Helical Magnetic Ordering Studied In Single-Crystalline Gdbe13

The beryllide GdBe13 with the NaZn13-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 GdBe13 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 Gd3+ moments at T-N = 24.8 K accompanied with strong magnetic fluctuations extending to temperatures well above T-N. Furthermore, we constructed a magnetic field-temperature (B-T) phase diagram for B parallel to [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 similar to 0.45 T and a possible single-domain conical one in the higher-field region in the ordering state. The helical structure of GdBe(13 )characterized by an incommensurate ordering vector q(0) of (0, 0, 0.285) is discussed on the basis of a competition of Heisenberg exchange interactions between the Gd3+ 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-c than the experimentally obtained one. To discuss the deviation of B-c from the MF calculation, we show a possibility of a fluctuation-induced first-order transition.