Comparison of the crystalline structure, morphology, and magnetic properties ofγ-phaseMn∕Cu3Au(100)ultrathin films by varying

Abstract

The structural and magnetic properties of room-temperature ͑RT: 300 K͒-grown and low-temperature ͑LT: 100 K͒-grown Mn/ Cu 3 Au͑100͒ thin films were investigated. Mn films deposited at RT and LT demonstrate very different behaviors in the crystalline structure, morphology, and magnetism. RT-Mn films reveal apparent layer-by-layer growth for 0 -2 ML ͑monolayer͒ followed by reduced oscillations. Although the medium-energy electron diffraction ͑MEED͒ oscillation is reduced, the intensity of specular spot increases monotonically after 6 -7 ML, inferring the tendency of smooth morphology. The study of scanning tunneling microscopy also shows that even in 19 ML Mn/ Cu 3 Au͑100͒, the surface morphology is composed of large terraces with the size up to hundreds of nanometers. The LT-Mn films reveal apparent layer-by-layer growth for 0 -5 ML followed by the reduced oscillations, and then the MEED intensity remains at low intensity, inferring the rough surface. The RT-and LT-Mn films exhibit a thickness-dependent structural transition from a face-centered cubic to a face-centered tetragonal structure at different critical thicknesses, ϳ12-14 and ϳ8 ML, respectively. Significant exchange bias is observed in Fe/ RT-Mn bilayers. It increases monotonously with Mn thickness. The exchange bias coupling in Fe/ LT-Mn is much weaker than Fe/ RT-Mn and drastically varies with Mn film thickness. The presence of exchange bias in the Fe/ Mn bilayers also indicates the antiferromagnetism of ␥-phase Mn/ Cu 3 Au͑100͒.

Flipping magnetization induced by noncollinear ferromagnetic-antiferromagnetic exchange coupling

“…The regular oscillation indicates a well-defined layer-by-layer growth mode, in which the flat surface with around two monoatomic steps has been observed by STM. 27,29 As t Mn > 11 ML, the oscillation was found to vanish coincidentally with the fcc-fct structural transition as reported in the previous studies. 27,30 Experimentally, there are four different phases observed for the bulk Mn.…”

“…27,29 As t Mn > 11 ML, the oscillation was found to vanish coincidentally with the fcc-fct structural transition as reported in the previous studies. 27,30 Experimentally, there are four different phases observed for the bulk Mn. The α phase has a complex cubic structure with 58 atoms per unit cell and noncollinear AFM order which disappears above the Néel temperature of 95 K. 31 For the temperature above 1073 K, a transition to a cubic structure with 20 atoms per unit cell occurs, namely the β phase.…”

“…Finally, there exists another δ phase with bcc structure for the temperature between 1406 K and the melting temperature 1517 K. Since the temperatures leading to the presence of the last three phases could be much higher than their Néel temperatures, the AFM characteristics of them are unlikely to be investigated in bulk form. Alternatively, it has been reported that the fcc-like phases of Mn films can be stabilized at room temperature through an epitaxial growth on Cu 3 Au(100) 27,30 or Co/Cu(001). 33,34 A metastable phase of fcc-Mn (c/a ∼ 1) can be stabilized at Cu 3 Au(100) for the thickness of Mn film less than ∼11 ML.…”

“…33,34 A metastable phase of fcc-Mn (c/a ∼ 1) can be stabilized at Cu 3 Au(100) for the thickness of Mn film less than ∼11 ML. 27,28 For the thicker Mn films, the presence of slight tetragonal distorted fct states (i.e., c/a ∼ 0.96 and c/a ∼ 1.05 for the former and latter cases) was suggested to be accompanied by two antiferromagnetic ground states of in-plane c(2×2) and layered AFM, respectively, as below the bulk Néel temperature of about 540 K. 30,35,36 Interestingly, as mentioned earlier, the ground-state energies of in-plane c(2×2) and layered-AFM states could become degenerate for a fcc Mn. 23,24 In such scenario, fcc-Mn film could reveal novel magnetic properties.…”

Probing magnetoelastic effects of ultrathin antiferromagnets via magnetic domain imaging in ferromagnetic-antiferromagnetic bilayers

“…Among various antiferromagnets, face-centered-cubic (fcc)-like Mn thin films are considered to be highly attractive systems because they can be fabricated with current epitaxial growth techniques [19][20][21][22][23][24][25][26]. Although theoretical studies have suggested that the behavior of bulk fcc-like Mn could be a function of the lattice parameters, on the basis of the rich magnetic phase diagram of bulk fcc-like Mn [27,28], for Mn thin films directly grown on FM films with stable in-plane magnetization (or vice versa), experiments involving spinpolarized scanning tunneling microscopy (SP-STM) and x-ray magnetic circular dichroism (XMCD)-based photoemission microscopy (PEEM) have supported in-plane layered AFM structures [10,23,24,29].…”