BiFeO $_3$ -Bi $_2$ Fe $_4$ O $_9$纳米复合材料中超自旋玻璃介导的巨自发交换偏压
Superspin Glass Mediated Giant Spontaneous Exchange Bias in a Nanocomposite of BiFeO$_3$-Bi$_2$Fe$_4$O$_9$
摘要：
我们观察到一个巨大的$\textit{spontaneous}$交换偏置（$\sim$ 300-600 Oe）-在零场冷却后的非磁化状态下测量-在BiFeO $_3$（$\sim$ 94%）-Bi $_2$ Fe $_4$ O $_9$（$\sim$ 6%）的纳米复合材料在5-300 K的温度范围内。取决于跟踪磁滞回线所遵循的路径-正（p）或负（n）-以及所施加的最大场，交换偏置（$H_E$）随$\mid-H_{Ep}\mid$ $>$ $\mid H_{En}\mid$而显著变化。$H_E$的温度依赖性是非单调的。当$T_B$接近阻断温度时，PDMATHABMN_（$\sim$）随温度的升高而减小.所有这些丰富的功能似乎起源于自发的对称性破缺和随后发生的单向各向异性驱动的“超相互作用偏置耦合”之间的铁磁核心的Bi $_2$ Fe $_4$ O $_9$（平均尺寸$\sim$ 19 nm）和倾斜的反铁磁结构的BiFeO $_3$（平均尺寸$\sim$ 112 nm）通过超自旋玻璃时刻在壳。
英文摘要：
We observe an enormous $\textit{spontaneous}$ exchange bias ($\sim$300-600 Oe) - measured in an unmagnetized state following zero-field cooling - in a nanocomposite of BiFeO$_3$ ($\sim$94%)-Bi$_2$Fe$_4$O$_9$ ($\sim$6%) over a temperature range 5-300 K. Depending on the path followed in tracing the hysteresis loop - positive (p) or negative (n) - as well as the maximum field applied, the exchange bias ($H_E$) varies significantly with $\mid-H_{Ep}\mid$ $>$ $\mid H_{En}\mid$. The temperature dependence of $H_E$ is nonmonotonic. It increases, initially, till $\sim$150 K and then decreases as the blocking temperature $T_B$ is approched. All these rich features appear to be originating from the spontaneous symmetry breaking and consequent onset of unidirectional anisotropy driven by "superinteraction bias coupling" between ferromagnetic core of Bi$_2$Fe$_4$O$_9$ (of average size $\sim$19 nm) and canted antiferromagnetic structure of BiFeO$_3$ (of average size $\sim$112 nm) via superspin glass moments at the shell.
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