T.M. Giebultowicz

Antiferromagnetic interlayer coupling in ferromagnetic semiconductor EuS/PbS(001) superlattices

Antiferromagnetic coupling between ferromagnetic layers has been observed for the first time in an all-semiconductor superlattice structure EuS/PbS(001), by neutron scattering and magnetization measurements. Spin-dependent superlattice band structure effects are invoked to explain the possible origin and the strength of the observed coupling.

Determination of antiferromagnetic interactions in Zn(Mn)O, Zn(Co)O, and Zn(Mn)Te by inelastic neutron scattering

The nearest-neighbor magnetic exchange interactions in Zn0.95Mn0.05O, Zn0.95Co0.05O, and Zn0.98Mn0.02Te were investigated by measuring inelastic neutron scattering from isolated exchange-coupled spin-spin pairs. The experiments on Zn0.98Mn0.02Te were carried out at atmospheric pressure and then at 4kbar pressure in order to determine the dependence of the exchange parameter on the spin-spin distance.

Neutron diffraction and reflectivity studies of interlayer correlations in magnetic semiconductor superlattices

Abstract An overview of neutron scattering studies on two classes of magnetic semiconductor superlattices, MnTe/II-Te (II=Cd, Zn) and Eu-VI/Pb-VI (VI=S, Te) is presented. Diffraction experiments reveal distinct correlations between layers of MnTe even though they are antiferromagnetic (AFM) and the systems are nearly-insulating. Current theory status is discussed. In EuTe/PbTe, pronounced correlations between AFM EuTe blocks are also seen. In EuS/PbS, the only ferromagnetic (FM) system in the group, neutron diffractometry and reflectometry show strong AFM correlations between the FM EuS block. A tight-binding model is used in both Eu-based systems to explain interaction transfer across the non-magnetic block without the assistance of carriers.

Interlayer correlations in ferromagnetic semiconductor superlattices EuS/PbS

Abstract Neutron diffraction and reflectivity data from all-semiconductor ferromagnetic/diamagnetic superlattices EuS/PbS provide direct evidence of antiferromagnetic coupling between EuTe layers across up to 90 A of diamagnetic PbS, despite the absence of mobile carriers that can support long-range RKKY interactions.

Polarized neutron reflectivity studies of magnetic semiconductor superlattices

Abstract Polarized neutron reflectivity studies of EuS/PbS, EuS/YbSe and GaMnAs/GaAs superlattices performed at the NIST Center for Neutron Research are presented. Pronounced antiferromagnetic (AFM) interlayer coupling has been found in EuS/PbS superlattices for a very broad range of PbS spacer thicknesses. Similar, but weaker, AFM coupling is also present in EuS/YbSe, although only for relatively thin YbSe layers. Neutron polarization analysis shows distinct in-plane asymmetry of the magnetization directions of EuS layers in both systems under investigation. For GaMnAs/GaAs superlattices, ferromagnetic (FM) interlayer correlations have been observed. Polarized neutron reflectometry investigations of several GaMnAs/GaAs superlattices have revealed that the manganese magnetic moments in individual GaMnAs layers, in spite of low Mn concentration, form a truly long range, that is in certain cases a single domain, ferromagnetic state.

INTERLAYER CORRELATIONS IN ANTIFERROMAGNETIC SEMICONDUCTOR SUPERLATTICES EUTE/PBTE

Abstract We report neutron diffraction studies of short-period (111) [(EuTe)ξ|(PbTe)η]N superlattices (SLs), with a special emphasis on the interlayer spin coherence phenomena seen in these systems. We summarize the results of experiments on over thirty samples, in which we have investigated the dependence of interlayer coupling effects on the EuTe and PbTe layer thicknesses, on doping of the PbTe layers, and on external magnetic fields.

Monte Carlo simulation of europium telluride under hydrostatic pressure

EuTe is a type II antiferromagnetic semiconductor that exhibits a constant Neel temperature under high pressures with a lattice constant varying between 6.25 and 6.6 A [I. N. Goncharenko and I. Mirebeau, Phys. Rev. Lett. 80, 1082 (1998); Europhys. Lett. 37, 633 (1997)]. Because mean field theory predicts a Neel temperature that is independent of J1, these results were interpreted to suggest a J2 independent of interstitial distances. Monte Carlo simulations of bulk EuTe with J2 held fixed and J1 varying from −.4(J2) to −.6(J2) using a Metropolis algorithm with a Hamiltonian comprised of nearest neighbor (NN) and next-nearest neighbor (NNN) terms have been performed. The Neel Temperature (TN) is observed to vary by 4% for a 20% change in the strength of J1, suggesting that interpretations of the behavior of EuTe based on mean field theory should be reevaluated. A linear relation between J1 and TN suggests that changes in NN and NNN interactions exactly cancel for EuTe under hydrostatic pressure.

Studies of intrinsic exchange interactions in Zn(Mn)O, Zn(Mn)S and Zn(Mn)Te at 4 kbar by inelastic neutron scattering

The intrinsic antiferromagnetic (AFM) interactions between nearest‐neighbor Mn ions in Zn(Mn)O, Zn(Mn)S, Zn(Mn)Te have been studied by inelastic neutron scattering at ambient pressure and at 4 kbar. To find how the J values in a single alloy change when the Mn‐Mn distance R decreases we have launched systematic measurements of the nearest‐neighbor exchange constants J1 in these alloys using inelastic neutron scattering spectrometry. We present the J1 data so far obtained at 4 kbar for the three aforementioned systems, as well as the result of measurements of the pressure dependence of the Mn‐Mn distance. We discuss our findings in the context of the analysis presented in the paper by Szuszkiewicz et al.

Neutron scattering studies of the spin structure of magnetic semiconductor superlattices

The ferromagnetic/nonmagnetic semiconductor superlattices, EuS/PbS and EuS/YbSe, were studied by neutron reflectivity. In order to determine the strength of the interlayer coupling, the intensity of the first magnetic Bragg peak vs. applied magnetic field was measured. The dependence of the intensity of the antiferromagnetic neutron reflectivity peak vs. magnetic field was simulated using a Stoner‐Wohlfarth model. The experimentally determined strength of the coupling was compared with the tight‐binding model calculations.

Numerical simulation of neutron diffraction from correlated/uncorrelated magnetic multilayers

Abstract We report stochastic diffraction simulations of magnetic multilayered systems. Results show that spectrum fringes from a system of many magnetic domains is a non-random effect - i.e., such fringes cannnot occur in the total absence of interlayer spin correlations. Simulation of diffraction spectra from superlattices with interlayer coupling probability 0