Antiferromagnetic MnO nanoparticles with ferrimagnetic Mn3O4 shells:: Doubly inverted core-shell system
Antiferromagnetic MnO nanoparticles with ferrimagnetic Mn3O4 shells:: Doubly inverted core-shell system
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DOI：
10.1103/physrevb.77.024403
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发表时间：
2008-01-01
影响因子：
3.7
通讯作者：
Fullerton, E. E.
中科院分区：
文献类型：
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作者：
Berkowitz, A. E.;Rodriguez, G. F.;Fullerton, E. E.
我们报告了具有亚铁磁性 Mn(3)O(4) 壳的反铁磁性 MnO 纳米颗粒的磁性和微观结构特性，这与反铁磁性涂覆的铁磁性纳米颗粒的通常排列相反。此外，反铁磁MnO核在比铁磁Mn(3)O(4)壳(T(C)=43 K)高得多的温度(T(N)=118 K)下有序化——这与通常情况相反。具有岩盐结构的单晶MnO核在晶体学上与Mn(3)O(4)壳的四方尖晶石结构对齐。在 50 kOe 下场冷却的粒子在低于 T(C) 时具有较大的矫顽力和交换偏置，例如，在 5 K 时分别为 5800 Oe 和 2950 Oe。T(C)(Mn(3)O(4)) 时的自发磁化强度类似于 5 K 时其值的 20%，并且在高于 T(C)(Mn(3)O(4)) 超过 20 K 时保持有限。该异常区域存在带有交换偏差的滞后现象。具有未补偿自旋的 MnO 核是导致 T(C)(Mn(3)O(4)) 以上行为的原因。 MnO 核心的阻断温度为 95 K，高于 T(C)(Mn(3)O(4)) 的磁滞和交换偏压是由 MnO 自旋晶格通过其未补偿的自旋进行切换而产生的。对 50 kOe 下的热剩磁和场冷却和/或零场冷却的分析，以及交换偏置对施加冷却场的温度的依赖性支持了该模型。
We report the magnetic and microstructural properties of antiferromagnetic MnO nanoparticles with shells of ferrimagnetic Mn(3)O(4), which is opposite the usual arrangement of antiferromagnetically coated ferromagnetic nanoparticles. In addition, the antiferromagnetic MnO cores order at much higher temperature (T(N)=118 K) than the ferrimagnetic Mn(3)O(4) shells (T(C)=43 K)-another reversal of the usual situation. The single crystal MnO cores, with rocksalt structure, are crystallographically aligned with the tetragonal spinel structure of the Mn(3)O(4) shells. Particles field cooled in 50 kOe have large coercive force and exchange bias below T(C), e.g., 5800 and 2950 Oe, respectively, at 5 K. The spontaneous magnetization at T(C)(Mn(3)O(4)) is similar to 20% of its value at 5 K, and remains finite for more than 20 K above T(C)(Mn(3)O(4)). Hysteresis with exchange bias is present in this anomalous region. The MnO cores with their uncompensated spins are responsible for the behavior above T(C)(Mn(3)O(4)). The MnO cores have a blocking temperature of 95 K, and the hysteresis and exchange bias above T(C)(Mn(3)O(4)) results from the switching of the MnO spin lattices by their uncompensated spins. Analysis of the thermoremanent magnetization and field cooling and/or zero field cooling in 50 kOe, and the dependence of exchange bias on the temperature at which the cooling field was applied support this model.