Transport properties of magnetic tunnel junctions withCo2MnSielectrodes: The influence of temperature-dependent interface magnetization and electronic band structure

Abstract

The transport properties of Co 2 MnSi/ AlO x / Co-Fe magnetic tunnel junctions showing a tunnel magnetorestistance of 95% at low temperatures are discussed with respect to temperature-dependent magnetic moments at the Co 2 MnSi/ AlO x interface and electronic band structure effects. These junctions show a considerably larger temperature and bias voltage dependence of the tunneling magnetoresistance compared to Co-Fe -B/AlO x / Co-Fe-B junctions, although the effective spin polarization of Co 2 MnSi ͑66%͒ is larger than CoFe-B ͑60%͒. Especially, the tunnel magnetoresistance of the Co 2 MnSi based junctions becomes inverse for large bias voltages. With increasing atomic disorder of the interfacial Co 2 MnSi its magnetic moments decrease and show a stronger temperature dependence. Even for the best atomic ordering achieved the corresponding spin-wave parameters of Mn and Co at the Co 2 MnSi/ AlO x interface are significantly larger than expected for Co 2 MnSi bulk and also larger than the spin-wave parameters of Co and Fe at a Co-Fe-B / AlO x interface. The influence of enhanced interfacial magnon excitation in the Co 2 MnSi/ AlO x / Co-Fe junctions on their transport properties will be discussed as well as possible origins for the negative tunnel magnetoresistance at high bias voltages.

Temperature dependence of the interface moments in Co2MnSi thin films

“…This behavior is opposite to that observed for disordered CMS films by Schmalhorst et al 9 However, in the previous work the tem- perature dependent magnetization is dominated by the onset of superparamagnetism in the polycrystalline films. 9 For an epitaxial CMS film in the disordered state, there is an increased probability of Mn-Mn nearest neighbor interactions with a corresponding antiferromagnetic coupling. Hybridization between Co and Mn atoms then results in a reduced moment on both sites, as has been previously seen.…”

“…This multiplet structure is characteristic for localized Mn ions in a d 5 ground state, such as in MnO, and has been previously observed in CMS thin films. 9,12 In addition, there is a slight shift in the position of the Mn L 3 peak for thicker capping layers, although the position of the XMCD L 3 peak ͑not shown͒ does not shift. MnO is paramagnetic at RT and will therefore not contribute to the XMCD signal, but does yield an XA spectrum shifted at higher energy compared to the corresponding metal.…”

“…Hybridization between Co and Mn atoms then results in a reduced moment on both sites, as has been previously seen. 4,9 As the sample is cooled below its effective Néel temperature, the antiferromagnetic coupling will dominate over ferromagnetic coupling leading to an overall reduction in average moments.…”

“…By measuring epitaxial samples, we avoid complications to the temperature dependence of the magnetization caused by intergranular exchange interactions in polycrystalline CMS films. 9 X-ray magnetic circular dichroism ͑XMCD͒ measured using the total electron yield ͑TEY͒ technique has been previously shown to be a unique method for obtaining elementspecific magnetic moments. 10 In a 3d transition metal in vacuum, the TEY signal is generated by secondary electrons following x-ray photon absorption.…”

Engineering the electronic, magnetic, and gap-related properties of the quinternary half-metallic Heusler alloys

“…One of the most interesting concepts in spintronics is the half-metallicity [4,5,6,7,8,9,10]. Halfmetals are hybrids between normal metals and semiconductors.…”