Elastic and magnetic properties of epitaxial MnAs layers on GaAs

Abstract

We have investigated the elasto-and magneto-optical properties of MnAs layers epitaxially grown on ͑001͒ GaAs for temperatures around the structural ͑hexagonal/orthorhombic͒ and magnetic ͑ferromagnetic/ paramagnetic͒ phase transition of MnAs at T c ϳ40°C. The phase transition is accompanied by a large variation of the MnAs lattice parameter a of ϳ1%, which induces a strong and anisotropic strain field in the MnAs/ GaAs heterostructures. The latter was measured by detecting the optical anisotropy induced on the GaAs substrate by means of polarization-sensitive light transmission measurements. The experimental results show clear evidence for the quasi-uniaxial strain induced on the GaAs substrate during the phase transition, which extends over a temperature range of ϳ30°C in the MnAs/GaAs heterostructures. The strain levels are well reproduced by an elastic model for the heterostructures which assumes that the strain is transferred across the MnAs/GaAs interface without relaxation. The elastic properties during the phase transition were compared to the average magnetization probed using a SQUID magnetometer and to the magnetization near the front and the back surfaces of the MnAs films detected using the magneto-optical Kerr effect. The smaller temperature range of the phase transition observed in the magneto-optical Kerr effect measurements indicates a lower stability of the ferromagnetic phase near the surface of the MnAs layers.

Ferromagnetic nanoclusters formed by Mn implantation in GaAs

“…This coexistence can arise from a single nanostructure and/or a distribution of pure ␣-and ␤-phase nanostructures and its origin is still a subject of investigation. Both the coexistence and the hysteresis have been observed in previous works [10][11][12] on thin MnAs films grown on GaAs and were attributed to strain effects.…”

Magnetization reversal and anomalous dependence of the coercive field with temperature in MnAs epilayers grown on GaAs

“…However, during the after-growth cooling cycle, a residual strain is introduced due to the large dilatation coefficients difference between MnAs and GaAs. 20 In fact, as the α − β phase transition proceeds mainly by a 1% lattice parameter contraction in the hexagonal plane, strain will accommodate differently for MnAs/GaAs(100) or MnAs/GaAs(111)B.…”

In Depth Spatially Inhomogeneous Phase Transition in Epitaxial MnAs Film on GaAs(001)

“…Assuming that the interface with Pt deposited by FIB for the lamella preparation is equivalent to a free surface, T T is lowered as the crystal is free to make its volume changes. This effect observed in nanoparticles and in thin films 38,39 would also explain the decrease of the temperature range for the transition as revealed in Figure 4.…”

“…In a similar way, T T is lowered for strained regions if a compressive epitaxial strain is applied on MnAs thin films. 33,36,37 The epitaxial strain generated from the interface and decreasing when going to the surface 37,38 explains the low values of T T for area close to the interface followed by a gradual increase. However, if this effect was the only one, T T should increase on the whole thickness of the layer.…”