2017/07/31 by David C. Johnston, D. C. Johnston · 40 citations
Chemistry · Materials Science · Physics and Astronomy · #Chemistry #Condensed matter physics #Crystallography #Geometry #Helix (gastropod) #Iron-based superconductors research #Magnetic and transport properties of perovskites and related materials #Magnetic field #Magnetic moment #Magnetization #Perpendicular #Physics #Physics of Superconductivity and Magnetism #Quantum mechanics #cond-mat.str-el
paper · pdf · doi:10.1103/physrevb.96.104405
published in Physical review. B./Physical review. B 96(10) (American Physical Society) · 29 pages, 32 figures, 4 tables; v2: minor corrections, published version
openalex publication_date 2017/09/05 · arxiv created 2017/09/06 · arxiv updated 2017/10/12 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
The zero-temperature angles of magnetic moments in a helix or sinusoidal fan confined to the xy plane, with respect to an in-plane magnetic field Hx applied perpendicular to the z axis of a helix or fan, are calculated for commensurate helices and fans with field-independent turn angles kd between moments in adjacent layers of the helix or fan using the classical J0\text\ensuremath-J1\text\ensuremath-J2 Heisenberg model. For 0<kd<4\ensuremathπ/9, first-order transitions from helix to a fan structure occur at fields Ht as previously inferred, where the fan is found to be approximately sinusoidal. However, for 4\ensuremathπ/9\ensuremath≤kd\ensuremath≤\ensuremathπ, different behaviors are found depending on the value of kd and these properties vary nonmonotonically with kd. In this kd range, the change from helix to fanlike structure is usually a crossover with no phase transition between them, although first-order transitions are found for kd=3\ensuremathπ/5 and 8\ensuremathπ/11 and a second-order transition for kd=3\ensuremathπ/4. At a critical field Hc, the fan or fanlike structures exhibit a second-order transition to the paramagnetic state. The Hc for a helix undergoing a field-induced change to a fan or fanlike structure is found to be the same as for a sinusoidal fan with the same kd and interlayer interactions. Analytical expressions for Hc versus kd are presented. We also calculated the average x-axis moment per spin \ensuremathμxave versus Hx for helices and fans with crossovers and phase transitions between them. When smooth helix to fanlike crossovers occur in the range 4\ensuremathπ/9\ensuremath≤kd\ensuremath≤\ensuremathπ,\phantom\rule0.16em0ex\ensuremathμxave exhibits an S-shape behavior with increasing Hx. This predicted behavior is consistent with \ensuremathμxave(Hx) data previously reported by Sangeetha et al. [Phys. Rev. B 94, 014422 (2016)] for single-crystal EuCo2P2 possessing a helix ground state with kd\ensuremath≈0.85\ensuremathπ. The low-field magnetic susceptibility and the ratio Ht/Hc are calculated analytically or numerically versus kd for helices, and are shown to approach the respective known limits for kd\ensuremath→0.