论文标题
低能量木元素,各向异性热传导和立方helimagnet Zncr2se4中磁性域的自发放松的磁场依赖性
Magnetic-field dependence of low-energy magnons, anisotropic heat conduction, and spontaneous relaxation of magnetic domains in the cubic helimagnet ZnCr2Se4
论文作者
论文摘要
通过中子散射,导热率,超声速度和扩张测量值的组合研究了单域旋转螺旋态在单域旋转螺旋状态中的各向异性低温特性。在应用的磁场中,中子光谱显示出跨量子临界点的自旋波光谱的复杂且非单调的演化,该光谱将自旋 - 螺旋相位与高场处的磁极极化相位。在结构等效但与旋转螺旋的传播载体正交的波矢量上观察到的伪石镁模式的微小自旋间隙在此量子临界点上消失,从而恢复了磁性子系统中的立方体对称性。旋转螺旋施加的各向异性对晶格结构和声速只有很小的影响,但对平行和垂直于磁传播载体的热电导率具有更强的影响。热传输在T <2 K处是各向异性,对外部磁场高度敏感,可能直接来自宏伟的热传导。我们还报告了由电容扩张法揭示的长期热弛豫现象,这是由于与单域磁态破坏有关的磁性域运动引起的,该运动最初是通过应用和去除磁场在样品中稳定的。我们的结果可以推广到一类众多的helimagnetic材料中,其中磁性离散的晶格对称性会自发打破。
Anisotropic low-temperature properties of the cubic spinel helimagnet ZnCr2Se4 in the single-domain spin-spiral state are investigated by a combination of neutron scattering, thermal conductivity, ultrasound velocity, and dilatometry measurements. In an applied magnetic field, neutron spectroscopy shows a complex and nonmonotonic evolution of the spin-wave spectrum across the quantum-critical point that separates the spin-spiral phase from the field-polarized ferromagnetic phase at high fields. A tiny spin gap of the pseudo-Goldstone magnon mode, observed at wave vectors that are structurally equivalent but orthogonal to the propagation vector of the spin helix, vanishes at this quantum critical point, restoring the cubic symmetry in the magnetic subsystem. The anisotropy imposed by the spin helix has only a minor influence on the lattice structure and sound velocity but has a much stronger effect on the heat conductivities measured parallel and perpendicular to the magnetic propagation vector. The thermal transport is anisotropic at T < 2 K, highly sensitive to an external magnetic field, and likely results directly from magnonic heat conduction. We also report long-time thermal relaxation phenomena, revealed by capacitive dilatometry, which are due to magnetic domain motion related to the destruction of the single-domain magnetic state, initially stabilized in the sample by the application and removal of magnetic field. Our results can be generalized to a broad class of helimagnetic materials in which a discrete lattice symmetry is spontaneously broken by the magnetic order.