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Magnetic reconfiguration of MnAs/GaAs(001) observed by Magnetic Force Microscopy and Resonant Soft X-ray Scattering  [PDF]
L. N. Coelho,R. Magalh?es-Paniago,B. R. A. Neves,F. C. Vicentin,H. Westfahl Jr.,R. M. Fernandes,F. Iikawa,L. D?weritz,C. Spezzani,M. Sacchi
Physics , 2006, DOI: 10.1063/1.2356794
Abstract: We investigated the thermal evolution of the magnetic properties of MnAs epitaxial films grown on GaAs(001) during the coexistence of hexagonal/orthorhombic phases using polarized resonant (magnetic) soft X-ray scattering and magnetic force microscopy. The results of the diffuse satellite X-ray peaks were compared to those obtained by magnetic force microscopy and suggest a reorientation of ferromagnetic terraces as temperature rises. By measuring hysteresis loops at these peaks we show that this reorientation is common to all ferromagnetic terraces. The reorientation is explained by a simple model based on the shape anisotropy energy. Demagnetizing factors were calculated for different configurations suggested by the magnetic images. We noted that the magnetic moments flip from an in-plane mono-domain orientation at lower temperatures to a three-domain out-of-plane configuration at higher temperatures. The transition was observed when the ferromagnetic stripe width L is equal to 2.9 times the film thickness d. This is in good agreement with the expected theoretical value of L = 2.6d.
Low Temperature Magnetic Domain Patterns in MnAs Films Grown on GaAs(001)  [PDF]
M. Cheon,S. Hegde,S. Wang,M. M. Bishara,G. B. Kim,H. Luo
Physics , 2004,
Abstract: Magnetic properties of MnAs were studied as a function of temperature with a superconducting interference device (5 K to 350 K), and atomic force microscopy/magnetic force microscopy (20 K to 360 K). Structural and magnetic properties of MnAs depend on film thickness both near and far below the Curie temperature. In samples with coexisting ferromagnetic alpha-MnAs and paramagnetic beta-MnAs, the domain structures are affected by the distribution of two phases. The magnetic domain structures below the temperature range of this mixed phase resemble that of a single domain structure with uniform magnetization along the easy axis, except there are regions elongated along the easy axis embedded where the magnetization is along the second easy axis, i.e., normal to the films. The shape of those regions and their temperature dependence are also related to the MnAs layer thickness.
Magnetostructure of MnAs on GaAs revisited  [PDF]
Ernst Bauer,Rachid Belkhou,Salia Cherifi,Andrea Locatelli,A. Pavlovska,Nicolas Rougemaille
Physics , 2007, DOI: 10.1116/1.2746353
Abstract: The ferromagnetic to nonferromagnetic (α-β) phase transition in epitaxial MnAs layers on GaAs(100) is studied by x-ray magnetic circular dichroism and x-ray magnetic linear dichroism photoemission electron microscopy in order to elucidate the nature of the controversial nonferromagnetic state of β-MnAs. In the coexistence region of the two phases the β phase shows a clear XMLD signal characteristic of antiferromagnetism. The nature and the possible causes of the elusiveness of this magnetic state are discussed.
GaAs:Mn nanowires grown by molecular beam epitaxy of (Ga,Mn)As at MnAs segregation conditions  [PDF]
J. Sadowski,P. Dluzewski,S. Kret,E. Janik,E. Lusakowska,J. Kanski,A. Presz,F. Terki,S. Charar,D. Tang
Physics , 2007, DOI: 10.1021/nl071190f
Abstract: GaAs:Mn nanowires were obtained on GaAs(001) and GaAs(111)B substrates by molecular beam epitaxial growth of (Ga,Mn)As at conditions leading to MnAs phase separation. Their density is proportional to the density of catalyzing MnAs nanoislands, which can be controlled by the Mn flux and/or the substrate temperature. Being rooted in the ferromagnetic semiconductor (Ga,Mn)As, the nanowires combine one-dimensional properties with the magnetic properties of (Ga,Mn)As and provide natural, self assembled structures for nanospintronics.
Strain-induced high ferromagnetic transition temperature of MnAs epilayer grown on GaAs (110)  [cached]
Xu Pengfa,Lu Jun,Chen Lin,Yan Shuai
Nanoscale Research Letters , 2011,
Abstract: MnAs films are grown on GaAs surfaces by molecular beam epitaxy. Specular and grazing incidence X-ray diffractions are used to study the influence of different strain states of MnAs/GaAs (110) and MnAs/GaAs (001) on the first-order magnetostructural phase transition. It comes out that the first-order magnetostructural phase transition temperature T t, at which the remnant magnetization becomes zero, is strongly affected by the strain constraint from different oriented GaAs substrates. Our results show an elevated T t of 350 K for MnAs films grown on GaAs (110) surface, which is attributed to the effect of strain constraint from different directions. PACS: 68.35.Rh, 61.50.Ks, 81.15.Hi, 07.85.Qe
Enhanced electron correlations, local moments, and Curie temperature in strained MnAs nanocrystals embedded in GaAs  [PDF]
M. Moreno,J. I. Cerdá,K. H. Ploog,K. Horn
Physics , 2010, DOI: 10.1103/PhysRevB.82.045117
Abstract: We have studied the electronic structure of hexagonal MnAs, as epitaxial continuous film on GaAs(001) and as nanocrystals embedded in GaAs, by Mn 2p core-level photoemission spectroscopy. Configuration-interaction analyses based on a cluster model show that the ground state of the embedded MnAs nanocrystals is dominated by a d5 configuration that maximizes the local Mn moment. Nanoscaling and strain significantly alter the properties of MnAs. Internal strain in the nanocrystals results in reduced p-d hybridization and enhanced ionic character of the Mn-As bonding interactions. The spatial confinement and reduced p-d hybridization in the nanocrystals lead to enhanced d-electron localization, triggering d-d electron correlations and enhancing local Mn moments. These changes in the electronic structure of MnAs have an advantageous effect on the Curie temperature of the nanocrystals, which is measured to be remarkably higher than that of bulk MnAs.
Imaging the antiparallel magnetic alignment of adjacent Fe and MnAs thin films  [PDF]
R. Breitwieser,M. Marangolo,J. Luning,N. Jaouen,L. Joly,M. Eddrief,V. H. Etgens,M. Sacchi
Physics , 2008, DOI: 10.1063/1.2990755
Abstract: The magnetic coupling between iron and alpha - MnAs in the epitaxial system Fe/MnAs/GaAs(001) has been studied at the sub-micron scale, using element selective x-ray photoemission electron microscopy. At room temperature, MnAs layers display ridges and grooves, alternating alpha (magnetic) and beta (non-magnetic) phases. The self-organised microstructure of MnAs and the stray fields that it generates govern the local alignment between the Fe and alpha - MnAs magnetization directions, which is mostly antiparallel with a marked dependence upon the magnetic domain size.
Depth profile photoemission study of thermally diffused Mn/GaAs (001) interfaces  [PDF]
Y. Osafune,G. S. Song,J. I. Hwang,Y. Ishida,M. Kobayashi,K. Ebata,Y. Ooki,A. Fujimori,J. Okabayashi,K. Kanai,K. Kubo,M. Oshima
Physics , 2007, DOI: 10.1063/1.2931040
Abstract: We have performed a depth profile study of thermally diffused Mn/GaAs (001) interfaces using photoemission spectroscopy combined with Ar$^+$-ion sputtering. We found that Mn ion was thermally diffused into the deep region of the GaAs substrate and completely reacted with GaAs. In the deep region, the Mn 2$p$ core-level and Mn 3$d$ valence-band spectra of the Mn/GaAs (001) sample heated to 600 $^{\circ}$C were similar to those of Ga$_{1-x}$Mn$_x$As, zinc-blende-type MnAs dots, and/or interstitial Mn in tetrahedrally coordinated by As atoms, suggesting that the Mn 3$d$ states were essentially localized but were hybridized with the electronic states of the host GaAs. Ferromagnetism was observed in the dilute Mn phase.
Magnetocrystalline anisotropy and uniaxiality of MnAs/GaAs(100) films  [PDF]
J. Magnus Wikberg,Ronny Knut,Sumanta Bhandary,Igor di Marco,Mikael Ottosson,Janusz Sadowski,Biplab Sanyal,P?l Palmgren,Cheuk W. Tai,Olle Eriksson,Olof Karis,Peter Svedlindh
Physics , 2010,
Abstract: We present an investigation of the magnetic behavior of epitaxial MnAs films grown on GaAs(100). We address the dependence of the magnetic moment, ferromagnetic transition temperature ($T_c$) and magnetocrystalline anisotropy constants on epitaxial conditions. From thorough structural and magnetic investigations, our findings indicate a more complex relationship between strain and magnetic properties in MnAs films than a simple stretch/compression of the unit cell axes. While a small increase is seen in the anisotropy constants the enhancement of the magnetic moment at saturation is significant. X-ray magnetic circular dichroism results show a behavior of the spin- and orbital-moment which is consistent with a structural transition at $T_c$. In particular, we find that the ratio of the orbital to spin moment shows a marked increase in the coexistence region of the ferromagnetic $\alpha$- and paramagnetic $\beta$-phases, a result that is well in accord with the observed increase of the $c/a$-ratio in the same temperature region. The \textit{ab initio} density functional calculations reveal that the magnetic properties are more sensitive towards change in in-plane axis as compared to a change of the out-of-plane axis, which is explained by the analysis of band structures. The effects of electron correlation in MnAs using \textit{ab initio} dynamical mean field theory are also presented.
Simultaneous existence of two spin-wave modes in ultrathin Fe/GaAs(001) films studied by Brillouin Light Scattering: experiment and theory  [PDF]
M. G. Pini,P. Politi,A. Rettori,G. Carlotti,G. Gubbiotti,M. Madami,S. Tacchi
Physics , 2004, DOI: 10.1103/PhysRevB.70.094422
Abstract: A double-peaked structure was observed in the {\it in-situ} Brillouin Light Scattering (BLS) spectra of a 6 \AA$ $ thick epitaxial Fe/GaAs(001) film for values of an external magnetic field $H$, applied along the hard in plane direction, lower than a critical value $H_c\simeq 0.9$ kOe. This experimental finding is theoretically interpreted in terms of a model which assumes a non-homogeneous magnetic ground state characterized by the presence of perperpendicular up/down stripe domains. For such a ground state, two spin-wave modes, namely an acoustic and an optic mode, can exist. Upon increasing the field the magnetization tilts in the film plane, and for $H \ge H_{c}$ the ground state is homogeneous, thus allowing the existence of just a single spin-wave mode. The frequencies of the two spin-wave modes were calculated and successfully compared with the experimental data. The field dependence of the intensities of the corresponding two peaks that are present in the BLS spectra was also estimated, providing further support to the above-mentioned interpretation.
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