Neeti Keswani | University of Delhi (original) (raw)

Papers by Neeti Keswani

Research paper thumbnail of B1-14 Magnetization Reversal Studies of Building Blocks of Square Artificial Spin Ice Probed by 2-DEG Based Micro-Hall Magnetometry

Authors: N. Keswani, P. Das, Physics, Indian Institute of Technology Delhi, New Delhi, Delhi, IND... more Authors: N. Keswani, P. Das, Physics, Indian Institute of Technology Delhi, New Delhi, Delhi, INDIA|Y. Nakajima, N. Chauhan, T. Ukai, T. Hanajiri, S. Kumar, Bio Nano Electronics Research Centre, Toyo University, Saitama, Kawagoe, Saitama, Tokyo, JAPAN|H. Chakraborti, K. Das Gupta, Physics, Indian Institute of Technology Bombay, Mumbai, Maharashtra, INDIA|Y. Ohno, Tsukuba Daigaku Daigakuin Suri Busshitsu Kagaku Kenkyuka, Tsukuba, Ibaraki, JAPAN|H. Ohno, Tohoku Daigaku, Sendai, Miyagi, JAPAN| Abstract Body: In recent years, a great deal of interest has been attracted by the physics of designer materials called `Artificial Spin Ice' (ASI) systems [1-2]. One of the most promising aspects of ASI system is their high tunability of the array geometry, which has opened new avenues [2]. While most efforts have focused on study of array of artificial spin ice structures [3-4], little work has been done on understanding the switching behavior of individual nanoislands coupled by dipolar in...

Research paper thumbnail of Magnetization reversal and emergent magnetic monopole-like state in square artificial spin ice vertex with defects

AIP Advances, 2018

We have investigated the micro-magnetic behavior as well as magnetization reversal of dipolar cou... more We have investigated the micro-magnetic behavior as well as magnetization reversal of dipolar coupled magnetic nanoislands with strong shape anisotropy arranged in a square artificial spin ice geometry. Our 0 K-temperature simulation results show that metastable two-in two-out state is stabilized at remanence of regular configurations. A complex interplay of defects and dipolar interaction leads to a predictable three-in one-out or three-out one-in higher energy state. Switching of the magnetic states is defined by the reduction of the no. of high-energy head-to-head or tail-to tail magnetic state.

Research paper thumbnail of Controlled creation and annihilation of isolated robust emergent magnetic monopole like charged vertices in square artificial spin ice

Scientific Reports, 2021

Magnetic analogue of an isolated free electric charge, i.e., a magnet with a single north or sout... more Magnetic analogue of an isolated free electric charge, i.e., a magnet with a single north or south pole, is a long sought-after particle which remains elusive so far. In magnetically frustrated pyrochlore solids, a classical analogue of monopole was observed as a result of excitation of spin ice vertices. Direct visualization of such excitations were proposed and later confirmed in analogous artificial spin ice (ASI) systems of square as well as Kagome geometries. However, such magnetically charged vertices are randomly created as they are thermally driven and are always associated with corresponding equal and opposite emergent charges, often termed as monopole–antimonopole pairs, connected by observable strings. Here, we demonstrate a controlled stabilisation of a robust isolated emergent monopole-like magnetically charged vertices in individual square ASI systems by application of an external magnetic field. The excitation conserves the magnetic charge without the involvement of a...

Research paper thumbnail of Complex switching behavior of magnetostatically coupled single-domain nanomagnets probed by micro-Hall magnetometry

Applied Physics Letters, Mar 9, 2020

We report here the results of two-dimensional electron gas based micro-Hall magnetometry measurem... more We report here the results of two-dimensional electron gas based micro-Hall magnetometry measurements and micromagnetic simulations of dipolar coupled nanomagnets of Ni 80 Fe 20 arranged in a double ring-like geometry. We observe that although magnetic force microscopy images exhibit single domain like magnetic states for the nanostructures, their reversal processes may undergo complex behavior. The details of such reversal behavior is observed as specific features in micro-Hall magnetometry data which compares well with the micromagnetic simulation data.

Research paper thumbnail of Complex switching behavior of magnetostatically coupled single-domain nanomagnets probed by micro-Hall magnetometry

Applied Physics Letters

We report here the results of two-dimensional electron gas based micro-Hall magnetometry measurem... more We report here the results of two-dimensional electron gas based micro-Hall magnetometry measurements and micromagnetic simulations of dipolar coupled nanomagnets of Ni 80 Fe 20 arranged in a double ring-like geometry. We observe that although magnetic force microscopy images exhibit single domain like magnetic states for the nanostructures, their reversal processes may undergo complex behavior. The details of such reversal behavior is observed as specific features in micro-Hall magnetometry data which compares well with the micromagnetic simulation data.

Research paper thumbnail of Magnetization reversal and emergent magnetic monopole-like state in square artificial spin ice vertex with defects

AIP Advances

We have investigated the micro-magnetic behavior as well as magnetization reversal of dipolar cou... more We have investigated the micro-magnetic behavior as well as magnetization reversal of dipolar coupled magnetic nanoislands with strong shape anisotropy arranged in a square artificial spin ice geometry. Our 0 K-temperature simulation results show that metastable two-in two-out state is stabilized at remanence of regular configurations. A complex interplay of defects and dipolar interaction leads to a predictable three-in one-out or three-out one-in higher energy state. Switching of the magnetic states is defined by the reduction of the no. of high-energy head-to-head or tail-to tail magnetic state.

Research paper thumbnail of Fabrication and characterization of sub-micron scale hall devices from 2-dimensional electron gas at the heterostrutcure of GaAs/AlGaAs

Research paper thumbnail of Accessing low-energy magnetic microstates in square artificial spin ice vertices of broken symmetry in static magnetic field

Physical Review B

In artificial spin ice systems, an interplay of defects and dipolar interactions is expected to p... more In artificial spin ice systems, an interplay of defects and dipolar interactions is expected to play important roles in stabilizing different collective magnetic states. In this work, we investigated the magnetization reversal of individual defective square artificial spin ice vertices where defects break fourfold rotational symmetry of the system. By varying the angle between the applied field and the geometrical axis of individual vertices, we are able to access different energy landscapes of the system. Thus, we find a tuning parameter to stabilize different collective magnetic configurations of a defective vertex. Interesting among them is the collective low-energy state which is otherwise observed in a fully demagnetized state. Micromagnetic simulations are performed for the exact experimental conditions the results of which are consistent with the experimental data.

Research paper thumbnail of On the micromagnetic behavior of dipolar-coupled nanomagnets in defective square artificial spin ice systems

Journal of Applied Physics

We report here the results of micromagnetic simulations of square artificial spin ice (ASI) syste... more We report here the results of micromagnetic simulations of square artificial spin ice (ASI) systems with defects. The defects are introduced by misaligning of a nanomagnet at the vertex. In these defective systems, we are able to stabilize emergent monopole-like state by applying a small external field. We observe a systematic change of dipolar energies of the systems with varying misalignment angle. The fields at which the emergent monopoles are created vary linearly with the dipolar energies of the systems. Our results clearly show that the magnetization reversal of the ASI systems is intricately related to the interplay of defects and dipolar interactions.

Research paper thumbnail of B1-14 Magnetization Reversal Studies of Building Blocks of Square Artificial Spin Ice Probed by 2-DEG Based Micro-Hall Magnetometry

Authors: N. Keswani, P. Das, Physics, Indian Institute of Technology Delhi, New Delhi, Delhi, IND... more Authors: N. Keswani, P. Das, Physics, Indian Institute of Technology Delhi, New Delhi, Delhi, INDIA|Y. Nakajima, N. Chauhan, T. Ukai, T. Hanajiri, S. Kumar, Bio Nano Electronics Research Centre, Toyo University, Saitama, Kawagoe, Saitama, Tokyo, JAPAN|H. Chakraborti, K. Das Gupta, Physics, Indian Institute of Technology Bombay, Mumbai, Maharashtra, INDIA|Y. Ohno, Tsukuba Daigaku Daigakuin Suri Busshitsu Kagaku Kenkyuka, Tsukuba, Ibaraki, JAPAN|H. Ohno, Tohoku Daigaku, Sendai, Miyagi, JAPAN| Abstract Body: In recent years, a great deal of interest has been attracted by the physics of designer materials called `Artificial Spin Ice' (ASI) systems [1-2]. One of the most promising aspects of ASI system is their high tunability of the array geometry, which has opened new avenues [2]. While most efforts have focused on study of array of artificial spin ice structures [3-4], little work has been done on understanding the switching behavior of individual nanoislands coupled by dipolar in...

Research paper thumbnail of Magnetization reversal and emergent magnetic monopole-like state in square artificial spin ice vertex with defects

AIP Advances, 2018

We have investigated the micro-magnetic behavior as well as magnetization reversal of dipolar cou... more We have investigated the micro-magnetic behavior as well as magnetization reversal of dipolar coupled magnetic nanoislands with strong shape anisotropy arranged in a square artificial spin ice geometry. Our 0 K-temperature simulation results show that metastable two-in two-out state is stabilized at remanence of regular configurations. A complex interplay of defects and dipolar interaction leads to a predictable three-in one-out or three-out one-in higher energy state. Switching of the magnetic states is defined by the reduction of the no. of high-energy head-to-head or tail-to tail magnetic state.

Research paper thumbnail of Controlled creation and annihilation of isolated robust emergent magnetic monopole like charged vertices in square artificial spin ice

Scientific Reports, 2021

Magnetic analogue of an isolated free electric charge, i.e., a magnet with a single north or sout... more Magnetic analogue of an isolated free electric charge, i.e., a magnet with a single north or south pole, is a long sought-after particle which remains elusive so far. In magnetically frustrated pyrochlore solids, a classical analogue of monopole was observed as a result of excitation of spin ice vertices. Direct visualization of such excitations were proposed and later confirmed in analogous artificial spin ice (ASI) systems of square as well as Kagome geometries. However, such magnetically charged vertices are randomly created as they are thermally driven and are always associated with corresponding equal and opposite emergent charges, often termed as monopole–antimonopole pairs, connected by observable strings. Here, we demonstrate a controlled stabilisation of a robust isolated emergent monopole-like magnetically charged vertices in individual square ASI systems by application of an external magnetic field. The excitation conserves the magnetic charge without the involvement of a...

Research paper thumbnail of Complex switching behavior of magnetostatically coupled single-domain nanomagnets probed by micro-Hall magnetometry

Applied Physics Letters, Mar 9, 2020

We report here the results of two-dimensional electron gas based micro-Hall magnetometry measurem... more We report here the results of two-dimensional electron gas based micro-Hall magnetometry measurements and micromagnetic simulations of dipolar coupled nanomagnets of Ni 80 Fe 20 arranged in a double ring-like geometry. We observe that although magnetic force microscopy images exhibit single domain like magnetic states for the nanostructures, their reversal processes may undergo complex behavior. The details of such reversal behavior is observed as specific features in micro-Hall magnetometry data which compares well with the micromagnetic simulation data.

Research paper thumbnail of Complex switching behavior of magnetostatically coupled single-domain nanomagnets probed by micro-Hall magnetometry

Applied Physics Letters

We report here the results of two-dimensional electron gas based micro-Hall magnetometry measurem... more We report here the results of two-dimensional electron gas based micro-Hall magnetometry measurements and micromagnetic simulations of dipolar coupled nanomagnets of Ni 80 Fe 20 arranged in a double ring-like geometry. We observe that although magnetic force microscopy images exhibit single domain like magnetic states for the nanostructures, their reversal processes may undergo complex behavior. The details of such reversal behavior is observed as specific features in micro-Hall magnetometry data which compares well with the micromagnetic simulation data.

Research paper thumbnail of Magnetization reversal and emergent magnetic monopole-like state in square artificial spin ice vertex with defects

AIP Advances

We have investigated the micro-magnetic behavior as well as magnetization reversal of dipolar cou... more We have investigated the micro-magnetic behavior as well as magnetization reversal of dipolar coupled magnetic nanoislands with strong shape anisotropy arranged in a square artificial spin ice geometry. Our 0 K-temperature simulation results show that metastable two-in two-out state is stabilized at remanence of regular configurations. A complex interplay of defects and dipolar interaction leads to a predictable three-in one-out or three-out one-in higher energy state. Switching of the magnetic states is defined by the reduction of the no. of high-energy head-to-head or tail-to tail magnetic state.

Research paper thumbnail of Fabrication and characterization of sub-micron scale hall devices from 2-dimensional electron gas at the heterostrutcure of GaAs/AlGaAs

Research paper thumbnail of Accessing low-energy magnetic microstates in square artificial spin ice vertices of broken symmetry in static magnetic field

Physical Review B

In artificial spin ice systems, an interplay of defects and dipolar interactions is expected to p... more In artificial spin ice systems, an interplay of defects and dipolar interactions is expected to play important roles in stabilizing different collective magnetic states. In this work, we investigated the magnetization reversal of individual defective square artificial spin ice vertices where defects break fourfold rotational symmetry of the system. By varying the angle between the applied field and the geometrical axis of individual vertices, we are able to access different energy landscapes of the system. Thus, we find a tuning parameter to stabilize different collective magnetic configurations of a defective vertex. Interesting among them is the collective low-energy state which is otherwise observed in a fully demagnetized state. Micromagnetic simulations are performed for the exact experimental conditions the results of which are consistent with the experimental data.

Research paper thumbnail of On the micromagnetic behavior of dipolar-coupled nanomagnets in defective square artificial spin ice systems

Journal of Applied Physics

We report here the results of micromagnetic simulations of square artificial spin ice (ASI) syste... more We report here the results of micromagnetic simulations of square artificial spin ice (ASI) systems with defects. The defects are introduced by misaligning of a nanomagnet at the vertex. In these defective systems, we are able to stabilize emergent monopole-like state by applying a small external field. We observe a systematic change of dipolar energies of the systems with varying misalignment angle. The fields at which the emergent monopoles are created vary linearly with the dipolar energies of the systems. Our results clearly show that the magnetization reversal of the ASI systems is intricately related to the interplay of defects and dipolar interactions.