Semiconductor EuS–PbS ferromagnetic multilayers

Abstract

EuS–PbS ferromagnetic multilayers constitute all‐semiconductor ferromagnetic‐nonmagnetic structures with magnetic layers of EuS (a model nonmetallic ferromagnet) and diamagnetic layers of PbS (IV–VI narrow gap semiconductor compound). The ferromagnetic transition temperature in EuS–PbS multilayers depends on the thickness of the magnetic layer as well as on thermal strain. For ultrathin PbS spacer layers one observes in EuS–PbS–EuS trilayers and superlattices pronounced magnetic effects related to the antiferromagnetic interlayer coupling between ferromagnetic layers of EuS via nonmagnetic semiconductor PbS spacer. These effects are discussed for EuS–PbS structures grown epitaxially on various substrates: insulating KCl(100) and BaF2(111) as well as conducting n‐PbS(100) monocrystals.

Temperature Dependence of Antiferromagnetic Interlayer Exchange Coupling in EuS-PbS Multilayers

“…In contra st to reg ul ar, appro xi matel y square-li ke, l oo ps f ound i n noncoupl ed tri l ayers (wi th PbS spacer thi cker tha n ab out 2 nm ) [1,2,6], the experi m enta l data clearl y show a chara cteri sti c al most zero magneti c rem anence and a l ow Ùeld l i near \ pl ateau" wi th a well -deÙned externa l m agneti c Ùel d correspondi ng to the switch b etween anti ferro m agneti c-and ferro m agneti c-l i ke al i gnm ent of magneti zati on vecto rs of two EuS l ayers. Qua l ita ti vely, the m agneti zati on l o ops of excha nge-coupl ed EuS{ PbS/ PbS (0 01) m ul -ti l ayers are very sim i l ar as for the previ ously studi ed EuS{ PbS structures gro wn on KCl (0 01) substra tes [1,2]. The key experi m enta l observati on i ll ustra ted i n Fi g. 1 i s tha t the ab ove-m enti oned exp eri menta l features rel ated to anti ferro m agneti c i nterl ayer coupl i ng exhi bi t a stro ng tem p erature dep endence, whi ch wi l l b e qua nti ta ti vely ana l yzed i n the next section.…”

“…i s observed even i n 2 mono l ayer (0 .6 nm ) thi ck layers of EuS. Ma gneti c pro perti es of EuS{ PbS m ulti layers are al so i n Ûuenced by stra in, present i n these structures m ai nl y due to the di˜erence i n therm al expansion coe£ ci ents of the m ulti l ayer and the KCl or Ba F 2 substra tes [1,2]. The e˜ect i s pa rti cul arl y l arg e for structures gro wn on KCl substra tes, i n whi ch stro ng compressi ve i n-pl ane stra i n resul ts i n ab out 3 K i ncrease i n the Curi e tem p erature.…”

Magnetic Properties of EuS-SrS Semiconductor Multilayer Structures

“…In previously studied EuS-PbS heterostructures, narrow band gap PbS spacer layers served as nonmagnetic quantum wells with ferromagnetic EuS barriers [1,2]. In EuS-SrS structures the wide gap (419) SrS layers are expected to form nonmagnetic electron barriers for ferromagnetic EuS quantum wells.…”

“…EuS belongs to the family of europium chalcogenides and is a well-known Heisenberg nonmetallic ferromagnet with the lattice parameter a 0 = 5.967Å and the energy gap of 1.65 eV. Ferromagnetic transition in EuS bulk crystals takes place at the Curie temperature T c = 16.5 K. In thin epitaxial layers of EuS grown on KCl substrates the Curie temperature is influenced by the strain and size effects [1,2]. The thermal strain present in EuS layers due to the large difference in expansion coefficients of the layer and the KCl substrate leads to the in-plane biaxial compression of the EuS lattice.…”

Synthesis of PbS/EuS Core/Shell Nanocrystals

“…Since PbS has a rock-salt crystal structure whose lattice constant is very close to that of EuS with the lattice mismatch as low as 0.5%, PbS/EuS heterostructure has been studied as a nonmagnetic/magnetic all-semiconductor multilayers. 7,8 In PbSEuS multilayers, wide-energy-gap EuS (E g = 1.65 eV) form electron barriers, whereas narrow-energy-gap PbS (E g = 0.3 eV) constitutes quantum wells for both electrons and holes. 8 Due to the relatively small energy difference in the valence band between PbS and EuS, 0.15 eV for bulk, together with the strong quantum confinement in PbS NCs 9 and the bulk properties of EuS NCs 2i with Bohr radii of 20 nm and below 1 nm, respectively, there might be a possibility for the tuning of band offset through type I to type II by the size control of each component.…”