Tc ~ 70 K). A charge-transfer induced spin-transition(CTIST) generates a lattice contraction in B during slow-cooling, and after irradiation with white light, the resulting stress is released by the photoinduced expansion of the B component at low temperatures (T < 150 K). The core of this work addresses the mechanism and extent of the strain in the A component of the heterostructures. With this goal, a series of BA core@shell nanoparticles with the same B cores and varying A shell thicknesses was investigated.In addition, the series of cubic nanoparticles allows a straightforward calculation of the high-field magnetization in the A shell. Thus, by employing the conjectured mechanisms of the decreased magnetism, the depth of the induced strain is extracted from the high-field data, revealing a strain depth of nominally 20 nm, which is a recurrent length scale appearing for the PBAs. To accompany the high-field analysis, the seemingly simple step of numerically differentiating the low-field susceptibility data provides further elucidation of the strain effects. Specifically, these derivatives expose a sharpening of the A ordering temperature in the light state of the core@shell nanoparticles, an effect which is found to be ubiquitous for all of the A-containing heterostructures. This finding asserts the understanding that the photoinduced expansion of the B core relieves the stress that is applied to the A shell in the dark state. These core@shell studies were initially guided by prior core@shell@shell findings, which reveal that, while a free surface of A is not needed, a stress-sensitivity must be established by growing the A material on an underlying phase possessing even a subtly disparate framework. Finally, studies which sought to achieve photoeffects at more practical temperatures incorporated a CrCr-PBA (C) with a high-Tc (220 K) in novel BC, CB, andCAB heterostructures. To complement the bulk magnetism results, electron magnetic resonance (EMR) studies reveal that demagnetizing effects from domains, which have previously been observed in A films, play a central role in the photoinduced strain in the A shells of theBA particles. Moreover, while the EMR results confirm overall decreases in the high-field magnetism of the A component of the heterostructures, this investigation also unveils a history dependence of the photoeffect, where the system must be cycled through the ordering temperature of the B core to allow the A domains to fully relax. In addition to the studies of the heterostructured PBAs, the…