Evidence for strong magnon contribution to the TMR temperature dependence in MgO based tunnel junctions

Abstract

We have prepared MgO based magnetic tunnel junctions which show up to 143% tunneling magnetoresistance ͑TMR͒ ratio at room temperature and 205% at 12 K. This TMR temperature dependence is mainly caused by a strong temperature dependence in the antiparallel magnetic state, while in the parallel state the change of condunctance is small. We found that a modified version of the magnon excitation model may be applied to these MgO magnetic tunnel junctions. If the thermal smearing of the tunneling electron's energy is included it is possible to fit the temperature dependence. We will show the results for our data and we have also tested our model successfully on data from other publications.

Temperature dependence of spin-dependent tunneling conductance of magnetic tunnel junctions with half-metallicCo2MnSielectrodes

“…4 are for MTJs having almost identical nominal t MgO values of 2.66 nm ± 1% (Table I). Thus, the smearing effect of the Fermi distribution function at finite temperatures to the tunneling conductance [50,52,61] can be regarded as almost identical for these MTJs.…”

“…Previous studies on MTJs with an amorphous AlO x tunnel barrier reported an increase in G P with increasing T up to room temperature [50,51]. Most of the epitaxial MTJs with an MgO or MgAl 2 O 4 tunnel barrier that have been reported so far have also shown an increase in G P [8,[52][53][54][55][56][57], while some epitaxial MTJs showed a decrease [58][59][60]. The increase in G P with T for MTJs, including epitaxial MTJs, has been mostly explained by spin-flip inelastic tunneling via a thermally excited magnon, i.e., the Zhang model with an evidence of the role played by magnons indicated by tunneling spectroscopy [51,52,56].…”

“…Most of the epitaxial MTJs with an MgO or MgAl 2 O 4 tunnel barrier that have been reported so far have also shown an increase in G P [8,[52][53][54][55][56][57], while some epitaxial MTJs showed a decrease [58][59][60]. The increase in G P with T for MTJs, including epitaxial MTJs, has been mostly explained by spin-flip inelastic tunneling via a thermally excited magnon, i.e., the Zhang model with an evidence of the role played by magnons indicated by tunneling spectroscopy [51,52,56]. Alternatively, the increase in G P with T for an epitaxial MTJ has been explained within the framework of the Shang model by taking into account the smearing effect of the Fermi distribution function at finite temperatures [53], which increases G as T increases [61].…”

“…The Shang model predicts that G AP increases with T , of which the effect on G AP (T ) is apparently in agreement with that of the Zhang model. Indeed, the experimental G AP (T ) had been explained and fitted by the original Zhang model in [51,52] or by the Shang model in [53]. However, note that the tunneling mechanisms that determine the T dependence are intrinsically different between these two models.…”

Magneto-optical investigation of epitaxial nonstoichiometric Co2MnGe thin films

“…13 It was recently shown that the temperature dependence of the TMR ratio of a Co 2 FeAl 0.5 Si 0.5 / MgAl 2 O x / CoFe TMJ followed a T 3/2 power law ͑T being the temperature͒, due to the thermal excitation of spin waves. 14 cussed in terms of the role of thermally excited magnons for spin-flip scattering 17 from the majority-spin band to minority spin gap states, including minority spin interface states, in the emitter electrode, and vice versa in the collector electrodes. 16,18 In this context, the knowledge of the exchange stiffness, which will largely determine the energy required to create a spin wave, is a crucial parameter that must be understood to gain insight into the construction of superior devices.…”