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首页> 外文期刊>Magnetics, IEEE Transactions on >Memory Effects and Relaxation Dynamics of src='/images/tex/20769.gif' alt='{rm MnCo}_{2}{rm O}_{4}'> Nanocrystallites
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Memory Effects and Relaxation Dynamics of src='/images/tex/20769.gif' alt='{rm MnCo}_{2}{rm O}_{4}'> Nanocrystallites

机译：<配方公式type =“ inline”> src =“ / images / tex / 20769.gif” alt =“ {rm MnCo} _ {2} {rm O} _ {4}”> <的记忆效应和松弛动力学/公式>纳米晶体

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摘要

We present a detailed analysis of the time decay of magnetization $(M)$ and ac-magnetic susceptibility $(chi_{rm ac})$ of hexagonal-shaped ${rm MnCo}_{2}{rm O}_{4}$ nanocrystals of average size 28 nm. The temperature $(T)$ and magnetic field $(H)$ dependence of the magnetization measurements reveal that even in the ferromagnetic state these nanocrystals do not exhibit conventional long-range ordering. The Curie temperature $T_{C}=176.4 {rm K}$ and the Hopkinson peak $T_{H}=146 {rm K}$ are found to be lower than those of the bulk values 184 and 175 K, respectively. Such a major decrease in $T_{C}$ and $T_{H}$ accounted for by the effect of finite-size scaling that has been thought to change the critical ordering temperatures. The dynamical properties studied by $chi_{rm ac}(T)$ measurements suggest the existence of a spin-glass phase for $Tleq T_{F}(=165 {rm K})$ associated with the magnetic frustration of spins in the nanocrystals. The presence of glassy magnetic state is supported by the frequency $(f)$ dependent studies of $chi_{rm ac}(T)$ and $H^{2/3- $ dependence of $T_{F}$ in the intermediate-field region $(50 {rm Oe}leq Hleq 1000 {rm Oe})$. Various measurement protocols including temperature quenching, step-field and wait-time dependence have been used to investigate the relaxation dynamics both in $M_{ZFC}$ and in $M_{rm FC}$ for $Tleq T_{F}$, which show prominent memory and aging effects and supports the spin-glass state that established below $T_{F}$. The magnetic viscosity $(S)$ and microscopic spin-flip time $(tau)$ were deduced from the time $(t)$ dependence of $M_{rm ZFC}$ using the expression $M(t,T)=M(0,T)+S ln(1+t/t_{0})$ in which the magnitude of $M(t)$ strongly depends on the wait-time spend at temperatures below $T_{F}$.
机译：我们对磁化强度的时间衰减进行了详细的分析 $（M）$ 和交流磁化率 $（chi_ {rm ac}）$ 六角形 $ {均方根MnCo} _ {2} {rm O} _ {4} $ 纳米晶体。温度 $（T）$ 和磁场 $（H）$ 磁化强度的测量结果表明，即使在铁磁状态下，这些纳米晶体也不会表现出常规的长程有序性。居里温度<配方公式类型=“ inline”> $ T_ {C} = 176.4 {rm K} $ 和霍普金森峰<配方公式类型=“ inline” > $ T_ {H} = 146 {rm K} $ 分别低于批量值184和175K。 $ T_ {C} $ 和 $ T_ {H} $ 是由有限大小缩放的影响所导致的，该缩放被认为会改变临界排序温度。通过 $ chi_ {rm ac}（T）$ 测量研究的动力学性质表明存在自旋玻璃相。 $ Tleq T_ {F}（= 165 {rm K}）$ 与纳米晶体中自旋的磁性受挫有关。 $（f）$ 依赖研究> $ chi_ {rm ac}（T）$ 和 $ H ^ {2 /在中间场区域中 $ T_ {F} $ 的3- $ 依赖性<公式Formulatype =“ inline”> $（50 {rm Oe} leq Hleq 1000 {rm Oe}）$ 。包括温度猝灭，阶跃场和等待时间相关性在内的各种测量协议已用于研究 $ M_ {ZFC} $ ，在 $ M_ {rm FC} $ 中=“ TeX”> $ Tleq T_ {F} $ ，它显示出显着的记忆和衰老效果，并支持在下建立的自旋玻璃状态。 “ TeX”> $ T_ {F} $ 。磁粘度<公式公式=“ inline”> $（S）$ 和微观自旋翻转时间<公式公式类型=“ inline”> $（tau）$ 是从 $（t）$ 使用表达式 $ M_ {rm ZFC} $ 的依赖性TeX“> $ M（t，T）= M（0，T）+ S ln（1 + t / t_ {0}）$ 其中 $ M（t）$ 很大程度上取决于温度低于 $ T_ {F} $ 。

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