CeRhIn$_5$ is a prototypical antiferromagnetic heavy-fermion compound, whose behavior in a magnetic field is unique. A magnetic field applied in the basal plane of the tetragonal crystal structure induces two additional phase transitions. When the magnetic field is applied along, or close to, the $c$ axis, a new phase characterized by a pronounced in-plane electronic anisotropy emerges at $B^* \approx$ 30 T, well below the critical field, $B_c \simeq$ 50 T, to suppress the antiferromagnetic order. The exact origin of this new phase, originally suggested to be an electronic-nematic state, remains elusive. Here we report low-temperature specific-heat measurements in CeRhIn$_5$ in high static magnetic fields up to 36 T applied along both the $a$ and $c$ axes. For fields applied along the $a$ axis, we confirmed the previously suggested phase diagram, and extended it to higher fields. This allowed us to observe a triple point at $\sim$ 30 T, where the first-order transition from an incommensurate to commensurate magnetic structure merges into the onset of the second-order antiferromagnetic transition. For fields applied along the $c$ axis, we observed a small but distinct anomaly at $B^*$, which we discuss in terms of a possible field-induced transition, probably weakly first-order. We further suggest that the transition corresponds to a change of magnetic structure. We revise magnetic phase diagrams of CeRhIn$_5$ for both principal orientations of the magnetic field based entirely on thermodynamic anomalies.
Heat capacity studies of Ce and Rh site substitution in the heavy fermion antiferromagnet CeRhIn_5;: Short-range magnetic interactions and non-Fermi-liquid behavior
Magnetic Properties of the low dimensional BaM$_2$Si$_2$O$_7$(M= Cu, Co, Mn) system
我们对单晶BaMn $_2$ Si $_2$ O $_7$进行了磁化率、磁化强度、比热和单晶中子衍射测量。在此基础上，我们重新研究了它的自旋结构，得到了更精确的解，并构造了磁场沿$b$轴的磁相图，其中包含了约6 T的自旋翻转跃迁.我们还利用磁化率、磁化强度和比热结果证实了多晶BaCo $_2$ Si $_2$ O $_7$中的类亚铁磁性。此外，我们进行了LSDA + U计算的BaM $_2$ Si $_2$ O $_7$（M = Cu，Co，Mn）系统。通过对所获得的磁交换相互作用的比较，我们认为不同的结构和电子构型是导致系统成员间磁性质不同的原因。
