Helical antiferromagnetic ordering in EuNi_1.95As₂ single crystals

Journal Article · 23 September 2019 · Physical Review B

DOI: https://doi.org/10.1103/PhysRevB.100.094438 · OSTI ID:1570835

Sangeetha, N. S. ^[1]; Smetana, V.  ^[2]; Mudring, A. -V. ^[2]; Johnston, D. C.  ^[3]

---

1. Ames Lab., and Iowa State Univ., Ames, IA (United States)
2. Stockholm Univ. (Sweden)
3. Ames Lab., and Iowa State Univ., Ames, IA (United States). Dept. of Physics and Astronomy

The Eu^{+ 2} spins-7/2 in EuNi₂ As₂ with the body-centered tetragonal ThCr₂ Si₂ structure order antiferromagnetically below the Néel temperature T_N = 15 K into a helical antiferromagnetic (AFM) structure with the helix axis aligned along the tetragonal c axis and the Eu ordered moments aligned ferromagnetically within the ab plane as previously reported from neutron diffraction measurements [T. Jin et al., Phys. Rev. B 99, 014425 (2019)]. Here we study the crystallographic, magnetic, thermal, and electronic transport properties of Bi-flux-grown single crystals using single-crystal x-ray diffraction, anisotropic magnetic susceptibility χ, isothermal magnetization M, heat capacity Cp, and electrical resistivity ρ measurements versus applied magnetic field H and temperature T. Vacancies are found on the Ni sites corresponding to the composition EuNi_{1.95 (1)} As 2. A good fit of the ρ (T) data by the Bloch-Grüneisen theory for metals was obtained. The _χab (T) data below T_N are fitted well by molecular field theory (MFT), and the helix turn angle kd and the Eu-Eu Heisenberg exchange constants are extracted from the fit parameters. The kd value is in good agreement with the neutron-diffraction result. The magnetic contribution to the zero-field heat capacity below T_N is also fitted by MFT. The isothermal in-plane magnetization M_ab exhibits two metamagnetic transitions versus H, whereas M_c (T = 2 K ) is nearly linear up to H = 14 T, both behaviors being consistent with MFT. The M_c (H, T) , ρ(H_c, T) , and Cp (H _c , T) data yielded a H_c- T phase diagram separating the AFM and paramagnetic phases in good agreement with MFT. Anisotropic χ(T) literature data for the ThCr ₂ Si₂ -type helical antiferromagnet EuRh₂ As₂ were also fitted well by MFT. A comparison is made between the crystallographic and magnetic properties of ThCr₂ Si₂-type Eu M₂ Pn₂ compounds with M = Fe , Co, Ni, Cu, or Rh, and Pn = P or As, where only ferromagnetic and c -axis helical AFM structures are found.

• Research Organization: Ames Laboratory (AMES), Ames, IA (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
• Grant/Contract Number: AC02-07CH11358
• OSTI ID: 1570835
• Report Number(s): IS-J--10052
• Journal Information: Physical Review B, Journal Name: Physical Review B Journal Issue: 9 Vol. 100; ISSN 2469-9950; ISSN PRBMDO
• Publisher: American Physical Society (APS)Copyright Statement
• Country of Publication: United States
• Language: English