Zero-field magnetic ground state of EuMg2Bi2

Abstract

Layered trigonal EuMg 2 Bi 2 is reported to be a topological semimetal that hosts multiple Dirac points that may be gapped or split by the onset of magnetic order. Here, we report zero-field single-crystal neutron-diffraction and bulk magnetic susceptibility measurements versus temperature χ (T) of EuMg 2 Bi 2 that show the intraplane ordering is ferromagnetic (Eu 2+ , S = 7/2) with the moments aligned in the ab plane while adjacent layers are aligned antiferromagnetically (i.e., A-type antiferromagnetism) below the Néel temperature.

A-type antiferromagnetic order and magnetic phase diagram of the trigonal Eu spin-7/2 triangular-lattice compound EuSn2As2

“…In particular, we find here that with increasing ab-plane field M ab becomes nearly independent of H for H 0.125 T. A similar result was interpreted in Ref. [48] as possibly arising from the spins rotating with increasing H ab to be perpendicular to H, which gives χ ab (T ≤ T N )/χ(T N ) ≈ χ c (T ≤ T N )/χ(T N ) ≈ 1 as also observed here.…”

“…( 6) is shown in Fig. 8 These χ α (H, T ≤ T N ) results are similar to those we observed previously for the trigonal compound EuMg 2 Bi 2 containing stacked triangular lattices of Eu 2+ spins S = 7/2 [47] where the magnetic structure in H = 0 was also found by neutron-diffraction measurements to be A-type AFM with the Eu moments aligned in the ab plane [48]. In particular, we find here that with increasing ab-plane field M ab becomes nearly independent of H for H 0.125 T. A similar result was interpreted in Ref.…”

“…The χ c (T ) below T N is nearly independent of T as expected from molecular-field theory (MFT) for crystallographically-equivalent Heisenberg ordered moments aligned in the ab plane [45,46]. On the other hand, the χ ab (T ) data decrease rapidly and attain a minimum value yielding the ratio χ ab,min /χ(T N ) ≈ 1/2, which is indeed the value expected for an A-type Heisenberg antiferromagnet on a triangular lattice with moments aligned in the ab plane within equally-populated three-fold domains [25].…”

“…Rare-earth intermetallic compounds are of considerable interest due to the observations of complex magnetism, superconductivity, heavy-fermion behavior, Kondo effect, valence fluctuation, large magnetocaloric effect, magnetoresistance, and quantum criticality [1][2][3][4][5][6][7][8][9][10][11][12][13][14]. Besides 4f -element magnetism, many rare-earth-based intermetallics have expanded in a new direction by hosting novel electronic states through a complex interplay of magnetism and band topology [15][16][17][18][19][20][21][22][23][24][25]. This interplay has generated immense interest due to the discovery of nontrivial quantum phenomena such as anomalous quantum Hall effect (AQHE), axion electrodynamics, and realization of relativistic particles like Majorana fermions [26][27][28][29][30][31][32][33][34][35][36].…”

Intrinsic exchange bias state in silicene and germanene materials EuX2

“…Layered compounds alternating such cationic Eu layers and covalent anionic layers typically demonstrate a particular type of spin configuration -A-type AFM structure with in-plane magnetic moments, formed by FM layers coupled antiferromagnetically along the c-axis. [52][53][54] The in-plane FM interactions in such layered structures are expected to be much stronger than the interlayer magnetic interactions. 53,55 It suggests that the magnetic ordering along the c-axis is not robust with respect to change of the spin configuration.…”