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首页> 外文OA文献 >Stabilization of an ambient pressure, collapsed tetragonal phase in CaFe2As2 and tuning of the orthorhombic / antiferromagnetic transition temperature by over 70 K by control of nano-precipitates
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Stabilization of an ambient pressure, collapsed tetragonal phase in CaFe2As2 and tuning of the orthorhombic / antiferromagnetic transition temperature by over 70 K by control of nano-precipitates

机译：稳定环境压力，坍塌四方相   CaFe2as2和正交/反铁磁转变的调整   通过控制纳米沉淀物，温度超过70K

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We have found a remarkably large response of the transition temperature ofCaFe2As2 single crystals grown out of excess FeAs to annealing / quenchingtemperature. Whereas crystals that are annealed at 400 C exhibit a first orderphase transition from a high temperature tetragonal to a low temperatureorthorhombic and antiferromagnetic state near 170 K, crystals that have beenquenched from 960 C exhibit a transition from a high temperature tetragonalphase to a low temperature, non-magnetic, collapsed tetragonal phase below 100K. By use of temperature dependent electrical resistivity, magneticsusceptibility, X-ray diffraction, Mossbauer spectroscopy and nuclear magneticresonance measurements we have been able to demonstrate that the transitiontemperature can be reduced in a monotonic fashion by varying the annealing /quenching temperature from 400 to 850 C with the low temperature stateremaining antiferromagnetic for transition temperatures larger than 100 K andbecoming collapsed tetragonal / non-magnetic for transition temperatures below90 K. This suppression of the orthorhombic / antiferromagnetic phase transitionand its ultimate replacement with the collapsed tetragonal / non-magnetic phaseis similar to what has been observed for CaFe2As2 under hydrostatic pressure.Transmission electron microscopy studies indicate that there is a temperaturedependent, width of formation of CaFe2As2 with a decreasing amount of excess Feand As being soluble in the single crystal at lower annealing temperatures. Forsamples quenched from 960 C there is a fine (of order 10 nm), semi-uniformdistribution of precipitate that can be associated with an average strain fieldwhereas for samples annealed at 400 C the excess Fe and As form mesoscopicgrains that induce little strain throughout the CaFe2As2 lattice.
机译：我们发现，由过量FeAs生成的CaFe2As2单晶的转变温度对退火/淬火温度的响应非常大。在400°C退火的晶体在170 K附近表现出从高温四方晶态到低温正交晶态和反铁磁态的一阶相变，而从960°C淬火的晶体表现出从高温四方晶态到低温无晶态的转变。 -低于100K的磁塌方四方相。通过使用随温度变化的电阻率，磁化率，X射线衍射，莫斯鲍尔光谱和核磁共振测量，我们已经能够证明，通过将退火/淬火温度从400°C改变为850°C，可以单调降低转变温度。在过渡温度大于100 K时保持反铁磁性的低温状态，在过渡温度低于90 K时变为倒塌的四方/非磁性状态。这种对正交/反铁磁相变的抑制以及其最终被塌方的四方/非磁性相替代类似于透射电子显微镜研究表明，CaFe2As2存在一定的温度依赖性，形成的宽度随过量Feand As的减少而降低，且在较低的退火温度下可溶于单晶中。对于从960°C淬火的样品，析出物具有精细的（约10 nm）半均匀分布，这可能与平均应变场有关，而在400°C退火的样品中，过量的Fe和As形成介观晶粒，在整个CaFe2As2中几乎不引起应变格子。

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