EuCo2P2: A Model Molecular-Field Helical Heisenberg Antiferromagnet

Abstract: The Eu spins-7/2 in EuCo2P2 with the tetragonal ThCr2Si2-type structure have the prototypical noncollinear helical antiferromagnetic structure below the Neel temperature TN = 66.5 K as previously determined from single-crystal neutron diffraction measurements. The helix axis is along the c axis with the ordered moments aligned within the ab plane. Our recent formulation of molecular field theory (MFT) is found to quantitatively fit the anisotropic magnetic susceptibility of single-crystal EuCo2P2 at T < TN with a helix turn angle comparable to the neutron diffraction value. The experimental and MFT magnetic heat capacities at T < TN are also in good agreement. Values of the Heisenberg exchange interactions between the Eu spins-7/2 within the J0-Jz1-Jz2 MFT model are derived. The results demonstrate the robust applicability of the MFT to model the thermodynamic properties of noncollinear Heisenberg antiferromagnets.