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A class of artifacts manifesting as soft magnetic components are revealed from magnetometry measurements of rare earth-transition metal (TbFe) thin films prepared by magnetron sputtering. They are not inherent to TbFe, but are a direct result of the manner in which the substrates are mounted prior to sample fabrication, with a material deposited at the substrate sides giving rise to a significant magnetic moment. The authors find the same artifacts to also be present in rare earth-free [Co/Pt] multilayers. Trying to supress the appearance of this type of artifact has an influence on the coercivity and, in some cases, on the shape of the reversal curves. Care needs to be taken during fabrication to ensure reliable and reproducible samples so that sensitive magnetic parameters, such as coercivity and compensation points, can be extracted accurately and that data are not misinterpreted for even more complex systems. This type of artifact is not limited to samples prepared by sputtering but can extend to other conventional thin-film deposition methods. [ABSTRACT FROM AUTHOR]

We describe the formation of a δ-doped manganese layer embedded within c-plane wurtzite gallium nitride using a special molecular beam epitaxy growth process. Manganese is first deposited on the gallium-poor GaN ([formula]) surface, forming a [formula] reconstructed phase. This well-defined surface reconstruction is then nitrided using plasma nitridation, and gallium nitride is overgrown. The manganese content of the [formula] phase, namely one Mn per each [formula] unit cell, implies that the MnGaN alloy layer has a Mn concentration of up to 33%. The structure and chemical content of the surface are monitored beginning from the initial growth stage up through the overgrowth of 20 additional monolayers (MLs) of GaN. An exponential-like drop-off of the Mn signal with increasing GaN monolayers, as measured by Auger electron spectroscopy, indicates that the highly concentrated Mn layer remains at the δ-doped interface. A model of the resultant δ-doped structure is formulated based on the experimental data, and implications for possible spintronic applications are discussed. [ABSTRACT FROM AUTHOR]

We report structural and magnetic properties of magnetostrictive Fe100-xGax (x ≈ 15) alloys when deposited onto antiferromagnetic manganese nitride and non-magnetic magnesium oxide substrates. From X-ray diffraction measurements, we find that the FeGa films are single crystalline. Scanning tunneling microscopy imaging reveals that the surface morphologies are dictated by the growth temperature, composition, and substrate. The magnetic properties can be tailored by the substrate, as found by magnetic force microscopy imaging and vibrating sample magnetometry measurements. In addition to pronounced tetragonal deformations, depositing FeGa onto manganese nitride leads to the formation of stripe-like magnetic domain patterns and to the appearance of perpendicular magnetic anisotropy. [ABSTRACT FROM AUTHOR]

We report structural, surface, and magnetic investigations of ferromagnetic Ga-rich MnGa thin and ultra-thin films grown on semiconducting GaN(0001) using molecular beam epitaxy. The Mn:Ga composition ratio is varied from ≈1 (stoichiometric) to ≈0.42 (very Ga-rich) for different samples. We find that the L1 0 MnGa phase is preserved down to a Mn:Ga ratio of ≈0.81. As the Ga concentration increases, we observe the coexistence of more Ga-rich phases, namely Mn 3 Ga 5 and Mn 2 Ga 5 . Room temperature scanning tunneling microscopy imaging reveals highly epitaxial films, with atomically smooth and highly reconstructed surfaces. Magnetic characterizations show how the magnetic properties evolve with changing composition and that giant perpendicular magnetic anisotropy is induced by reducing the size of our films. [ABSTRACT FROM AUTHOR]

We present first principles spin-polarized calculations of the adsorption and incorporation of iron in the Mn 3 N 2 (0 0 1) surfaces. By means of a surface formation energy criterion, it is demonstrated that Fe incorporation is energetically stable for all studied surfaces. An Fe bilayer formation is achieved after Fe atoms displace Mn atoms in the sub-surface N-vacancy layers. An analysis of the magnetic coupling shows an antiferromagnetic alignment along the [0 0 1] direction as in the clean, ideal surfaces. Also, the in-plane magnetic coupling between Fe–Fe and Fe–Mn shows a ferromagnetic tendency, similar to the clean, ideally terminated surfaces. These results clearly indicate that Fe behaves like Mn when adsorbed into the Mn 3 N 2 surface. Density of states calculations of the stable structures show a slight deviation from the antiferromagnetic-like behavior, with the most important contribution around the Fermi level coming from the Fe- d and Mn- d orbitals. [ABSTRACT FROM AUTHOR]

Spin-polarized first-principles total energy calculations have been performed to study the structural, electronic and magnetic properties of Mn 3 N 2 (0 0 1) surfaces. It is found that three surface terminations are energetically stable, in agreement with previous scanning tunneling microscopy experiments that have found three different electronic contrasts in their images. It is also found that in all three cases, the topmost layer has a MnN stoichiometry. Density of states calculations show a metallic behavior for all the stable structures with the most important contribution close to the Fermi level coming from the Mn-d orbitals. Our Tersoff–Hamann scanning tunneling microscopy simulations are in good agreement with previous experimental results. [ABSTRACT FROM AUTHOR]

In addition to the usual set of the well-known reconstructions that have been observed on the N-polar GaN surface, namely 1 × 1, 3 × 3, 6 × 6, and c(6 × 12), an additional structure is occasionally seen at high Ga coverage, which can extend over a large area of the surface. This structure, which is referred to as trench line structure, is partially ordered and consists of parallel-running dark (trench) lines separating wide and narrow strips of atomically ordered regions. There are also randomly placed defects interrupting the ideal ordering. Reflection high energy electron diffraction and scanning tunneling microscopy in ultrahigh vacuum are applied to investigate this trench line structure on samples prepared using molecular beam epitaxy. It is found that the trench line structure results from annealing the Ga-rich c(6 × 12) at high temperature followed by quenching to room temperature. By careful comparison of the scanning tunneling microscopy images with those from neighboring c(6 × 12) regions, it is found that the trench line structure can be decomposed into subunits of the c(6 × 12). Using these subunits, some simple models for the trench line structure are created. It is proposed that the trench line structure is composed of two primary c(6 × 12) subunits consisting of first and second layer Ga adatoms and that the trench lines are regions devoid of Ga adatoms, going down to the Ga adlayer. [ABSTRACT FROM AUTHOR]

Submonolayer deposition of manganese on gallium-rich, nitrogen polar $$\hbox {GaN}(000\bar{1})$$ surface using radio-frequency nitrogen plasma molecular beam epitaxy leads to the spontaneous formation of manganese gallium into two distinct quantum height islands, 5-layer and 6-layer islands. Atomically resolved scanning tunneling microscopy reveals the atomically flat but unstable 5-layer island surface and the 6-layer island surface with relatively stable row structures. We propose possible surface models for these islands' surfaces and discuss the clear structural differences explained with strains and partial relaxations. It is found that the 5-layer islands form under lateral strains and a relaxation process leading to non-uniform alternating strains results in the more energetically favorable row structures on the 6-layer island. [ABSTRACT FROM AUTHOR]

The initial stages of interface formation for a real-world ferromagnet/antiferromagnet bi-layer system (iron/manganese nitride) are investigated down to the atomic scale using a combination of molecular beam epitaxy, in situ scanning tunneling microscopy, and first-principles theoretical calculations. Submonolayer deposition of iron onto manganese nitride nanopyramid surfaces results in an unexpected yet well-ordered structural and magnetic arrangement. It is shown that although the island structures seen in scanning tunneling microscopy images are of single monolayer height, their chemical composition, based on Auger electron spectroscopy, conductance map imaging, and theoretical models, does not consist of iron. It is found theoretically that models that consider iron on the surface of manganese nitride are highly unfavorable. Instead, models with iron atoms incorporated into specific subsurface layers are most stable, in excellent agreement with Auger spectroscopy measurements. Calculations also reveal the magnetic alignment of iron with the manganese nitride layers. [ABSTRACT FROM AUTHOR]

We have investigated sub-monolayer iron deposition on atomically smooth GaN(0001) pseudo- 1×1 (1+1/12). The iron is deposited at a substrate temperature of 360 °C, upon which reflection high energy electron diffraction shows a transformation to a √3 × √3-R30° pattern. After cooling to room temperature, the pattern transforms to a 6×6, and scanning tunneling microscopy reveals 6×6 reconstructed regions decorating the GaN step edges. First-principles theoretical calculations have been carried out for a range of possible structural models, one of the best being a Ga dimer model consisting of 2/9 monolayer of Fe incorporated into 7/3 monolayer of Ga in a relaxed but distorted structure. [ABSTRACT FROM AUTHOR]

L10-structured MnGa(111) ultra-thin films were heteroepitaxially grown on GaN(0001) under lightly Mn-rich conditions using molecular beam epitaxy. Room-temperature scanning tunneling microscopy (STM) investigations reveal smooth terraces and angular step edges, with the surface structure consisting primarily of a 2 × 2 reconstruction along with small patches of 1 × 2. Theoretical calculations were carried out using density functional theory, and the simulated STM images were calculated using the Tersoff-Hamman approximation, revealing that a stoichiometric 1 × 2 and a Mn-rich 2 × 2 surface structure give the best agreement with the observed experimental images. [ABSTRACT FROM AUTHOR]