United States

Rare earth/transition metal permanent magnets have gained significant interest due to their outstanding performance, which has made them key materials for many applications. The most well-known compounds Nd2Fe14B, SmCo5, and Sm2Co17 combine a large energy density, high Curie temperature, and a large magnetocrystalline anisotropy (MCA). Besides, SmCo5 exhibits the highest known uniaxial MCA1. Due to their importance, a detailed understanding of their hysteresis behavior has come into the focus of research2.
Since the extrinsic magnetic properties of magnetic materials depend on their complex defect and nanostructure, we follow the strategy to disentangle intrinsic and extrinsic properties as well as the effect of specific defects by investigating SmCo5 and Sm2Co17 phases in thin film model systems grown by molecular beam epitaxy (MBE).&lt;br&gt;
The Sm-Co system, when grown as thin films in a certain parameter range, undergoes a phase decomposition into a nanocomposite of SmCo5 and Sm2Co17 phases. Due to the structural similarity of the two phases, it is challenging to discriminate their phase contributions. Extended X-ray absorption fine structure (EXAFS) analysis combined with transmission electron microscopy (TEM) allows the unambiguous quantification of the nano-domain phase decomposition in the thin films3.&lt;br&gt;
In this work, we have studied the behavior of the magnetic anisotropy of Co and Sm using - for the first time, to our knowledge - angle-dependent X-ray magnetic circular dichroism (XMCD) at Sm M4,5 and Co L2,3 edges in 1.9 Tesla external applied field. SmCo5 and Sm2Co17 thin films have been grown onto Al2O3 substrates and pre-characterized by X-ray diffraction (XRD) and superconducting quantum interface device (SQUID). XMCD and X-ray absorption spectroscopy (XAS) gave access to element-specific information and have been complemented by detailed atomistic spin dynamics (ASD) calculations.&lt;br&gt;
Element-specific hysteresis curves demonstrate strong coupling between Sm and Co, however, the spectroscopy indicates different saturation behavior. The XMCD spectra for the Sm M4,5 edges show surprisingly only a minor angle dependence. Using ASD simulations, we estimate the exchange field at the Sm site to be of the order of -200 T.&lt;br&gt;
**References:**&lt;br&gt;[1] K. J. Strnat &amp; R. M. W. Strnat, J. Magn. Magn. Mater. 100, 36 (1991).&lt;br&gt;
[2] O. Gutfleisch et al., Adv. Mater. 23, 821 (2011).&lt;br&gt;
[3] S. Sharma et al., ACS Appl. Mater. Interfaces 13, 32415 (2021).&lt;br&gt;



MMM 2022

Element specific magnetocrystalline anisotropy of Sm

Rare earth/transition metal permanent magnets have gained significant interest due to their outstanding performance, which has made them key materials for many applications. The most well-known compounds Nd2Fe14B, SmCo5, and Sm2Co17 combine a large energy density, high Curie temperature, and a large magnetocrystalline anisotropy (MCA). Besides, SmCo5 exhibits the highest known uniaxial MCA1. Due to their importance, a detailed understanding of their hysteresis behavior has come into the focus of research2.
Since the extrinsic magnetic properties of magnetic materials depend on their complex defect and nanostructure, we follow the strategy to disentangle intrinsic and extrinsic properties as well as the effect of specific defects by investigating SmCo5 and Sm2Co17 phases in thin film model systems grown by molecular beam epitaxy (MBE). 
The Sm-Co system, when grown as thin films in a certain parameter range, undergoes a phase decomposition into a nanocomposite of SmCo5 and Sm2Co17 phases. Due to the structural similarity of the two phases, it is challenging to discriminate their phase contributions. Extended X-ray absorption fine structure (EXAFS) analysis combined with transmission electron microscopy (TEM) allows the unambiguous quantification of the nano-domain phase decomposition in the thin films3. 
In this work, we have studied the behavior of the magnetic anisotropy of Co and Sm using - for the first time, to our knowledge - angle-dependent X-ray magnetic circular dichroism (XMCD) at Sm M4,5 and Co L2,3 edges in 1.9 Tesla external applied field. SmCo5 and Sm2Co17 thin films have been grown onto Al2O3 substrates and pre-characterized by X-ray diffraction (XRD) and superconducting quantum interface device (SQUID). XMCD and X-ray absorption spectroscopy (XAS) gave access to element-specific information and have been complemented by detailed atomistic spin dynamics (ASD) calculations. 
Element-specific hysteresis curves demonstrate strong coupling between Sm and Co, however, the spectroscopy indicates different saturation behavior. The XMCD spectra for the Sm M4,5 edges show surprisingly only a minor angle dependence. Using ASD simulations, we estimate the exchange field at the Sm site to be of the order of -200 T. 
**References:** [1] K. J. Strnat & R. M. W. Strnat, J. Magn. Magn. Mater. 100, 36 (1991). 
[2] O. Gutfleisch et al., Adv. Mater. 23, 821 (2011). 
[3] S. Sharma et al., ACS Appl. Mater. Interfaces 13, 32415 (2021).

poster

#### Welcome to the 67th Annual Conference on Magnetism and Magnetic Materials, MMM 2022!

The Conference was held from October 31 to November 4 and offers both in-person and on-demand content.

MMM 2022 is sponsored jointly by AIP Publishing and the IEEE Magnetics Society. Members of the international scientific and engineering communities interested in recent developments in fundamental and applied magnetism are invited to attend and contribute to the technical sessions. The technical program will include invited and contributed papers in oral and poster sessions, invited symposia, a tutorial, and several special sessions. This Conference provides an outstanding opportunity for worldwide participants to meet their colleagues and collaborators and discuss developments in all areas of magnetism research.

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This Conference provides an outstanding opportunity for worldwide participants to meet their colleagues and collaborators and discuss developments in all areas of magnetism research.

Hole doped La2/3Sr1/3MnO3 (LSMO) is an auspicious candidate for spintronic applications due to its high spin polarization [1] and colossal magnetoresistance [2]. However, the growth of LSMO thin films on silicon, and other substrates important for applications, is extremely challenging due to their structural incompatibility and high reactivity with oxygen. 
Here, we demonstrate the possibility to grow strain-free LSMO thin films on silicon substrates with magnetic, magneto-optical and optical properties comparable to epitaxial layers grown on SrTiO3 (STO). This growth was achieved using a two-dimensional Ca2Nb3O10 nanosheet (NS) seed layer which induces epitaxial stabilization of LSMO. The 20 and 40 nm thick films of LSMO were grown by pulsed laser deposition with identical conditions for both the silicon and STO substrates. X-ray diffraction characterization of the samples confirmed strained epitaxial LSMO layers on STO and relaxed fibre textured films with unified out-of-plane orientation on Si with NS seed layer. Magnetization measurements, shown in Fig. 1, revealed smaller saturation magnetization for samples grown on Si. This might be attributed to the textured nature of the samples. However, these samples exhibit a higher Curie temperature by more than 10 K, which is the result of strain relaxation. For a closer insight into the electronic structure of the material a combination of spectroscopic ellipsometry and magneto-optical spectroscopy experiments were performed. The results allowed to derive the full permittivity tensor of the material in the spectral range from 1.5 to 5 eV. The spectral dependence of the off-diagonal element of the permittivity tensor, shown in Fig. 2, revealed striking similarity between the LSMO samples grown on STO and Si. Three electronic transitions around 1.9, 2.9, and 3.5 eV were identified in the spectra, suggesting the main contribution to the optical response arises from Mn states [3]. 
**References:** 1 M. Bowen, M. Bibes, A. Barthélémy, et al., Appl. Phys. Lett., Vol. 82, p.233–235 (2003) 
2 A.P. Ramirez, J. Phys.: Condens. Matter, Vol. 9, p.8171–8199 (1997) 
3 M. Zahradník, T. Maroutian, M. Zelený, et al., Phys. Rev. B, Vol. 99, p.195138 (2019) 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/e466a8c107bf99ccb2449812508ecd27.png) 
Fig. 1: Temperature dependent magnetization of LSMO samples on STO and Si in saturation. 
![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/883d8cb08244cf7b151eed0cd2e1fbb5.png) 
Fig. 2: Spectral dependence of the off-diagonal element of the permittivity tensor of LSMO samples on Si and STO.

Magnetic, optical and magneto optical properties of strain

β-Mn type CoZnMn is one of chiral magnets and is reported to host Bloch skyrmions above room temperature [1]. CoZnMn epitaxial thin films are attractive for the device application, however, there is no report on the fabrication of the epitaxial film, although polycrystalline CoZnMn films were reported in the previous study [2]. Here, we report CoZnMn epitaxial films grown on MgO(001) single crystal substrates. [Co-Zn(10 – t nm)/Mn(t nm)]15 multilayers were prepared by rf magnetron sputtering of Co-Zn composite target and Mn target. The multilayers were grown on 10 nm-thick W buffer layer. The total thickness of the multilayers was kept constant at 150 nm, and the Mn composition was controlled by varying the Mn layer thickness t. The composition of Co-Zn layer was estimated to be Co/Zn = 0.8 by energy dispersive x-ray spectroscopy. 10 nm-thick W capping layer was deposited on the multilayers. After the deposition, the multilayers were annealed at 300 °C in vacuum to obtain the CoZnMn alloy. Crystal structure was characterized by x-ray diffraction. Figure 1(a) shows a reciprocal space mapping of the sample for t = 2 nm in the plane parallel to MgO(130), where Qy and Qz are parallel to MgO[310] and MgO[001], respectively. In the figure, β-Mn type CoZnMn 103, 104 and 204 diffraction spots were observed, indicating the epitaxial growth of β-Mn type CoZnMn film with (001) orientation. Figure 1(b) shows φ scan profile for β-Mn type CoZnMn 103 diffractions. 8 peaks were observed in the in-plane scanning even though β-Mn type CoZnMn has 4-fold symmetry, which means the existence of twinned crystal grains with CoZnMn[100]//MgO[310] and CoZnMn[100]//MgO[3 -1 0] in the film. Although there exists twin crystals in the film, β-Mn CoZnMn (001) film was successfully fabricated on a MgO single crystal substrate. 
**References:** [1] Y. Tokunaga et.al., Nat. Comm. 6, 7638 (2015). 
[2] Ishikawa et.al., The 66th JSAP Spring Meeting, 9p-PB1-15 (2019). 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/ec451b1f310d93f08abb3bea2a1cb469.png) 
Fig. 1 (a) Reciprocal space mapping of the CoZnMn film in the plane parallel to MgO(130). (b) φ scan for β-Mn type CoZnMn 103 diffractions.

Fabrication of β Mn type CoZnMn(001) film on MgO single crystal substrate

Future embedded and standalone magnetic random access memory (MRAM) solutions require materials possessing bulk magnetocrystalline anisotropy at sub-10 nm feature sizes. FePd in its L10-ordered phase delivers MJ/m3 bulk anisotropy energy density (Ku) [1], large interlayer exchange coupling through Ru [2], Gilbert damping (α) below 0.008 [3] and robust compatibility across a range of Pt-group buffer layers [4]. Transitioning FePd films into mature spintronic applications requires a higher level of process control realize highly uniform microstructural, magnetic and magnetotransport properties. 
We demonstrate control of the orientation distribution of the c-axis in highly (001)-oriented L10 FePd. Using direct current magnetron sputtering on (001)-cut, polished MgO substrates, we explore an N2 substrate anneal, variation in the individual thicknesses of the Cr/Pt underlayer and post-anneal modules between layers. Each sample had an 8-nm-thick FePd layer grown at 350 °C and post-annealed at 500 °C, leading to a high degree of L10 ordering, with Ku ranging between 0.8 MJ/m3 and 1.1 MJ/m3 and α ranging from 0.0067 to 0.0133. Despite the relatively narrow spread in these key parameters, we observed a wide range of inhomogeneous linewidth broadening (µ0ΔH0) from ferromagnetic resonance measurements, ranging from below 0.01 T to nearly 0.2 T (Fig. 1(a)). Variation in µ0ΔH0 correlates with the FePd grain orientation distribution, as measured by x-ray diffraction rocking curve scans of the (002) Bragg peak (Fig. 1(b)). Our process controls enable varying the full-width-half-maximum (FWHM) of the (002) peak from 14 degrees down to nearly 2 degrees, leading to narrowing of the local anisotropy distribution and reduction in the µ0ΔH0 (Fig. 1(b) inset). These process improvements will deliver the large-scale uniformity needed to implement FePd-based MRAM solutions. 
**References:** [1] M. Futamoto et al., AIP Advances 6, 085302 (2016) 
[2] D.-L. Zhang et al., Phys. Rev. Appl. 9, 044028 (2018) 
[3] D.-L. Zhang et al., Appl. Phys. Lett. 117, 082405 (2020) 
[4] X. Wang et al., AIP Advances 11, 025106 (2021) 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/aa4b6704bacd0147dba693b652175112.png) 
Figure 1: (a) FMR Linewidth versus frequency for three samples with inhomogeneous line broadening of 0.178 T (blue), 0.075 T (green) and 0.015 T (red). (b) Inhomogeneous line broadening versus FWHM of FePd(002) (Δω), with (inset) exemplary FePd(002) rocking curve scans of the red, blue and green star samples highlighted with colored markers in (a)

Control of grain orientation spread and inhomogeneous broadening in L10 phase FePd thin films with low damping and high perpendicular magnetic anisotropy

Exchange coupling in as-deposited and annealed magnetic trilayers Co80Fe20 (CoFe)/MgO/Co80Fe20 (CoFe) for MgO thickness spanning 0.45 to 4.5 nm has been studied. Unlike relevant existing results and theories, antiferromagnetic exchange coupling behavior was observed in annealed CoFe/MgO/CoFe with 2.7-nm MgO insulating barrier. Figure 1 shows in-plane minor hysteresis loops of the as-deposited and annealed CoFe/MgO/CoFe trilayer for MgO thickness spanning 1.8 to 4.5 nm, respectively. Interestingly, the shift of the hysteresis loop toward positive or negative field depends on the temperature. For the temperature range of 25 to 500 deg. C, the hysteresis loop is shifted to the negative and to the positive field for 600 deg. C as shown in Fig. 2(a) [1]. Figure 2(b) a transition from antiferromagnetic to nearly paramagnetic response to applied magnetic field was found around 520 deg. C—conceptually called as Neel temperature. Based on grazing incidence x-ray diffraction study, formation of CoO and CoFe2O4 were found at annealed CoFe/MgO interfaces [2], which indicates they act as antiferromagnetic sources giving rise to the exchange-coupled antiferromagnetic/ferromagnetic interface and then antiferromagnetic coupling across the magnetic trilayer [3]. 
**References:** [1] T. Ambrose et al., Phys. Rev. B 56, 83 (1997). 
[2] S. Grytsyuk et al., Eur. Phys. J. B. 85, 254. (2012). 
[3] J. Spray et al., J. Phys. D: Appl. Phys. 39, 4536 (2006). 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/78800643a37d3cd33a576952b551a2d5.png) 
Fig. 1 Magnetic hystereis loops of (a) as-deposited and (b) annealed CoFe/MgO/CoFe films for MgO thickness spanning 1.8 to 4.5 nm. 
![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/3a0ae8452ec77a8b35e2f1f3e85f1fe5.png) 
Fig. 2 (a) Temperature dependence of magnetic hysteresis loops of 4-nm CoFe/2.7-nm MgO/8-nm CoFe film annealed at 250 deg. C for 1 hour at the rotation angle 75 deg. (b) exchange coupling field of the same film as mentioned in (a).

Antiferromagnetically coupled CoFe/MgO/CoFe Thin Films

Artificial spin ices (ASI) are arrays of nanoscale magnets, usually arranged in frustrated geometries. Among the ASI, the kagome geometry (AKSI) has been extensively studied and considered to explore a wide range of interesting Physics phenomena, including mimicking bulk spin ice materials, and acting as a metamaterial for applications in magnonics [1]. 
The goal of this work is to study the global and local spatial dependence of the coercivity of a Permalloy AKSI (20 nm thick elliptical magnetic islands). The magnetization curves were acquired by magneto-optic Kerr effect measurements with the laser spot adjusted for the required purpose (either global or local).
The angular dependence of coercivity exhibits a periodic behavior with a period of 60°, which reflects the symmetry of the underlying honeycomb pattern. The coercivity values vary from ~120 Oe to ~145 Oe, resulting in a peak-to-peak amplitude of ~25 Oe. The minima (maxima) occur when the applied field is perpendicular (parallel) to the magnet's long axis. This result agrees with the fact that the long axis direction being an easy axis of a single nanomagnet. A 20 nm permalloy continuous thin film with similar lateral dimensions as the AKSI lattice shows a nearly constant coercivity around only a few Oe. This indicates that the higher magnitude of the AKSI coercivity is due to the thin film patterning.
On the other hand, it is well known that small systems with long range order interactions exhibit pronounced size effects, intuitively understood from the fact that long range interactions are limited by the sample size [2]. By controlling the position of the laser spot to 2 um nominal diameter it was possible to scan the whole sample and determine a spatial map of the coercivity, where each point of the map corresponds to a distinct subregion of the lattice. The results clearly show that the magnetisation reversal properties are locally affected depending on how close to the edge the hysteresis loop is measured. A continuous decrease of the coercive fields close to the array edges reveals that surface effects are present in AKSI and, in principle, could be explained in the light of translation symmetry breaking in systems with long range order interactions. 
**References:** [1] S. Skjærvø, H. Christopher and R. Stamps, Nature Reviews, Vol. 2, p. 13 (2020). 
[2] K. Binder and P. C. Hohenberg, Phys. Rev. B, Vol. 6, p. 3461 (1972).

Surface effects and spatial distribution of magnetic properties in a Kagomé artificial spin ice

Flexible electronics has been widely studied for the future applications, such as flexible display, wearable health care device and electronic skin for robots [1-2]. In particular, the stress effect on the thin film is a key element to develop magnetic sensors and actuators. Permalloy is well known material for the flexible applications due to its very low magnetostriction under the stress [3]. 
In this study, we have measured the mechanical magnetostriction effect on the Permalloy thin film and dot array patterns, where the aspect ratio (length/width) varied 0.5, 1.0, and 2.0, as shown in Figure 1. The width of the dot array was fixed as 10 μm. The stress anisotropy field was measured using ferromagnetic resonance (FMR) method and calculated by Kittel model. The FMR signals depending on the aspect ratio of the dot array are shown in Figure 2, where the excitation microwave frequency was 6 GHz. The stress anisotropy field was significantly affected by the bending repetition and the curved direction with the shape of the dot arrays. The details of the experimental and results will be discussed. 
**References:** [1] A. Nathan, A. Ahnood, M.T. Cole, S. Lee, Y. Suzuki, P. Hiralal, F. Bonaccorso, T. Hasan, L. Garcia-Gancedo, A. Dyadyusha, S. Haque, P. Andrew, S. Hofmann, J. Moultrie, D. Chu, A.J. Flewitt, A.C. Ferrari, M.J. Kelly, J. Robertson, G.A.J. Amaratunga, and W.I. Milne, Proc. IEEE 100, 1486 (2012). 
[2] R. Dahiya, N. Yogeswaran, F. Liu, L. Manjakkal, E. Burdet, V. Hayward, and H. Jörntell, Proc. IEEE 107, 2016 (2019). 
[3] R. Bonin, M. Schneider, T. Silva, and J. Nibarger, J. Appl. Phys. - J APPL PHYS 98, (2005). 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/793a647c9d75bf312f935c06d122e4cf.png) 
Figure 1. Permalloy dot arrays, where the aspect ratio varied 0.5 (a), 1.0 (b), and 2.0 (c). 
![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/7bf2d69db7f1a472b7ba180157cb044e.png) 
Figure 2. Ferromagnetic resonance signals depending on the aspect ratio of the dot arrays.

Mechanical magnetostriction effect of Permalloy dots depending on aspect ratio and bending direction.

Magnetization reversal in NiFe/IrMn exchange-biased thin films was investigated under thermal cycling in an external magnetic field, applied opposite to the direction of
the exchange bias field. Thermal hysteresis of magnetization accompanied by changes in magnetization polarity was observed in the applied field close to the exchange bias value. This
effect appears when thermally induced variations of the exchange bias exceed the corresponding variations in coercivity. The amplitude of magnetization reversal in NiFe/IrMn structures
exceeds ∼100 times the corresponding amplitude in spin-crossover molecular compounds. The observed bistability of the magnetic state, revealed by thermal hysteresis, gradually
disappears with an increase in the number of cooling–heating thermal cycles, that indicates an irreversible quenching of the interfacial magnetization configuration. This effect paves the
way for the creation of a new class of switching devices with thermally assisted bistability in the ferromagnetic state.
The work was supported by AAAA-A19-119092390079-8 government task of Institute of Problems of Chemical Physics.

Effect of thermal cycling on exchange bias in NiFe/IrMn bilayers

Cubic spinel ferrites are a class of oxides represented by the chemical formula AB2O4 with A and B being divalent and trivalent cations occupying octahedral and
tetrahedral voids. Magnetization arises from superexchange interactions between cations via the oxygen anion. Among these, cobalt ferrites have been shown to undergo spinodal
decomposition to form periodic microstructures at the nm length scale. The resultant changes in magnetic properties have been shown to be dependent on the periodicity and degree of
decomposition. Complex nanostructured microstructures with concomitant spatial variations of intrinsic magnetic properties and magnetic interactions can yield wasp-waisted major
hysteresis loops indicative of multiple magnetization reversal events1. Detailed analysis requires advanced magnetometry techniques, in order to disentangle reversible, irreversible, and
viscous magnetization processes and their dependence on previous magnetic history.
In this work, cobalt ferrite samples have been synthesized using standard powder processing techniques. Different degrees of decomposition have been achieved by varying the annealing
time within the coherent spinodal range. TEM has been used to determine periodicity, degree of decomposition, lattice mismatch and the associated coherency strains between the
decomposed phases. Magnetization processes occurring in these materials have been investigated through vibrating sample magnetometry using major M-H loops and temperaturedependent
magnetization. These measurements have been complemented with non-saturating high-resolution first order reversal curve (FORC) diagrams obtained with different preconditioning
fields, in order to explore magnetic states inaccessible to the major loops. Various switching events corresponding to the features observed in the FORC diagrams have been
identified and correlated with microstructural observations. Finally, a better insight into the nature of the switching events has been obtained with Rayleigh loop measurements along
selected FORCs. 

**References:** 

1. M. V. Suraj, A. Talaat, B. C. Dodrill, Y. Wang, J. K. Lee, and P. R. Ohodnicki Jr., AIP Advances 12, 035031 (2022) 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/a9096f2d8e5c30f9dface322187ec225.png)

Understanding magnetization reversal mechanisms and exchange interactions in nanostructured cobalt ferrites using first order reversal curves (FORC)

When two materials are brought into close proximity, the magnetic proximity effects, including the exchange anisotropy, exchange bias (EB), and coercivity, are among the
most fascinating and active materials research areas today. Among them, the interlayer exchange coupling (IEC) plays a crucial role to manipulate the magnetic hysteresis loop in a variety
of solid-state magnetic heterostructures. Such IEC can be understood by the equilibrium field-like spin torque (FLST) of magnetic tunnel junctions (MTJs) in noncollinear magnetic
configuration. Recently, electrical and spin switches across a single organic molecule connecting ferromagnetic electrodes are also burgeoning fields for possible applications in the socalled
molecular spintronics. The ability to calculate the noncollinear spin torque effect and spin dynamics of magnetic heterostructures is difficult but important to include the complex
structural, electronic, and magnetic properties at spinterfaces for nanoscale spintronics devices.
In this study, the molecular scale magnetic proximity effect is proposed in single-molecule magnetic junctions (SMMJs) consisting of an amine-ended 1,4-benzenediamine (BDA) molecule
coupled to two ferromagnetic Co electrodes. The magnetotransport calculation is carried out using the generalized Landau-Lifshitz-Gilbert (LLG) equation combined with density
functional theory (DFT) and our self-developed JunPy calculated spin-torque effect. We first demonstrate that the equilibrium FLST plays a crucial role in the strain-controlled exchange
bias with current-controlled magnetic coercivity in single-molecule magnetic junctions [1]. In consideration of the resonant tunnelling and the multi-reflection processes at interfaces, our
DFT+JunPy+LLG calculation results [2,3] illustrate the underlying mechanism in an important aspect, namely, molecular scale exchange bias effect, via the modulation of angular
dependence of equilibrium FLST in amine-ended SMMJs with complex contact deformation and interfacial bonding during breaking junction techniques. This work is supported by the
Ministry of Science and Technology (108-2628-M-008-004-MY3). 

**References:** 

[1] Y. -H. Tang and B. -H. Huang, Phys. Rev. Research 3, 033264 (2021) 
[2] K. -R. Chiang and Y. -H. Tang, ACS Omega 6, 19386 (2021) 
[3] Y. -H. Tang, Y. -C. Chuang, and B. -H. Huang, submitted to Front. Phys. : Charge, Heat and Spin Transport Through Molecular Nanostructures

Underlying mechanism for exchange bias in single molecule magnetic junctions

Iron oxide-based magnetic nanoparticles offer ample possibilities for a wide range of biomedical applications such as magnetic resonance imaging, hyperthermia treatment,
targeted drug delivery, etc. [1] Understanding the complex magnetic textures in the microscopic dimensions by tailoring the size and morphology of these multifunctional structures is of
utmost importance for controlled and optimized applications. The coexistence of multiple phases in these nanostructures provides an additional degree of freedom to tune their
functionalities. Despite extensive investigations on the magnetic properties of core-shell iron oxide nanostructures with different shapes, sizes and morphologies, limited studies are
available on the influence of phase coexistence on iron oxide nanocubes. Here we report on a comprehensive investigation of magnetic properties of multiphase iron oxide nanocubes with
different sizes ranging between 10-43 nm synthesized using a chemical decomposition technique.[2] The exposure to air resulted in an α-Fe2O3 shell layer on the surface of the nanocubes,
with the core formed of a possible composite mixture of Fe3O4 and FeO phases. Magnetometry indicative of the Morin (α-Fe2O3) and Verwey (Fe3O4) transitions at ~250 K and ~120 K,
respectively identify the two phases, while FeO, the third phase is identified through XRD and Raman spectra. The smaller nanocubes up to average size 24 nm showed the exchange bias
(EB) effect below 250 K with 15 nm showing the strongest. The EB effect is attributed to the strong interfacial coupling between the ferrimagnetic (FiM) Fe3O4 phase and
antiferromagnetic (AFM) FeO phase. The Fe3O4/α-Fe2O3 (FiM/AFM) interfaces are found not to contribute to the EB effect. [3] Our results have enabled us to view the basis of the EB
effect in multi-phase iron oxide nanosystems and could open up possibilities to design tunable exchange-coupled nanomaterials with desirable magnetic properties for biomedical and
spintronic applications. 


**References:** 

[1] C. S. S. R. Kumar and F. Mohammad, Adv. Drug Deliv. Rev. 63, 789 (2011). 
[2] H. Khurshid, S. Chandra, W. Li, M. H. Phan, G. C. Hadjipanayis, P. Mukherjee, and H. Srikanth, Journal of Applied Physics, Vol. 113 (2013). 
[3] S. B. Attanayake, A. Chanda, R. Das, M. H. Phan, and H. Srikanth, AIP Adv. 12, 035136 (2022).

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