United States

In order to improve the multiferroic properties of BiFeO3 (BFO), partial substitution of the A site for Bi has been reported to effective method. Last decade, two classes of dopants used include rare earth elements (R), such as Y, La, Nd, Pr, and Sm (1), and alkali earth elements, e.g. Ca, Sr, and Ba (2). These dopants could reduce the leakage current density and improve the ferroelectric as well as magnetic properties of BFO. Although the investigations on multiferroic properties of R-doped BFO are extensive, BFO doped with heavy rare earth (H) is less discussed. To substitute H, such as Gd, Tb, Dy, Ho, and Er, for Bi in BFO is expected to improve the magnetic properties because the larger magnetic moment (7.8-10.6 μB) for H ions may introduce an additional magnetic interactions and ordering in BFO (3). In this work, we adopted pulsed laser deposition (PLD) to develop Bi0.9H0.1FeO3 (BHFO) films on glass substrates. The microstructure, ferroelectric, and magnetic properties of BHFO films are studied. BHFO films were confirmed to mainly consist of the perovskite phase. The desired multiferroic properties with the suppressed leakage is reached. The magnetic properties with the enhanced magnetization are found for BHFO films: their Ms are 18.8, 18.9, 21.3, 25.6, 18.5 emu/cm3, for the films with H = Gd, Tb, Dy, Ho, and Er, respectively. The higher magnetic moment of H ion is, and larger Ms of the films is. The above behavior reveals magnetization of BFO films with H substitution is mainly dominated by the magnetic moment of H ion. Besides, good ferroelectric properties are also attained for BHFO films, where the largest remanent polarization (2Pr) of 120.1 µC/cm2 is achieved for H = Gd, related to low leakage and high BHFO(110) texture. It might be related to the larger ionic radius for Gd than other H. Relationship between leakage mechanisms and microstructure are also discussed in those BHFO films.&lt;br&gt;

**References:**&lt;br&gt;
(1) D. Kan et al., J. Appl. Phys. 110, 014106 (2011).&lt;br&gt;
(2) H.W. Chang et al., J. Alloys Compd. 683, 427 (2016).&lt;br&gt;
(3) N. Jeon et al., Appl. Phys. Lett. 98, 072901 (2011).&lt;br&gt;



MMM 2022

Enhanced multiferroic properties in Bi0.9H0.1FeO3 polycrystalline films (H = heavy rare earth elements)

In order to improve the multiferroic properties of BiFeO3 (BFO), partial substitution of the A site for Bi has been reported to effective method. Last decade, two classes of dopants used include rare earth elements (R), such as Y, La, Nd, Pr, and Sm (1), and alkali earth elements, e.g. Ca, Sr, and Ba (2). These dopants could reduce the leakage current density and improve the ferroelectric as well as magnetic properties of BFO. Although the investigations on multiferroic properties of R-doped BFO are extensive, BFO doped with heavy rare earth (H) is less discussed. To substitute H, such as Gd, Tb, Dy, Ho, and Er, for Bi in BFO is expected to improve the magnetic properties because the larger magnetic moment (7.8-10.6 μB) for H ions may introduce an additional magnetic interactions and ordering in BFO (3). In this work, we adopted pulsed laser deposition (PLD) to develop Bi0.9H0.1FeO3 (BHFO) films on glass substrates. The microstructure, ferroelectric, and magnetic properties of BHFO films are studied. BHFO films were confirmed to mainly consist of the perovskite phase. The desired multiferroic properties with the suppressed leakage is reached. The magnetic properties with the enhanced magnetization are found for BHFO films: their Ms are 18.8, 18.9, 21.3, 25.6, 18.5 emu/cm3, for the films with H = Gd, Tb, Dy, Ho, and Er, respectively. The higher magnetic moment of H ion is, and larger Ms of the films is. The above behavior reveals magnetization of BFO films with H substitution is mainly dominated by the magnetic moment of H ion. Besides, good ferroelectric properties are also attained for BHFO films, where the largest remanent polarization (2Pr) of 120.1 µC/cm2 is achieved for H = Gd, related to low leakage and high BHFO(110) texture. It might be related to the larger ionic radius for Gd than other H. Relationship between leakage mechanisms and microstructure are also discussed in those BHFO films. 

**References:** 
(1) D. Kan et al., J. Appl. Phys. 110, 014106 (2011). 
(2) H.W. Chang et al., J. Alloys Compd. 683, 427 (2016). 
(3) N. Jeon et al., Appl. Phys. Lett. 98, 072901 (2011).

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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Holmium substituted Samarium iron garnet i.e., Sm3-xHoxFe5O12 (x = 0 and 0.6) were synthesized using solid-state reaction route by sintering at 1400°C for 8 hours. Samples are found to be in single phase form as per XRD patterns and refined by Rietveld refinement technique using Ia-3d space group. The lattice constant is found to be decrease from 12.53Å to 12.43Å with Ho doping. Magnetic hysteresis loops (M-H) are measured at room temperature shows that saturation magnetization is decreases from 21.05 emu/g for x = 0 to 12.06 emu/g for x = 0.6 sample. The anisotropy constant is decreasing from 2.42×105 erg/cc for x = 0 to 1.7×105 erg/cc for x = 0.6 sample. Negative magnetization is observed for x = 0.6 sample which can be explained by using the equation i.e., Mnet = 3MFe(d) – [2MFe(a) + (3-x) MSm + xMHo], where Fe(d) and Fe(a) are the Fe atoms at tetrahedral and octahedral site respectively. The frequency dependence of real part of impedance Z' show a step like behavior which indicates the presence of dielectric relaxation in the samples. The merger of all Z' values at higher frequency is due to release of space charges. - Z'' vs. frequency is also plotted and all the plots show relaxation peaks. With the increase in temperature, the peaks are shifting towards higher frequency which suggests that the relaxation is due to thermally activated charge carriers.
Keywords: Ferrimagnetic, negative magnetization, relaxation behavior. 

**References:** 
1. Xiaobo Wu, Study on dielectric and magnetodielectric properties of Lu3Fe5O12 ceramics, Applied Physics Letters 87, 042901 (2005). 
2. Canglong Li, Spin reorientation, normal and inverse magnetocaloric effects in heavy rare-earth iron garnets, Ceramics International 46 (2020) 18758–18762. 
3. Tingsong Zhang, Dielectric and ferroelectric properties of Nd3Fe5O12, Solid State Communications 305 (2020) 113766. 
4. Yu-Jhan Siao, Journal of Applied Physics 109, 07A508 (2011). 

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Tuning of Magnetic and Electrical properties of Samarium Iron Garnet by Holmium Substitution

Transition metal oxides exhibit rich electrical and magnetic properties. The epitaxial strain plays a vital role to manipulate their magnetic ground state. In addition, Oxygen vacancies (Vo) are one of the most common point defects to play a key role in regulating the physicochemical properties of oxides. (1-4) 
In this context, LCO exhibits interesting phenomena in terms of the origin of magnetism.
In this work, Perovskite LaCoO3 (PV-LCO) films were grown at STO and LAO substrate. Then brownmillerite LaCoO2.5 (BM-LCO) films are formed by annealing in a vacuum at 450 °C for 4h and 500 °C for 4h, respectively. The XRD spectra show that there is no impurity phase during phase transitions, indicating that the films can be fully transformed. (Fig.1a) The magnetic properties were confirmed by SQUID-VSM. The 50-nm-thick PV-LCO film on STO exhibits an obvious ferromagnetism phase. (Fig.1b-c) The tensile strain leads to a decrease of ΔCF due to distortion of CoO6 octahedron, promotes the spin state transition. (5,6) 
However, the same thickness coherently strain film in compression on LAO exhibits extremely weak ferromagnetism. We anticipate the reason for this is because the eg orbitals are split into two separate energy levels due to existence of the JTD distortion, it is always accompanied by an increase of the bond distance rCo–O and suppression of CoO6 octahedral rotation and distortion. Interestingly, the BM-LCO shows no hysteresis loop. We believe the reason for this novel phenomenon is that the increase in ordered Vo leads to the expansion of the lattice, thus inhibiting the rotation and distortion of the CoO6 octahedron and causing the generation of anti-ferromagnetic behavior. (7,8)
In sum, we find that BM-LCO films in epitaxial strain and Vo ordering show no ferromagnetism. This phenomenon provided an effective way to regulate the physical properties of cobalt oxides. It would have a good application value in the fields of ion electrochemical sensors. 

**References:** 
(1) J. H. Ngai, F. J. Walker, and C. H. Ahn, Annual Review of Materials Research 44 (1), 1 (2014). 
(2) A. La Spina, P. Paolicchi, and A. Kryszczynska, Nature 428 (6981), 400 (2004). 
(3) J. Jeong, N. Aetukuri, and T. Graf, Science 339 (6126), 1402 (2013) 
(4) G.E. Sterbinsky, R. Nanguneri, and J.X. Ma, Ryan, Phys. Rev. Lett. 120 197201(2018). 
(5) Er-Jia Guo, Ryan D. Desautels, and David Keavney, Physical Rev B 75 (14) (2007). 
(6) Fuchs, D. C. Pinta, and T. Schwarz, Physic Rev. B 75, 144402 (2007). 
(7) D. Fuchs, E. Arac, and C. Pinta, Phys. Rev. B 77, 014434, (2008). 
(8) Q. Zhang, A. Gao, and F. Meng, Nat Commun 12(1), 1853 (2021). 

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Strain independent Regulation of Magnetic Properties by Topotactic Phase Transformation in LaCoO3 Thin Films

Bimagnetic nanoparticles show promise for applications in energy efficient magnetic storage media and magnetic device applications. The magnetic properties, including the exchange bias of nanostructured materials can be tuned by variation of the size, composition, and morphology of the core vs overlayer of the nanoparticles (NPs). The purpose of this study is to investigate the optimal synthesis routes, structure and magnetic properties of novel CoO/NiFe2O4 heterostructured nanocrystals (HNCs). In this work, we aim to examine how the size impacts the exchange bias, coercivity and other magnetic properties of the CoO/NiFe2O4 HNCs. The nanoparticles with sizes ranging from 10 nm to 24 nm were formed by the synthesis of an antiferromagnetic (AFM) CoO core and deposition of a ferrimagnetic (FiM) NiFe2O4 overlayer. A highly crystalline magnetic phase is more likely to occur when the morphology of the core-overgrowth is present, which enhances the coupling at the AFM-FiM interface. The CoO core NPs are prepared using thermal decomposition of Co(OH)2 at 600 °C for 2 hours in a pure argon atmosphere, whereas the HNCs are obtained first using thermal evaporation followed by hydrothermal synthesis. The structural and morphological characterization made using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) techniques verify that the HNCs are comprised of a CoO core and a NiFe2O4 overgrowth phase. Rietveld refinement of the XRD data shows that the CoO core has the rocksalt (Fd3(bar)m) crystal structure and the NiFe2O4 overgrowth has the spinel (C12/m1) crystal structure. SEM-EDS data indicates the presence and uniform distribution of Co, Ni, and Fe in the HNCs. XPS analysis of the O 1s, Co 2p, Ni 2p, and Fe 2p regions shows that both the core and overgrowth phases are well-structured. The results from PPMS magnetization measurements and high-resolution transmission electron microscopy (HR-TEM) of the CoO/NiFe2O4 HNCs will be discussed.

On the synthesis and characterization of bimagnetic CoO/NiFe2O4 heterostructured nanoparticles

In this work, we investigate the synthesis, along with the structural, magnetic, and surface chemical environment properties, of novel Mn-Co-NiO-based heterostructured nanocrystals (HNCs). The objective is to develop novel, well structurally ordered inverted antiferromagnetic (AFM) NiO – ferrimagnetic (FiM) spinel phase overgrowth HNCs. Inverted HNCs are particularly promising for magnetic device applications because their magnetic properties are more easily controlled by having well-ordered AFM cores, which can result in magnetic structures having large coercivities, tunable blocking temperatures, and other enhanced magnetic effects. The synthesis of the HNCs is accomplished using a two-step process: In the first step, NiO nanoparticles are synthesized using a thermal decomposition method. Subsequently, Mn-Co overgrowth phases are grown on the NiO nanoparticles via hydrothermal nanophase epitaxy, using a fixed pH level (~5.3) of the aqueous medium. This pH level was selected based on previous work in our laboratory showing that NiO/Mn3O4 HNCs of constant size have optimal coercivity and exchange bias when synthesized at a pH of 5.0.1 The crystalline structure, surface/interface chemical environment and gross morphology of the Mn-Co-NiO-based HNCs have been analyzed using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Scanning Electron Microscopy (SEM) techniques, respectively. Analysis using these techniques shows that the HNCs are composed of a NiO core and a CoMn2O4 overgrowth phase. Rietveld refinement of XRD data shows that the NiO core has the rocksalt (Fm-3m) cubic crystal structure and the CoMn2O4 overgrowth has the spinel (I41/amd) crystal structure. Moreover, an increased relative amount of the CoMn2O4 overgrowth phase is deposited with decreasing NiO core particle size during the synthesis of the HNCs. Analysis of the O 1s, Ni 2p, Co 2p, and Mn 2p regions of the XPS spectra measured from our samples is consistent with well-structured core/overgrowth phases having M-OH (M: Ni, Co, Mn) bonding at their surface regions. The results from PPMS magnetization and high-resolution transmission electron microscopy (HR-TEM) characterization of the Mn-Co-NiO-based HNCs will be discussed. 

**References:** 
(1) Shafe et al., ACS Applied Materials & Interfaces, 13, 24013−24023 (2021)

Investigations of Size Dependent Properties of Mn

Stoichiometric LaMnO3 has an orthorhombic crystal structure with an antiferromagnetic (TN ~ 140 K) insulating nature (1). The substitution of aliovalent cations (Sr2+ or Na1+) induce holes in the partially filled 3d shell of Mn and oxidizes the Mn3+ (t2g3eg1) to Mn4+ (t2g3eg0) and transforms the LaMnO3 to ferromagnetic metal through the double exchange coupling of Mn4+-O-Mn3+ (2). Since the Na1+ (1.39 Å) has an ionic radii closer to La3+ (1.36 Å) this would induce a twice number of holes compared to Sr2+ substitution. Drastic variations in their physical properties have also been found in different synthesis methods (3,4). Therefore, in this work, we adopted a recently emerging microwave (MW) heating to synthesise La1-xNaxMnO3 (x = 0, 0.1, 0.3) from the oxide precursors. Conduction or dielectric loss heating by MW irradiation enables the fast and homogenous reaction in few minutes. We achieved 1000 oC in 10 min and dwelled the samples for 20 min. The operating MW power alone was varied from 1000 W to 1200 W and 1400 W for x = 0.3 to examine the effect of MW power on its physical properties. Temperature-dependent magnetization and resistivity of x = 0, 0.1, 0.3 with fixed MW power (1200 W) are shown in Fig. 1 (a)&(b). A broad Curie transition is observed for undoped LaMnO3 with TC of 200 K, unlike our previous report on solid-state prepared La1-xNaxMnO3 where we observed TN = 140 K for undoped LaMnO3 (5), and the transition becomes narrow with increased TC as x increases. Insulating LaMnO3 transforms to metallic below TC upon Na doping. TC is denoted in the figure by dotted vertical lines. As the MW power increases from 1000 W to 1200 W, the resistivity of x = 0.3 decreases drastically and the metal-insulator transition also becomes sharp at a temperature very close to TC (Fig. 1(c)). The obtained microwave absorption peaks at a specific field show only a little increase with increasing the frequency of the MW signal. These findings will be correlated and discussed with the structural and morphological features acquired by microwave irradiation. 

**References:** 
(1) T. Tokura, et al., Mater. Sci. Eng. B 31(1-2), 187–191 (1995). 
(2) G.H. Rao, et al., J. Phys. Condens. Matter 11, 1523 (1999). 
(3) Y. Regaieg, et al., Materials Letters 80, 195–198 (2012). 
(4) Shuai Zhang, et al., Ceramics International 46, 584–591 (2020). 
(5) Rajasree Das, et al., Ceramics International 47, 393–399 (2021). 

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Effect of microwave instant heating on magnetic, electric, thermoelectric and microwave absorption properties of La0.7Na0.3MnO3

The inverse Faraday effect (IFE) [1,2,3] phenomenologically describes the static magnetization induced by the circularly polarized light. In experiments, the IFE is able to reverse the magnetization of magnets with strong laser pulse, providing an optical method of ultrafast magnetization manipulation. Recently, sensitive detection of the effective magnetic field induced by a continuous laser can be carried out electrically through the inverse spin Hall effect [4]. Here, we study inverse Faraday effect in Dirac Hamiltonian with random impurities using Keldysh formalism and diagrammatic perturbation theory in low frequency regime [5]. The mass term in Dirac Hamiltonian is essential for the IFE, where the spin magnetic moment induced by circularly polarized light is proportional to frequency of the incident light within THz regime. For massive Dirac electrons, the corrections due to the short-range impurities on spin magnetic moment vertex exhibits mixing of spin magnetic moment vertex and spin angular momentum vertex. The spin magnetic density response is divergently enhanced by the vertex corrections near the band edge. 
**References** [1] P. Pershan, Physical Review 130, 919 (1963).
[2] K. Taguchi, and G. Tatara, Physical Review B 84, 174433 (2011).
[3] K. Taguchi, T. Imaeda, M. Sato, and Y. Tanaka, Phys. Rev. B 93, 201202(R) (2016).
[4] M. Kawaguchi, H. Hirose, Z. Chi, Y.-C. Lau, F. Freimuth, and M. Hayashi, arXiv preprint arXiv:2009.01388 (2020).
[5] G. Qu, and G. Tatara. arXiv preprint arXiv:2201.10155(2022).

Theory of Inverse Faraday effect in massive Dirac electrons

The rare-earth nitrides are the only known series of intrinsic ferromagnetic semiconductors, with a range of magnetic behaviours stemming from the contribution of both spin and orbital 4f moments. The similar chemistry of the rare-earths and the common structure of the nitrides simplifies their combination in superlattices and solid solutions. Recent studies of rare-earth nitride superlattices have shown enhanced superconductivity [1] and magnetic exchange spring behaviour that results from the competition between the Zeeman and Exchange interactions [2]. Yet, little has been published to date exploring the combination of these nitrides in solid-solutions.

We show (with reference to magnetometry, XMCD and anomalous Hall effect measurements) that the same Exchange/Zeeman competition that leads to a complex twisted magnetic phase in superlattices manifests quite differently in solid solutions. Leading, where an orbital-dominant ferromagnet (SmN) is paired with a spin-only ferromagnet (GdN), to a composition exhibiting a net zero magnetic moment (A compensation point). 
**References** [1] E.-M. Anton, S. Granville, A. Engel et. al. , Phys. Rev. B, Vol. 94, 024106 (2016)
[2] E.-M. Anton, W. Holmes-Hewett, J. McNulty et. al. , AIP Advances, Vol. 1, 015348 (2021)

Exchange/Zeeman Competition in the Rare Earth Nitrides and the Resulting Magnetic Compensation

VCMA effect describes the fact that in a capacitor, in which one of electrodes is made of a thin ferromagnetic metal, the magnetic properties of the ferromagnetic metal changes, when a voltage is applied to the capacitor[1]. Inside a metal the electrical field is screened by free electrons and cannot penetrate deep inside the metal. As a result, the voltage, which is applied to the capacitor dielectric (gate), may penetrate into and affect only the few uppermost atomic layers of the metal near the gate. However, the change of magnetic properties of the uppermost layer by the gate voltage affects the magnetic properties of the whole film. This can be only the case if the interfacial perpendicular magnetic anisotropy (PMA) is affected by the gate voltage [2]. The strength of PMA is characterized by the anisotropy field Hani and proportional to the strength of spin-orbit interaction, demagnetization field and magnetization of nanomagnet.
Fig.1 shows the measured Hani and coefficient of spin-orbit interaction kso in FeCoB nanomagnet under a different gate voltage. kso defies the strength of the spin-orbit interaction[3]. Hani decreases and kso increases under an increase of gate voltage. It is unexpected because Hani is linearly proportional to kso [3] and should increase when kso increases. It means that even though the strength of the spin-orbit interaction is affected by the gate voltage, but additionally to kso there is another voltage- dependent parameter, which defines the voltage dependence of Hani. The intrinsic field in nanomagnet or demagnetization field might be such a parameter.
Fig.2 shows measured Hani and kso of different nanomagnet of different wafers. The same tendency exists in all measured nanomagnets. 
**References** [1] Y. Shiota, T. Nozaki, F. Bonell, S. Murakami, T. Shinjo, Y. Suzuki, Nat. Mater. 11 (2012) 39–43.
[2] V. Zayets, T. Nozaki, H.Saito, A. Fukushima, S.Yuasa, arXiv:1812.07077 ( 2018).
[3] V.Zayets, IOA-07, MMM 2021. 

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Unexpected opposite dependencies of anisotropy field and strength of spin orbit interaction on gate voltage measured in FeCoB nanomagnet

This study aims to fabricate a voltage-tuneable magneto resistive sensor with the ability to measure small magnetic field signals in three dimensions. Sensing direction in magneto resistive sensors is linked to the magnetization of reference layer. Materials like CoFe1, CoFeB2 and Heusler alloys3 are good choices as reference layers due to their adjustable magnetic anisotropies. Here, using ionic liquid gating (ILG), we observed that magnetic anisotropy of reference layer CoFeB is switchable in MgO(1.5nm)/CoFeB(1.6nm)/W(0.5nm) stack. We used ionic liquid N, N-diethyl-N-methyl N-(2-methoxyethyl) ammonium bis (trifluoromethylsulfonyl) imide (DEME TFSI) (IoLiTec) for applying the gate voltage (VG) ranging between ±3.5V. Using the magneto-optical Kerr effect, we have investigated the change of anisotropy using different gate voltages. We found that magnetic anisotropy switches from out-of-plane (virgin state) to in-plane upon the application of +3.5V, whereas removal of applied voltage +3.5V or application of -3.5V, switches magnetic anisotropy back to out-of-plane, demonstrating the switching behaviour of the stack is reversible and repeatable. Moreover, we observed that out-of-plane to in-plane anisotropy switching time is higher (~45 sec) compared to in-plane to out-of-plane switching time (~25 sec). Hence, a stack having stronger out-of-plane and switchable anisotropy is ideal to use in voltage tuneable magneto resistive sensors. 
**References** 1. Parkin, S. S. P. et al., Nat. Mater., 2004, 3, 862–867.
2. Yuasa, S. & Djayaprawira, D. D., J. Phys. D. Appl. Phys., 2007, 40, 337-354.
3. Palmstrøm, C. J., Prog. Cryst. Growth Charact. Mater., 2016, 62, 371–397. 

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Switching of Magnetic Anisotropy in MgO/CoFeB/W stack by Ionic Liquid Gating for Voltage Tuneable Magneto Resistive Sensor

Reservoir computing (RC) has been considered as one of the key computational principles beyond von-Neumann computing. Magnetic skyrmions, topological particle-like spin textures in magnetic thin films, are particularly promising for implementing RC [1] since they respond strongly nonlinear to external stimuli and feature inherent multiscale dynamics. We propose and demonstrate experimentally a conceptually new approach to skyrmion RC that exploits the thermally activated diffusive motion of skyrmions [2]. By confining the thermal and low-energy, electrically gated skyrmion motion, together with employing spatially resolved input and readout, we find that already a single skyrmion in a confined, triangular geometry (Fig. 1) suffices to realize non-linearly separable functions, which we demonstrate for the XOR gate along with all other Boolean logic gate operations [3] (Fig. 2). Our proposed concept can be readily extended by linking multiple confined geometries and/or by including more skyrmions in the reservoir, suggesting high potential for scalable and low-energy reservoir computing.

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Enhanced multiferroic properties in Bi0.9H0.1FeO3 polycrystalline films (H = heavy rare earth elements)

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Tuning of Magnetic and Electrical properties of Samarium Iron Garnet by Holmium Substitution

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