Abstract
The beryllide with the -type face-centered-cubic structure has been known to undergo a proper helical-magnet ordering from experimental studies using polycrystalline samples. In the present study, we carried out electrical resistivity, specific heat, and magnetization measurements of single-crystalline in order to investigate a mechanism of its helical ordering. These measurements reveal that the present compound is a metallic system exhibiting the magnetic ordering of local moments at = 24.8 K accompanied with strong magnetic fluctuations extending to temperatures well above . Furthermore, we constructed a magnetic field–temperature (–) phase diagram for [001]. It consists of a multidomain state, which is composed of magnetic structures with applied parallel and perpendicular to the helical plane, in the lower-magnetic-field region below and a possible single-domain conical one in the higher-field region in the ordering state. The helical structure of characterized by an incommensurate ordering vector of (0, 0, 0.285) is discussed on the basis of a competition of Heisenberg exchange interactions between the moments assuming an one-dimensional layer crystal. The sequential change in the exchange interactions determined by a mean-field (MF) calculation can be essentially understood by the Ruderman-Kittel-Kasuya-Yosida interaction via anisotropic Fermi surfaces, whereas the orientation of the magnetic moments will be determined by the dipole-dipole interaction. On the other hand, the MF theory predicts a much smaller critical field than the experimentally obtained one. To discuss the deviation of from the MF calculation, we show a possibility of a fluctuation-induced first-order transition.
5 More- Received 3 June 2020
- Accepted 20 October 2020
DOI:https://doi.org/10.1103/PhysRevB.102.174408
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