Statistical characterization of the spin Hall magnetoresistance in YIG/Pt heterostructures

The spin Hall magnetoresistance (SMR) is widely used to study the interplay between charge and spin currents in bilayers of a magnetic insulator and a normal metal. However, not much is known about the spatial variation of the SMR across the surface of the same sample. In this work, we investigate the statistical distribution of the SMR in hundreds of nominally identical Hall bar structures patterned into prototypical yttrium iron garnet (YIG)/Pt heterostructures. We find a Gaussian-distributed SMR with a narrow standard deviation of approximately <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"> <a:mrow> <a:mn>10</a:mn> <a:mo>%</a:mo> </a:mrow> </a:math> of the mean value in each YIG/Pt bilayer studied. However, the variation of the mean SMR between different YIG/Pt samples can be as large as <b:math xmlns:b="http://www.w3.org/1998/Math/MathML"> <b:mrow> <b:mo>∼</b:mo> <b:mn>35</b:mn> <b:mo>%</b:mo> </b:mrow> </b:math> , despite nominally identical fabrication conditions. Additionally, we compare the SMR statistics in YIG/Pt heterostructures prepared (without breaking the vacuum) and (with the YIG layer exposed to air before Pt deposition), as well as in CoFeB/Pt. We find the SMR standard deviation to be systematically smaller for interfaces. We conclude that on a microscopic level, local variations of the interface quality captured by the spin mixing conductance are the most likely origin for the observed SMR amplitude variations.