Helical magnetic ordering studied in single-crystalline GdBe13

Abstract

The beryllide ${\mathrm{GdBe}}_{13}$ with the ${\mathrm{NaZn}}_{13}$-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 ${\mathrm{GdBe}}_{13}$ 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 ${\mathrm{Gd}}^{3+}$ moments at ${T}_{\mathrm{N}}$ = 24.8 K accompanied with strong magnetic fluctuations extending to temperatures well above ${T}_{\mathrm{N}}$. Furthermore, we constructed a magnetic field--temperature ($B$--$T$) phase diagram for $B\phantom{\rule{4pt}{0ex}}\ensuremath{\parallel}$ [001]. It consists of a multidomain state, which is composed of magnetic structures with $B$ applied parallel and perpendicular to the helical plane, in the lower-magnetic-field region below $\ensuremath{\sim}0.45\phantom{\rule{0.16em}{0ex}}\mathrm{T}$ and a possible single-domain conical one in the higher-field region in the ordering state. The helical structure of ${\mathrm{GdBe}}_{13}$ characterized by an incommensurate ordering vector ${\mathbit{q}}_{0}$ of (0, 0, 0.285) is discussed on the basis of a competition of Heisenberg exchange interactions between the ${\mathrm{Gd}}^{3+}$ 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 ${B}_{\mathrm{c}}$ than the experimentally obtained one. To discuss the deviation of ${B}_{\mathrm{c}}$ from the MF calculation, we show a possibility of a fluctuation-induced first-order transition.