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Thermoelectric Signal Enhancement by Reconciling the Spin Seebeck and Anomalous Nernst Effects in Ferromagnet/Non-magnet Multilayers.

Lee KD, Kim DJ, Yeon Lee H, Kim SH, Lee JH, Lee KM, Jeong JR, Lee KS, Song HS, Sohn JW, Shin SC, Park BG - Sci Rep (2015)

Bottom Line: The thermoelectricity in FM/non-magnet (NM) heterostructures using an optical heating source is studied as a function of NM materials and a number of multilayers.It is observed that the overall thermoelectric signal in those structures which is contributed by spin Seebeck effect and anomalous Nernst effect (ANE) is enhanced by a proper selection of NM materials with a spin Hall angle that matches to the sign of the ANE.Moreover, by an increase of the number of multilayer, the thermoelectric voltage is enlarged further and the device resistance is reduced, simultaneously.

View Article: PubMed Central - PubMed

Affiliation: Department of Materials Science and Engineering, KI for the Nanocentury, KAIST, Daejeon, 305-701, Korea.

ABSTRACT
The utilization of ferromagnetic (FM) materials in thermoelectric devices allows one to have a simpler structure and/or independent control of electric and thermal conductivities, which may further remove obstacles for this technology to be realized. The thermoelectricity in FM/non-magnet (NM) heterostructures using an optical heating source is studied as a function of NM materials and a number of multilayers. It is observed that the overall thermoelectric signal in those structures which is contributed by spin Seebeck effect and anomalous Nernst effect (ANE) is enhanced by a proper selection of NM materials with a spin Hall angle that matches to the sign of the ANE. Moreover, by an increase of the number of multilayer, the thermoelectric voltage is enlarged further and the device resistance is reduced, simultaneously. The experimental observation of the improvement of thermoelectric properties may pave the way for the realization of magnetic-(or spin-) based thermoelectric devices.

No MeSH data available.


Numerically calculated temperature profile of [CoFeB(8 nm)/Pt(3 nm)]10 multilayer.(a) Relative temperature variation. (b) Temperature gradient as a stack unit. The average temperature gradient for each stack is shown. Laser beam is illuminated from left where z = 0.
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f6: Numerically calculated temperature profile of [CoFeB(8 nm)/Pt(3 nm)]10 multilayer.(a) Relative temperature variation. (b) Temperature gradient as a stack unit. The average temperature gradient for each stack is shown. Laser beam is illuminated from left where z = 0.

Mentions: While the exact origin of the enhancement of multilayer heterostructure remains yet to be understood, this can be inferred to the fact that the thermally induced spin current can be injected into both upper and lower NM material in the multilayer system, which may increase the STE effect more than simple multiplication as shown in Fig. 5(a). Moreover, a reduced thermal conductivity by the formation of the multiple interfaces can possibly contribute to the STE enhancement of the multilayer31. Importantly, optical absorption of metal layer enhances its thermal gradient induced by laser illumination. Fig. 6(a) shows the relative temperature variation of [CoFeB(8 nm)/Pt(3 nm)]10 multilayer sample when P = 27 mW and d = 5 μm of the experimental condition. Its average temperature gradient, as defined previously, is shown in Fig. 6(b) as a stack unit. Interestingly, this figure reveals that the exponential attenuation of optical source accelerates the rate of temperature gradient as the optical beam penetrates multilayer sample up to the number of repeat (n) ~ 4. This explains the rapid increase of ΔV, when n is less than 3~4. The ∇T dependence on the various optical absorption coefficients was given in the Supplementary information. One of reasons for the additional increase of ΔV, even when n > 6 in Fig. 5(b), could be interpreted by the injection as well as extraction of spin current of NM layer. Overall, this means that ANE as well as SSE could be further enhanced in case of multilayer with optical heating.


Thermoelectric Signal Enhancement by Reconciling the Spin Seebeck and Anomalous Nernst Effects in Ferromagnet/Non-magnet Multilayers.

Lee KD, Kim DJ, Yeon Lee H, Kim SH, Lee JH, Lee KM, Jeong JR, Lee KS, Song HS, Sohn JW, Shin SC, Park BG - Sci Rep (2015)

Numerically calculated temperature profile of [CoFeB(8 nm)/Pt(3 nm)]10 multilayer.(a) Relative temperature variation. (b) Temperature gradient as a stack unit. The average temperature gradient for each stack is shown. Laser beam is illuminated from left where z = 0.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4447118&req=5

f6: Numerically calculated temperature profile of [CoFeB(8 nm)/Pt(3 nm)]10 multilayer.(a) Relative temperature variation. (b) Temperature gradient as a stack unit. The average temperature gradient for each stack is shown. Laser beam is illuminated from left where z = 0.
Mentions: While the exact origin of the enhancement of multilayer heterostructure remains yet to be understood, this can be inferred to the fact that the thermally induced spin current can be injected into both upper and lower NM material in the multilayer system, which may increase the STE effect more than simple multiplication as shown in Fig. 5(a). Moreover, a reduced thermal conductivity by the formation of the multiple interfaces can possibly contribute to the STE enhancement of the multilayer31. Importantly, optical absorption of metal layer enhances its thermal gradient induced by laser illumination. Fig. 6(a) shows the relative temperature variation of [CoFeB(8 nm)/Pt(3 nm)]10 multilayer sample when P = 27 mW and d = 5 μm of the experimental condition. Its average temperature gradient, as defined previously, is shown in Fig. 6(b) as a stack unit. Interestingly, this figure reveals that the exponential attenuation of optical source accelerates the rate of temperature gradient as the optical beam penetrates multilayer sample up to the number of repeat (n) ~ 4. This explains the rapid increase of ΔV, when n is less than 3~4. The ∇T dependence on the various optical absorption coefficients was given in the Supplementary information. One of reasons for the additional increase of ΔV, even when n > 6 in Fig. 5(b), could be interpreted by the injection as well as extraction of spin current of NM layer. Overall, this means that ANE as well as SSE could be further enhanced in case of multilayer with optical heating.

Bottom Line: The thermoelectricity in FM/non-magnet (NM) heterostructures using an optical heating source is studied as a function of NM materials and a number of multilayers.It is observed that the overall thermoelectric signal in those structures which is contributed by spin Seebeck effect and anomalous Nernst effect (ANE) is enhanced by a proper selection of NM materials with a spin Hall angle that matches to the sign of the ANE.Moreover, by an increase of the number of multilayer, the thermoelectric voltage is enlarged further and the device resistance is reduced, simultaneously.

View Article: PubMed Central - PubMed

Affiliation: Department of Materials Science and Engineering, KI for the Nanocentury, KAIST, Daejeon, 305-701, Korea.

ABSTRACT
The utilization of ferromagnetic (FM) materials in thermoelectric devices allows one to have a simpler structure and/or independent control of electric and thermal conductivities, which may further remove obstacles for this technology to be realized. The thermoelectricity in FM/non-magnet (NM) heterostructures using an optical heating source is studied as a function of NM materials and a number of multilayers. It is observed that the overall thermoelectric signal in those structures which is contributed by spin Seebeck effect and anomalous Nernst effect (ANE) is enhanced by a proper selection of NM materials with a spin Hall angle that matches to the sign of the ANE. Moreover, by an increase of the number of multilayer, the thermoelectric voltage is enlarged further and the device resistance is reduced, simultaneously. The experimental observation of the improvement of thermoelectric properties may pave the way for the realization of magnetic-(or spin-) based thermoelectric devices.

No MeSH data available.