Spin-Hall and anisotropic magnetoresistance in ferrimagnetic Co-Gd/Pt layers

Abstract

We present the Co-Gd composition dependence of the spin-Hall magnetoresistance (SMR) and anisotropic magnetoresistance (AMR) for ferrimagnetic Co 100-x Gd x / Pt bilayers. With Gd concentration x, its magnetic moment increasingly competes with the Co moment in the net magnetization. We find a nearly compensated ferrimagnetic state at x = 24. The AMR changes sign from positive to negative with increasing x, vanishing near the magnetization compensation. On the other hand, the SMR does not vary significantly even where the AMR vanishes. These experimental results indicate that very different scattering mechanisms are responsible for AMR and SMR. We discuss a possible origin for the alloy composition dependence.Page 5 the anisotropic magnetoresistance (AMR) that occur simultaneously in all-metal magnetic bilayers, which should help to establish microscopic models for both effects.We report the different composition dependences of SMR and AMR for the Co-Gd / Pt bilayers with in-plane magnetization. The sign of the AMR monotonically changes from positive to negative by increasing the Gd concentration and vanishes near the magnetization compensation composition. On the other hand, the SMR remains finite even when the AMR vanishes, which is a direct proof for different physics. We interpret the composition dependence of the SMR in terms of a spin mixing conductance that, in contrast to the conventional wisdom, depends on the magnet. Experimental ProcedureThin films were deposited on a thermally oxidized Si substrate using an ultrahigh vacuum compatible magnetron sputtering system with the base pressure below 2 × 10 -7 Pa. First, a 4 nm-thick Cr buffer was deposited on the Si-O substrate. Then Co and Gd were co-deposited to form the Co 100-x Gd x layers with a thickness of 30 nm. Finally, a 4 nm-thick Pt layer was deposited. All the layers were deposited at room temperature. By tuning the sputtering powers of Co and Gd targets, the Gd concentration x (at. %) was widely varied from x = 0 to x = 45. Except for x = 0, i.e. pure cobalt, the Co-Gd layers were amorphous alloys, as confirmed by reflection high energy electron diffraction (RHEED) in Fig. 1(c). In contrast to the amorphous

Dephasing of transverse spin current in ferrimagnetic alloys

“…FIM Co100-xGdx films with various Gd concentrations (x in atomic %) were deposited by co-sputtering Co and Gd targets at different Gd sputtering powers (resulting in an uncertainty in composition of ≈±0.5 at.% Gd), except for Co80Gd20 and Co70Gd30 films that were deposited by compositional alloy targets. Our vibrating sample magnetometry results (shown in the Supplemental Material [37]) reveal the magnetic compensation composition for Co100-xGdx thin films to be x ≈ 22-26, consistent with prior reports [38,39]. The angular momentum compensation composition is only ≈1 Gd at.…”

“…The diamagnetic Cu spacer also accommodates spin transport mediated solely by conduction electrons, such that direct interlayer magnon coupling [14,[41][42][43] does not play a role here 3 . Vibrating sample magnetometry [38] reveals the magnetic compensation composition for Co100-xGdx thin films to be x ≈ 22-26, consistent with prior reports [44,45]. The angular momentum compensation composition is only ≈1 Gd at.…”

“…More generally, it might be expected that transverse spin current interacts more strongly with the Co magnetization (from the spin-split itinerant 3d bands near the Fermi level) [48,77] than the Gd magnetization (primarily from the localized 4f levels ≈7-8 eV below the Fermi level [78,79]). This is analogous to magnetotransport dominated by itinerant 3d band magnetism in TM-RE FIMs [45,80]. We observe evidence of this in the modeling result for Co75Gd25 (Fig.…”

“…% below the magnetic compensation composition, since the gfactors of Co and Gd are similar (gCo ≈ 2.15, gGd = 2.0) [46]. CoGd layers in our stack structures do not show perpendicular magnetic anisotropy [15,[47][48][49][50][51][52][53][54][55][56], i.e., CoGd films here are in-plane magnetized [44,45,57,58].…”

Interlayer exchange coupling and spin Hall effect through an Ir-doped Cu nonmagnetic layer

“…Although those characteristics fascinate us largely, one of the major challenges of AF spintronics is to establish a method to manipulate the magnetic moments of the AF structure efficiently because of the difficulty in the control of their magnetic moments by applying an external magnetic field due to low magnetic susceptibility. Recently, several works reported the interaction between AF structures and electric current [3,[9][10][11][12][13][14][15][16][17]. The electrical switching in CuMnAs, which is one of the representative materials for AF spintronics, was demonstrated using current-induced internal fields originating from its crystal structure with broken inversion symmetry [9].…”