Department of Physics, University of South Florida, Tampa, FL 33620, USA.
J Phys Condens Matter. 2013 Oct 23;25(42):426003. doi: 10.1088/0953-8984/25/42/426003. Epub 2013 Sep 27.
The development of positive magnetic entropy change in the case of ferromagnetic (FM) nanostructures is a rare occurrence. We observe positive magnetic entropy change in core/shell (Fe/γ-Fe2O3) and hollow (γ-Fe2O3) nanoparticles and its origin is attributed to a disordered state in the nanoparticles due to the random distribution of anisotropy axes which inhibits any long range FM ordering. The effect of the energy barrier distribution on the magnetic entropy change and its impact on the universal behavior based on rescaled entropy change curves for core/shell and hollow nanostructures is discussed. Our study emphasizes that the magnetic entropy change is an excellent parameter to study temperature and field dependent magnetic freezing in such complex nanostructures.
在铁磁（FM）纳米结构的情况下，正磁熵变化的发展是罕见的。我们观察到核/壳（Fe/γ-Fe2O3）和空心（γ-Fe2O3）纳米颗粒中的正磁熵变化，其起源归因于由于各向异性能量轴的随机分布而导致纳米颗粒中处于无序状态，这抑制了任何长程 FM 有序。讨论了能量势垒分布对磁熵变化的影响及其对基于核/壳和空心纳米结构的重标熵变化曲线的普遍行为的影响。我们的研究强调，磁熵变化是研究此类复杂纳米结构中温度和场依赖性磁冻结的一个极好参数。
