Interface and bulk properties of Fe/Mn sandwich structures

Abstract

Structural and magnetic properties of Fe(5 nm)/Mn(t Mn )/Fe(5 nm) (t Mn from 0.5 to 3.0 nm͒ sandwich structures, grown by molecular-beam epitaxy between 50°C and 150°C, were investigated using reflection high-energy electron diffraction ͑RHEED͒, x-ray-diffraction, Mössbauer spectroscopy, and magnetization measurements. Epitaxial bct-Mn structures only form for t Mn Ͻ1 nm, independently of the growth temperature. Room-temperature conversion electron Mössbauer spectra are composed of two magnetic components with in-plane magnetic moments. The first subspectrum has hyperfine parameters close to ␣-Fe and is therefore associated with Fe atoms far from the interface regions. The second component, fitted with a hyperfine field ͑hf͒ distribution, has an isomer-shift value similar to ␣-Fe and a maximum in the distribution curve at about 31 T. This subspectrum is related to the Fe atoms close to the Mn layer ͑interface regions͒. Low-field components in the hf distribution curves indicate the presence of Fe atoms or/and Fe clusters in the Mn spacers. An Fe-Mn alloy was observed for the samples grown for temperatures higher than or equal to 50°C and where the RHEED patterns show the presence of the ␣-Mn phase. Magnetization data show that the Fe layers are ferromagnetically coupled for all trilayers prepared at substrate temperatures lower than 150°C. A noncollinear coupling was found for the trilayer with Mn thickness of 1 nm and grown at 150°C.

Bottom and top AF/FM interfaces of NiFe/FeMn/NiFe trilayers

“…Passamani et al [32] have applied a thermodynamic model based on the different melting points of the deposited materials to explain the larger atomic interdiffusion at the upper Mn/Fe interface in Fe/Mn/Fe trilayers deposited by MBE. If we apply this model to our results, it is easy to explain why the atomic diffusion at the top NiFe/FeMn interface is stronger than that obtained for the bottom.…”

Enhancement of magnetic coercivity in Fe/Mn and Co/Mn bilayers

“…Within these heterostructures, previous works on Ferromagnetic(F)/Mn-based systems have shown that finite size effects, hybridization mechanism and interfacial mixing could lead to very diverse type of magnetic behavior. Some authors have determined a F arrangement of the Mn based layer [7][8][9], whereas an antiferromagnet(AF) arrangement was revealed by others [10][11][12][13][14][15]. It could also be noted that even F x Mn 1À x bulk materials exhibit competing interactions with stoichiometric regions of F and AF order, enclosing intermediate stoichiometric region in which only short range order occurs [16].…”

“…It should be noted that Fe x Mn 1À x (Co x Mn 1À x ) was determined as antiferromagnetic at room temperature if x is smaller than 0.8 [17][18][19][20][21] (0.68 [22]). The assumption that interdiffusion is taking place at the interface is also supported by previous experimental study on annealed Fe/Mn [13] and by thermodynamic consideration involving binding energies between Fe and Mn [7]. Considering a dead interfacial layer, the M s dependence with t F can be described as [23]:…”

Interface local chemistry and magnetic asymmetry in (Fe/Mn) multilayers

“…Different models, either thermodynamic [11] or ballistic [9], have been proposed to explain the asymmetry of the interfaces. These models do not account for the cause of this chemical asymmetry, which in our case could originate from the difference between Fe and Mn surface energies, 2.939 J m À 2 and 1.440 J m À 2 , respectively [12,13].…”