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La&lt;sub&gt;1&lt;i&gt;-x&lt;/i&gt;&lt;/sub&gt;Sr&lt;i&gt;&lt;sub&gt;x&lt;/sub&gt;&lt;/i&gt;CoO&lt;sub&gt;3 &lt;/sub&gt;(LSCO) changes from a paramagnetic semiconductor for x= 0 to a ferromagnetic metal for x≥ 0.2. &lt;sub&gt; .&lt;/sub&gt;Magnetoelastic property of these oxides has been overlooked so far despite it showed giant anisotropic magnetostriction (1000-3000 ppm at 14.2 T) for &lt;i&gt;x&lt;/i&gt; = 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 Co&lt;sup&gt;3+&lt;/sup&gt; ions, and the creation of spin-orbit coupling. Subias et al.[2] report the atomic-scale origin of the magnetostriction in La&lt;sub&gt;0.5&lt;/sub&gt;Sr&lt;sub&gt;0.5&lt;/sub&gt;CoO&lt;sub&gt;3&lt;/sub&gt; by measuring local changes in Co-O bond length by analyzing the differential X-ray absorption data. Magnetic interactions among Co&lt;sup&gt;3+&lt;/sup&gt;/Co&lt;sup&gt;4+ &lt;/sup&gt;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 La&lt;sub&gt;0.5&lt;/sub&gt;Ba&lt;sub&gt;0.5&lt;/sub&gt;CoO&lt;sub&gt;3&lt;/sub&gt; by microwave irradiation with short-time irradiation of 20 minutes at 1200&lt;sup&gt;o&lt;/sup&gt;C, and measured its magnetization (M) and Joule magnetostriction λ&lt;sub&gt;par&lt;/sub&gt; 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 La&lt;sub&gt;0.5&lt;/sub&gt;Sr&lt;sub&gt;0.5&lt;/sub&gt;CoO&lt;sub&gt;3&lt;/sub&gt; for which M = 2 μ&lt;sub&gt;B&lt;/sub&gt;/f.u.which suggests the lack of long-range ferromagnetic order in this sample. λ&lt;sub&gt;par&lt;/sub&gt; smoothly increases with H without showing a saturation. The value of λ&lt;sub&gt;par &lt;/sub&gt;at 50 kOe is 265 ppm, which is smaller than in LSCO but yet a significant value among most transition metal perovskite oxides. λ&lt;sub&gt;par&lt;/sub&gt; for 50 kOe has the maximum value at 10 K and decreases smoothly as the ferromagnetic -paramagnetic transition is approached (T&lt;sub&gt;C&lt;/sub&gt; = 177 K) and becomes negligible above T&lt;sub&gt;C&lt;/sub&gt;.&lt;sub&gt; &lt;/sub&gt;(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]&lt;br/&gt;R.M. thanks the Ministry of Education, Singapore (Grant no. R144-000-422-114 and R144-000-442-114).

![](https://assets.underline.io/uploads/markdown_image/1/image/85e902d17082690389e6c12fb4a193f8.jpg)

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.

2022 Joint MMM-INTERMAG

Magnetostriction in microwave synthesized La0.5Ba0.5CoO3

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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).

![](https://assets.underline.io/uploads/markdown_image/1/image/85e902d17082690389e6c12fb4a193f8.jpg)

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.

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Ternary silicide LaFeSi with tetragonal CeFeSi-type structure (space group, P4/nmm) has been known for more than three decades [1-3]. However, the weak Pauli paramagnetic behavior [4] indicating zero Fe moment makes it unusable for any magnetic applications. A recent study [5, 6] has reported two transitions in a LaFe2Si composite alloy containing two phases, LaFe13-xSix (magnetically active) and LaFeSi0.95 (magnetically inactive), with a high dTc/dH = 0.85 K/kOe and large positive magnetoresistance near Tc for the first transition while the second transition does not respond to the applied magnetic field. These emergent phenomena cannot be explained by a simple combination of pure LaFe13-xSix and LaFeSi phase properties. In order to explore the role that non-magnetic LaFeSi plays in increasing the magnetoresistance and magnetocaloric effect, we studied the LaFeSi phase using density functional theory based full-potential linearized augmented plane wave (FP-LAPW) [7, 8]. Specifically, we examined the effect of p-element substitution on the electronic and magnetic properties focusing on pathways to induce Fe magnetic moments. Surprisingly, we found that the substitution of p-block elements partially or completely at the Si (2c-sites) of the LaFeSi compound leads to non-zero Fe moments. Our theoretical study confirms that the small atomic radii elements “C and Al” are better substitutes compared to the large atomic radii elements “Ga and Ge”, and lead to moments 3 – 4 times higher. In addition, this theoretical simulation gives a clear picture to the understanding of the quenched Fe-moments with the LaFeSi phase and will also help in advancing the magnetic functionality of the LaFeSi compound.

Inducing Fe moment in LaFeSi with p-block elements substitution

Ternary RScGe intermetallics (R = Rare earth) crystallizing in a layered CeScSi-type structure (space group I4/mmm) demonstrate rich physics and a range of diverse magnetic phenomena. For example, PrScGe exhibits multiple magnetic transitions: paramagnetic (PM) to antiferromagnetic (AFM), then AFM to ferrimagnetic (FIM), and finally FiM-I to FiM-II upon cooling.1 GdScGe, in contrast, remains ferromagnetic below its Curie temperature (TC) of 350 K, which is notably higher than the TC (= 293 K) of its only magnetic constituent, Gd.2 These RScGe systems become even more interesting with substitutional alloying or additions of interstitials. Thus, Sm1-xNdxScGe shows an extraordinary large exchange bias3 and GdScGeH exhibits a loss of dimensionality and magnetic order.4 Here, through x-ray magnetic circular dichroism (XMCD) measurements, we report the interplay between Gd and Pr atoms in representatives of pseudo-ternary Pr1-xGdxScGe. We present direct evidence of antiparallel coupling between heavy and light lanthanide ions that occupy the same sublattice resulting in near zero magnetization. We explain how coupling magnetic compensation with small cooling fields can create magnetic memory – possibly opening up a new avenue for magneto-thermal memory devices. Lastly, we discuss the addition of hydrogen and its effects on dimensionality and electronic structure. This work was supported by the Office of Science of the U.S. Department of Energy (DOE), Division of Materials Sciences and Engineering, Office of Basic Energy Sciences. The Ames Laboratory is operated for the U.S. Department of Energy (DOE) by Iowa State University of Science and Technology under contract No. DE-AC02-07CH11358. XMCD research at the Advanced Photon Source was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Science, under contract DE-AC02-06CH11357.

Magnetic Interplay Between Gd and Pr in the CeScSi-type Layered Structure

The R2TX3 (R = rare-earth, T = transition and X = s and p block element) series of compounds are interesting owing to their fascinating structural and magnetic properties [1-3]. In this present work, we have studied the magnetic properties of the new Pr2AgSi3 polycrystalline compound. The sample was synthesized by arc-melting method and confirmed to crystallize in the tetragonal α-ThSi2 structure with space group I4/amd. The Pr atoms are arranged on a triangular lattice in this crystal structure. The sample was studied by dc– and ac–magnetic susceptibility and specific heat measurements. A ferromagnetic transition was observed at Tc≈15 K which is slightly above the spin freezing temperature Tf ≈ 13 K. The high-temperature dc-magnetic susceptibility exhibit ferromagnetic exchange. The irreversibility observed between zero-field cooled (ZFC) and field cooled (FC) dc-susceptibility data suggests a spin-glass behaviour in the compound. The characteristics of spin-glass behaviour were further confirmed in ac-magnetic susceptibility, aging and memory effect measurements in both ZFC and FC modes. An asymmetric response during heating and cooling of the system is observed in the magnetic relaxation measurement with a positive heating cycle in both ZFC and FC mode. It therefore follows the hierarchical model of spin glass systems. The existence of frustrated moments due to the triangular arrangements of Pr atoms is discussed in terms of the magnetic cluster model observed in Pr2AgSi3.

Ferromagnetic Spin Glass State Behaviour in Pr2AgSi3

The magnetic phase diagram (MPD) of the Cr100-zOsz alloy system exhibits possible quantum critical behavior (QCB), with the commensurate spin-density-wave to paramagnetic (CSDW-PM) phase line terminating at z ≈ 14 in a superconducting dome emerging at z ≈ 12 [1]. The co-existence of SDW antiferromagnetism (AFM) and superconductivity (SC) is also reported for the z = 12.2 sample with bcc structure [1]. Considering the unique behavior in the Cr100-zOsz system [1], the present study reports on the temperature dependence of the thermoelectric power or Seebeck coefficient, S(T), for this system. In general, S(T) is sensitive to changes in the electronic structure as well as to various scattering mechanisms, and can be used to probe the presence of phonon and magnon drag effects [2,3], making it the perfect tool to investigate the magnetic behavior in the mentioned system. S(T) measurements were performed on polycrystalline Cr100-zOsz (2.1 ≤ z ≤ 14.1) samples prepared using arc-melting techniques. Only primary bcc reflections were observed in the x-ray diffraction results. For a magnetic material the absolute thermoelectric power can be approximated as [4]: S = Spd + Smag + Sdiff, where Spd and Smag is the phonon and magnon drag terms and Sdiff is due to the diffusion of electrons. The first two terms dominate at low T and the latter at elavated T. The low-temperature thermoelectric power of Cr and its alloys can be written in the simplified form of [2]: S = aT + bT3, where a and b are constants. Thus, at low T a plot of S/T as a function of T2 should be linear and can be used to obtain a and b. Resulting plots of a(z) and b(z) show anomalies associated with three crucial points in the Cr100-zOsz MPD: (i) z ≈ 7 is associated with the destabilization of the CSDW phase, (ii) z ≈ 12 where SC manifest and (iii) z ≈ 14 linked to QCB [1]. Considering dS/dT where T approaches 0 K, dS/dT│T→0, as function of z, anomalies are also observed at z ≈ 12 and 14, linked to the onset of SC and QCB in this system. Thus, as was previously suggested for selected Cr based alloy systems [5], S can be a decisive parameter that can be utilized in characterizing and understanding the critical behavior reflected in the MPD of Cr100-zOsz.

Anomalous Behaviour in the Seebeck Coefficient of Cr100-zOsz Alloy System

Single crystals of the triangular lattice Heisenberg antiferromagnet (TLHAF) Ca3NiNb2O9 and its non – magnetic analogue Ca3MgNb2O9 were grown using the four - mirror optical float zone furnace. Here we have studied the influence of various growth atmospheres and pulling rates on the crystal quality and phase homogeneity. Both the compounds melt congruently and the grown crystal specimens suffer from cracks when the crystal boule is cooled, thus making it difficult to obtain large single crystalline pieces. To overcome this difficulty, an after – heater was used to reduce the formation of cracks. Interestingly, the crystal boule of Ca3NiNb2O9 exhibits two regions of distinct colours and optical opacities i.e. opaque black and translucent green. Further, the as - grown, opaque, black specimen was subjected to air annealing at 1200oC for 24hrs, wherein its appearance changed from black to translucent green, without any change of weight. Low temperature specific heat and magnetization measurements carried out on the as - grown black sample (AGO) and the air annealed sample (ANT) revealed contrasting ground state properties. While the as - grown specimen exhibits a broad hump close to 10 K in specific heat measurement, the air annealed sample showcases two transitions at TN1 = 4.6 K and TN2 = 4.3 K, in agreement with the previous reports by J Ma et al 1. Moreover, room temperature synchrotron XRD further revealed that AGO specimen crystallizes in a higher symmetry orthorhombic space group while the ANT specimen crystallizes in the reported monoclinic space group. Thus, the ground state of this triangular lattice system is very sensitive to the growth conditions and annealing experiments help recover the properties reported for the polycrystalline sample.

![](https://assets.underline.io/uploads/markdown_image/1/image/85de8c1c92d82b2319726be39907dba1.jpg)

![](https://assets.underline.io/uploads/markdown_image/1/image/7eae1aa5f12df7726cd9f06806846048.jpg)

Single crystal growth and low temperature physical properties of triangular lattice antiferromagnet - Ca3NiNb2O9

Single crystal growth and low temperature physical properties of triangular lattice antiferromagnet - Ca3NiNb2O9

Half-metallic Heusler alloys have attracted much attention due to their potential application in spin-transport-based devices. We have synthesized one such alloy, CoFeV0.5Mn0.5Si, using arc melting and high-vacuum annealing. The vacuum annealing was done at 600oC for 24 hours. First principles calculation indicates that CoFeV0.5Mn0.5Si shows nearly half-metallic band structure with the degree of spin polarization of about 93%. The room temperature x-ray diffraction patterns are indexed with the cubic crystal structure without disorder and secondary phases. The annealed sample show ferromagnetic order with the Curie temperature well above room temperature (Tc = 657 K) and the high-field (3T) magnetization at room temperature of about 83 emu/g. Figure 1 below shows the magnetization as a function of temperature of CoFeV0.5Mn0.5Si measured at 1 kOe which shows a smooth magnetic transition at the Curie temperature. The observed structural and magnetic properties are consistent with the theoretical results and these results indicate that CoFeV0.5Mn0.5Si has a potential for room temperature spin-transport-based devices. This research is supported by the National Science Foundation (NSF) under Grant Numbers 2003828 and 2003856 via DMR and EPSCoR.

![](https://assets.underline.io/uploads/markdown_image/1/image/bd63234b2eeb383951e6554ddc76dd14.jpg)

Figure 1: Thermomagnetic curve M(T) of CoFeV0.5Mn0.5Si alloy. The inset shows the dM/dT versus T curve

Electronic band structure and magnetism of CoFeV0.5Mn0.5Si

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.

![](https://assets.underline.io/uploads/markdown_image/1/image/8270706ca20995363a54b4e33edb73db.jpg)

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.

![](https://assets.underline.io/uploads/markdown_image/1/image/683d74f2557c122585bafe57a4a52001.jpg)

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.

![](https://assets.underline.io/uploads/markdown_image/1/image/daf1593b8518e7c79c5e0788783035f1.jpg)

![](https://assets.underline.io/uploads/markdown_image/1/image/350cb35caeba8beee06fc1435f6c2b37.jpg)

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.

Magnetostriction in microwave synthesized La0.5Ba0.5CoO3

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