Solid State Physics Division, Bhabha Atomic Research Centre, Mumbai 400085, India.
J Phys Condens Matter. 2011 Dec 21;23(50):506004. doi: 10.1088/0953-8984/23/50/506004. Epub 2011 Dec 1.
We report the magnetic proximity effect in a ferrimagnetic Fe(3)O(4) core/ferrimagnetic γ-Mn(2)O(3) shell nanoparticle system, in terms of an enhancement of the Curie temperature (T(c)) of the γ-Mn(2)O(3) shell (66 K) compared to its bulk value (40 K), and the presence of magnetic ordering in its so-called paramagnetic region (i.e. above 66 K). The ferrimagnetic nature of both core and shell has been found from a neutron diffraction study. The origin of these two features of the magnetic proximity effect has been ascribed to the proximity of the γ-Mn(2)O(3) shell with a high-T(c) Fe(3)O(4) core (~858 K in bulk form) and an interface exchange coupling between core and shell. Interestingly, we did not observe any exchange bias effect, which has been interpreted as a signature of a weak interface exchange coupling between core and shell. The present study brings out the importance of the relative strength of the interface coupling in governing the simultaneous occurrence of the magnetic proximity effect and the exchange bias phenomenon in a single system.
我们报告了在铁磁 Fe(3)O(4) 核/铁磁 γ-Mn(2)O(3) 壳纳米粒子系统中的磁近邻效应，表现在 γ-Mn(2)O(3)壳的居里温度 (T(c)) 增强（相对于其体值 (40 K)，约为66 K），以及在其所谓的顺磁区（即高于 66 K）中存在磁有序。从中子衍射研究中发现了核和壳的铁磁性质。这些磁近邻效应的两个特征的起源归因于 γ-Mn(2)O(3)壳与具有高 T(c) 的 Fe(3)O(4)核（在体形式下为~858 K）的近邻以及核和壳之间的界面交换耦合。有趣的是，我们没有观察到任何交换偏置效应，这被解释为核和壳之间界面交换耦合较弱的特征。本研究表明，在单个系统中，界面耦合的相对强度对于同时发生磁近邻效应和交换偏置现象的重要性。
