Influence of heat flow directions on Nernst effects in Py/Pt bilayers

Abstract

We investigated the voltages obtained in a thin Pt strip on a Permalloy film which was subject to in-plane temperature gradients and magnetic fields. The voltages detected by thin W-tips or bond wires showed a purely symmetric effect with respect to the external magnetic field which can be fully explained by the planar Nernst effect (PNE). To verify the influence of the contacts measurements in vacuum and atmosphere were compared and gave similar results. We explain that a slightly in-plane tilted temperature gradient only shifts the field direction dependence but does not cancel out the observed effects. Additionally, the anomalous Nernst effect (ANE) could be induced by using thick Au-tips which generated a heat current perpendicular to the sample plane. The effect can be manipulated by varying the temperature of the Au-tips. These measurements are discussed concerning their relevance in transverse spin Seebeck effect measurements.Comment: 6 pages, 8 figures, added two paragraphs in section II

Anomalous Nernst effect in Ir22Mn78/Co20Fe60B20/MgO layers with perpendicular magnetic anisotropy

“…21 A typical setup, utilizing an out-of-plane temperature gradient and an in-plane magnetic field, has been used to investigate the ANE in previous works. [22][23][24][25][26] The trouble with this configuration is that, in addition to generating an ANE voltage, the out-of-plane temperature gradient can also generate a spin current through the so-called longitudinal spin Seebeck effect (LSSE), 22,[27][28][29][30][31][32][33] which flows directly from the ferromagnetic (FM) into the adjacent non-magnetic metal (NM) and generates a voltage because of the inverse spin Hall effect (ISHE). In order to distinguish the spin Seebeck effect (SSE) and ANE, extensive efforts [34][35][36][37] have been made to compare the voltage in different temperature gradient configurations.…”

Dependence of transverse magnetothermoelectric effects on inhomogeneous magnetic fields

“…AMTEP amplitude; V of f set is the voltage signal produced in the Au wires due to the conventional charge Seebeck effect (for details see Appendix B). The peaks in V y (H) are caused by the alignment procedure of the magnetization M parallel to the magnetic easy axis of the Py film [16]. The easy axis of the sample has an angle of ϕ ≈ 35 • with respect to the x-axis of the sample.…”

“…3 we show a typical set of experimental data of the voltages V y (H) (green lines) measured across the Pt strip for the following parameters: base temperature T str = 360 K; temperature difference on the sample ∆T The peaks visible in the V y (H) curves as well as the sin 2Θ H dependence of A(Θ H ) are related to the AMTEP, for details see [15,16]. The transverse voltage, associated with the AMTEP traces, can be described as: (1) where Θ 0 is the angle between the temperature gradient ∇ x T and the magnetization vector M ; A 0 is the (2) and is placed in the middle of the vacuum chamber (3) without contact to its walls.…”

“…However, it turned out that the TSSE [3][4][5][6][7][8][9][10][11][12][13][14][15][16], especially when using metallic ferromagnets [3-7, 13, 15, 16], is under strong discussion. Other magneto-thermoelectric effects, like the anomalous Nernst effect (ANE) [6,7,[15][16][17] and the anisotropic magneto-thermopower (AMTEP, also known as the planar Nernst effect (PNE)) [4,15,16,18,19] play an important role in the TSSE measurements and contribute to the detected signals. ANE and TSSE signals are antisymmetric with respect to the external magnetic field, have the shape of hysteresis loops and both follow the cos Θ 0 dependence, where Θ 0 is the angle between the magnetization vector M and the temperature gradient ∇T .…”

“…The AMTEP can be identified by its sin 2Θ 0 angular dependence and symmetric shape. Thus, it was postulated that the ANE caused by an unintended outof-plane temperature gradient (due to heat flux into surrounding area by radiation [15] and through electrical contacts by thermal conductivity [16]) is the main effect masking TSSE in metallic ferromagnets. Small static environmental magnetic fields of the Earth magnetic field's order of magnitude and lower are typically not considered in experimental set-ups.…”