Magnetic Properties of Heisenberg Antiferromagnetic EuTe/PbTe Superlattices

Abstract

High quality MBE-grown EuTe/PbTe superlattices (SLs) with EuTe thicknesses ranging from one atomic monolayer to seven atomic layers per SL period have recently been made available. High resolution x-ray diffraction measurements and cross-sectional TEM images on these SL samples confirm the SL structure.Bulk EuTe with its highly symmetric rocksalt structure, spherically symmetric Eu 2+ 8S7/ 2 ground state and zero magnetic anisotropy is considered to be an ideal Heisenberg antiferromagnet. The small lattice mismatch between EuTe and PbTe allows EuTe in our SLs to retain the same isotropic magnetic couplings as in bulk EuTe. In addition, our SL samples provide a good realization of a 2D Heisenberg antiferromagnet, since (1) the EuTe thicknesses in each SL period are on the order of several atomic monolayers; (2) the non-magnetic PbTe layers separating neighboring EuTe layers are sufficiently thick to prevent any inter-period magnetic coupling. Thus, the study of the magnetic properties of EuTe/PbTe SLs is of great interest, since they provide an experimental realization of an ideal 2D Heisenberg antiferromagnet with localized spins, isotropic exchange interactions and no inter-period coupling.Having SLs with different EuTe layer thicknesses ranging from one to seven monolayers makes it possible to study the behavior of the magnetization and susceptibility as a function of the layer thickness. High magnetic field M(H) studies show that EuTe/PbTe SLs cross from a canted antiferromagnetic phase to a spin-aligned paramagnetic phase in high fields at low temperatures just like bulk EuTe, although the phase boundary moves toward lower fields and temperatures in the H-T plane as the EuTe thickness is decreased. The temperature-dependent susceptibility measurements show strong anisotropy between the in-plane and out-of-plane susceptibilities, starting at temperatures slightly above T, and extending to near T=0 K. The isotropic exchange couplings and the absence of magnetic anisotropy in EuTe/PbTe SLs implied by our M(T, H) studies lead us to believe that the dipolar interaction is the main source of anisotropy. Finally, Monte Carlo simulations, using a Heisenberg model with dipolar interactions show that these interactions, can stabilize long-range antiferromagnetic order in EuTe/PbTe SLs.

Synthesis, Crystal Structure, and Optical and Magnetic Properties of the New Quaternary Erbium Telluride EuErCuTe3: Experiment and Calculation

“…Europium chalcogenides have the potential to create new magnetoelectronic devices, including magnetic random-access memory and magnetic tunneling transistors [19,20]. Bulk EuTe is an antiferromagnetic Heisenberg II type with a Néel temperature of T N = 9.6 K [21][22][23][24] and a wide bandgap semiconductor with a bandgap width of 2.5 eV [24]. The optical and magnetic properties of europium tellurides can be controlled by changing their sizes [21,24,25].…”

“…The optical and magnetic properties of europium tellurides can be controlled by changing their sizes [21,24,25]. In isolated monolayers, both ferrimagnetic and antiferromagnetic phase transitions can occur [23], and nanoparticles exhibit pronounced superantiferromagnetic transitions between 2 K and 20 K [21].…”