Multiferroic Ba₂CuGe₂O₇ was anticipated as a potential member of the exciting group of materials hosting a skyrmion or vortex lattice because of its profound Dzyaloshinskii–Moriya interaction (DMI) and the absence of single ion anisotropy (SIA). This phase, however, could not be evidenced and instead, it exhibits a complex incommensurate antiferromagnetic (AFM) cycloidal structure. Its sister compound Ba₂MnGe₂O₇, in contrast, is characterized by a relatively strong in-plane exchange interaction that competes with a non-vanishing SIA and the weak DMI, resulting in a quasi-two-dimensional commensurate AFM structure. Considering this versatility in the magnetic interactions, a mixed solid solution of Cu and Mn in Ba₂Cu_1−xMn_xGe₂O₇ can hold an interesting playground for its interactive DMI and SIA depending on the mixed spin states of the transition metal ions towards the skyrmion physics. Here, we present a detailed study of the micro- and macroscopic spin structure of the Ba₂Cu_1−xMn_xGe₂O₇ solid solution series using high-resolution neutron powder diffraction techniques. We have developed a remarkably rich magnetic phase diagram as a function of the applied magnetic field and x, which consists of two end-line phases separated by a potentially quantum-critical phase at x = 0.57. An AFM conical structure at zero magnetic field is demonstrated to persist up to x = 0.50. Our results provide crucial information on the spin structure and magnetic properties, which are necessary for the general understanding and theoretical developments on multiferroicity in the frame of skyrmion type or frustrated AFM lattice where DMI and SIA play an important role.

多铁性 Ba ₂ CuGe ₂ O ₇由于其深刻的 Dzyaloshinskii-Moriya 相互作用 (DMI) 且不存在单离子各向异性 (SIA)，因此被认为是具有斯格明子或涡旋晶格的令人兴奋的材料组的潜在成员。然而，这个阶段无法被证实，相反，它表现出复杂的不相称反铁磁（AFM）摆线结构。相比之下，其姊妹化合物Ba ₂ MnGe ₂ O ₇的特点是具有相对较强的面内交换相互作用，与非消失的SIA和弱DMI竞争，从而产生准二维相称的AFM结构。考虑到磁相互作用中的这种多功能性，Ba ₂ Cu _{1− x} Mn _x Ge ₂ O ₇中的 Cu 和 Mn 混合固溶体可以为其交互式 DMI 和 SIA 提供一个有趣的游乐场，具体取决于过渡金属的混合自旋态离子走向斯格明子物理。在这里，我们使用高分辨率中子粉末衍射技术对 Ba ₂ Cu _{1 − x} Mn _x Ge ₂ O ₇固溶体系列的微观和宏观自旋结构进行了详细研究。我们开发了一个非常丰富的磁相图，作为施加磁场和x的函数，它由两个端线相组成，这两个端线相被x = 0.57 处的潜在量子临界相分开。零磁场下的 AFM 锥形结构被证明可以持续到x = 0.50。 我们的结果提供了有关自旋结构和磁特性的重要信息，这对于斯格明子型或受挫 AFM 晶格框架中多铁性的一般理解和理论发展是必要的，其中 DMI 和 SIA 发挥着重要作用。