Tailoring of the structural and magnetic properties of MnAs films grown on GaAs—Strain and annealing effects

Abstract

MnAs films were deposited by molecular-beam epitaxy on GaAs͑001͒ and GaAs͑111͒B surfaces. Imaging of the temperature-dependent magnetic structure by x-ray magnetic circular dichroism photoemission electron microscopy, and the comparison with magnetization measurements by superconducting quantum interference device ͑SQUID͒ magnetometry, is used to study the impact of the different strain state of MnAs/GaAs͑001͒ and of MnAs/GaAs͑111͒B films on the phase transition between ferromagnetic ␣-MnAs and paramagnetic ␤-MnAs, the spatial distribution of the two structural and magnetic phases, and the transition temperature. For the isotropically strained MnAs/GaAs͑111͒B films, the phase coexistence range is much wider than for the anisotropically strained MnAs/GaAs͑001͒ films. The characteristic change of the saturation magnetization with film thickness is found to be a universal property of films with different epitaxial orientation, if at least one MnAs͗1120͘ direction is in the film plane. For MnAs/GaAs͑001͒ films this variation is related to the striped coexistence of ␣ and ␤ MnAs and the changing intra-and inter-stripe magnetic interaction with film thickness and temperature. The magnetic structure of MnAs/GaAs͑111͒B is more complex due to the existence of three symmetry-equivalent ␣-phase domains superimposed by a honeycomb-like network of the coexisting ␤ phase. The magnetic properties ͑saturation magnetization, domain size͒ of thin MnAs/GaAs͑001͒ films can be improved by postgrowth annealing. Above a certain film thickness this is inhibited by the complex magnetic structure of the film.

Micromagnetic properties of epitaxial MnAs films on GaAs surfaces

“…The initial magnetization was assumed to be fully randomized. The surface magnetization pattern is in good agreement with the experimental results [12], however, the three-dimensional magnetization distribution deserves further attention. The magnetization distribution in the c-plane that leads to the rather simple domain types on the surface is shown in Fig.…”

“…Since the ferromagnetic areas are laterally confined and their arrangement is a function of temperature, the varying magnetic coupling geometry leads to a large variety of micromagnetic structures. They were characterized by surface magnetization [12] and stray field [13] sensitive imaging techniques -photoemission microscopy and magnetic force microscopy (MFM), respectively. The classification of the magnetic domains in MnAs films on GaAs(001) is based on the number of domains across the width of the ferromagnetic stripe, i.e.…”

Self‐organization and finite size effects in epitaxial ferromagnetic MnAs films on GaAs

“…On the other hand, it has been demonstrated that the magnetic properties of MnAs films can be improved by annealing [3,20,21]. In the present work, we report about self-organization effects and magnetic properties of MnAs/GaAs(001) films which were prepared under conditions closer to the thermodynamic equilibrium.…”

Structural and magnetic properties of ferromagnetic In1−xMnxAs1−yPy layers

“…The T B is taken to be 300 K where the FC and ZFC coincide. Upon substituting this value of T B , K V ¼ 1.4 Â 10 6 erg/cm 3 [18], M MnAs (T) of bulk hexagonal MnAs ( ¼ 910 emu/cm 3 [19]), the value of H C at 5 K is calculated to be 1380 G. The measured experimental value, however, is only 380 G. This difference in the experimental and calculated values of coercive field has previously been attributed to the breakdown of the assumption of completely isolated clusters used in Neel model [18]. This suggests that the clusters in InMnAsP are interacting through an inter-cluster exchange mechanism.…”