Magnetic Properties of Heisenberg Antiferromagnetic EuTe/PbTe Superlattices
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Abstract Bulk EuTe is a type II Heisenberg antiferromagnet (AF 2) with a single magnetic phase transition temperature at 9.6 K. However, for several isolated EuTe (111) monolayers (MLs) as can be achieved in a superlattice (SL) structure, both ferrimagnetic-like and antiferromagnetic-like phase transitions can take place, depending on the SLs configuration. The temperature-dependent magnetization M(T) of such SLs has been studied near the transition temperature (Ta) by SQUID magnetometry. The functional forms of M(T) at T < TZcan be described by mean-field theory for SLs with 3, 4 and 5 EuTe MLs per SL cell. The magnetic transition temperatures obtained by mean-field analysis, using bulk exchange coupling values, are in close agreement with observed T, values for SLs with 2, 3, 4 and 5 EuTe MLs. The qualitative behavior of the surface specific heat can be deduced from M(T) data for SLs with three EuTe monolayers.
Introduction Magnetization measurements provide a macroscopic probe of magnetic systems. In surface magnetism studies, direct magnetization measurements are usually not possible be-
cause of the small signals (except for magnetic graphite intercalation compounds, in which case, direct magnetization measurements have been made). However, with the help of MBE technology, magnetic superlattices (SLs) can be prepared as "bulk" materials with many internal magnetic surfaces, so that the surface magnetization can be investigated directly. The purpose of this paper is twofold. First, we want to show that the temperature dependence of the magnetization [M(T)] of a Heisenberg antiferromagnet can be predictably modified when that antiferromagnet is combined with another non-magnetic compound in a SL structure. Mean-field theory is the simplest description of such a magnetic system. For SLs of EuTe/PbTe reliable predictions of T, can be obtained for SLs with two or more EuTe monolayers (MLs) per SL unit cell. In addition, the functional forms of M(T) at T
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