United States

Microwave spin resonance behaviour of these mixed ferrites are of key consideration for various applications.Mixed ferrites based magnetic nanofluids have a potential candidature in various biomedical and spintronics filed like magnetic fluid hyperthermia, MRI ,optical sensor,switches and targeted drug delivery.In this work, a series of zinc doped Fe&lt;sub&gt;3&lt;/sub&gt;O&lt;sub&gt;4&lt;/sub&gt;magnetic nano-fluids with different Zn concentrations represented as Zn&lt;sub&gt;x&lt;/sub&gt;Fe&lt;sub&gt;3-x&lt;/sub&gt;O&lt;sub&gt;4 &lt;/sub&gt;(x=0,0.1,0.2,0.3 &amp; 0.4)were synthesized by the wet chemical co-precipitated techniqueand oleic acid is used as surfactant to prevent the agglomeration of magnetic nanoparticles.Structural, optical, elastic and spin dynamics properties of these ferrofluids have been investigated using different sophisticated characterization techniques such as XRD, HRTEM, SEM, FTIR,UV and EPR etc. The structural and Rietveld refinement was carried out by the XRD data and the result confirms that single cubic spinel phase belongs to Fd3m (227) space group and the average crystallite size calculated from the XRD data varies from 12 to 15 nm. HRTEMstudies revealed that the particles are spherical in nature and mean particle size varies from 15 to 20 nm and all samples are polycrystalline in nature. SEM result was also demonstrated the surface morphology of magnetic particle is spherical in shape with slight agglomeration. FTIR spectroscopy showed the molecular dynamics and the formation of cubic spinel phase of frequency peaks at 535 cm&lt;sup&gt;-1&lt;/sup&gt;and 420 cm&lt;sup&gt;-1&lt;/sup&gt;respectively and also other different functional group which gives the evidences that oleic acid are present on the surface of MNPs.The UV-Visible measurement gives the estimate of the band gap of the materials which lies between(2.2 to 2.8, 3.1 and 3.8 e V) of the all the sample obtained from optical absorption spectra fitting by Tauc plot method. The room temperature microwave spins resonance studies was carried out by using X-band (9.8GHz) EPR spectrometer and calculated various spin resonance parameters[1,2]. In sample compositions the broad resonance signal is observed and enhancement of peak to peak line width is perceived due to the strong super-exchange interaction between the magnetic ions through oxygen ions[1-3].

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2022 Joint MMM-INTERMAG

Finite size effect on Structural, optical, elastic and spin resonance properties of oleic acid coated ZnxFe3-xO4 (0.4≤x≤0) ferrite nanofluids

The 65th Annual Conference on Magnetism and Magnetic Materials (MMM 2020) was held in a virtual form. The COVID-19 pandemic, with its associated uncertainty about international travel and the ability to gather in large groups, meant that the Steering Committee decided to cancel the face-to-face meeting that had been planned in Palm Beach, Florida November 2-6, 2020.

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MMM 2020

Microwave spin resonance behaviour of these mixed ferrites are of key consideration for various applications.Mixed ferrites based magnetic nanofluids have a potential candidature in various biomedical and spintronics filed like magnetic fluid hyperthermia, MRI ,optical sensor,switches and targeted drug delivery.In this work, a series of zinc doped Fe3O4magnetic nano-fluids with different Zn concentrations represented as ZnxFe3-xO4 (x=0,0.1,0.2,0.3 & 0.4)were synthesized by the wet chemical co-precipitated techniqueand oleic acid is used as surfactant to prevent the agglomeration of magnetic nanoparticles.Structural, optical, elastic and spin dynamics properties of these ferrofluids have been investigated using different sophisticated characterization techniques such as XRD, HRTEM, SEM, FTIR,UV and EPR etc. The structural and Rietveld refinement was carried out by the XRD data and the result confirms that single cubic spinel phase belongs to Fd3m (227) space group and the average crystallite size calculated from the XRD data varies from 12 to 15 nm. HRTEMstudies revealed that the particles are spherical in nature and mean particle size varies from 15 to 20 nm and all samples are polycrystalline in nature. SEM result was also demonstrated the surface morphology of magnetic particle is spherical in shape with slight agglomeration. FTIR spectroscopy showed the molecular dynamics and the formation of cubic spinel phase of frequency peaks at 535 cm-1and 420 cm-1respectively and also other different functional group which gives the evidences that oleic acid are present on the surface of MNPs.The UV-Visible measurement gives the estimate of the band gap of the materials which lies between(2.2 to 2.8, 3.1 and 3.8 e V) of the all the sample obtained from optical absorption spectra fitting by Tauc plot method. The room temperature microwave spins resonance studies was carried out by using X-band (9.8GHz) EPR spectrometer and calculated various spin resonance parameters[1,2]. In sample compositions the broad resonance signal is observed and enhancement of peak to peak line width is perceived due to the strong super-exchange interaction between the magnetic ions through oxygen ions[1-3].

![](https://assets.underline.io/uploads/markdown_image/1/image/8b32fddf83acb76352c659c6c766fe84.jpg)

poster

The 15th Joint MMM-INTERMAG Conference (2022 Joint) 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 plenary session, and an evening session, with about 1500 presentations overall. 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.

A gap opening in the surface state bands via breaking of TRS in topological insulators (TI) is needed for realization of dissipationless Quantum Anomalous Hall Effect (QAH) and other fascinating topological properties [1-5]. Here, we report formation of an antiferromagnetic (AFM) phase at the interface of sputter grown crystalline textured TI, Bi2Te3 when coupled with ferromagnetic metal (FM), Ni80Fe20 (Permalloy, Py). We grew samples of 40 nm c-axis oriented Bi2Te3 at 250 degC followed by 20 nm of Py at room temperature. Diffusion of Ni from Py and formation of distinct Ni-doped Bi2Te3 interfacial phase was observed. Zero Field Cooled (ZFC) magnetic hysteresis loop measurements at low temperatures showed a large spontaneous exchange bias of ~80 Oe at 6 K which suggests presence of strong FM/AFM coupling in the samples (Figure. 1). Location of the antiferromagnetic phase at Ni intercalated Bi2Te3 interfacial layer was identified using Polarized Neutron Reflectometry (PNR) (Figure 2) at 7 K. The magnetic scattering length density (MSLD) has a value of ~0.26 at 1T saturation field but is ~0 at a low field of 50 Oe when the magnetic moments in the interfacial layer are antiferromagnetically ordered. The large exchange bias in the Ni intercalated Bi2Te3 interfacial layer clearly suggests a large exchange energy which is characteristic of super-exchange mediated coupling of moments in Ni, Bi and Te based Van der Waals (VdW) MTI compounds [8]. This large exchange bias raises the possibility of formation of topologically nontrivial magnetic material at the interface. The observation of magnetic phase at the interface layer further raises the possibility of QAH state and paves the way for further exploration of TI/FM based heterostructures and applications for energy efficient spintronic devices which are compatible with industrial CMOS processes.

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ZFC hysteresis loop measured at 300 K and 6 K. At 6 K a large exchange bias of ~80 Oe emerges because of coupling of AFM interface layer with FM Py layer.

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PNR measurement at 7 K showing finite moments at 1 T saturation and AFM ordering at the Ni intercalated interface at 50 Oe. Inset: STEM-HAADF image with clear indication of the AFM Ni-intercalated Bi2Te3 layer.

Antiferromagnetic Phase in Sputtered Topological Insulator/Ferromagnetic Heterostructure Interface

Recently, Co2TiSi Heusler alloy is theoretically predicted that is one of the Weyl semimetal (WSM) candidates, and also the half-metal [1, 2, 3]. Since it is expected that a large anomalous Hall effect (AHE) can be observed in the WSM materials, Co2TiSi is an attractive material showing both a large AHE and a large spin polarization. And it is also expected that the AHE can be enhanced by the Fermi level tuning in Co2TiSi with V doping [4, 5]. In this research, we optimized the fabrication conditions for producing Co2Ti1-xVxSi thin films, and investigated their AHE. The ultra-high vacuum magnetron co-sputtering method was used for the preparation of thin films using Co2TiSi and Co2VSi targets. The structure of the sample was MgO (001) sub. / Co2Ti1-xVxSi (50 nm) / Ta (5 nm). For the preparation of Co2Ti1-xVxSi films, we changed the doping amount of x, and the post annealing temperature (Ta) was changed in the range of 300 to 700°C. We characterized the crystal structure, magnetic properties, and anomalous Hall effect by XRD, SQUID, and PPMS, respectively. Four-hold symmetric (111) superlattice diffractions from Co2TiSi and Co2Ti0.84V0.16Si are observed, shown in Fig.1, meaning that the L21 ordered epitaxial films were successfully fabricated. High magnitude of saturation magnetization was also confirmed at low measurement temperature for both films. By the plot of anomalous Hall conductivity vs electric conductivity, all samples show that the intrinsic mechanism dominates over the extrinsic mechanism which is also expected in WSM. The anomalous Hall conductivity of Co2TiSi sample was only 53 S/cm at low temperature and it was enhanced to 98 S/cm by the Fermi level tuning in Co2Ti0.84V0.16Si, shown in Fig.2. We infer that the Fermi level for the prepared Co2TiSi is not cross the Weyl points and it is expected that the AHE can be huge enhanced by the Fermi level tuning in Co2Ti0.61V0.39Si. This research was conducted by participating in the GP-Spin, Tohoku University, and supported by CSIS Organization for Advanced Studies and the CSRN.

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Enhancement of Anomalous Hall Effect in Magnetic Weyl Semimetal Co2TiSi Heusler Alloy Thin Films with V doping

Quantum phase transition (QPT) is a 2nd order solid state phase transition that starts at a quantum critical point (QCP) and continues to 0 K. Since all thermal fluctuations are absent at 0 K, QPT is caused by strong quantum fluctuations1. Since the lowest measuring temperature that can be experimentally reached in a research laboratory is between 20 mK and 50 mK, the QCP is generally determined by performing an extrapolation of the experimental data points (to 0 K) in the p vs. T (p is the control parameter and T is the temperature) phase diagram. ZrNi2Ga is a superconductor and belongs to the Ni-based Heusler family. The material exhibits a superconducting phase transition at ~2.9 K.2 When Ni is partially replaced by Cu in ZrNi2-xCuxGa the transition temperature linearly decreased to 1.85 K for x = 0.25.3 This is indicative of QPT in the system. Here, we have studied the magneto-transport properties of ZrNi2-xCuxGa (0.25 &lt; 0 ≤ 0.5) to further explore the possible QPT in the system. The samples were prepared by arc melting and the transport measurements were done on a Physical Property Measurement system with Helium-3 attachment. All samples exhibited the L21 cubic structure at room temperature. A superconducting phase transition temperature of as low as ~1 K was observed in the system, which nearly confirms the possibility of QPT in the ZrNi2-xCuxGa system. The experimental results will be presented in details.

Quantum Phase Transition in Partially Cu-Doped ZrNi2-xCuxGa Heusler Alloys

Ni2MnGa is an exemplary Heusler alloy to exhibit the martensitic phase transformation (MPT) from the high-temperature austenite phase to a lower temperature martensite phase.[1] The martensitic transformation occurs at TM ≈ 202 K followed by a ferromagnetic phase transition at TCA ≈ 380 K. When Mn is partially substituted by Cr in Ni2Mn1-xCrxGa TM increased while TC decreased, such that the two transitions overlapped at ~260 K for x = 0.50.[2] Additionally, the alloys exhibited resistivity drops of 2.5 - 18 % at the MPT. The largest magnitude drop occurred in materials exhibiting TM &gt; TC. Here, we present an experimental study on the transport and magnetic properties of Fe doped Ni2Mn0.4-xFexCr0.6Ga and Ni2Mn0.4FexCr0.6-xGa Heusler alloy systems. The goal was to compare the magnetic and transport properties of the two systems where Mn is replaced by Fe in one system and Cr is replaced by Fe in the other. All compounds were prepared by arc melting and annealing techniques. The samples were subjected to x-ray diffraction, electrical resistivity, and dc magnetization measurements. The diffraction data showed the samples were either tetragonal or Cubic at room temperature. For both systems TM and TC decreased with increasing x. However, TM decreased much rapidly for the Ni2Mn0.4FexCr0.6-xGa system while the rate of decrease of TC was slower. The experimental results will be presented and discussed taking the valence electron concentration, e/a, and the structural disorder into consideration.

A comparative study of the martensitic phase transitions in Fe doped Ni2Mn0.4-xFexCr0.6Ga and Ni2Mn0.4FexCr0.6-xGa Heusler alloy systems

La1-xSrxCoO3 (LSCO) changes from a paramagnetic semiconductor for x= 0 to a ferromagnetic metal for x≥ 0.2. .Magnetoelastic property of these oxides has been overlooked so far despite it showed giant anisotropic magnetostriction (1000-3000 ppm at 14.2 T) for x = 0.3 and 0.5 [1]. Its origin was suggested to the field-induced spin-state transition [low (S= 0) to intermediate (S= 3/2) spin] of Co3+ ions, and the creation of spin-orbit coupling. Subias et al.[2] report the atomic-scale origin of the magnetostriction in La0.5Sr0.5CoO3 by measuring local changes in Co-O bond length by analyzing the differential X-ray absorption data. Magnetic interactions among Co3+/Co4+ ions and their spin states are sensitive to the crystal field effect and average ionic radius of the rare earth and alkaline earth cations. We successfully synthesized the polycrystalline La0.5Ba0.5CoO3 by microwave irradiation with short-time irradiation of 20 minutes at 1200oC, and measured its magnetization (M) and Joule magnetostriction λpar whose field dependence at 10 K are shown in Fig.1(a). M shows hysteresis at low fields and increases without saturation up to H = 50 kOe. The M value at 50 kOe is much smaller than La0.5Sr0.5CoO3 for which M = 2 μB/f.u.which suggests the lack of long-range ferromagnetic order in this sample. λpar smoothly increases with H without showing a saturation. The value of λpar at 50 kOe is 265 ppm, which is smaller than in LSCO but yet a significant value among most transition metal perovskite oxides. λpar for 50 kOe has the maximum value at 10 K and decreases smoothly as the ferromagnetic -paramagnetic transition is approached (TC = 177 K) and becomes negligible above TC. (see Fig. 1(b)). Work is in progress to correlate the magnetostriction, spin state of Co ions, electronic phase separation, and negative thermal expansion proposed in this compound[3,4] R.M. thanks the Ministry of Education, Singapore (Grant no. R144-000-422-114 and R144-000-442-114).

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Fig 1: (a) Field dependence of magnetization (M) on left y-axis and parallel magnetostriction (λpar) on right y-axis of La0.5Ba0.5CoO3 at 10 K. (b) Temperature dependence of the maximum value of λpar at H = 50 kOe on left-yaxis and M for H = 1 kOe on right y-axis.

Magnetostriction in microwave synthesized La0.5Ba0.5CoO3

![](https://assets.underline.io/uploads/markdown_image/1/image/e4291e97a4d1c263e5030565a90a038f.jpg)The development of new materials with tunable properties are in demand for different applications in novel technologies and devices. In this regard, magnetoelectric laminated composites based on the coupling between magnetostrictive and piezoelectric phases have emerged over the last years due to their high induced electric response at the electromechanical resonance frequencies [1][2]. However, their application in areas requiring high working frequencies requires further development of these materials due to the difficult compromise between the increase of the frequency (obtained with shorter samples) and the high ME response (higher for larger areas of ME laminates). This work presents novel geometrically modified magnetoelectric laminates based on the Fe64Co17Si6.6B12.4 metallic glass and the polyvinylidene fluoride (PVDF) piezoelectric polymer. Laminates with rectangular, triangular and rhombic shapes with an area of 25 mm2 have been fabricated. The induced ME responses of the laminates under an applied DC magnetic field and as a function of the frequency have been analyzed. The results evidence that, at the electromechanical resonance frequency, the triangular and rhombic shaped laminates show an improved induced ME response (102 mV and 103 mV, respectively) in comparison with the common rectangular shaped one (98 mV). Furthermore, the working frequencies of the triangular and rhombic laminates significantly increase up to 83 kHz and 102 kHz, respectively, with respect to the rectangular one (67 kHz). Going a step forward, the novel geometries have been compared with that of rectangular magnetoelectric laminates of equivalent EMR frequencies (19 mm and 17 mm long laminates for 83 kHz and 102 kHz, respectively). These rectangular laminates show a drastic drop of their induced ME responses (29 mV and 6.7 mV, respectively), due to the quality factor impair caused by the demagnetizing effects in these shorter samples. This study represents a critical advance in the performance of magnetoelectric laminated composites through geometry modification, opening the door to their implementation in enhanced high frequency devices.

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Enhanced performance of magnetoelectric laminated composites by geometry engineering for high frequency applications

Magnetoelectric (ME)-controlled antiferromagnet (AFM) based random access memory has outstanding energy efficiency and excellent robustness to magnetic disturbances, but how to read out the data is a topic of research. Conventionally, it can be read out by the magnetization of the adjacent ferromagnetic layer coupled with the ME AFM layer via exchange bias [1,2]. However, the interfacial exchange coupling with the ferromagnetic layer has a non-negligible effect on the switching of AFM order-parameter causing excess energy. In this paper, we use the spinning-current anomalous Hall magnetometry [3] to access to the AFM order parameter of ME AFM of 40-nm-thick Cr2O3 thin film. In this technique, the AFM order parameter (interfacial AFM moment) manifests as the remanent Hall resistance RH_Rem. Pt(2 nm)/Cr2O3(40 nm)/Pt(20 nm) thin film was prepared on α-Al2O3(0001) substrate by using the DC magnetron sputtering system. Structural characterizations were carried out using reflection high-energy electron diffraction (RHEED), X-ray diffraction, and X-ray reflectivity. RH_Rem was evaluated as a function of temperature after cooling the film from 320 K (above the Néel temperature TN). Magnetic-field dependence of Hall resistance, i.e. anomalous Hall effect (AHE) were also measured. For the Hall measurements, a micro-fabricated Hall device (width: 2 µm and length: 50 µm) were used. Figure 1 shows the temperature dependence of RH_Rem for the difference cooling field. The finite RH_Rem is observed and the sign of RH_Rem reverses by the cooling field. With increasing temperature, RH_Rem slightly increases, reaches maximum around 225 K and decreases again. Finally, RH_Rem becomes zero around 290 K which is near TN of the Cr2O3 thin film characterized by the spin Hall magnetoresistance measurements [4]. Hence, RH_Rem is emerged by the AFM order parameter. We also found that the magnetic-field dependence of Hall resistance exhibits the hysteresis, which is a signature of the spin-flip transition of the Cr2O3 thin film.

![](https://assets.underline.io/uploads/markdown_image/1/image/9b183a6cadc89984ab21d4803fc0a2aa.jpg)

Figure 1 Temperature dependence of anomalous Hall effect resistances under different cooling fields of -20 kOe (blue), +20 kOe (red).

Detection of antiferromagnetic order parameter based on Hall measurements for Pt/Cr2O3/Pt trilayer

The anomalous Nernst effect (ANE), one of the long-studied thermomagnetic effects, has been regarded as a promising next-generation energy harvesting technology for large-area and flexible devices. However, since the ANE power is too short for practical use, it is necessary to enhance ANE and many ferromagnetic materials have been widely investigated [1]. We experimentally investigated the anomalous Nernst effect (ANE) in an Fe3Si film whose ANE was predicted to be large, based on the topological band structure [2]. We also measured the Seebeck and anomalous Hall effects to separate the ANE term from the Hall effect of the carrier flow induced by the Seebeck effect. The sample structure and measurement system are shown in Fig. 1. In addition to Fe3Si, Fe2Si, FeSi, and FeSi2 50nm films were fabricated on SiO2 substrate by co-sputtering and annealed in vacuum at 1123K for 1 hour. Figure 2 shows the ANE coefficient as a function of Si composition in Fe-Si compounds. The ANE coefficients were estimated as 1.0 and 0.5 µVK-1 for the Fe3Si and Fe2Si samples, respectively. These values are much larger than the ANE coefficient of film Fe, whereas Fe3Si and Fe2Si both have a smaller saturation magnetization than Fe. In general, the Nernst coefficient can be decomposed into two terms: Syx= ρxxαyx - tanθAHESxx. Here, the first term S1 exhibits the intrinsic ANE term that converts heat flow into a transverse voltage, and the second term S2 reflects the voltage originating from the Hall effect of the carrier flow induced by the Seebeck effect during the anomalous Nernst effect. From Fig. 2, it was found that the first term S1 was dominant in the ANE improvement of Fe3Si, suggesting that the ANE of Fe3Si is enhanced because of its band structure, as expected from the theoretical calculation. Fig.1 Schematics of the sample structure and ANE measurement configuration. Fig.2 Negative value of the ANE coefficient Sxy, the first term S1 , and the second term S2 as a function of Si composition in Fe-Si compounds.

![](https://assets.underline.io/uploads/markdown_image/1/image/1a38d99e3e16bb20f0ad9211f86d83f3.jpg)

Fig.1 Schematics of the sample structure and ANE measurement configuration.

![](https://assets.underline.io/uploads/markdown_image/1/image/2ec8641a0197aa716c6bbd15067d45b9.jpg)

Fig.2 Negative value of the ANE coefficient Sxy, the first term S1 , and the second term S2 as a function of Si composition in Fe-Si compounds.

Anomalous Nernst effect in Fe-Si alloy films

Introduction The Spheroidal graphite cast iron is used for high-strength parts of large heavy machinery. The cementite (Fe3C) may be contained in cast iron during the casting process. Since the strength is reduced if the cemenite is contained in the cast iron, the evaluation of the cementite content is important. The permeability and conductivity of the cementite domain are less than that of the domain in the cast iron without cementite. It is possible to evaluate the cemenite content using an electromagnetic field. However, the flux density is also influenced by the changing distance (lift-off: Lo) between the cast iron and the inspection sensor. Since the surface of the cast iron may be coated with rust preventive, it may not be possible to determine the exact Lo. In this paper, the inspection method for estimating the cementite content and Lo at the same time is proposed. Inspection model and tesults Fig.1 shows the inspection model. The sensor is composed of an AC excition coil with 10 kHz and 2A, a mangetic yoke and a detection coil. The B-H curves of the cast iron with and without cementite are shown in Fig.2. The conductivities of the cast iron with and without cementite are 1.9 x 106 S/m and 1.63 x 106 S/m, respectively. The permeability and conductivity of the cast iron with cementite are smaller than those of cast iron without cementite. Fig.3 shows a complex plane of the output voltage in a detection coil by changing the Lo and the cementite content. This figure shows the real VRe and imaginary VIm components of the output voltage. The output voltage due to the changes of the Lo and the cementite content is distinguished even if the ampulitude output voltage is the same value. In this resarch, when both cementite content and Lo are unknown, these values are estimated by the linear interpolation using this complex plane in Fig.3. Table 1 shows the estimation results of both unknown cementite content and Lo. This table shows that the actual cementite content and Lo are mostly estimated.

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Electromagnetic evaluation method for both air-gap distance of non-contact sensor and cementite content inside spheroidal graphite cast iron

Electromagnetic evaluation method for both air-gap distance of non-contact sensor and cementite content inside spheroidal graphite cast iron

Recently, studies on the Y-type hexaferrites are being actively conducted because they exhibit multiferroic properties. Y-type hexaferrite is being used to high-density memories, wireless communication devices, etc. Therefore, to utilize it in these various fields, research on various characteristic changes through ion substitution is attracting attention [1]. Sr substituted Y-type Barium hexaferrite increased the saturation magnetization (Ms) and coercivity (Hc ) [2]. Nonmagnetic Al ion substitution at BaSrCo2Fe12O22 stabilized the spin structure [3]. This study, we have investigated the various effect of nonmagnetic Mg ion doping at Ba2Co2Fe12O22. Polycrystaline Ba2Co2-xMgxFe12O22 (x = 0.0, 0.1, 0.3, 0.5) was synthesized by solid state reaction method. We used XRD to analyze the crystal structure of the sample and analyzed the patterns with Rietveld refinement using the Fullprof. To measure magnetic properties, we used VSM and Mössbauer spectroscopy. We measured M-T and M-H values using VSM. The M-T experiments and Mössbauer experiments were conducted from 4.2 to 295 K. The Mössbauer spectra were fitted the six Lorentzian sextets. The Ba2Co2-xMgxFe12O22 were analyzed as hexagonal in the R-3m space group. We observed that the lattice constants a0 and c0 decreased as the concentration of Mg increased. This is because the ionic radius Mg (0.72 Å) is smaller than that of Co (0.745 Å). In the result of M-T experiment, we found the spin reorientation temperature (Ts). Ts were 215, 212, 209 and 202 K at x = 0.0, 0.1, 0.3 and 0.5, respectively. The Mössbauer spectra were analyzed by six sites of Fe. Each lines represented the six different sites of Fe (3bVI, 6c*IV, 6cVI, 18hVI, 6cIV, and 3aVI). The result of the analysis, the magnetic hyperfine field (Hhf) of 3bVI site was largest. Hhf and the quadrupole splitting values showed abrupt changes at Ts. The isomer shift values were maintained between 0.1 ~ 0.4 mm/s, indicating that Fe exhibited the Fe3+ ion state at all temperatures. The Hhf values decreased with increasing Mg doping. Along with the decrease of Ms and Hc in the M-H experiment, these results can be explained by the substitution of nonmagnetic Mg ion for magnetic Co ion.

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Antiferromagnetic Phase in Sputtered Topological Insulator/Ferromagnetic Heterostructure Interface

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