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Polycrystalline Ba0.96Sr0.04Ti1-3x/4FexO3 samples (0.06 ≤ x ≤ 0.15) were prepared using solid state reaction technique. The Rietveld refined XRD data confirmed the phase purity and tetragonal crystal structure up to x = 0.08. An additional hexagonal Fe doped BaSrTiO3 phase along with small amount of segregated Fe2O3 was also detected in x ≥ 0.08 samples. The average grain size as measured using FESEM was observed to be ≈ 0.67 μm. The presence of both Fe2+/ Fe3+ ions in all the samples and a decreasing Fe3+ concentration with x was confirmed using XPS analysis. The remnant polarization value was found to decrease with increasing Fe concentration. The magnetization data reveal that all the samples exhibit magnetic ordering with x = 0.08 sample exhibiting best magnetic parameters. The M-E coupling strength ≈10.05 and 9.62% has been observed in x = 0.08 and x = 0.10 samples. The conductivity vs frequency measurements (at different temperatures) reveal that the samples conduct via correlated barrier hopping of electrons trapped at the singly charged oxygen vacancy sites. [ABSTRACT FROM AUTHOR]

First order antiferromagnetic (AFM) to ferromagnetic (FM) transition in Hf1-xTaxFe2 with x~0.225 compounds was studied by resistivity, magnetization and X-ray diffraction (XRD) measurements at low temperature. Magnetization measurements as a function of temperature and magnetic field show path dependent FM phase fraction at 5K for x=0.225. XRD measurements at 15K show co-existing AFM and FM phases for this composition with ~0.9% unit cell volume difference of FM and AFM phase. [ABSTRACT FROM AUTHOR]

We report on high-temperature crystallographic structure, magnetic and physical properties of chemically B-site disordered lead-bismuth iron tungstate, (PFW)1−x(BFO)x (which can be written as Pb0.8Bi0.2Fe0.728W0.264O3 (0.8PFW–0.2BFO) for x = 0.2 and Pb0.7Bi0.3Fe0.762W0.231O3 (0.7PFW–0.3BFO) for x = 0.3) or PBFW), solid solutions through neutron diffraction (ND), magnetization, electron paramagnetic resonance, and Mössbauer spectroscopic studies. From the high temperature magnetic susceptibility measurement, it is observed that increase antiferromagnetic to paramagnetic phase transition around TN = 435 K (Pb0.8Bi0.2Fe0.728W0.264O3) and 504 K (Pb0.7Bi0.3Fe0.762W0.231O3), compared to pure PFW. Room-temperature crystallographic study confirms the formation of pseudo cubic structure with Pm-3m space group, whereas the magnetic structure is commensurate G-type antiferromagnetic ordering. The obtained temperature dependent structural parameters from the ND, evidenced to existence of strong spin-lattice coupling around TN for both the compounds. The discontinuity in the Pb/Bi–O bond length around ferroelectric transition (TC) indicates the presence of magnetoelectric coupling. Interestingly, microscopic 1:1 B-site ordered nanoclusters of PBFW exhibits the ferrimagnetic clusters along with antiferromagnetic order and it observed through the opening of M vs H hysteresis curves in the lower field regime. The EPR and Mössbauer spectroscopic studies well support the magnetic property and also reveal the Fe+3 state, and the weak signal in EPR and broader linewidth in the Mössbauer spectra exhibit the B-site disorderliness. [ABSTRACT FROM AUTHOR]

In this communication, we report the preparation and properties of nano-CoFe2O4 by gel combustion in presence of KCl and subsequent heat treatments. The products were characterized by X-ray diffraction, Infrared spectroscopy, and Mössbauer Spectroscopy. Spinel type structure with all Fe in 3+ oxidation states was confirmed from the XRD and Mossbauer spectroscopy. The average crystallite sizes of the studied samples were about 6 and 50 nm. Low temperature magnetic and dielectric properties of the samples were studied by superconducting quantum interference device magnetometry and ac-impedance spectroscopy. The field and temperature dependent magnetization studies indicated superparamagnetic nature for 6 nm sample and ferromagnetic nature for 50 nm sample. The temperature-dependent dielectric properties measured over a wide range of frequencies indicated an increasing trend of dielectric permittivity with the decrease in crystallite size. Variable range polaron hopping conduction was observed in both samples. [ABSTRACT FROM AUTHOR]

Perovskite oxides are an important and exciting class of materials owing to the structural diversity with remarkable magnetic, optical and electronic behaviours. Here, a single-phase multiferroic orthoferrite, Y0.74Bi0.25FeO2.97 (YBFO), has been synthesized by a conventional solid-state method. The crystal structure was refined using the Rietveld refinement method from powder X-ray diffraction data, and confirms an orthorhombic structure with the Pnma space group. The Curie-Weiss fitting to the magnetic susceptibility shows that the θ-value is –926 K and μeff = 5.59 µB, exhibiting canted antiferromagnetism. Room temperature magnetic and ferroelectric hysteresis loops verify the presence of magnetic as well as ferroelectric ordering in the material with a remnant polarization (Pr) of 0.27 μC cm–2 and electric coercivity (Ec) of 15 kV cm–1. Temperature-dependent P–E loops and pyrocurrent response confirm the inherent multiferroic nature of the material. The UV–visible study indicates a semiconductor nature with the bandgap of 1.86 eV. Density-functional theory calculations support the observed experimental behaviour and it signified the role of Bi-substitution. Even a very less concentration of Bi-doping can form an exciting room temperature multiferroic material. [ABSTRACT FROM AUTHOR]

Unconventional thermal effects across the first-order antiferromagnetic (AFM)-ferromagnetic (FM) transition in an intermetallic alloy are reported. They show instances of warming when heat is extracted from the sample, and cooling when heat is provided to the sample across the AFM-FM transition in Ta-doped HfFe2, thus providing indisputable evidence of metastable supercooled AFM and superheated FM states, respectively. Such thermal effects are observed in a magnetic solid prepared from commercially available materials. The transition proceeds in multiple steps which is interpreted in the framework of quenched disorder broadening of the AFM-FM transition and classical nucleation theory. Measurements in the presence of a magnetic field conform to the above framework. [ABSTRACT FROM AUTHOR]

We report a detailed experimental study of the structural, magnetic and electrical properties of La and Ru doped (Sr 1- x La x ) 2 Ir 1- x Ru x O 4 ( x = 0.05, 0.15). X-ray diffraction analysis reveals that both samples crystallize in a tetragonal structure with a space group I 4 1 / acd without impurities. Substitution with La and Ru leads to an increase in the lattice parameter a and a decrease in c . With increasing doping concentration, the Ir-O-Ir bond angle increases while the Ir-O bond length decreases. X-ray photoelectron spectroscopy (XPS) shows that Ir has Ir 3+ (5 d 6 ) and Ir 4+ (5 d 5 ) charge states, where the Ir 4+ charge state decreases with an increase in doping concentration. The dc magnetic susceptibility χ ( T ) of x = 0.05 reveals a transition from paramagnetic to weak ferromagnetic (wFM) at T C ∼ 229 K, arising from the canted antiferromagnetic (AFM) spin arrangement. The magnetic ordering temperature T C remains unaltered for higher doping, whereas the magnetic moment is significantly reduced. The analysis of real and imaginary components of ac susceptibility data, based on conventional critical slow model, frequency shift per decade and Vogel-Fulcher law, unanimously evidences the existence of reentrant spin-glass behavior (RSG), i.e. the coexistence of weak ferromagnetism and spin glass phases for the lowest doping of x = 0.05. On the other hand, for higher doping ( x = 0.15) of hole and electron, the RSG phase vanishes, leaving only the wFM phase at the same temperature as observed in x = 0.05. This suggests the higher doping of La and Ru does not affect the magnetic order, but removes the disorder between FM and AFM phases. The electrical resistivity ( ρ ) measurement analysis reveals that both the samples show semiconducting/insulating behavior across the temperature range. The ρ of the x = 0.05 sample is lower than that of pure sample Sr 2 IrO 4 (Bhatti et al 2015 J. Phys.:Condens. Matter 27 016005), while ρ of x = 0.15 shows two orders of magnitude larger than the x = 0.05 sample at low temperatures. The conduction mechanism of both samples is described by the 2D Mott's variable-range hopping model. Our results demonstrate that co-doping of two cation sites generates intriguing, competing hopping and magnetic processes., (© 2025 IOP Publishing Ltd. All rights, including for text and data mining, AI training, and similar technologies, are reserved.)

The effect of negative chemical pressure with the substitution of transition metal V in an itinerant helimagnetically ordered MnSi, Mn1-xV x Si with x = 0-0.1, is explored using dc and ac-susceptibilities. With increasing x , the manifestations are unaffected crystal structure with increasing unit cell volume, suppression of long-range magnetic order, weakening of itinerant character and reduced spin-cooperative phenomenon. The emergence of spin-glass behaviour forx⩾0.1intervenes in the occurrence of quantum phase transition. The constructed concentration-temperature x-T phase diagram illustrates the substitution-driven changes in the magnetism of MnSi. Further, the study suggests that the presence of a precursor state can favour the formation of spin-textures in magnetically ordered compositions0

We report on the magnetic, electrical transport, caloric and electronic structure properties of TbFe 4.4 Al 7.6 polycrystalline alloy using experiment and theory. The alloy crystallizes in tetragonal structure with I4/mmm space group with lattice parameters a = b = 8.7234(5) Å and c = 5.0387(6) Å. It is ferrimagnetic with a compensation temperature ofTcmp∼151 K, Curie-Weiss temperatureθCW∼172.11 K and an effective magnetic momentμeff= (2.37±0.07)μB/f.u with Z = 2. At low temperatures, kinetic arrest-like first-order phase transition is realized through the thermal hysteresis between field-cooled cooling and field-cooled warming curves of M ( T ) and virgin curves of M ( H ) andρ(H)which are outside the hysteresis loops with metamagnetic transition. The high magnetic field suppression of multiple transitions and reduced coercive fieldHcoerand remnant magnetizationMremwith increasing temperature are reported.HcoerandMremcease to exist above the compensation temperatureTcmp. A correlation between the isothermal magnetization and resistivity is discussed. Specific heat C ( T ) analysis reveals a Sommerfeld parameter of γ = 0.098 J⋅mol-1⋅K-2and a Debye temperature ofθD∼351.2 K. The sample is metallic as inferred from theρ(T)behavior and Sommerfeld parameter. The magnetoresistance of the alloy is low and negative which indicates the suppression of weak spin-fluctuations. This alloy avoids the tricritical point despite first-to-second order phase transition. The electronic and magnetic structure calculations, by making use of full potential linearized augmented plane wave method, suggest metallic ferrimagnetic ground state of TbFe 4.4 Al 7.6 with Tb atoms contributing ferromagnetically (5.87μB) and Fe atoms with antiferromagnetic contribution (2.67μB), in close agreement with the experimental observation., (© 2024 IOP Publishing Ltd.)

Ni-substituted Mn 3 Ga displays a weak ferromagnetism embedded in an antiferromagnetic (AF) phase. Upon field cooling, the alloy exhibits exchange bias and an open hysteresis loop, signifying kinetic arrest at room temperature. For the first time, a kinetic arrest is seen in a compound due to the first order transition of an embedded defect phase. A systematic study of crystal structure, local structure, and magnetic properties of Mn3-xNi x Ga ( x = 0, 0.25) alloys reveal the origin of ferromagnetism in Mn 2.75 Ni 0.25 Ga is due to the segregation of a Heusler-type environment around Ni in the cubic Mn 3 Ga matrix. Upon temper annealing at 400 ∘ C, these local structural defects around the Ni phase separate into a modulated ferromagnetic (FM) Ni-Mn-Ga Heusler phase. A strong interaction between the AF host and the FM defect phase gives rise to exchange bias. The first-order transition of the defect phase seems to be responsible for the observed kinetic arrest in Mn 2.75 Ni 0.25 Ga., (© 2023 IOP Publishing Ltd.)

In this study, manganese substituted strontium hexaferrite (SrFe 12- x Mn x O 19 ; x = 0, 3, 5, and 7) prepared by the sol-gel auto-combustion method are studied. We observed that the substituted Mn preferentially goes to the 2a and 12k sites of Fe. Raman modes related to the 12k site suggest the stiffening of the lattice. The transformation of the grain's shape from hexagonal ( x = 0 and 3) to rhombohedral ( x = 7) was observed, as shown in the micrographs obtained from FESEM. The thermomagnetic curves show the shift of T C to lower temperatures with the increase in the Mn content. From x = 5 onwards, the growth of another magnetic phase (FiM2) of lower coercivity apart from the parent phase (FiM1) of higher coercivity is seen. The FiM2 phase was found to increase with the Mn content in the sample (16.4(3)% for x = 5 but 66.2(5)% for x = 7). Although the magnetization for both FiM1 and FiM2 decreases with the increase in temperature, both magnetic phases behave in contrast to each other for x = 5 and x = 7. The study suggests a transformation of the compound from high magnetic anisotropy ( x = 0) to low magnetic anisotropy ( x = 7). The x = 5 composition sample displays the highest value of the first-order ME coefficient (0.83(2) mV × cm -1 × Oe -1 ). The observed value for x = 5 composition is ∼2.5 times higher than that of the parent x = 0 composition sample (0.33(2) mV × cm -1 × Oe -1 ). The studies thus suggest that the x = 5 composition is one of the viable candidates for magnetoelectric applications.

We have investigated the Mn 2 PtAl Heulser alloy to unravel its structural, magnetic, calorimetric and electronic structure properties. At room temperature, the alloy crystallizes in a hexagonal structure. Magnetization reveals a weak martensitic transition at 307 K, followed by a long range ferrimagnetic transition at 90 K. Griffiths phase-like signature and positive Weiss temperature in dc-magnetization, isothermal magnetic hysteresis loops and a frequency-independent peak confirm a nearly compensated ferrimagnetic order of Mn 2 PtAl. The theoretical electronic structure calculations also reveal the ferrimagnetic ground state of Mn 2 PtAl and Mn ions (occupying different sites) with a very small total magnetic moment. A giant exchange bias field of 2.73 kOe, at a temperature of 3 K and a cooling field of 70 kOe, has been estimated and is attributed to the unidirectional anisotropy associated with possible ferromagnetic clusters formed by the field cooling process in the ferrimagnetic matrix.

Green and sustainable energy production through renewable sources is an enormously exciting field of research. Herein, we report an A-site lanthanum doped oxygen excess ruthenate (predominantly Ru 5+ -ions) double perovskite system, CaLaScRuO 6+ δ (CLSR), as an excellent photocatalyst for water splitting. The well characterized polycrystalline compound shows canted antiferromagnetic (AFM) behavior due to the existence of disordered Ru-ions at the B-site. Based on density functional theory + U (Hubbard U ) calculations, we have estimated various magnetic exchange interactions and found that the ground state is antiferromagnetic in nature which is in perfect agreement with our experimental results. Detailed analysis of the electronic structure further reveals that the present system belongs to the family of charge transfer semiconductors with an energy gap of ∼0.45 eV. Finally, the material is found to proficiently work for the oxygen evolution reaction (OER) via visible-light driven water splitting at neutral pH in an ecofriendly manner.

Neutron diffraction and ab initio studies were carried out on Mn 2 V 1- x Co x Ga ( x = 0, 0.25, 0.5, 0.75, 1) Heusler alloys which exhibits high T C fully compensated ferrimagnetic characteristics for x = 0.5. A combined analysis of neutron diffraction and ab initio calculations revealed the crystal structure and magnetic configuration which could not be determined from the x-ray diffraction and magnetic measurements. As reported earlier, Rietveld refinement of neutron diffraction data confirmed L 2 1 structure for Mn 2 VGa and X a structure for Mn 2 CoGa. The alloys with x = 0.25 and 0.5 possess L 2 1 structure with Mn (C) -Co disorder. As the Co concentration reaches 0.75, a structural transition has been observed from disordered L 2 1 to disordered X a . Detailed ab initio studies also confirmed this structural transition. The reason for the magnetic moment compensation in Mn 2 (V 1- x Co x )Ga was identified to be different from that of the earlier reported fully compensated ferrimagnet (MnCo)VGa. With the help of neutron diffraction and ab initio studies, it is identified that the disordered L 2 1 structure with antiparallel coupling between the ferromagnetically aligned magnetic moments of (Mn (A) -Mn (C) ) and (V-Co) atom pairs enables the compensation in Mn 2 V 1- x Co x Ga., (© 2022 IOP Publishing Ltd.)

We report on the structure, spin-lattice and magneto-electric coupling in (1- x )Pb(Fe 2/3 W 1/3 )O 3 -( x )BiFeO 3 (where x = 0.1 and 0.4) (PBFW) solid solution synthesized through two-step solid-state reaction method. The room temperature (RT) crystallographic studies were carried out using x-ray diffraction and neutron diffraction measurements which show a single-phase Pseudocubic crystal system with Pm -3 m space group. Rietveld refinement was carried out to obtain the structural parameters using Fullprof software and the observed structural parameters are in good agreement with the previous reports. Temperature-dependent neutron diffraction measurements reveal the presence of commensurate G-type antiferromagnetic structure. The magnetic structure was analyzed using the propagation wave vector k ∼ (½ ½ ½) for both the solid solutions. The obtained lattice constants increase linearly and the magnetic moment decrease with temperature, which shows a remarkable anomaly around the magnetic ( T N ∼ 405 K for x = 0.1 and 531 K for x = 0.4) transition temperatures. This anomaly clearly indicates the existence of spin-lattice and magnetoelectric coupling. The magnetic susceptibility (ZFC and FC at 500 Oe) and M - H hysteresis loop measurements show spontaneous magnetic moment due to the Fe 3+ -O 2- -Fe 3+ superexchange interaction coexisting with the weak ferromagnetism. Bifurcation of ZFC and FC curve reveals the strong anisotropic nature. Astonishingly, magnetic measurements show the non-zero magnetic moment above T N and broadening of the magnetic transition indicates the presence of short-range uncompensated sublattice weak ferromagnetic clusters in the paramagnetic region. The Mossbauer spectroscopy and electron paramagnetic resonance studies exhibit the RT magnetically ordered system and confirm the +3 state of Fe along with the fraction of Fe 2+ ions., (© 2020 IOP Publishing Ltd.)

The magnetocaloric effect of intermetallic compounds of Tb 3 Co and Ho 3 Co is studied under high pressures up to ∼1 GPa using pressure dependent dc magnetisation and specific heat measurements at ambient conditions. The magnetic entropy change (-Δ S M ) obtained from magnetisation data and adiabatic change in temperature (Δ T ad ) determined from zero-field specific heat and magnetisation data are found to be nearly identical within error limits with those deduced from purely field dependent specific heat experiments. With increasing hydrostatic pressure to ∼1 GPa, the -Δ S M and Δ T ad , both show a significant enhancement of about 37% and 13%, respectively for 9 T field change in case of Tb 3 Co. On the other hand, Ho 3 Co exhibits a decrease of about 8% in both -Δ S M and Δ T ad with increasing pressure. The refrigerant capacity (RC) also increases from 650 J kg -1 to 847 J kg -1 in the case of Tb 3 Co and it goes down from 665 J kg -1 to 615 J kg -1 for Ho 3 Co for an increase of pressure to 1 GPa. With increasing pressure, the peak widths of both -Δ S M and Δ T ad increase in case of Tb 3 Co, although the increase is more in -Δ S M . However, such noticeable changes in peak widths with pressure were not observed in Ho 3 Co. At ambient pressure, peak of -Δ S M (-ΔSMpk) scales with(H/TN)2/3for both the compounds, consistent with the prediction of mean field theory (MFT) for second order magnetic transition. However, deviation from MFT was noticed at high pressures as-ΔSMpkwas found to scale with(H/TN)3/4instead of(H/TN)2/3for both the alloys. Further, normalised -Δ S M curves for different Δ H and pressures collapse on a single universal curve in both the compounds thereby indicating that the second order magnetic transition persists even up to ∼1 GPa pressure., (© 2020 IOP Publishing Ltd.)

Polycrystalline samples of Ba 0.96 Ca 0.04 Ti 0.91 Fe 0.09 O 3 were prepared using a conventional solid state reaction route with different Fe starting precursors (Fe 2 O 3 , Fe 3 O 4 ). The Rietveld refined XRD data confirmed the phase purity and tetragonal crystal structure of both the samples. The average grain size measured using SEM was ≈0.40 μm in both the samples. XPS analysis confirmed the presence of only Fe 2+ and both Fe 2+ /Fe 3+ in Fe 2 O 3 and Fe 3 O 4 doped BCT samples. The P r and M r values have been measured to be 1.34 μC cm -2 , 2.88 μC cm -2 and 0.0015 emu g -1 and 0.135 emu g -1 in Fe 2 O 3 and Fe 3 O 4 doped BCT samples, respectively. The Fe 3 O 4 doped samples exhibit much better M-E coupling (≈22%) as compared to Fe 2 O 3 (≈7%) doped BCT samples. The results obtained hence suggest that Fe 3 O 4 doping in BCT is better suited for multiferroic applications., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

The intriguing coupling phenomena among spin, phonon, and charge degrees of freedom in materials having magnetic, ferroelectric and/or ferroelastic order have been of research interest for the fundamental understanding and technological relevance. We report a detailed study on structure and phonons of Al 0.5 Ga 0.5 FeO 3 (ALGF), a lead-free magnetoelectric material, carried out using variable temperature dependent powder neutron diffraction and Raman spectroscopy. Neutron diffraction studies suggest that Al 3+ ions are distributed in one tetrahedrally (BO 4 ) and three octahedrally (BO 6 ) coordinated sites of the orthorhombic (Pc2 1 n) structure and there is no structural transition in the temperature range of 7-800 K. Temperature dependent field-cooled and zero-field-cooled magnetization studies indicate ferrimagnetic ordering below 225 K (T N ), and that is reflected in the low temperature powder neutron diffraction data. An antiferromagnetic type arrangement of Fe 3+ ions with net magnetic moment of 0.13 μ B /Fe 3+ was observed from powder neutron diffraction analysis and it corroborates the findings from magnetization studies. At the magnetic transition temperature, no drastic change in lattice strain was observed, while significant changes in phonons were observed in the Raman spectra. The deviation of several mode frequencies from the standard anharmonicity model in the ferrimagnetic phase (below 240 K) is attributed to coupling effect between spin and phonon. Spin-phonon coupling effect is discernable from Raman bands located at 270, 425, 582, 695, 738, and 841 cm -1 . Their coupling strengths (λ) have been estimated using our phonon spectra and magnetization results. BO n (n = 4, 6) libration (restricted rotation) mode at 270 cm -1 has the largest coupling constant (λ∼ 2.3), while the stretching vibrations located at 695 and 738 cm -1 have the lowest coupling constant (λ∼ 0.5). In addition to the libration mode, several internal stretching and bending modes of polyhedral units are strongly affected by spin ordering.

The magnetic properties of rare earth rich intermetallic compound, Tb 3 Co, were studied under external pressures up to  ∼1.21 GPa. The application of external pressure results in a decrease of the transition temperatures, [Formula: see text] (paramagnetic to modulated antiferromagnetic) by about 6 K, and the order to order transition that coincides with a glass transition at 72 K by about 15 K, respectively. The low temperature drop in the zero-field cooled magnetisation signifying the strengthening of spin-orbit coupling remains more or less unaffected (shifts only by 3 K) by the external pressures but significant changes in the magnetic behaviour were observed above 40 K. The overall long range non-collinear magnetic order coexisting with glassy behaviour (below 72 K) is sustained even at  ∼1.07 GPa pressure. The rate of decay of [Formula: see text] (d[Formula: see text]) is found to be linear with  -7.2 K GPa -1 up to  ∼0.9 GPa and then it deviates from linearity. The magnetic relaxations and memory effects studied under different measurement protocols confirm the presence of glassiness right up to the highest pressure, although the glassy behaviour is weakened to some extent with increasing pressure as reflected by faster relaxations.

Detailed and systematic study of rare earth rich intermetallic compound Tb 3 Co, using dc magnetisation, neutron powder diffraction, and linear and non-linear ac-susceptibilities, shows the presence of an unexpected magnetic glassy state along with complex non-collinear or modulated antiferromagnetic (AFM) order. Our neutron diffraction study shows that the magnetic structure remains more or less the same except for a decrease in moment values in the temperature range of 2 K-70 K and rules out any phase transition around 30 K. However, it reveals sharp changes in structural parameters around 30 K, which indicates strong spin-lattice coupling and change in strength. It appears to be mainly responsible for the observed increase in ZFC magnetisation on warming around 30 K. Another important unexpected result of this study is the strong frequency dispersion in linear and non-linear (higher order harmonics) ac-susceptibilities below [Formula: see text] K. The analysis in terms of various spin glass theoretical formulisms and even stronger frequency dispersion in non-linear susceptibilities provides evidence for the presence of a spin glass like state in Tb 3 Co. The final picture that emerges out of this study is that a spin glass like state coexists with the long range modulated AFM order below 72 K.

Oxygen reduction reaction (ORR) is increasingly being studied in oxide systems due to advantages ranging from cost effectiveness to desirable kinetics. Oxygen-deficient oxides like brownmillerites are known to enhance ORR activity by providing oxygen adsorption sites. In parallel, nitrogen and iron doping in carbon materials, and consequent presence of catalytically active complex species like C-Fe-N, is also suggested to be good strategies for designing ORR-active catalysts. A combination of these features in N-doped Fe containing brownmillerite can be envisaged to present synergistic effects to improve the activity. This is conceptualized in this report through enhanced activity of N-doped Ca 2 Fe 2 O 5 brownmillerite when compared to its oxide parents. N doping is demonstrated by neutron diffraction, UV-vis spectroscopy, X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy. Electrical conductivity is also found to be enhanced by N doping, which influences the activity. Electrochemical characterization by cyclic voltammetry, rotating disc electrode, and rotating ring disk electrode (RRDE) indicates an improved oxygen reduction activity in N-doped brownmillerite, with a 10 mV positive shift in the onset potential. RRDE measurements show that the compound exhibits 4-electron reduction pathways with lower H 2 O 2 production in the N-doped system; also, the N-doped sample exhibited better stability. The observations will enable better design of ORR catalysts that are stable and cost-effective.