Structural, electronic, and magnetic properties of a Mn monolayer on W(110)

Abstract

In this paper we establish a monolayer of Mn on W͑110͒ as a model system for two-dimensional itinerant antiferromagnetism. Combining scanning tunneling microscopy ͑STM͒, low-energy electron diffraction, and ab initio calculations performed with the full-potential linearized augmented plane wave method we have studied the structural, electronic, and magnetic properties of a Mn monolayer on W͑110͒. Our experimental results indicate that in spite of the huge tensile strain Mn grows pseudomorphically on W͑110͒ up to a thickness of three monolayers. Intermixing between the Mn overlayer and the W substrate can be excluded. Using these structural data as a starting point for the ab initio calculations of one monolayer Mn on W͑110͒ we conclude that ͑i͒ Mn is magnetic and exhibits a large magnetic moment of 3.32 B , ͑ii͒ the magnetic moments are arranged in a c(2ϫ2) antiferromagnetic order, ͑iii͒ the easy axis of the magnetization is in plane and points along the ͓11 0͔ direction, i.e., the direction along the long side of the ͑110͒ surface unit cell with a magnetocrystalline anisotropy energy of 1.3-1.5 meV, and ͑iv͒ the Mn-W interlayer distance is 2.14 Å. The calculated electronic structure of a Mn monolayer on W͑110͒ is compared with experimental scanning tunneling spectroscopy results. Several aspects are in nice agreement, but one cannot unambiguously deduce the magnetic structure from such a comparison. The proposed two-dimensional antiferromagnetic ground state of a Mn monolayer on W͑110͒ is directly verified by the use of spin-polarized STM ͑SP-STM͒ in the constant-current mode, and an in-plane easy magnetization axis could be confirmed using tips with different magnetization directions. We compare the measurements with theoretically determined SP-STM images calculated combining the Tersoff-Hamann model extended to SP-STM with the ab initio calculation, resulting in good agreement.

Thermal properties of a spin spiral: Manganese on tungsten(110)

“…For the latter one it is w = μ 2 s μ 0 /4πa 3 with the vacuum permeability μ 0 , the atomic magnetic moment μ s = 3.5μ B taken from our ab initio calculations, and the distance between sites r ij (normalized to the lattice constant along the [001] direction, a = 0.3165 nm, as taken from Ref. [8]) and the respective unit vectorê ij . Due to the C2v point-group symmetry of the system, K i introduces a biaxial on-site anisotropy.…”

“…Here we took into account a layer relaxation of −6.9% of the Mn layer [8]. The potentials were treated within the atomic sphere approximation and valence orbitals were considered up to an angular momentum of = 3.…”

“…The development of spin-polarized (SP) scanning tunneling microscopy (STM) [4,5], however, made it possible to visualize the magnetic properties in real space with unprecedented resolution. This technique, initially used to study the magnetic ground state of bulk crystal surfaces [6,7] and thin films [8], was then rapidly applied to study a large variety of different magnetic systems like nanostructures [9][10][11] and domain walls [12,13], and in more recent years, it has been pushed to its ultimate limit: studies of the magnetic state of single atoms [14].…”

Fundamental studies of magnetism down to the atomic scale: present status and future perspectives of spin-polarized scanning tunneling microscopy

“…On the other hand, SP-STM and SP-STS can be applied to study antiferromagnetic samples which has proven to be difficult by other magnetic imaging techniques. Most striking results in this field have been the experimental proof of the topological antiferromagnetic order of the Cr(0 0 1) surface [1,8,14,15] and of the existence of twodimensional antiferromagnetic order for a single atomic layer of Mn on a W(1 1 0) substrate [4,16].…”

Preparation and photoemission investigation of bulklikeα-Mnfilms on W(110)

“…Recently, the possibility to stabilize thin distorted ␦-Mn films up to several monolayers ͑MLs͒ on W͑110͒ was confirmed by low-energy electron diffraction ͑LEED͒ and scanning tunneling microscopy. 15,16 The epitaxial relationship is maintained up to a coverage of about 3 ML but in contrast to Fe/W͑110͒, already the first Mn layer exhibits a modest growth anisotropy in the ͗001͘ direction. 15 These results were analyzed in the framework of the densityfunctional theory ͑DFT͒ ͑Ref.…”