Spin-flop magnetoresistance in Gd/Co multilayers

Abstract

Low-temperature magnetotransport and magnetization measurements have been performed at high magnetic fields in samples of a layered artificial ferrimagnet: multilayers made by sequential sputtering of Gd and Co. Strong interfacial reaction leads to severe alloying and, if the Co layer is nominally thick enough (\ensuremath{\gtrsim}4 nm), the samples are mainly comprised of alternated pure Co and ${\mathrm{Gd}}_{0.7}{\mathrm{Co}}_{0.3}$ alloy layers. Such spin systems are antiferromagnetically coupled at the interface region, and the compensation temperature of this ``giant'' ferrimagnet is determined by the thickness of Gd and Co layers. Both magnetization and magnetoresistance measurements indicate the so-called spin-flop transition at temperatures below the Curie point of the alloy layer (\ensuremath{\sim}180 K). Spin-flop magnetoresistance resembles the anisotropic magnetoresistance of ferromagnets except for the field range in which it develops: $H>{10}^{3}--{10}^{4}$ Oe for modulation length of \ensuremath{\sim}15 nm. The effect arises in the Co layers from anisotropic carrier scattering.