Magnetic Properties of Semiconductor-Antiferromagnet Superlattices

Abstract

Magnetic resonance investigations of ultra-thin antiferromagnetic EuTe layers show a specific behaviour in the quasi-2D antiferromagnetic ordering: (i) an anisotropy of the critical broadening, (ii) a substantial increase in the Néel temperature and (iii) an anisotropic shift of the resonance frequency which diverges at the Néel point. The results show that exchange coupling is stronger in quasi-2D than in 3D antiferromagnetic samples and that correlation of spin chains aligned in the perpendicular direction occurs already well above the Néel point.PACS numbers: 75.50. Ee, 75.50.Pp, 76.50.+g There is a substantial difference between the macroscopic and the microscopic nature of antiferromagnets (AFs). Macroscopic AFs are described by stable Néel sublattices with opposite spin orientation and the magnetizations of the sublattices compensate each other completely. For microscopic objects, in contrast, quantum mechanical calculations show that there is no stable magnetization of any sublattice. Neighbouring spins are anti-correlated but the mean value of each individual spin vanishes. There is no obvious answer which type of AF is more appropriate for ultra-thin AF 1ayers where one dimension is a microscopic one. In this paper we show that magnetic phase transitions of such layers can be regarded as an ordering of short quantum AF strings which are oriented from one interface to another.The Eu chalcogenides are known as magnetic model systems where coupling among the spins is described by pure Heisenberg coupling. We investigate the magnetic resonance ("EPR") of a series of MBE grown EuTe/PbTe superlattices (SLs) and we compare the experimental results obtained with those from a feẁ (973)

Oscillating Antiferromagnetism of Ultrathin EuTe Layers

“…The ratio is diÍferent from sample to sample. The increase in the resonance field at high temperatures is caused by a critical increase in the field fluctuations [8]. The observed resonance frequency at low temperature allows to estimate the anisotropy field.…”

“…We evaluate the real interdiffusion by two independent methods: (i) by analysing the magnetic anisotropy [8] and (ii) by estimating the number of isolated Εu ions which diffuse into the PbTe wells. It can be shown that in the paramagnetic regime the magnetic dipole anisotropy of the layered structure is proportional to the effective composition of the SL: xeff = Σx2 i /Σxi , where xi is the mean composition of the i-th plane.…”

Ferromagnetic transition in EuS-PbS multilayers

“…13,[22][23][24][25][26] Until now, the properties of antiferromagnetic/nonmagnetic EuTe-PbTe structures have been studied, for which an interlayer coupling, 6,27 a decrease of Néel temperature with decreasing EuTe layer thickness, 28 and anisotropy effects [28][29][30][31] were found. A ferromagnetic/ nonmagnetic multilayer system of EuS intercalated with insulating SrS has been studied as well.…”

Small Antiferromagnetic Clusters

“…The experimental data [4], however, show that in ultrathin AF layers, where spins within each monolayer are ferromagnetically correlated, an increase in the exchange energy is observed. In spite of a spin diffusion at the interface, the Néel temperature in EuTe superlattices is by factor 2 bigger than in bulk crystals.…”

“…The open question is the estimation of the classical limit for 2D and 3D AFM. The experimental data [4,6] suggest, however, that quasi 2D layers where one dimension is reduced to a few monolayers exhibits already a quantum character of AF.…”