Single-crystal investigation of the proposed type-II Weyl semimetal CeAlGe

Abstract

We present details of materials synthesis, crystal structure, and anisotropic magnetic properties of single crystals of CeAlGe, a proposed type-II Weyl semimetal. Single-crystal x-ray diffraction confirms that CeAlGe forms in noncentrosymmetric I41md space group, in line with predictions of non-trivial topology. Magnetization, specific heat and electrical transport measurements were used to confirm antiferromagnetic order below 5 K, with an estimated magnon excitation gap of ∆ = 9.11 K from heat capacity and hole-like carrier density of 1.44 × 10 20 cm −3 from Hall effect measurements. The easy magnetic axis is along the [100] crystallographic direction, indicating that the moment lies in the tetragonal ab-plane below 7 K. A spin-flop transition to less than 1 µB/Ce is observed to occur below 30 kOe at 1.8 K in the M (H) (H a) data. Small magnetic fields of 3 kOe and 30 kOe are sufficient to suppress magnetic order when applied along the a-and c-axes, respectively, resulting in a complex T-H phase diagram for H a and a simpler one for H c.

Bulk single-crystal growth of the theoretically predicted magnetic Weyl semimetals RAlGe ( R = Pr, Ce)

“…Using a scanning electron microscope (SEM), we performed an EDS analysis on several powder and single-crystal samples prepared by all the above-described methods. This characterization is crucial, since both the structure type and physical property transition temperatures can vary according to small compositional variations of RAl x Ge 2−x [17,21].…”

“…For CeAlGe contradictory results have been published for the magnetic properties; early bulk susceptibility data show the magnetic Ce ions to order below ∼6 K, but the system has been reported to order as a ferromagnet (FM) [20] and an antiferromagnet (AFM) [17]. Most recently, a study on flux-grown CeAlGe single crystals was reported [21], with bulk magnetization measurements evidencing ferromagnetic coupling in one direction, and antiferromagnetic coupling in another, apparently resolving contradictions so far. In more detail, the identified easy axis of [100] suggested antiferromagnetic order in the ab plane.…”

“…Importantly, however, the crystals studied in Ref. [21] were prepared following the same route as reported in Ref. [19], using SiO 2 ampoules.…”

“…As discussed in Refs. [19,21], this choice of ampoule often leads to Si inclusions and a stable coexisting CeAlSi phase, while at the same time, samples that are even slightly Al-rich can lead to different crystal structures that maintain SI symmetry [17,21], thus greatly limiting the propensity for the formation of topological Weyl nodes. Therefore, a stoichiometric analysis is necessary to ensure the intended 1:1:1 stoichiometry of RAlGe is achieved, and we will show that this is less likely to be achieved in flux-grown samples compared with crystals grown by the floating-zone method.…”

Seeing is believing: visualization of antiferromagnetic domains

“…[10][11][12][13][14] It turns out that many of these multiferroics and topological magnets are AFM. 5,[10][11][12][14][15][16][17] Spintronics where spin and charge degrees of freedom are mutually coupled and manipulated through crossing conjugate fields (i.e. electric fields for spins and magnetic fields for charges) has been an active research area for the last three decades since the discovery of giant magnetoresistance, and has been well implemented in real devices.…”