Sutapa Dutta

Indian Institute of Technology Bombay

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Ashwin A. Tulapurkar

Indian Institute of Technology Bombay

Arnab Bose

Johannes Gutenberg University Mainz

Swapnil Bhuktare

Indian Institute of Technology Tirupati

Hanuman Singh

University of California, Berkeley

Ambika Shanker Shukla

Indian Institute of Technology Bombay

Heston A. Mendonca

Indian Institute of Technology Bombay

Venu Gopal Achanta

Tata Institute of Fundamental Research

Rachit R. Pandey

Indian Institute of Technology Bombay

Shinji Miwa

The University of Tokyo

Minori Goto

Spintronics Research Network of Japan

Cooperative Institutions

Indian Institute of Technology Bombay

Motilal Nehru National Institute of Technology

Osaka University

Tata Institute of Fundamental Research

Japan Science and Technology Agency

Spintronics Research Network of Japan

Cornell University

Indian Institute of Technology Kanpur

Centre National de la Recherche Scientifique

CEA Grenoble

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Effect of Edge Roughness on Resistance and Switching Voltage of Magnetic Tunnel Junctions

IEEE Electron Device Letters (2023)

Rachit R. Pandey Sutapa Dutta Heston A. Mendonca Ashwin A. Tulapurkar

We investigate the impact of edge roughness on the electrical transport properties of magnetic tunnel junctions using non-equilibrium Greens function formalism. We have modeled edge roughness as a stochastic variation in the cross-sectional profile of magnetic tunnel junction characterized by the stretched exponential decay of the correlation function. The stochastic variation in the shape and size changes the transverse energy mode profile and gives rise to the variations in the resistance and switching voltage of the magnetic tunnel junction. We find that the variations are larger as the magnetic tunnel junction size is scaled down due to the quantum confinement effect. A model is proposed for the efficient calculation of edge roughness effects by approximating the cross-sectional geometry to a circle with the same cross-sectional area. Further improvement can be obtained by approximating the cross-sectional area to an ellipse with an aspect ratio determined by the first transverse eigenvalue corresponding to the 2D cross section. These results would be useful for reliable design of the spin transfer torque-magnetic random access memory (STT-MRAM) with ultra-small magnetic tunnel junctions.

Tunnel magnetoresistance

Tunnel junction

Spin-transfer torque

Biasing

Ellipse

10.1109/led.2023.3254811

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Citations (4)

Enhanced spin–orbit torques in strained NiFe/Pt bi-layers on flexible substrate

Journal of Magnetism and Magnetic Materials (2023)

Akanksha Chouhan Heston A. Mendonca Sutapa Dutta Ambika Shanker Shukla Rachit R. Pandey

Magnetization dynamics

Damping torque

10.1016/j.jmmm.2023.171337

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Observation of nonlocal orbital transport and sign reversal of dampinglike torque in Nb/Ni and Ta/Ni bilayers

Physical review. B./Physical review. B (2022)

Sutapa Dutta Ashwin A. Tulapurkar

We study the efficiencies of dampinglike and fieldlike torques in Nb/Ni and Ta/Ni bilayers and compare them with $\mathrm{Nb}/{\mathrm{Ni}}_{81}{\mathrm{Fe}}_{19}$(Py) and Ta/Py as a function of the thickness of a ferromagnet. In both these systems, we observe that the sign of the dampinglike torque is negative for Py whereas it is positive for nickel. The negative sign of the dampinglike torque in Nb/Py and Ta/Py is consistent with the negative sign of the spin Hall effect in niobium and tantalum. The sign reversal of the dampinglike torque in Nb/Ni and Ta/Ni suggests a strong generation of the orbital current from niobium and tantalum, which is converted into the spin current inside nickel and produces the orbital torque. We also find that both the dampinglike and fieldlike efficiencies change signs when nickel is replaced by Py.

10.1103/physrevb.106.184406

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Citations (17)

Sign Reversal of Fieldlike Spin-Orbit Torque in an Ultrathin Cr/Ni Bilayer

Physical Review Applied (2018)

Arnab Bose Hanuman Singh Varun K. Kushwaha Swapnil Bhuktare Sutapa Dutta

In this work report unconventional sign change of field like spin orbit torque in ultra-thin Chromium(1.5nm-5nm)/Nickel(8nm) bi-layer. We performed standard spin-torque ferromagnetic resonance (ST-FMR) experiment in Cr/Ni bi-layer by passing radio frequency current and measuring DC voltage. We observe that when thickness of Cr layer is critically low (<6nm) spin orbit torque by Cr on Ni significantly increases. Most importantly the sign of field like torque is opposite to the Oersted field generated torque. To verify interracial nature of this torque, 2 nm thin Cu is inserted between Cr and Ni and field like torque behaves same as Oersted field induced torque. Hence possible origin of such unconventional sign change of field like torque could be inter-facial Rashba like spin orbit interaction which is present between Cr and Ni but vanishes in Cr/Cu/Ni hetero-structure. From our experiment we can estimate that approximately 35 Oe of effective Rashba like magnetic field is created on 8 nm thicker Ni layer, when 1E12 A/m^2 current flows through Cr layer. All experiments are done at room temperature. So Cr thin film is expected to behave like paramagnet (Neel temperature of bulk Cr is 311K). Hence Cr can be a good choice as a heavy metal to employ large spin orbit torque combining bulk spin Hall effect and inter-facial Rashba interaction.

10.1103/physrevapplied.9.014022

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Citations (30)

Observation of Anomalous Spin Torque Generated by a Ferromagnet

Physical Review Applied (2018)

Arnab Bose D. D. Lam Swapnil Bhuktare Sutapa Dutta Hanuman Singh

Through the anomalous Hall effect (AHE), a ferromagnet can generate spin current in the direction transverse to an applied charge current, and hence exert a torque on another ferromagnet. The authors observe, however, that when in-plane current is passed through a spin-valve structure, an out-of-plane effective magnetic field is created, which exerts torque on the free layer. This effective field, originating from the broken mirror symmetry of the spin valve, completely dominates the dampinglike torque that one expects from the AHE. Such a strong out-of-plane field would be useful for switching perpendicular magnetic bits in spintronic high-density nonvolatile memory applications.

Spin-transfer torque

Spin valve

10.1103/physrevapplied.9.064026

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Citations (53)

Observation of interface-induced nonlocal spin-torques from Gd/Pt interface

Applied Physics Letters (2024)

Sutapa Dutta Ashwin A. Tulapurkar Anurita Bose

We investigate spin–orbit torques (SOTs) generated by Gd/Pt and Ti/Pt interfaces by performing spin-torque ferromagnetic resonance measurements at room temperature. We report a sizable spin-current created by the Gd/Pt interface, exhibiting the damping-like-torque efficiency per unit electric field, ξDLE=−8 ± 0.6×104ℏ2e(Ωm)−1 as observed in Gd(5 nm)/Pt(1.5 nm)/Py(3 nm-6 nm)/Pt(1.5 nm) heterostructures. This interface-induced spin-current is attributed to the vertical electric field produced by the broken structural inversion symmetry, with a work function difference of 2.75 eV between Gd and Pt. This is further substantiated by varying the thickness of the Gd-layer. We compare these results with the Ti/Pt interface, which has a work function difference of 1.3 eV, by implementing Ti(5 nm)/Pt(1.5 nm)/Py(3 nm-6 nm)/Pt(1.5 nm) heterostructures. We find that the spin-current induced by the Ti/Pt interface is too small to overcome the remnant SOTs caused by the asymmetrically grown Pt layers on both sides of Py. Our work reveals the role of interface-induced spin currents for practical applications, which can be leveraged to produce robust spin torques that complement the bulk spin-Hall torque.

Interface (matter)

10.1063/5.0234088

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Control of magnetization dynamics by spin-Nernst torque

Physical review. B./Physical review. B (2018)

Arnab Bose Ambika Shanker Shukla Sutapa Dutta Swapnil Bhuktare Hanuman Singh

Relativistic interaction between an electron's spin and orbital angular momentum has provided an efficient mechanism to control the magnetization of nanomagnets. Extensive research has been done to understand and to improve spin-orbit-interaction-driven torques generated by nonmagnets by applying electric current. In this work, we show that heat current in a nonmagnet can also couple to its spin-orbit interaction to produce torque on the adjacent ferromagnet. Hence, this work provides a platform to study spin-orbito-caloritronic effects in heavy metal/ferromagnet bilayers.

Magnetization dynamics

Nernst effect

Dynamics

10.1103/physrevb.98.184412

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Citations (14)

Sensitive measurement of spin-orbit torque driven ferromagnetic resonance detected by planar Hall geometry

Applied Physics Letters (2017)

Arnab Bose Sutapa Dutta Swapnil Bhuktare Hanuman Singh Ashwin A. Tulapurkar

The magnetization of a nano-magnet can be manipulated and even switched by spin-orbit torques. Hence, accurate characterization of these torques is essential from the application perspective. In this work, we present an alternative method to characterize the spin-orbit torque utilizing the planar Hall effect of a ferromagnet. We show that while the ferromagnet is excited to resonance due to spin-orbit torque, its planar Hall resistance also varies, which leads to sensitive detection of spin-orbit torque. We further demonstrate that planar Hall geometry enables us to estimate spin Hall angle measuring change in magnetic damping very accurately while rf current and dc current are applied perpendicular to each other. Using these techniques, we show that in the Pt/Py bilayer, the spin-Hall effect dominates over interfacial field like spin-orbit torques, which is consistent with previous studies.

Orbit (dynamics)

Spin pumping

10.1063/1.4999948

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Citations (19)

Direct detection of spin Nernst effect in platinum

Applied Physics Letters (2018)

Arnab Bose Swapnil Bhuktare Hanuman Singh Sutapa Dutta Venu Gopal Achanta

Generation of spin current lies at the heart of spintronic research. The spin Hall effect and the spin Seebeck effect have drawn considerable attention in the last few years to create pure spin current by heavy metals and ferromagnets, respectively. In this work, we show the direct evidence of heat current to spin current conversion in non-magnetic Platinum by the spin Nernst effect (SNE) at room temperature. This is the thermal analogue of the spin Hall effect in non-magnets. We have shown that the 8 K/μm thermal gradient in Pt can lead to the generation of pure spin current density of the order of 108 A/m2 by virtue of SNE. This opens up an additional possibility to couple the relativistic spin-orbit interaction with the thermal gradient for spintronic applications.

Nernst effect

Spin pumping

Spinplasmonics

10.1063/1.5021731

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Citations (38)

Interfacial and bulk spin Hall contributions to fieldlike spin-orbit torque generated by iridium

Physical review. B./Physical review. B (2021)

Sutapa Dutta Arnab Bose Ashwin A. Tulapurkar R. A. Buhrman Daniel C. Ralph

We present measurements of spin orbit torques generated by Ir as a function of film thickness in sputtered Ir/CoFeB and Ir/Co samples. We find that Ir provides a damping-like component of spin orbit torque with a maximum spin torque conductivity 1.4e5 in SI unit and a maximum spin-torque efficiency of 0.04, which is sufficient to drive switching in an 0.8 nm film of CoFeB with perpendicular magnetic anisotropy. We also observe a surprisingly large field like spin orbit torque. Measurements as a function of Ir thickness indicate a substantial contribution to the FLT from an interface mechanism so that in the ultrathin limit there is a non-zero FLT with a maximum torque conductivity -5.0E4 in the SI unit. When the Ir film thickness becomes comparable to or greater than its spin diffusion length, 1.6 nm, there is also a smaller bulk contribution to the fieldlike torque.

Spin diffusion

Orbit (dynamics)

10.1103/physrevb.103.184416

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Citations (21)