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Giant magnetothermopower of magnon-assisted transport in ferromagnetic tunnel junctions | | Edward McCann
; Vladimir I. Fal’ko
; | | Date: |
23 Sep 2002 | | Journal: | Phys. Rev. B 66, 134424 (2002) | | Subject: | Mesoscopic Systems and Quantum Hall Effect | cond-mat.mes-hall | | Abstract: | We present a theoretical description of the thermopower due to magnon-assisted tunneling in a mesoscopic tunnel junction between two ferromagnetic metals. The thermopower is generated in the course of thermal equilibration between two baths of magnons, mediated by electrons. For a junction between two ferromagnets with antiparallel polarizations, the ability of magnon-assisted tunneling to create thermopower $S_{AP}$ depends on the difference between the size $Pi_{uparrow, downarrow}$ of the majority and minority band Fermi surfaces and it is proportional to a temperature dependent factor $(k_{B}T/omega_{D})^{3/2}$ where $omega_{D}$ is the magnon Debye energy. The latter factor reflects the fractional change in the net magnetization of the reservoirs due to thermal magnons at temperature $T$ (Bloch’s $T^{3/2}$ law). In contrast, the contribution of magnon-assisted tunneling to the thermopower $S_P$ of a junction with parallel polarizations is negligible. As the relative polarizations of ferromagnetic layers can be manipulated by an external magnetic field, a large difference $Delta S = S_{AP} - S_P approx S_{AP} sim - (k_B/e) f (Pi_{uparrow},Pi_{downarrow}) (k_BT/omega_{D})^{3/2}$ results in a magnetothermopower effect. This magnetothermopower effect becomes giant in the extreme case of a junction between two half-metallic ferromagnets, $Delta S sim - k_B/e$. | | Source: | arXiv, cond-mat/0209520 | | Services: | Forum | Review | PDF | Favorites | |
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