Characterizing the nonequilibrium response of FeRh thin films using time-domain thermoreflectance,Physical Review B

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Characterizing the nonequilibrium response of FeRh thin films using time-domain thermoreflectance
Physical Review B ( IF 3.2 ) Pub Date : 2024-09-10 , DOI: 10.1103/physrevb.110.094417
Renee M. Harton ₁ , Alejandro Ceballos-Sanchez _{2,

3} , Vivek Unikandanunni ₄ , Alexander X. Gray ₅ , Stefano Bonetti _{4,

6} , Peter Krüger ₇ , Frances Hellman _{2,

2,

3}

Affiliation

Time-domain thermoreflectance (TDTR) characterization of FeRh throughout its first-order antiferromagnetic (AF) to ferromagnetic (FM) transition shows that the transient reflectance

Δ R (t) / R

strongly depends on the magnetic order of the sample. Using TDTR, which uses optical pulses to induce small temperature excursions, we have found that

Δ R (t) / R

of the AF phase exhibits a large negative response, while the response of the FM phase is positive. This magnetic phase sensitivity has allowed us to study the transient response of both the AF and FM phases to the pump-pulse excitation and the mixed phase of the material. These results are significant since the ultrafast properties of antiferromagnetic materials and mixed antiferromagnetic and ferromagnetic materials are difficult to detect using other conventional techniques. We have found that the AF phase exhibits a strong subpicosecond decaying signal not observed in the FM phase. The magnetic phase dependence of the sign of

Δ R (t) / R

is qualitatively explained using the results of ab initio density functional theory calculations. Using the two-temperature model, we found that the change in the thermalization time across the transition is caused by differences in both the electronic heat capacity and the electron-phonon coupling factor of the AF and FM phases. The electron-phonon coupling constant in the AF phase is also determined using the two-temperature model conducted using the ntmpy code package. For the FM phase, we provide boundaries for the magnitude of the electron-phonon coupling factor for the FM phase. These results indicate that TDTR can be used to study the transient properties of magnetic materials that are otherwise challenging to probe.

中文翻译：

使用时域热反射表征 FeRh 薄膜的非平衡响应

FeRh 在其一阶反铁磁 (AF) 到铁磁 (FM) 转变过程中的时域热反射 (TDTR) 表征表明，瞬态反射率

Δ R (t) / R

很大程度上取决于样品的磁序。使用 TDTR（使用光脉冲引起小的温度偏移），我们发现：

Δ R (t) / R

AF 阶段表现出较大的负响应，而 FM 阶段的响应为正。这种磁相敏感性使我们能够研究 AF 和 FM 相对泵浦脉冲激励和材料混合相的瞬态响应。这些结果意义重大，因为使用其他传统技术很难检测反铁磁材料以及反铁磁和铁磁混合材料的超快特性。我们发现 AF 阶段表现出 FM 阶段未观察到的强亚皮秒衰减信号。符号的磁相位依赖性

Δ R (t) / R

使用从头算密度泛函理论计算的结果进行定性解释。使用双温度模型，我们发现转变过程中热化时间的变化是由 AF 和 FM 相的电子热容和电子声子耦合因子的差异引起的。 AF 阶段的电子-声子耦合常数也是通过使用ntmpy代码包进行的双温度模型来确定的。对于 FM 相位，我们提供了 FM 相位的电子声子耦合因子大小的边界。这些结果表明 TDTR 可用于研究磁性材料的瞬态特性，否则这些特性很难探测。

更新日期：2024-09-11

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