Department of Physics and Astronomy, University of Denver, Denver, Colorado 80208, USA.
Phys Rev Lett. 2012 Nov 9;109(19):196602. doi: 10.1103/PhysRevLett.109.196602. Epub 2012 Nov 7.
We present experimental evidence of a transverse thermopower, or planar Nernst effect, in ferromagnetic metal thin films driven by thermal gradients applied in the plane of the films. Samples of 20 nm thick Ni and Ni(80)Fe(20) were deposited on 500 nm thick suspended Si-N thermal isolation platforms with integrated platinum strips designed originally to allow measurement of thermally generated spin currents (the spin Seebeck effect). The low thermal conductivity of the thin supporting Si-N structure results in an essentially 2D geometry that approaches the zero substrate limit, dramatically reducing the contribution of thermal gradients perpendicular to the sample plane typically found in similar experiments on bulk substrates. The voltage on the platinum strips generated transverse to the applied thermal gradient (V(T)) is linear with increasing ΔT and exhibits a sign reversal on hot and cold sides of the sample. However, V(T) is always even in applied magnetic field and shows a sinθ cosθ angular dependence, both key indicators of the planar Nernst effect. Within the 5 nV estimated error of our experiment there is no evidence of a signal from the spin Seebeck effect, which would have cosθ angular dependence, suggesting a reduced spin Seebeck coefficient in a planar, entirely thin-film geometry.
我们提出了实验证据，证明在平面热梯度驱动下，铁磁金属薄膜中存在横向热电压，或平面诺尔特效应。20nm 厚的 Ni 和 Ni(80)Fe(20)薄膜沉积在 500nm 厚的悬浮 Si-N 热隔离平台上，该平台集成了最初用于测量热产生自旋电流（自旋 Seebeck 效应）的铂条。薄支撑 Si-N 结构的低热导率导致了基本上是 2D 的几何形状，接近零衬底极限，极大地减少了在类似的块状衬底实验中通常发现的垂直于样品平面的热梯度的贡献。在施加的热梯度（V(T))横向产生的铂条上的电压（V(T))随 ΔT 的增加呈线性变化，并在样品的热侧和冷侧表现出符号反转。然而，V(T)在施加的磁场中总是偶数，并表现出 sinθ cosθ 角依赖性，这都是平面诺尔特效应的关键指标。在我们实验估计的 5nV 误差范围内，没有来自自旋 Seebeck 效应的信号的证据，自旋 Seebeck 效应会具有 cosθ 角依赖性，这表明在平面、完全薄膜几何形状中，自旋 Seebeck 系数降低。
