Spin reorientation of the Fe moments in Eu0.5Ca0.5Fe2As2 : Evidence for strong interplay of Eu and Fe magnetism (original) (raw)

Helical spin order in EuFe2As2 and EuRbFe4As4 single crystals

2021

In this work, fabrication and characterization of magnetic properties of EuFe2As2 and EuRbFe4As4 single crystals is reported. Magnetization measurements of samples with well defined thin film geometry and crystal orientation demonstrate a striking similarity in ferromagnetic properties of Eu subsystems in these two compounds. Measurements with magnetic field applied along ab crystal planes reveal meta-magnetic transition in both compounds. Numerical studies employing the Jz1 and Jz2 Heisenberg model suggest that the ground state of the magnetic order in Eu subsystem for both compounds is the helical spin order with the helical angle about 2π/5, while the meta-magnetic transition is the helix-to-fan first order phase transition. Introduction The new class of ferromagnetic superconductors based on EuFe2As2 parent compound is a unique playground in material science and solid state physics due to accessible temperatures for the coexistence of superconducting and ferromagnetic orders on ...

The EuFe2As2 magnetic state peculiarities as revealed by ESR

The magnetic state of the EuFe2As2 single crystal was investigated by means of electron spin resonance (ESR). ESR spectra of europium ions were obtained in the temperature range from 250 K to 4 K. To study the anisotropy, the in-plane angular dependences were obtained at temperatures of 15 K upon rotating a crystal around c-axis. The data analysis has shown that EuFe2As2 is an antiferromagnet with an easy anisotropy plane. Moreover, the second-order easy magnetization axis is observed for each of the two types of magnetic domains connected to structure twins arising from the tetragonal-to-orthorhombic crystal lattice transition.

Magnetic and structural properties of Co-substituted single crystal EuFe_1.9Co_0.1As_2

The magnetic and structural properties of single crystal EuFe_1.9Co_0.1As_2 were studied by combining X-ray diffraction, magnetization, and 75As NMR measurements. The strength of the hyperfine interaction between the 75As nuclei and the Eu^(2+) 4f states suggests a strong coupling between the Eu and Fe_1.9Co_0.1As_2 layers. Such a strong interlayer coupling may be due to an indirect exchange interaction between the localized Eu^(2+) 4f moments, mediated by the Fe 3d conduction electrons. We found that Co-substitution of this system leads to an enhancement of the tetragonal-orthorhombic (TO) structural transition temperature T_str, while the spin density wave (SDW) ordering temperature is suppressed. As a result, in EuFe_2As_2 the strongly coupled SDW and TO transitions are split into two distinct transitions, like in BaFe_(2-x)Co_xAs_2. The fact that T_str increases with Co-substitution is in contrast to the general view that the structural transition temperature is suppressed upon ...