AI 中文总结
该研究针对MnF₂的弱交替磁交换争议，通过第一性原理确定第七近邻不平衡尺度，利用纵向场放大效应实现两种可探测的读出方式，使μeV级交替磁交换可被现有仪器测量。
AI 中文摘要
MnF₂作为经典的双亚晶格反铁磁体，已重新成为原型交替磁体，但定义其属性的亚晶格奇交换仍存在争议：该交换仅与偶极-偶极相互作用正交时才会进入磁振子分裂，其大小被抑制且符号被抹去。通过超定第一性原理总能量映射，确定该交换的尺度为第七近邻不平衡δJ₇≈+8 μeV。包含偶极-偶极相互作用的哈密顿量可重现低能隙和可见的有限动量分裂。纵向场B∥c作为该隐藏尺度的线性放大器，产生两个带符号的场线性读出：第一个是补偿场B*(Q)，即分裂最小值的位置，在旋转相关的配对动量处大小相等、方向相反，其从零场的偏移本身就是有限不平衡的证据，偏移侧给出符号，大小| B* |≈0.34 T给出尺度；第二个是固定场下配对分裂的对比度，在1 T时约为0.14 meV，是零场过剩的6倍，仅需两个光谱即可完成符号验证。两种读出方式在0.12 meV的能量分辨率下均有效，该构造可推广至所有易轴共线交替磁体，使μeV级的交替磁交换可被现有仪器探测。
英文摘要
MnF$_2$, the textbook two-sublattice antiferromagnet, has reemerged as a prototypical altermagnet, yet the sublattice-odd exchange that defines this identity remains under active debate: it enters the magnon splitting only in quadrature with the dipole--dipole interaction, its magnitude suppressed and its sign erased. An overdetermined first-principles total-energy mapping resolves this scale as a seventh-neighbor imbalance $δ{J_7}\simeq+8~μ$eV. The resulting Hamiltonian, with the dipole--dipole interaction included explicitly, reproduces the low-energy gap and the visible finite-momentum splitting. A longitudinal field $B\parallel c$ then acts as a linear amplifier of the hidden scale, opening two signed, field-linear readouts. The first is the compensation field $B^\ast(\mathbf Q)$, the position of minimum splitting, which is equal and opposite at the rotation-related partner momenta: a shift from zero field is itself evidence of a finite imbalance, its side gives the sign, and its magnitude, $|B^\ast|\simeq0.34$~T here, gives the scale. The second is the fixed-field contrast of the partner splittings, $\simeq0.14$~meV at $1$~T, six times the zero-field excess: a sign check from just two spectra. Both readouts survive a $0.12$~meV energy resolution, and the construction carries over to any easy-axis collinear altermagnet, bringing $μ$eV altermagnetic exchange within present instrumental reach.
CommentsFig. S1 updated
