Effective bilinear-biquadratic model for noncoplanar ordering in itinerant magnets
Effective bilinear-biquadratic model for noncoplanar ordering in itinerant magnets
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DOI：
10.1103/physrevb.95.224424
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发表时间：
2017-06-20
影响因子：
3.7
通讯作者：
Motome, Yukitoshi
中科院分区：
文献类型：
--
作者：
Hayami, Satoru;Ozawa, Ryo;Motome, Yukitoshi
非共线和非共面的磁性织构，包括Skyrmions和涡旋作为新兴的电磁场，并产生新的电子和输运性质。我们在这里报告一个统一的理解，从巡游磁铁的自旋-电荷耦合出现的非共面磁序。该机制的根源在于有效的多重自旋相互作用，超越了传统的Ruderman-Kittel-Kasuya-Yosida（RKKY）机制，该机制普遍存在于具有局部磁矩的巡回电子系统中。通过仔细研究高阶微扰的自旋-电荷耦合，我们构建了一个最小的有效自旋模型组成的双线性和双二次相互作用与特定的波数决定的费米面。以二维系统为例，我们发现我们的有效模型捕捉到了最近发现的非共面多Q态不稳定性的基本物理：RKKY理论所预期的单Q螺旋态被具有手征密度波的双Q涡旋晶体所取代，即使在一般晶格上的自旋-电荷耦合是无限小的[R. Ozawa等人，日本物理学会85，103703（2016）]，并且在三角形晶格上增加自旋-电荷耦合的同时出现具有高拓扑数2的三重QSkyrmion晶体[R. Ozawa，S. Hayami和Y. Motome，Phys. Rev. Lett. 118，147205（2017）]。我们发现，通过引入外部磁场，我们的有效模型表现出过多的多Q态。我们的有效模型将作为一个指南，探索进一步的异国情调的磁有序巡回磁铁，不仅在二维空间，而且在三维空间。
Noncollinear and noncoplanar magnetic textures including Skyrmions and vortices act as emergent electromagnetic fields and give rise to novel electronic and transport properties. We here report a unified understanding of noncoplanar magnetic orderings emergent from the spin-charge coupling in itinerant magnets. The mechanism has its roots in effective multiple spin interactions beyond the conventional Ruderman-Kittel-Kasuya-Yosida (RKKY) mechanism, which are ubiquitously generated in itinerant electron systems with local magnetic moments. By carefully examining the higher-order perturbations in terms of the spin-charge coupling, we construct a minimal effective spin model composed of the bilinear and biquadratic interactions with particular wave numbers dictated by the Fermi surface. Taking two-dimensional systems as examples, we find that our effective model captures the underlying physics of the instability toward noncoplanar multiple-Q states discovered recently: a single-Q helical state expected from the RKKY theory is replaced by a double-Q vortex crystal with chirality density waves even for an infinitely small spin-charge coupling on generic lattices [R. Ozawa et al., J. Phys. Soc. Jpn. 85, 103703 (2016)], and a triple-QSkyrmion crystal with a high topological number of two appears while increasing the spin-charge coupling on a triangular lattice [R. Ozawa, S. Hayami, and Y. Motome, Phys. Rev. Lett. 118, 147205 (2017)]. We find that by introducing an external magnetic field, our effective model exhibits a plethora of multiple-Q states. Our effective model will serve as a guide for exploring further exotic magnetic orderings in itinerant magnets, not only in two dimensions but also in three dimensions.