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STRAIN DRIVEN DYNAMICS OF PHASE TRANSITIONS IN OXIDE ANTIFERROMAGNETS

氧化物反铁磁体中应变驱动的相变动力学

基本信息

批准号：
1409622
负责人：
Shireen Adenwalla
金额：
$ 55万
依托单位：
University of Nebraska-Lincoln
依托单位国家：
美国
项目类别：
Standard Grant
财政年份：
2014
资助国家：
美国
起止时间：
2014-09-01 至 2019-08-31
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=1409622&HistoricalAwards=false
关键词：
STRAIN DRIVEN DYNAMICS PHASE TRANSITIONS

项目摘要

Non-technical abstractPhase transitions refer to changes in a material's properties, often driven by temperature changes. The ubiquitous phase transition of water, which transforms from ice to liquid water to steam as the temperature increases, serves as an excellent example. Pressure significantly alters the temperature of water's transitions, as anyone who has baked a cake at high altitude well knows. The research component of this project will investigate the effects of rapidly changing pressure on phase transitions of technologically important magnetic materials by focusing a very fast (ultrasonic) sound wave on the material. By varying the pressure at rates of up to 10 billion times a second, the investigators will probe how the material's properties vary. The fundamental questions being probed are how quickly can the material respond, what will the response be and why does a particular material respond the way it does. The educational component is informed by the PIs' extensive experience in outreach and education at all levels ranging from preschool, K-12 and undergraduate education. New activities on phase transitions, tailored to the needs of a particular age group, will be developed to tie in with this research project. Technical AbstractThe research activity will investigate the dynamics of strain driven phase transitions in materials that show intricate entanglement between structure and ordering, viz. the magnetoelectric antiferromagnet Cr2O3 and the antiferromagnetic Mott insulator NdNiO3. In both cases the antiferromagnetic ordering is coincident with the appearance of another transition, surface boundary magnetization for Cr2O3 and a metal-insulator transition for NdNiO3. Focused surface acoustic wave transducers will generate strains that are comparable in magnitude to fixed, epitaxial strains and allow for controlled variable strain on a single sample, as well as the ability to drive strain at high frequencies. This approach of precisely controlled lattice excitation is unique in its the ability to drive materials back and forth across the phase transition at GHz frequencies, resulting in large changes in the order parameter, rather than small perturbative changes. This approach can be extended to a wide variety of strain sensitive ordering in thin film materials and will answer two fundamental questions. First, it will quantify the effects of external strain on the phase transition temperature of a single thin film sample, eliminating the uncertainties associated with thin film growth. Second, it will measure the temporal scale over which these strain driven phase transitions occur. The educational objectives will extend the reach of this cutting edge science by expanding the PIs' portfolios to include topics that are relevant to this project. The PIs will share their knowledge, skills and excitement with the already extensive ongoing outreach and education projects that include K-12 students and teachers, science cafes, science clubs, and senior citizen groups.

非技术摘要相变是指材料性质的变化，通常由温度变化驱动。水的普遍相变就是一个很好的例子，随着温度的升高，水从冰变成液态水再变成蒸汽。压力会显著改变水的转变温度，任何在高海拔地区烤过蛋糕的人都知道这一点。该项目的研究部分将通过将非常快的（超声波）声波聚焦在材料上，研究快速变化的压力对技术上重要的磁性材料相变的影响。通过以每秒100亿次的速度改变压力，研究人员将探索材料的性质如何变化。正在探索的基本问题是材料的反应速度有多快，反应会是什么，以及为什么特定材料会以这种方式反应。教育部分是由PI的广泛经验，在推广和教育各级从学前教育，K-12和本科教育。为配合这项研究计划，我们会因应个别年龄组别的需要，发展有关相变的新活动。技术摘要本研究活动将研究材料中应变驱动相变的动力学，这些材料表现出结构和有序之间的复杂纠缠，即磁电反铁磁体Cr2 O3和反铁磁Mott绝缘体NdNiO 3。在这两种情况下的反铁磁秩序是一致的外观的另一个过渡，表面边界磁化Cr2 O3和NdNiO 3的金属-绝缘体过渡。聚焦表面声波换能器将产生在幅度上与固定的外延应变相当的应变，并且允许在单个样品上控制可变应变，以及在高频下驱动应变的能力。这种精确控制晶格激发的方法是独特的，因为它能够在GHz频率下来回驱动材料穿过相变，从而导致序参数的大变化，而不是小的微扰变化。这种方法可以扩展到各种各样的薄膜材料的应变敏感排序，并将回答两个基本问题。首先，它将量化外部应变对单个薄膜样品相变温度的影响，消除与薄膜生长相关的不确定性。其次，它将测量这些应变驱动相变发生的时间尺度。教育目标将通过扩大PI的投资组合来扩展这一前沿科学的范围，以包括与该项目相关的主题。 PI将分享他们的知识，技能和兴奋与已经广泛的正在进行的推广和教育项目，包括K-12学生和教师，科学咖啡馆，科学俱乐部和老年公民团体。