The theory of quantum order-by-disorder (QOBD) explains the formation of modulated magnetic states at the boundary between ferromagnetism and paramagnetism in zero field. PrPtAl has been argued to provide an archetype for this. Here, we report the phase diagram in magnetic field, applied along both the easy $a$-axis and hard $b$-axis. For field aligned to the $b$-axis, we find that the magnetic transition temperatures are suppressed and at low temperature there is a single modulated fan state, separating an easy $a$-axis ferromagnetic state from a field polarised state. This fan state is well explained with the QOBD theory in the presence of anisotropy and field. Experimental evidence supporting the QOBD explanation is provided by the large increase in the $T^2$ coefficient of the resistivity and direct detection of enhanced magnetic fluctuations with inelastic neutron scattering, across the field range spanned by the fan state. This shows that the QOBD mechanism can explain field induced modulated states that persist to very low temperature.
Cycloidally modulated magnetic order stabilized by thermal fluctuations in the Néel-type skyrmion host GaV$_4$S$_8$
我们报告的小角中子散射研究的空隙尖晶石GaV $_4$ S $_8$，揭示了长波长的磁状态是摆线调制。这为最近声称存在于该化合物中的Néel型skyrmions的形成提供了直接支持。与所有其他大块Skyrmion基质材料形成鲜明对比的是，在冷却时，调制的磁性状态转变为铁磁状态。这些结果表明，GaV $_4$ S $_8$中的所有调制态，包括Skyrmion态，都能从热涨落中获得稳定性，而在较低温度下，铁磁态的出现符合强易轴磁各向异性。在铁磁态和调制态之间的过渡附近，我们的研究也证明了相位共存和类孤子状态。
Realization of the Axial Next-Nearest-Neighbor Ising model in U$_3$Al$_2$Ge$_3$
本文报道了U $_3$ Al $_2$ Ge $_3$的小角中子散射（SANS）测量和理论模型。对SANS数据的分析表明，在$T_{\mathrm{N}}=63$ ~K处发生了向正弦调制磁有序的相变，为二阶相变，在$T_{\mathrm{c}}=48$ ~K处发生了向铁磁有序的一阶相变。在正弦调制的磁相位（$T_{\mathrm{c}} < T < T_{\mathrm{N}}$），我们发现了一个戏剧性的变化，由三个因素，在有序波矢量作为温度的函数。这些观察都表明，U $_3$铝$_2$锗$_3$是一个密切实现的三维轴向次近邻伊辛模型，一个原型框架，用于描述相称的不相称的相变在挫折磁铁。
Strain-enhanced edge ferromagnetism and bipolar magnetic semiconducting behavior in Janus graphene nanoribbons
School of Physics and Astronomy, and Key Laboratory of Multiscale Spin Physics (Ministry of Education), Beijing Normal University（北京师范大学物理与天文学院，多尺度自旋物理教育部重点实验室）；School of Physics and Electronics, Shandong Normal University（山东师范大学物理与电子科学学院）
