Effect of a magnetic field on the magnetostructural phase transition of MnAs films on GaAs

Abstract

We present a systematic investigation of the effect of an external magnetic field on the first order structural ͑hexagonal/orthorhombic͒ and magnetic ͑ferromagnetic/paramagnetic͒ phase transition of MnAs films grown epitaxially on GaAs͑001͒. The experimental results obtained using x-ray diffraction, magneto-optical Kerr effect, and SQUID magnetometry clearly show two magnetic field regimes where the temperature evolution of the magnetic and structural macroscopic properties of the films exhibit different behavior near the phase transition. The different evolution of the magnetic and structural properties fades away when an external magnetic field larger than 1 kOe is applied along the easy magnetization axis. These results are attributed to two effects induced by the external magnetic field. The first one is the field-induced phase transition, similar to that reported in MnAs bulk. The second one, which dominates for fields below 1 kOe, is attributed to the effect of the geometry of the microstructured domains formed during the phase transition on the macroscopic magnetic properties of the film. As a result, the changes in the magnetic properties detected by macroscopic measurements take place at temperatures lower than those observed by structural measurements, even though structural and magnetic phase transitions must occur simultaneously.

Ultrasonic triggering of giant magnetocaloric effect in MnAs thin films

“…Below in the text, we will show that this ∆s m -shift leads to the attenuation peak shift that we have observed (4.6 • CT −1 ). It also recalls the α-fraction shift versus magnetic field observed by Iikawa et al [24], with the same order of magnitude (5 • CT −1 ). The same group reported a similar shift equal to δǫ where ǫ is the strain applied along the MnAs easy axis, and δ is temperature independant between 30 and 40 • C (see fig.…”

Magnetic analysis of MnAs films grown on GaAs and Si substrates for potential spintronics and magnetocaloric applications

“…A relatively large thermal hysteresis (about 10 K) is instead evident from the temperature dependence of initial susceptibility of MnAs(290 nm)/(0 0 1)GaAs sample, although this effect vanishes on increasing the applied field, such as at 10 kOe it can no more be revealed. A similar disappearance of thermal hysteresis with increase in field has been reported for some MBE-grown MnAs/ (0 0 1)GaAs thin films with comparable thickness (130 nm) [24].…”

“…Therefore, one expects an increase of T c with decrease in p that should correspond to the release of strains exerted by the substrate when increasing film thickness. It has to be noted that the transition temperatures of MBE-grown MnAs/ (0 0 1)GaAs films deduced from both magnetization measurements [24] and X-rays diffraction curves [9,26] show a variety that depends on thickness and growing conditions, and in general the intermediate value between T c (1) and T c (2) is slightly but appreciably lower ( E300-310 K) than that measured in our samples. However, an increase of T c by about 15 K together with a reduction of its thermal hysteresis has been reported for epitaxial MnAs/(0 0 1)GaAs with the orientation of the hexagonal c-axis of MnAs cell tilted with respect to the GaAs substrate [26].…”

Interplay of stress and magnetic properties in epitaxial MnAs films

“…MnAs Azimuthal orientation Notation Reference (001) ( 1 100) MnAs [11 20]||GaAs [110] A-A 0 [10,12,42,44] MnAs[0001]||GaAs[ 1 10] (1 101) MnAs [11 20]||GaAs [110] A 1 [45,46] MnAs [11 20]||GaAs[ 1 10] (1 100)…”