Magneto-transport properties of oriented Mn2CoAl films sputtered on thermally oxidized Si substrates

Abstract

Spin gapless semiconductors are interesting novel class of materials by embracing both magnetism and semiconducting. Its potential application in future spintronics requires realization in thin film form. In this letter, we report a successful growth of spin gapless Mn 2 CoAl films on thermally oxidized Si substrates by magnetron sputtering deposition. The films deposited at 673K are well oriented to (001) direction and display a uniform-crystalline surface. Magnetotransport measurements on the oriented films reveal a semiconducting-like resistivity, small anomalous Hall conductivity and linear magnetoresistance (MR) representative of the transport signatures of spin gapless semiconductors. The magnetic properties of the films have also been investigated and compared to that of bulk Mn 2 CoAl, with small discrepancy induced by the composition deviation.------------------------------a) Author to whom correspondence should be addressed. . In this letter, we report the growth of oriented Mn 2 CoAl films on thermally oxidized Si substrates using magnetron sputtering.Magnetotransport measurements on the oriented films revealed a semiconducting-like resistivity, small Hall conductivity and linear magnetoresistance indicative of the transport features of SGS.We have deposited a series of Mn 2 CoAl films on thermally oxidized Si substrates using magnetron sputtering system with the base pressure of below 5×10 -5 Pa. The optimized sample we chose for present study is deposited under an Ar pressure of 0.2Pa while the substrate was kept at 673K with dc power of 30W. The typical thickness of the film determined by the stylus profile is about 200-nm-thick under a deposition rate of ~4 Å/s. The structure was determined by X-ray diffraction (XRD) using the Cu-Kα radiation. The composition and morphology of the film were examined by scanning electron microscope (SEM) equipped with an energy-dispersive X-ray spectroscopy (EDX). The magnetic and transport measurements were performed using a superconducting quantum interference device magnetometer (MPMS, Quantum Design) and Physics property measurement system (PPMS, Quantum Design), respectively. The electronic band structure is calculated by employing the coherent potential approximation (CPA) The sign change of ( ) xx T  slope is commonly observed in semimetals or narrow-gap semiconductors where atomic disorder, defects or nonstoichiometry gives rise to impurity levels governing low temperature conduction. 11,12 In our case, the general shape of ( ) xx T  is characteristics of semimetals or doped semiconductors which can be described by an thermal activation model with a small energy gap. 13As shown in the inset of Fig. 2(a), the conductivity is well approximated by a simple model:, where 0  indicates possible nonstoichiometry generated conduction at low temperatures. The best parameter fit yields an energy gap of 90meVThe magnetoresistance (MR) in Fig. 2 , just equivalent to the slope, is actually a temperature independent value. We plot the Hall conductivity as a funct...

First-principles calculations of exchange interactions, spin waves, and temperature dependence of magnetization in inverse-Heusler-based spin gapless semiconductors

“…for Mn 2 CoAl has been measured which has been found to be 1.95 and exactly 2 µ B , respectively, in agreement with our calculated value of 2 µ B . A similar total spin magnetic moment (1.94 µ B ) has been measured by Xu and collaborators 41 for Mn 2 CoAl films on Si substrates at 5 K. The only discrepancy occurs in the study of Jamer et al 40 in Mn 2 CoAl films on GaAs(001), where X-ray magnetic circular dichroism (XMCD) experiments where carried out. Although XMCD is a powerful technique, in Mn 2 CoAl there exist two Mn atoms with opposite spin magnetic moments.…”

“…40 On the contrary, films -grown on top of a thermally oxidized Si substrate-were found to be SGS with a Curie temperature of 550 K. 41 First-principles calculations of Skaftouros et al identified among the inverse Heusler compounds four additional potential SGS materials: Ti 2 CoSi, Ti 2 MnAl, Ti 2 VAs and Cr 2 ZnSi, the latter three being also fully-compensated ferrimagnets, and V 3 Al for which one V sublattice is not magnetic and the other two form a conventional antiferromagnet.…”

Equiatomic quaternary Heusler alloys: A material perspective for spintronic applications

“…i.e., Mn2CoAl [26], CoFeMnSi [8] and CoFeCrGa [10]. Very recently, thin films of Mn2CoAl were synthesized to check its applicability in the devices [33,34]. an additional disorder scattering and thus the spin diffusion length becomes very short [36].…”

Magnetic properties of low-moment ferrimagnetic Heusler Cr2CoGa thin films grown by molecular beam epitaxy

“…The AHE conductivity was found to be σ xy = 50 S/cm, a small value consistent with other SGS materials and arises from intrinsic Berry phase curvature. 5,6,[30][31][32][33] The as-grown Cr 2 CoGa exhibits SGS behavior indicated by the small AHE coefficient and the small activation energy characteristic of a low energy band gap.…”