I10-Beamline for Advanced Dichroism
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Maciej
Dabrowski
,
Takafumi
Nakano
,
David
Burn
,
Andreas
Frisk
,
David G.
Newman
,
Christoph
Klewe
,
Qian
Li
,
Mengmeng
Yang
,
Padraic
Shafer
,
Elke
Arenholz
,
Thorsten
Hesjedal
,
Gerrit
Van Der Laan
,
Zi Q.
Qiu
,
Robert J.
Hicken
Diamond Proposal Number(s):
[17745, 19116, 20760]
Abstract: Insulating antiferromagnets have recently emerged as efficient and robust conductors of spin current. Element-specific and phase-resolved x-ray ferromagnetic resonance has been used to probe the injection and transmission of ac spin current through thin epitaxial NiO(001) layers. The spin current is found to be mediated by coherent evanescent spin waves of GHz frequency, rather than propagating magnons of THz frequency, paving the way towards coherent control of the phase and amplitude of spin currents within an antiferromagnetic insulator at room temperature.
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May 2020
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I06-Nanoscience
I10-Beamline for Advanced Dichroism
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C. J.
Durrant
,
L. R.
Shelford
,
R. A. J.
Valkass
,
R. J.
Hicken
,
A. I.
Figueroa
,
A. A.
Baker
,
G.
Van Der Laan
,
L. B.
Duffy
,
P.
Shafer
,
C.
Klewe
,
E.
Arenholz
,
S. A.
Cavill
,
J. R.
Childress
,
J. A.
Katine
Diamond Proposal Number(s):
[8782, 11585]
Abstract: Spin pumping has been studied within Ta / Ag / Ni81Fe19 (0–5 nm) / Ag (6 nm) / Co2MnGe (5 nm) / Ag / Ta large-area spin-valve structures, and the transverse spin current absorption of Ni81Fe19 sink layers of different thicknesses has been explored. In some circumstances, the spin current absorption can be inferred from the modification of the Co2MnGe source layer damping in vector network analyzer ferromagnetic resonance (VNAFMR)
experiments. However, the spin current absorption is more accurately determined from element-specific phase-resolved x-ray ferromagnetic resonance (XFMR) measurements that directly probe the spin transfer torque (STT) acting on the sink layer at the source layer resonance. Comparison with a macrospin model allows the real part of the effective spin mixing conductance to be extracted. We find that spin current absorption in the outer Ta layers has a significant impact, while sink layers with thicknesses of less than 0.6 nm are found to be discontinuous and super-paramagnetic at room temperature, and lead to a noticeable increase of the source layer damping. For the thickest 5-nm sink layer, increased spin current absorption is found to coincide with a reduction of the zero frequency FMR line width that we attribute to improved interface quality. This study shows that the transverse spin current absorption does not follow a universal dependence upon sink layer thickness but instead the structural quality of the sink layer plays a crucial role.
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Oct 2017
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J.
Li
,
L. R.
Shelford
,
P.
Shafer
,
A.
Tan
,
J. X.
Deng
,
P. S.
Keatley
,
C.
Hwang
,
E.
Arenholz
,
G.
Van Der Laan
,
R. J.
Hicken
,
Z. Q.
Qiu
Abstract: Despite recent progress in spin-current research, the detection of spin current has mostly remained indirect. By synchronizing a microwave waveform with synchrotron x-ray pulses, we use the ferromagnetic resonance of the Py (Ni 81 Fe 19 ) layer in a Py/Cu/Cu 75 Mn 25 /Cu/Co multilayer to pump a pure ac spin current into the Cu 75 Mn 25 and Co layers, and then directly probe the spin current within the Cu 75 Mn 25 layer and the spin dynamics of the Co layer by x-ray magnetic circular dichroism. This element-resolved pump-probe measurement unambiguously identifies the ac spin current in the Cu 75 Mn 25 layer.
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Aug 2016
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I06-Nanoscience
I10-Beamline for Advanced Dichroism
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Robert Alexander James
Valkass
,
Leigh R.
Shelford
,
Chris J.
Durrant
,
Adriana
Figueroa
,
Alex A.
Baker
,
Padraic
Shafer
,
Elke
Arenholz
,
Jeffrey R.
Childress
,
Jordan A.
Katine
,
Gerrit
Van Der Laan
,
Robert
Hicken
Diamond Proposal Number(s):
[8782, 11585, 13063]
Open Access
Abstract: In spin valve structures the damping of a ferromagnetic layer driven at resonance can be modified by the transfer of spin angular momentum into a ‘sink’ ferromagnetic layer. This effect, known as spin pumping, is interface dominated and expected to increase with increasing sink layer thickness up to a saturation absorption depth, previously reported to be 1.2 nm regardless of the sink layer’s composition [1]. Using vector network analyser ferromagnetic resonance (VNA-FMR), we have studied the variation in damping as a function of sink layer thickness in a series of CoMnGe (5 nm) / Ag (6 nm) / NiFe (x nm) spin valves. These measurements show only small variations in the CoMnGe Gilbert damping parameter for x ≤ 1.8 nm, although damping is observed to increase at x = 0.3 and 0.6 nm. Element-resolved x-ray detected ferromagnetic resonance (XFMR) [2] measurements confirm spin transfer torque due to spin pumping as the origin of the damping for x = 1.5 and 1.8 nm, with both thicknesses having the same effective spin mixing conductance, supporting the findings of Ghosh et al [1]. For thicker sink layers the source and sink FMR fields are seen to coincide, hampering the identification of spin pumping. [1] A Ghosh, et al. Physical Review Letters 109, 127202 (2012) [2] M Marcham, et al. Physical Review B 87, 180403 (2013)
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Apr 2016
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I09-Surface and Interface Structural Analysis
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Paul C.
Rogge
,
Ravini U.
Chandrasena
,
Antonio
Cammarata
,
Robert J.
Green
,
Padraic
Shafer
,
Benjamin M.
Lefler
,
Amanda
Huon
,
Arian
Arab
,
Elke
Arenholz
,
Ho Nyung
Lee
,
Tien-lin
Lee
,
Slavomir
Nemsak
,
James M.
Rondinelli
,
Alexander
Gray
,
Steven J.
May
Diamond Proposal Number(s):
[17824]
Abstract: We investigated the metal-insulator transition for epitaxial thin films of the perovskite CaFeO3, a material with a significant oxygen ligand hole contribution to its electronic structure. We find that biaxial tensile and compressive strain suppress the metal-insulator transition temperature. By combining hard x-ray photoelectron spectroscopy, soft x-ray absorption spectroscopy, and density functional calculations, we resolve the element-specific changes to the electronic structure across the metal-insulator transition. We demonstrate that the Fe sites undergo no observable spectroscopic change between the metallic and insulating states, whereas the O electronic configuration undergoes significant changes. This strongly supports the bond-disproportionation model of the metal-insulator transition for CaFeO3 and highlights the importance of ligand holes in its electronic structure. By sensitively measuring the ligand hole density, however, we find that it increases by ∼5–10% in the insulating state, which we ascribe to a further localization of electron charge on the Fe sites. These results provide detailed insight into the metal-insulator transition of negative charge transfer compounds and should prove instructive for understanding metal-insulator transitions in other late transition metal compounds such as the nickelates.
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Jan 2018
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I10-Beamline for Advanced Dichroism
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Christoph
Klewe
,
Qian
Li
,
Mengmeng
Yang
,
Alpha T.
N’diaye
,
David M.
Burn
,
Thorsten
Hesjedal
,
Adriana
Figueroa
,
Chanyong
Hwang
,
Jia
Li
,
Robert J.
Hicken
,
Padraic
Shafer
,
Elke
Arenholz
,
Gerrit
Van Der Laan
,
Ziqiang
Qiu
Diamond Proposal Number(s):
[18542, 19116, 20483, 20493, 21616]
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Apr 2020
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I06-Nanoscience
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M.
Marcham
,
W.
Yu
,
P.
Keatley
,
L.
Shelford
,
P.
Shafer
,
S.
Cavill
,
H.
Qing
,
A.
Neudert
,
J. R.
Childress
,
J. A.
Katine
,
E.
Arenholz
,
N. D.
Telling
,
G.
Van Der Laan
,
R.
Hicken
Abstract: Precessional dynamics of a Co50Fe50(0.7)/Ni90Fe10(5)/Dy(1)/Ru(3) (thicknesses in nm) thin film have been explored by low temperature time-resolved magneto-optical Kerr effect and phase-resolved x-ray ferromagnetic resonance measurements. As the temperature was decreased from 300 to 140?K, the magnetic damping was found to increase rapidly while the resonance field was strongly reduced. Static x-ray magnetic circular dichroism measurements revealed increasing ferromagnetic order of the Dy moment antiparallel to that of Co50Fe50/Ni90Fe10. Increased coupling of the Dy orbital moment to the precessing spin magnetization leads to significantly increased damping and gyromagnetic ratio of the film while leaving its magnetic anisotropy effectively unchanged.
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Feb 2013
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Abstract: Synthesis of Ni and Zn substituted nano-greigite, Fe3S4, is achieved from single source diethyldithiocarbamato
precursor compounds, producing particles typically 50–100 nm in diameter with plate-like pseudohexagonal morphologies. Up to 12 wt.% Ni is incorporated into the greigite structure, and there is evidence that Zn is also incorporated but Co is not substituted into the lattice. The Fe L3 X-ray absorption spectra for these materials have a narrow single peak at 707.7 eV and the resulting main X-ray magnetic circular dichroism (XMCD) has the same sign at 708.75 eV. All XMCD spectra also have a broad positive feature at 711 eV, a characteristic of covalent mixing. The greigite XMCD spectra contrast with the three clearly defined XMCD site specific peaks found in the ferrite spinel, magnetite. The Fe L2,3 X-ray absorption spectra and XMCD spectra of the greigite reflect and reveal the high conductivity of greigite and the very strong covalency of the Fe–S bonding. The electron hopping between Fe3+ and Fe2+ on octahedral sites results in an intermediate oxidation state of the Fe in theOh site of Fe2.5+ producing an effective formula
of [Fe3þ "]A-site[2Fe2:5þ #]B-siteS24 ]. The Ni L2,3 X-ray absorption spectra and XMCD reveal substitution on the Oh site with a strongly covalent character and an oxidation state
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Aug 2016
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I10-Beamline for Advanced Dichroism
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Maciej
Dabrowski
,
Andreas
Frisk
,
David M.
Burn
,
David G.
Newman
,
Christoph
Klewe
,
Alpha T.
N’diaye
,
Padraic
Shafer
,
Elke
Arenholz
,
Graham J.
Bowden
,
Thorsten
Hesjedal
,
Gerrit
Van Der Laan
,
Gino
Hrkac
,
Robert J.
Hicken
Diamond Proposal Number(s):
[17745, 19116, 20760]
Abstract: Microwave and heat-assisted magnetic recordings are two competing technologies that have greatly increased the capacity of hard disk drives. The efficiency of the magnetic recording process can be further improved by employing non-collinear spin structures that combine perpendicular and in-plane magnetic anisotropy. Here, we investigate both microwave and optically excited magnetization dynamics in [Co/Pt]/NiFe exchange spring samples. The resulting canted magnetization within the nanoscale [Co/Pt]/NiFe interfacial region allows for optically stimulated magnetization precession to be observed for an extended magnetic field and frequency range. The results can be explained by formation of an imprinted domain structure, which locks the magnetization orientation and makes the structures more robust against external perturbations. Tuning the canted interfacial domain structure may provide greater control of optically excited magnetization reversal and optically generated spin currents, which are of paramount importance for future ultrafast magnetic recording and spintronic applications.
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Nov 2020
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I06-Nanoscience
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M.
Marcham
,
P. S.
Keatley
,
A.
Neudert
,
R.
Hicken
,
S.
Cavill
,
L.
Shelford
,
G.
Van Der Laan
,
N.
Telling
,
J.
Childress
,
J.
Katine
,
P.
Shafer
,
E.
Arenholz
Diamond Proposal Number(s):
[1842]
Abstract: Phase-resolved x-rayferromagnetic resonance (XFMR) has been measured in fluorescence yield, extending the application of XFMR to opaque samples on opaque substrates. Magnetization dynamics were excited in a Co50Fe50(0.7)/Ni90Fe10(5) bilayer by means of a continuous wave microwave excitation, while x-ray magnetic circular dichroism (XMCD) spectra were measured stroboscopically at different points in the precession cycle. By tuning the x-ray energy to the L 3 edges of Ni and Fe, the dependence of the real and imaginary components of the element specific magnetic susceptibility on the strength of an externally applied static bias field was determined. First results from measurements on a Co50Fe50(0.7)/Ni90Fe10(5)/Dy(1) sample confirm that enhanced damping results from the addition of the Dy cap.
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Apr 2011
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