Antisymmetric magnetoresistance and helical magnetic structure in a compensated Gd/Co multilayer

Abstract

Using spin dependent specular and off-specular polarized neutron reflectivity (PNR), we report the observation of a twisted helical magnetic structure with planar 2π domain wall (DW) and highly correlated magnetic domains in a Gd/Co multilayer. Specular PNR with polarization analysis reveals the formation of planar 2πDWs below a compensation temperature (T Comp ), resulting to positive exchange bias in this system. Off-specular PNR with spin polarization showed development of magnetic inhomogenities (increase in magnetic roughness) for central part (thickness ~ 25-30 Å) of each Gd layer, where magnetization is aligned perpendicular (in-plane) to an applied field. These magnetic roughness are vertically correlated and results into Bragg sheet in spin flip channel of Offspecular PNR data, which is contributing towards an antisymmetric magnetoresistance at T Comp in the system. The growth and tunability of highly correlated magnetic inhomogeneities (roughness) and domain structure around T Comp in combination of twisted helical magnetic structure with planar 2πDWs will be key for application in all-spin-based technology.The current-induced manipulation of magnetic order through spin-orbit torque (SOT) has recently attracted great interest for the realization of magnetic memory and logic application devices with fast switching [1][2][3][4][5]. The Dzyaloshinskii-Moriya interaction [6], and the spin Hall effect via heavy-metal layers [7-9] were the major phenomena that attributed for large chiral spin torques. Exchange coupling torque (ECT) recently showed a significant enhancement of the spin-torque efficiency in artificial antiferromagnetic (AF) structures [10,11], which allows moving nanoscale magnetic domain walls (DW) with current at large velocities [10].The compensated rare earth (RE)-transition metal (TM) alloys and heterostructures,where the RE and TM moments are aligned antiparallel due to the strong AF interaction and the total net moment tends to zero, are potential candidate materials for realizing devices with higher speed and density [12][13][14][15][16]. A class of ferrimagnets consisting of RE-TM alloys and heterostructures also have the potential to exhibit DW motion via an ECT [17,18]. Fast switching in compensated systems can further be influenced by magnetic [16,19] and optical [20] fields. Recently Vedmedenko et al. [21], have pointed out theoretically that nano-sized stable magnetic helices can be used for magnetic energy storage. Realization of magnetic helices with stable magnetic properties have also been studied theoretically [22] and experimentally [23] in exchange-coupled thin films and RE/TM multilayers, respectively. It is recognized that magnetization reversal and a magnetic helical configuration (planar 2πDWs) in RE-TM multilayer with no external magnetic field around the compensation temperature (T Comp , the temperature at which total moments of RE-TM multilayer tend to zero) is the key to manipulating magnetic devices [20,23]. However the response of interface DWs in RE-TM heterostr...

Interface morphology driven exchange interaction and magnetization reversal in a Gd/Co multilayer

“…4(a and b) show the temperature-dependent normalized magnetization [ M ( T )/ M (300 K)] data for the pristine and annealed multilayer, respectively, after zero-field cooling (ZFC, blue open circles) and field cooling (FC, red closed circles) in an in-plane applied field of 500 Oe. The FC M ( T ) data are consistent with the results from other RE/TM multilayers reported earlier, 1,2,6,7,28–31 suggesting temperature-dependent magnetic states and phase transitions. The FC M ( T ) data for both the pristine and annealed multilayer show a minimum in the magnetization at a temperature ( T comp ) of 128 and 150 K, respectively.…”

“…1(a) shows the GIXRD pattern (intensity in log scale) for Gd/Co in the pristine and annealed (at 573 K) conditions, which shows a similar pattern with fcc and hcp structures for Gd and Co, respectively, and is consistent with earlier measurements. 28,29,31 The Bragg peaks are labelled for different reflections from a crystalline phase of Gd and Co. In Fig.…”

“…23,24 Thus the spin configurations like helices in the form of planar DW structures with stable magnetic properties in the exchange-coupled RE-TM systems near the compensation temperature is the key to manipulating high-speed magnetic devices. 25–27 Recently the realization of a twisted helical magnetic structure with planar 2π DWs and highly correlated magnetic domains in Gd/Co multilayers 28–31 and other RE-TM systems 5,27,32 has been reported. In addition, a double hysteresis loop (DHL) and an exchange bias (EB) were also observed in these RE-TM heterostructure systems, which was attributed to the depth-dependent magnetic helical structures.…”

“…In addition, a double hysteresis loop (DHL) and an exchange bias (EB) were also observed in these RE-TM heterostructure systems, which was attributed to the depth-dependent magnetic helical structures. 5,27,28,31,32 The interface structure and morphology have been found to play a vital role in determining the temperature-dependent magnetic configuration and phases in the Gd/TM based multilayers. 6,7,28–31 Here we report the influence of the interface morphology on the evolution of the macroscopic magnetic properties, i.e.…”

“…5,27,28,31,32 The interface structure and morphology have been found to play a vital role in determining the temperature-dependent magnetic configuration and phases in the Gd/TM based multilayers. 6,7,28–31 Here we report the influence of the interface morphology on the evolution of the macroscopic magnetic properties, i.e. , exchange bias field ( E B ), coercive field, compensation temperature ( T comp ), and a vertical shift in the magnetization curve, in the Gd/Co multilayer across the T comp , by combining the experimental methods and theoretical calculations using a one-dimensional-spin based model.…”