Anisotropic magnetic-field-induced phase transition in MnAs nanoribbons

LAURA B. STEREN; FEDERICO FERNANDEZ BALDIS,MARTIN SIRENA; VICTOR H. ETGENS, MAMMOUD EDDRIEF; CHRISTIAN ULYSSE, GIANCARLO FAINI.

Barcelona

Conferencia; International Conference on Magnetism; 2015

MnAs thin films are known to present a phase coexistence of regularly arranged ferromagnetic  and paramagnetic  stripes below the Curie temperature, when grown onto GaAs(100) substrates. The observation of the effect in nanostructures whose sizes matched the characteristic length of the / arrays allowed us to tune the phase coexistence regime by changing different parameters. In our work, we report the observation of a magneto-structural phase transition induced by magnetic field on MnAs nano-ribbons. The transformation of high-resistance paramagnetic regions into low-resistance ferromagnetic ones explains the sharp resistivity drops that are observed when critical magnetic fields are applied to the samples. The critical field required to induce the phase transition in MnAs, depends of the magnetic history and the temperature. As the temperature of the system increases, higher fields are needed to stabilize the ferromagnetic phase. The phenomenon is hysteretic, highly anisotropic and size dependent. We show that confinement effects in MnAs ribbons produce extraordinary features in the field dependence of the MR. Our results highlights and provides with unique evidences of the magnetic-field phase-induced transition and its characteristics