The helimagnet FeP is part of a family of binary pnictide materials with the MnP-type structure, which share a nonsymmorphic crystal symmetry that preserves generic band structure characteristics through changes in elemental composition. It shows many similarities, including in its magnetic order, to isostructural CrAs and MnP, two compounds that are driven to superconductivity under applied pressure. Here we present a series of high magnetic field experiments on high-quality single crystals of FeP, showing that the resistance not only increases without saturation by up to several hundred times its zero-field value by 35 T, but that it also exhibits an anomalously linear field dependence over the entire range when the field is aligned precisely along the crystallographic c-axis. A close comparison of quantum oscillation frequencies to electronic structure calculations links this orientation to a semi-Dirac point in the band structure, which disperses linearly in a single direction in the plane perpendicular to field, a symmetry-protected feature of this entire material family. We show that the two striking features of magnetoresistance—large amplitude and linear field dependence—arise separately in this system, with the latter likely due to a combination of ordered magnetism and topological band structure.

螺旋磁体 FeP 是具有 MnP 型结构的二元磷化物材料家族的一部分，该材料具有非对称晶体对称性，可通过元素组成的变化保留通用能带结构特征。它与同质结构的 CrAs 和 MnP 显示出许多相似之处，包括在磁序方面，这两种化合物在施加压力下会被驱动为超导性。在这里，我们对高质量 FeP 单晶进行了一系列高磁场实验，结果表明，电阻不仅在不饱和的情况下增加了 35 T 的零场值的数百倍，而且还表现出异常的变化。当场沿晶体c轴精确排列时，整个范围内的线性场依赖性。量子振荡频率与电子结构计算的密切比较将这个方向与能带结构中的半狄拉克点联系起来，该点在垂直于场的平面中沿单个方向线性分散，这是整个材料家族的对称保护特征。我们表明，磁阻的两个显着特征——大振幅和线性场依赖性——分别出现在该系统中，后者可能是由于有序磁性和拓扑能带结构的组合所致。