论文标题
NDB $ _4 $的磁弹性耦合和Grüneisen缩放
Magnetoelastic coupling and Grüneisen scaling in NdB$_4$
论文作者
论文摘要
我们报告了关于NDB $ _4 $单晶的单轴长度变化的高分辨率电容扩张学研究。磁有序阶段以下$ t _ {\ rm n} $ = 17.2〜K（相称的反铁磁相，CAFM），$ t _ {\ rm it} $ = 6.8〜k（Intermedimed Inmedimed Issurate阶段，IT）和$ t _ {在热膨胀系数中有明显的异常。数据暗示着明显的磁弹性耦合和在$ t _ {\ rm lt} $处的结构相变的证据。虽然CAFM和LT都均均受面式内部和非平面长度变化之间的结构各向异性$δ$，但它与订单的IT型竞争，即在该阶段被抑制$δ$。值得注意的是，有限各向异性远高于$ t _ {\ rm n} $表示短范围的相关性，但是，CAFM，IT和LT-type均不为CAFM。 Grüneisen对热膨胀系数和比热比率的分析可以使单轴和静水压力依赖性衍生。虽然$α$/$ c _ {\ rm p} $在LT中证明了单个主要能量量表，但我们的数据分别表示IT和CAFM中竞争阶段的前保性波动。我们的结果表明，存在与CAFM竞争的轨道自由度以及磁性和轨道有序的基态的连续演变。
We report high-resolution capacitance dilatometry studies on the uniaxial length changes in a NdB$_4$ single crystal. The evolution of magnetically ordered phases below $T_{\rm N}$= 17.2~K (commensurate antiferromagnetic phase, cAFM), $T_{\rm IT}$= 6.8~K (intermediate incommensurate phase, IT), and $T_{\rm LT}$= 4.8~K (low-temperature phase, LT) is associated with pronounced anomalies in the thermal expansion coefficients. The data imply significant magneto-elastic coupling and evidence of a structural phase transition at $T_{\rm LT}$ . While both cAFM and LT favor structural anisotropy $δ$ between in-plane and out-of-plane length changes, it competes with the IT-type of order, i.e., $δ$ is suppressed in that phase. Notably, finite anisotropy well above $T_{\rm N}$ indicates short-range correlations which are, however, of neither cAFM, IT, nor LT-type. Grüneisen analysis of the ratio of thermal expansion coefficient and specific heat enables the derivation of uniaxial as well as hydrostatic pressure dependencies. While $α$/$c_{\rm p}$ evidences a single dominant energy scale in LT, our data imply precursory fluctuations of a competing phase in IT and cAFM, respectively. Our results suggest the presence of orbital degrees of freedom competing with cAFM and successive evolution of a magnetically and orbitally ordered ground state.
