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178 items found (0 items not approved), displaying 1 to 10.[First/Prev] 1, 2, 3, 4, 5, 6, 7, 8 [Next/Last]

Instruments / Technical Area	Publication Details	Published
	Electronic and magnetic structure of Fe/Co-doped multiwalled carbon nanotubes using X-ray absorption and magnetic circular dichroism spectroscopy Sanjeev Gautam , Priyal Singhal , Pardeep K. Thakur , Saji Augustine , Navdeep Goyal , Nicholas B. Brookes , Jae-Young Kim , Keun Hwa Chae 16th Joint MMM-Intermag Conference DOI: 10.1063/9.0000872 Open Access Show Abstract ▼ Abstract: Multi-walled carbon nanotubes (MWCNTs), synthesized using the microwave plasma-enhanced chemical vapor deposition (MPCVD) technique, have been examined to elucidate their electronic and magnetic structures through near-edge X-ray absorption fine structure (NEXAFS) and X-ray magnetic circular dichroism (XMCD) spectroscopy. NEXAFS analysis at the Fe and Co L-edges reveals the presence of Fe-metal nanoparticles embedded within the CNT lattice, along with divalent Co ions coordinated to the matrix in an octahedral symmetry. Furthermore, the appearance of two distinct NEXAFS peaks between the π* and σ* transitions indicates 1s to sp3 hybridization, attributed to the interaction of Fe and Co2+ ions with the carbon nanotube structure. Additionally, XMCD spectra confirm that MWCNTs exhibit room temperature ferromagnetism, primarily driven by Fe–C and Co–C bonding within the nanotubes. This intrinsic ferromagnetic behavior, along with the high aspect ratio and unique electronic properties of MWCNTs, highlights their promising potential for applications in spintronic storage devices.	Mar 2025
I18-Microfocus Spectroscopy	Tailoring of creep regime domain wall dynamics in perpendicularly magnetized Pd/Co/Pd trilayers Anurag Keloth , Rakhul Raj , V. Raghavendra Reddy , Mukul Gupta , Ilaria Carlomagno , Andrei Gloskovksii , Timo Kuschel , Ajay Gupta , Sarathlal Koyiloth Vayalil Advanced Materials Interfaces 9 DOI: 10.1002/admi.202400804 Open Access Show Abstract ▼ Abstract: Understanding magnetic domain wall (DW) dynamics is vital for improving the performance of heavy metal/ferromagnet based spintronic devices. Pd/Co/Pd multilayers hosting perpendicular magnetic anisotropy and interfacial Dzyaloshinskii-Moriya interaction are prototypes for high density magnetic memory devices. This work presents the creep regime DW dynamics in Pd/Co/Pd trilayers with Ta buffer layer excited by symmetric field-induced domain wall motion using Kerr microscopy. A systematic increment of DW velocity with increasing Co thickness is observed. SQUID-VSM measurements reveal that the effective anisotropy constant decreases with the Co layer, leading to an increased DW width. Kerr microscopy images confirm that the DW is becoming rougher with magnetic layer thickness because of the dominance of magnetostatic energy over the DW energy. Hard X-ray photoemission spectroscopy (HAXPES) reveals the presence of alloying at interfaces of Co/Pd. The asymmetry in magnetic circular dichroism HAXPES at the Pd 3d edge pictures the induced magnetic moment in Pd which is consistent with the larger saturation magnetization obtained from vibrating sample magnetometry. Extended X-ray absorption fine structure performed in out-of-plane and in-plane geometry shows the disordered nature of the Co local environment with the interdiffusion of Pd atoms into Co causing an asymmetry in the bonds.	Feb 2025
I09-Surface and Interface Structural Analysis	Stabilizing Schottky-to-ohmic switching in HfO2-based ferroelectric films via electrode design Moritz L. Müller , Nives Strkalj , Maximilian T. Becker , Megan O. Hill , Ji Soo Kim , Dibya Phuyal , Simon M. Fairclough , Caterina Ducati , Judith L. Macmanus-Driscoll Advanced Science 98 DOI: 10.1002/advs.202409566 Diamond Proposal Number(s): [31918] Open Access Show Abstract ▼ Abstract: The discovery of ferroelectric phases in HfO2-based films has reignited interest in ferroelectrics and their application in resistive switching (RS) devices. This study investigates the pivotal role of electrodes in facilitating the Schottky-to-Ohmic transition (SOT) observed in devices consisting of ultrathin epitaxial ferroelectric Hf0.93Y0.07O2 (YHO) films deposited on La0.67Sr0.33MnO3-buffered Nb-doped SrTiO3 (NbSTO\|LSMO) with Ti\|Au top electrodes. These findings indicate combined filamentary RS and ferroelectric switching occurs in devices with designed electrodes, having an ON/OFF ratio of over 100 during about 105 cycles. Transport measurements of modified device stacks show no change in SOT when the ferroelectric YHO layer is replaced with an equivalent hafnia-based layer, Hf0.5Zr0.5O2 (HZO). However, incomplete SOT is observed for variations in the top electrode thickness or material, as well as LSMO electrode thickness. This underscores the importance of employing oxygen-reactive electrodes and a bottom electrode with reduced conductivity to stabilize SOT. These findings provide valuable insights for enhancing the performance of ferroelectric RS devices through integration with filamentary RS mechanism.	Jan 2025
I10-Beamline for Advanced Dichroism - scattering	Annealing induced interface intermixing and its effect on exchange coupling in IrMn/(Fe, Co, CoFe) bilayers Y. Khaydukov , A. Dobrynin , S. Hassan , M. Ormston , K. Nikolaev , P. Bencok , R. Fan , P. Steadman , A. Csik , A. Vorobiev Journal Of Magnetism And Magnetic Materials 192 DOI: 10.1016/j.jmmm.2024.172762 Show Abstract ▼ Abstract: Depth resolved characterization of structural and magnetic profiles of antiferromagnetic/ferromagnetic (AFM/FM) system upon annealing was performed in this work. We studied systems comprising of AFM IrMn and FM (Co, Fe, Co70Fe30) bilayer structures using magnetometry, polarized neutron reflectometry, soft X-ray magnetic circular dichroism and secondary neutral spectrometry. Structural depth profiles obtained from neutron reflectometry indicate non-homogeneity of the AFM layer even before annealing, which is associated with the migration of manganese to the surface of the sample. Annealing of samples with CoFe and Co layers leads to a slight increase ( 5 %) in the migration of manganese, which, however, does not lead to significant degradation of the exchange coupling at the AFM/FM interface. A significantly different picture was observed in the Fe/IrMn systems where a strong migration of iron into the AFM layer was observed upon annealing of the sample, leading to erosion of the magnetic profile, the formation of a non-magnetic alloy and degradation of the pinning strength. This study can be useful in the optimization of AFM/FM systems in different spintronics devices, including HDD read heads, where thermal annealing is applied at different stages of the device manufacturing process.	Jan 2025
I06-Nanoscience (XPEEM)	Handle on the antiferromagnetic spin structure of NiO using a ferromagnetic adlayer E. Heppell , F. Maccherozzi , L. S. I. Veiga , S. Langridge , Gerrit Van Der Laan , T. Hesjedal , D. Backes Physical Review Materials 9 DOI: 10.1103/PhysRevMaterials.9.014408 Diamond Proposal Number(s): [35404] Open Access Show Abstract ▼ Abstract: Antiferromagnets (AFs) are characterized by spin structures that are resistant to external magnetic fields, rendering them ideal for persistent information storage but challenging to control. This study demonstrates that a thin ferromagnetic adlayer can serve as a magnetic ‘lever’ to provide a strong handle on the spin texture of an adjacent antiferromagnet. In bilayers composed of NiO(001) and Co, the expected exchange bias effect—a unidirectional shift in the Co hysteresis due to coupling with NiO—is notably absent. Instead, a strong interfacial coupling is observed, causing the NiO to partially follow the magnetization of Co under an applied magnetic field. Using x-ray magnetic linear dichroism, we detect an inversion of dichroism, indicating a reorientation of the Néel vector in NiO. X-ray spectromicroscopy imaging further reveals a direct correlation between ferromagnetic and antiferromagnetic domain structures. These findings are explained using a toy model that distinguishes between stable and unstable AF domains, highlighting the dynamic interplay between NiO and the Co adlayer in the presence of a magnetic field.	Jan 2025
E01-JEM ARM 200CF E02-JEM ARM 300CF	Exploring spin-orbit and spin-transfer torque through magnetic tunnel junctions Megan Smith Show Abstract ▼ Abstract: As digital technology advances, so must the memory capacity of such devices; with conventional electronics reaching their limitations, attention turns to spintronics for more energy efficient devices. Spin-transfer-torque and spin- orbit-torque magnetoresistive random access memory (STT-MRAM and SOT- MRAM) offer enormous potential as non-volatile data storage technologies due to their scalability, energy efficiency, and fast read/write speed. However, the magnetic recording trilemma, often associated with hard disk drive me- dia, remains a problem that must be addressed to develop ultra-high-density STT/SOT-MRAM. The ability to fabricate high-quality magnetic tunnel junc- tions (MTJs) in the laboratory is essential if solutions to address the trilemma are to be explored. Whilst MTJs with MgO tunnel barriers have been commer- cially produced for many years, building successful structures for research re- mains a significant challenge. To fabricate an MTJ, the individual layers within a MTJ must be optimised to produce the desired magnetic and electrical prop- erties. For instance, smooth, pinhole-free MgO tunnel barriers (~1 nm thick) are essential to achieve sufficiently high tunnelling magnetoresistance ratios and a low resistance area product. The work presented in this thesis focuses on sputter deposited CoFeB/MgO MTJ stacks with a CoFeB thickness of less than 1.5 nm to obtain perpendicular magnetic anisotropy (PMA), interfacial lattice matching, and thin continuous layers, which are essential properties for good quality MTJs. The physical and magnetic properties of MTJ thin films were investigated using scanning transmission electron microscopy, vibrating sample magnetometry, electrical measurements, and polarised neutron reflectivity; together, these techniques provide insight into these structures allowing the thin film stack to be optimised whilst contributing to the overall understand- ing of this material system. The results are consistent with literature where post-deposition annealing is required for strong PMA.	Dec 2024
I06-Nanoscience (XPEEM)	Engineering exchange bias at the interface of self-polarized ultrathin ferroelectric Ba⁢Ti⁢O3 and ferromagnetic La0.67⁢Sr0.33⁢Mn⁢O3 Tuhin Maity , Manisha Bansal , Nives Strkalj , Kapildeb Dolui , Di Zhang , Zihao He , Guillaume F Nataf , Adam Lovett , Massimo Ghidini , Sarnjeet S. Dhesi , Ping Lu , Haiyan Wang , Weiwei Li , Judith L. Macmanus-Driscoll Physical Review Applied 22 DOI: 10.1103/PhysRevApplied.22.054035 Diamond Proposal Number(s): [22427] Open Access Show Abstract ▼ Abstract: We investigate the emergence and optimization of conventional exchange bias (EB) in ultrathin (<10 nm) ferroelectric (FE) Ba⁢Ti⁢O3 (BTO)/ferromagnetic (FM) La0.67⁢Sr0.33⁢Mn⁢O3 (LSMO) epitaxial bilayers without an antiferromagnetic (AFM) material. The EB originates from the electronic orbital reconstruction at the FE-FM interface due to the ferroelectric polarization. We achieve maximum EB of approximately 42 Oe with single-domain polarization in nine-unit-cell-thick BTO, setting the BTO thickness above the critical threshold for ferroelectricity yet below the thickness of strain relaxation and multidomain breakdown. Furthermore, the LSMO layer needs to be thick enough to sustain both the FM layer and polarization-induced AFM spin configuration at the LSMO/BTO interface, yet as thin as possible to enable the EB loop shift. The temperature, training, field, and thickness dependence of the EB confirm that the LSMO/BTO interface exhibits conventional EB despite its unconventional origin. Using x-ray magnetic circular dichroism, scanning transmission electron microscopy, and density-functional-theory calculations, we confirm that the macroscopic EB effect originates from the interfacial AFM spin configuration in LSMO driven by FE-induced d-orbital modifications in interfacial Mn ions. Thus, we engineer strong interfacial EB coupling in artificial multiferroics without a conventional AFM material by controlling FE polarization, highlighting the potential for advanced spintronic applications.	Nov 2024
	Tailoring magnetism in chromium-doped zinc cobalt ferrite nanostructure for advanced spintronic memory devices Sanjeev Gautam , Ritika Charak , Shaffy Garg , Pardeep K. Thakur , Navdeep Goyal , Keun Hwa Chae , Younghak Kim Materials Today Chemistry 41 DOI: 10.1016/j.mtchem.2024.102291 Show Abstract ▼ Abstract: Soft magnetic ferrites serve as a crucial component in a wide array of sensing and actuating applications across various industries, including consumer electronics, automotive systems, spintronics, and more. These materials also find utility in spintronics, particularly for next-generation magnetic random-access memory (MRAM) due to their excellent inductive properties, which enhance the performance and scalability of spintronic memory devices. This study focuses on fine-tuning soft magnetic ferrites for inductive applications by doping them with Cr ions. By utilizing advanced experimental techniques such as the vibrating sample magnetometer (VSM) for bulk magnetometry and X-ray magnetic circular dichroism (XMCD) alongside X-ray absorption spectroscopy for atomic studies, the research aims to investigate the structural, electronic, and magnetic properties of the nanoferrites. Addition of doping in the soft ferrites observes reduction in the general magnetic parameters, with the only exception being coercivity, which decreases from 381 Oe to 275 Oe as the doping concentration increases from x = 0 to x = 0.02, and then increases to 350 Oe at x = 0.03. Through such precise tuning of the nanoparticles, this study aims to investigate the controllable soft magnetic properties of the nanoferrites, thereby paving the way for fast access times, non-volatility, and low energy consumption, presenting a compelling alternative to conventional memory technologies.	Oct 2024
I10-Beamline for Advanced Dichroism - scattering	Chiral magnets in the slow lane Diamond Light Source Diamond Proposal Number(s): [34423, 34827] Show Abstract ▼ Abstract: A groundbreaking study led by Thorsten Hesjedal, Gerrit van der Laan, and Shilei Zhang from Oxford, Diamond, and ShanghaiTech University has uncovered unexpected slow relaxation processes in chiral magnets, a discovery that challenges the conventional understanding of magnetic dynamics. The study highlights the critical role of topological defects in slowing down the relaxation of non-collinear magnetic states considered for emerging skyrmionics applications.	Oct 2024
I10-Beamline for Advanced Dichroism - scattering	Slow equilibrium relaxation in a chiral magnet mediated by topological defects Chenhao Zhang , Yang Wu , Jingyi Chen , Haonan Jin , Jinghui Wang , Raymond Fan , Paul Steadman , Gerrit Van Der Laan , Thorsten Hesjedal , Shilei Zhang Physical Review Letters 133 DOI: 10.1103/PhysRevLett.133.166707 Diamond Proposal Number(s): [34423, 34827] Show Abstract ▼ Abstract: We performed a pump-probe experiment on the chiral magnet Cu2⁢OSeO3 to study the relaxation dynamics of its noncollinear magnetic orders, employing a millisecond magnetic field pulse as the pump and resonant elastic x-ray scattering as the probe. Our findings reveal that the system requires ∼0.2 s to stabilize after the perturbation applied to both the conical and skyrmion lattice phase, which is significantly slower than the typical nanosecond timescale observed in micromagnetics. This prolonged relaxation is attributed to the formation and slow dissipation of local topological defects, such as emergent monopoles. By unveiling the experimental lifetime of these emergent singularities in a noncollinear magnetic system, our study highlights a universal relaxation mechanism in solitonic textures within the slow dynamics regime, offering new insights into topological physics and advanced information storage solutions.	Oct 2024

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