Magnetic phase diagram of CeAu2Ge2: High magnetic anisotropy due to crystal electric field

Abstract

CeAu 2 Ge 2 single crystals (with tetragonal ThCr 2 Si 2 structure) have been grown in Au-Ge flux (AGF) as well as in Sn flux (SF). X-ray powder diffraction and EDX measurements indicate that in the latter case, Sn atoms from the flux are incorporated in the samples, leading to a decrease of the lattice constants by ≈0.3% compared to AGF samples. For both types of samples, a strong anisotropy of the magnetization M for the magnetic field B parallel and perpendicular to the c direction is observed with M || /M ⊥ ≈ 6-7 in low fields just above 10 K. This anisotropy is preserved to high fields and temperatures and can be quantitatively explained by crystal electric field effects. Antiferromagnetic ordering sets in around 10 K as previously found for polycrystalline samples. From the magnetization data of our single crystals we obtain the phase diagrams for the AGF and SF samples. The magnetic properties depend strongly on the flux employed. While the AGF samples exhibit a complex behavior indicative of several magnetic transitions, the SF samples adopt a simpler antiferromagnetic structure with a single spin-flop transition. This effect of a more ordered state induced by disorder in form of Sn impurities is qualitatively explained within the anisotropic next-nearest neighbor Ising (ANNNI) model, which assumes ferromagnetic and antiferromagnetic interactions in agreement with the magnetic structure previously inferred from neutron-scattering experiments on polycrystalline CeAu 2 Ge 2 by Loidl et al. [Phys. Rev. B 46, 9341 (1992)].

Ising-type Magnetic Anisotropy in CePd2As2

“…Their magnetism is commonly determined by a large magneto-crystalline anisotropy. This leads to the presence of distinct field-induced metamagnetic transitions [8][9][10][11][12][13][14][15] . Depending on the strength of the magnetic anisotropy, the nature of the metamagnetic transition(s) may differ.…”

CeIr3Ge7: A local moment antiferromagnetic metal with extremely low ordering temperature

“…If the hybridization between f electrons and conduction electrons is very weak, the ground states of these systems are dictated by RKKY exchange interaction and crystal electric field (CEF) effects, resulting in long-range magnetic order. [14][15][16] In the case of the Ce local moment metals without the Kondo effect, the ordering temperatures range from T C = 115 K 17,18 in ferromagnetic CeRh 3 B 2 , to T N = 2.75 K 19 in antiferromagnetic (AFM) CeSbTe, while much lower temperatures can be expected for the Yb analogues 20 . Lower ordering temperatures in both Ce 3+ and Yb 3+ compounds could occur from any combination of effects including Kondo, competition between different exchange interactions, strong CEF anisotropy, or large distances between rare-earth ions (d R−R ) that minimize the RKKY exchange coupling J RKKY .…”

Multiple magnetic structures of correlated Ce ions in intermetallic CeAu2Ge2

“…The magnetic susceptibility of CeAu 2 Ge 2 exhibits strong anisotropy with an easy [001] direction perpendicular to the tetragonal plane. 16,17 Previous measurements on a powder of CeAu 2 Ge 2 showed that the correlated Ce-ions develop a long range antiferromagnetic order below T N 16 K. 13 In this article, we report elastic neutron scattering measurements on a high quality single crystal sample of CeAu 2 Ge 2 . The crystals were synthesized by high temperature solution growth method using Bi flux and the quality was verified using X-ray measurements.…”

“…13,16,17 However, as the sample is cooled below 10 K new magentic peaks start appearing with different temperature dependencies. As shown in the series of plots in Fig.…”