High-Frequency Sound Propagation near Magnetic Phase Transitions
High-Frequency Sound Propagation near Magnetic Phase Transitions
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磁相变附近的高频声音传播
DOI：
10.1103/physrevb.4.122
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发表时间：
1971
影响因子：
3.7
通讯作者：
B. Lüthi
中科院分区：
文献类型：
--
作者：
T. J. Moran;B. Lüthi
给出了 RbMn${\mathrm{F}}_{3}$ 和 Mn${\mathrm{F}}_{2}$ 磁相变附近的超声衰减和速度实验结果。对于 $Tg{T}_{N}$，数据提供了额外的证据，表明声音与自旋能量密度波动耦合，该波动通过自旋晶格弛豫而衰减。 RbMn${\mathrm{F}}_{3}$ 的衰减结果可以用单一弛豫公式拟合，频率范围为 90-930 MHz，温度范围为 $\ensuremath{\epsilon}[=\frac{(T\ensuremath{-}{T}_{N})}{{T}_{N}}]$ 从 ${10}^{\ensuremath{-}4}$ 到 ${10}^{\ensuremath{-}2}$。自旋晶格弛豫时间 ${\ensuremath{\tau}}_{L}$ 的变化范围为 4\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}10}$ 到 2\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}10}$ 秒，在相同的 $\ensuremath{\epsilon}$ 范围内。此外，临界衰减和速度变化都与声波传播方向无关。在 Mn${\mathrm{F}}_{2}$ 中，我们从临界速度色散中发现了恒定的弛豫时间 ${\ensuremath{\tau}}_{L}=(2.7\ifmmode\pm\else\textpm\fi{}0.2)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}9}$ 秒 $\ensuremath{\epsilon}\ensuremath{\ge}{10}^{\ensuremath{-}3}$，与川崎和生岛的引用值非常一致。对于较小的 $\ensuremath{\epsilon}$ 发现了一个小分歧。对于$Tl{T}_{N}$，我们发现随着RbMn${\mathrm{F}}_{3}$中频率的增加，衰减的最大值和速度的最小值向较低的温度移动。此外，在RbMn${\mathrm{F}}_{3}$中，在${T}_{N}$下方发现了第二个衰减峰，该衰减峰随着频率的增加而向较低温度移动。发现该辅助衰减峰强烈依赖于样本。在 Mn${\mathrm{F}}_{2}$ 中，在有序区域中观察到广泛的衰减最大值和速度最小值。讨论了这些影响的可能机制。
The results of ultrasonic attenuation and velocity experiments near the magnetic phase transitions in RbMn${\mathrm{F}}_{3}$ and Mn${\mathrm{F}}_{2}$ are presented. For $Tg{T}_{N}$, the data give additional evidence that the sound couples to the spin-energy-density fluctuations which decay via spin-lattice relaxation. The attenuation results for RbMn${\mathrm{F}}_{3}$ could be fitted with a single relaxation formula for the frequency range 90-930 MHz and for the temperature range of $\ensuremath{\epsilon}[=\frac{(T\ensuremath{-}{T}_{N})}{{T}_{N}}]$ from ${10}^{\ensuremath{-}4}$ to ${10}^{\ensuremath{-}2}$. The spin-lattice relaxation time ${\ensuremath{\tau}}_{L}$ was found to vary from 4\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}10}$ to 2\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}10}$ sec in the same $\ensuremath{\epsilon}$ range. Furthermore, both the critical attenuation and velocity changes are independent of sound-wave propagation direction. In Mn${\mathrm{F}}_{2}$, we found from the critical velocity dispersion a constant relaxation time ${\ensuremath{\tau}}_{L}=(2.7\ifmmode\pm\else\textpm\fi{}0.2)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}9}$ sec for $\ensuremath{\epsilon}\ensuremath{\ge}{10}^{\ensuremath{-}3}$, in good agreement with Kawasaki and Ikushima's quoted value. A small divergence was found for smaller $\ensuremath{\epsilon}$. For $Tl{T}_{N}$, it was found that the maxima of the attenuation and the minima of the velocity shifted to lower temperatures with increasing frequency in RbMn${\mathrm{F}}_{3}$. In addition, in RbMn${\mathrm{F}}_{3}$, a second attenuation peak was found below ${T}_{N}$ which shifted to lower temperatures with increasing frequency. This subsidiary attenuation peak was found to be strongly sample dependent. In Mn${\mathrm{F}}_{2}$, broad attenuation maxima and velocity minima are observed in the ordered region. Possible mechanisms for these effects are discussed.