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"The interesting question here is whether or not the singular angular magnetoresistance can be widely observed in magnetic materials and, if this feature can be ubiquitously observed, what is the key ingredient for engineering the materials with this effect," Suzuki says.
The theoretical model indicates that the singular response may indeed be found in other materials and predicts material properties beneficial for realizing this feature. One of the important ingredients is an electronic structure with a small number of free charges, which occurs in a point-like electronic structure referred to as nodal. The material in this study has so-called Weyl points that achieve this. In such materials, the allowed electron momenta depends on the configuration of the magnetic order. Such control of the momenta of these charges by the magnetic degree of freedom allows the system to support switchable interface regions where the momenta are mismatched between domains of different magnetic order. This mismatch also leads to the large increase in resistance observed in this study.
This analysis is further supported by the first-principles electronic structure calculation performed by Jianpeng Liu, research assistant professor at the HKUST, and Balents. Using more traditional magnetic elements such as iron or cobalt, rather than rare-earth cerium, may offer a potential path to higher temperature observation of the singular angular magnetoresistance effect. The study also ruled out a change in the arrangement of the atoms, called a structural phase transition, as a cause of the change in resistivity of the cerium-based material.
Kenneth Burch, graduate program director and associate professor of physics at Boston College, whose lab investigates Weyl materials, notes: “The discovery of remarkable sensitivity to magnetic angle is a completely unexpected phenomena in this new class of materials. This result suggests not only new applications of Weyl semimetals in magnetic sensing, but the unique coupling of electronic transport, chirality and magnetism.” Chirality is an aspect of electrons related to their spin that gives them either a left-handed or right-handed orientation.
The discovery of this sharp but narrowly confined resistance peak could eventually be used by engineers as a new paradigm for magnetic sensors. Notes Checkelsky, “One of the exciting things about fundamental discoveries in magnetism is the potential for rapid adoptions for new technologies. With the design principles now in hand, we are casting a wide net to find this phenomena in more robust systems to unlock this potential.”
This research was supported in part by the Gordon and Betty Moore Foundation and the National Science Foundation.
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