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Electrical resistivity (ρ), magnetic susceptibility (χ) and thermoelectric power (S) studies reported previously on the (Cr1-x Al x )99V1 alloy system indicate a suppression of antiferromagnetism in the concentration range 0.015 ≤ x ≤ 0.040. The present study incorporates Sommerfeld electronic specific heat coefficient (γ), thermal conductivity (κ), Hall coefficient (R H) and analyses of the previous results in order to have a comprehensive study of the alloy system. γ(x) depicts two peaks close to the same concentrations where dS/dT|T→2K(x) have minima, i.e. at x c1 ≈ 0.015 and x c2 ≈ 0.040. Such peaks and minima, respectively, have been considered as key signatures of quantum criticality (QC) in alloys of Cr. Evidence of band structure modification in the alloy system is shown by a change of slope in the Nordheim-Gorter (N-G) relationship showing a minimum at an extrapolated concentration x = 0.035. The slope is positive for the incommensurate (I) spin-density-wave (SDW) alloys with x < 0.035 and a negative for the commensurate (C) SDW alloys with x > 0.035. A behaviour reminiscent of changes in the band structure is also observed in the Lorenz number, L(x), for the alloy with x = 0. R H(T) results in the range 0 ≤ x ≤ 0.026 have a sharp increase in the charge carrier density, n 2K = [qR H(2k)]−1, at the ISDW to paramagnetic (P) phase transition. The concentrations x = 0.015 and x = 0.040 are therefore considered ISDW to P and P to CSDW quantum critical points, respectively.

This study reports the effect of 120 MeV swift Au9+ ion irradiation on the structures of monoclinic, tetragonal and cubic ZrO2, probed through x-ray diffraction (XRD) and Raman spectroscopy. Three phases of ZrO2 were prepared using the solution combustion method. The tetragonal and cubic phases of ZrO2 were stabilized at room temperature by adding 6% and 10% of yttrium ions, respectively. Both the XRD and Raman results confirm the partial phase transition from monoclinic to tetragonal, which was approximately 74%. Tetragonal ZrO2 is stable under 120 MeV Au9+ ion irradiation. Interestingly, a phase transition from cubic to tetragonal ZrO2 was observed under 120 MeV Au9+ ion irradiation. The roles of transient temperature, defects and strain in the lattice induced by swift heavy ions are discussed. This study reveals the structural stability of different phases of ZrO2 under swift heavy ion irradiation and should be helpful in choosing potential hosts for various applications such as inert fuel matrix inside the core of nuclear reactors, oxygen sensors and accelerators, and radiation shielding.

The role of oxidation on the structural, magnetic and electronic properties of a Ni-NiO compound is reported. XRD results indicate that NiO is formed at the expense of metallic Ni and complete NiO phase formation was observed at 1000 °C. The average crystallite size of NiO is found to increase from 12 to 35 nm upon calcination. Using transmission electron microscopy (TEM) the average particle size for the samples calcined at 1000 °C was found to be approximately 126 nm. Hence, comparing it to the crystallite sizes estimated from the XRD, it is clear that the powder samples are polycrystalline in nature, consisting of smaller crystallites clustered together. Both the ferromagnetic and AFM contributions from Ni and NiO, respectively, were observed in the magnetization data. The saturation magnetization and coercivity were found to decrease with increasing calcination temperature with a shifting of hysteresis loop towards the negative axis. The optical band-gap of the powders was found to be unchanged upon calcination (3.3 eV or 3.4 eV). The density of electrons near the Fermi level was found to be higher in the non-calcined and dried sample, resulting in a higher magnetic moment compared to the other samples.

Indications of quantum critical behaviour (QCB), driven by electron-hole pair breaking effects through Mo doping of Cr98.4Al1.6 are reported. Previous studies on the electrical resistivity ( ρ ) , Seebeck coefficient ( S ) , Sommerfeld electronic specific heat coefficient ( γ ) and magnetic susceptibility ( χ ) as a function of temperature on the (Cr98.4Al1.6)100-yMoy alloy system point towards the existence of a quantum critical point (QCP) at y c ≈ 4.5. In the present study the Hall coefficient R H measurements and an analysis of the previous results are used to substantiate the presence of a QCP in the alloy system. The charge carrier density at 2 K, ( q R H ( 2 K ) ) − 1 , of the alloy systems increases continuously with y from the antiferromagnetic (AFM) phase through y c ≈ 4.5 and into the paramagnetic (P) phase. Scaling relationships between the magnetic contribution to the electrical resistivity, Δ ρ 2 K , the magnetic contribution to the Sommerfeld electronic specific heat coefficient, Δ γ , and ( q R H ( 2 K ) ) − 1 , are furthermore used to support the presence of a QCP in the alloy system. d S / d T in the temperature limit T → 2 K depicts an anomalous behaviour in the form of an upturn on decreasing y through the QCP, y c ≈ 4.5. The critical exponents in the vicinity of the QCP were found to be β = 0.5 ± 0.1 for the Δ ρ 2 K / ρ 2 K ( y ) curve and γ = 0.4 ± 0.1 for the T N ( y ) curve. The nature of the QCP in the present alloy system is classified as an incommensurate (I) spin-density-wave (SDW) type, driven mainly by electron-hole pair breaking effects.

For La-doped BaSnO$_\text{3}$ thin films grown by pulsed laser deposition, we combine chemical surface characterization and electronic transport studies to probe the evolution of electronic states in the band structure for different La-doping content. Systematic analyses of spectroscopic data based on fitting the core electron line shapes help to unravel the composition of the surface as well as the dynamics associated with increasing doping. This dynamics is observed with a more pronounced signature in the Sn 3d core level, which exhibits an increasing asymmetry to the high binding energy side of the peak with increasing electron density. The present results expand the current understanding of the interplay between the doping concentration, electronic band structure and transport properties of epitaxial La:BaSnO$_\text{3}$ films., Comment: 7 Figures, 4 Tables in manuscript; and 6 Figures and 1 Table in the Supplementary Information

The effect of multiaxial mechanical stress on angle-dependent magnetization reversals is studied on a single 10-nm ${\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}$ film, a single 10-nm ${\mathrm{Fe}}_{81}{\mathrm{Ga}}_{19}$ film, and a ${\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}$(10 nm)/${\mathrm{Fe}}_{81}{\mathrm{Ga}}_{19}$(10 nm) bilayer. These films are grown on flexible $\mathrm{Al}$ ``kitchenlike'' foils. These flexible foils are bent on two convex optical lenses to apply multiaxial mechanical stresses of different magnitudes. In order to understand the mechanisms driving the physical properties of the flexible systems, the magnetic films are also grown on hard native-oxide-covered $\mathrm{Si}$(100) substrates. By probing the angular dependence of the coercive field and the remanent magnetization, we show that the ${\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}$ single layer and the ${\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}/{\mathrm{Fe}}_{81}{\mathrm{Ga}}_{19}$ bilayer grown on $\mathrm{Si}$ present a uniaxial anisotropy. Along their easy axis, their domain structure at the coercive field exhibits large domains with sawtooth domain walls. However, the ${\mathrm{Fe}}_{81}{\mathrm{Ga}}_{19}$ layer grown on $\mathrm{Si}$ shows a cubic anisotropy and sharp domain walls with a right-angle geometry along its easy axis. All layers grown on $\mathrm{Al}$ foils show development or enhancement of a uniaxial anisotropy arising from the $\mathrm{Al}$ surface morphology. Multiaxial mechanical stress applied to the flexible $\mathrm{Al}$ foils results in very different nonreversible effects as a function of the composition of the layered system. For ${\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}$, multiaxial mechanical stress has no effect, as expected for a nonmagnetostrictive system. For ${\mathrm{Fe}}_{81}{\mathrm{Ga}}_{19}$, it results in a full in-plane randomization of its magnetization-reversal properties. For the bilayer, multiaxial mechanical stress does not fully randomize the in-plane magnetization-reversal properties: the bilayer retains a uniaxial character.

International audience; In this article, the magnetic properties of gadolinium chloride-filled double-walled carbon nanotubes (GdCl3@DWNTs) in the temperature range 2-300 K are explored. The temperature-dependent phonon frequencies of the G-band were studied from 80-300 K to investigate the effect of temperature on the magnetic ordering. Temperature-dependent susceptibility measurements show that the GdCl3@DWNTs sample has a pronounced superparamagnetic phase from 83 K. The temperature dependence of the G-band frequency for filled tubes exhibited a distinct difference compared to pristine nanotubes, where a sharp phonon hardening at low temperatures was observed. A correlation between the onset temperature of superparamagnetism and the abrupt G-band phonon hardening in the filled tubes was verified. GdCl3@DWNTs were characterized by a finite remnant magnetization at 300 K which decreased as the temperature was lowered because of the presence of the discontinuous magnetic nanoparticles, providing a superparamagnetic contribution characterized by an S-shaped non-saturating hysteresis loop at 2 K. Remarkably, the onset of superparamagnetism, marked by the bifurcation point, occurred at roughly the same temperature where the G-band phonon frequency showed a pronounced hardening at approximately 80 K, indicating a close correlation between phonon modes and spin clusters.

Cubic spinel CoCr

Magnetoelectric composites are an important class of multiferroic materials that are paving the way towards a new generation of multifunctional devices directly integrable into data-storage technology and spintronics. This study focuses on strain-mediated electrical manipulation of magnetization in an extrinsic multiferroic. The composite used includes 5- or 60-nm ${\mathrm{Fe}}_{81}{\mathrm{Ga}}_{19}$ thin films coupled to a piezoelectric (011) $\mathrm{Pb}({\mathrm{Mg}}_{1/3}{\mathrm{Nb}}_{2/3}){\mathrm{O}}_{3}$-$\mathrm{Pb}({\mathrm{Zr}}_{x}{\mathrm{Ti}}_{1\ensuremath{-}x}){\mathrm{O}}_{3}$ (PMN-PZT) material. A magnetization-reversal study reveals a converse magnetoelectric coefficient ${\ensuremath{\alpha}}_{\mathrm{CME},max}\ensuremath{\approx}2.7\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}\phantom{\rule{0.2em}{0ex}}\mathrm{s}\phantom{\rule{0.1em}{0ex}}{\mathrm{m}}^{\ensuremath{-}1}$ at room temperature. This reported value of ${\ensuremath{\alpha}}_{\mathrm{CME}}$ is among the highest so far, compared with previous reports on single-phase multiferroics and on composites. An angular dependence of ${\ensuremath{\alpha}}_{\mathrm{CME}}$ is also shown, arising from the intrinsic magnetic anisotropy of $\mathrm{Fe}\text{\ensuremath{-}}\mathrm{Ga}$. The highly efficient magnetoelectric composite $\mathrm{Fe}\text{\ensuremath{-}}\mathrm{Ga}$/PMN-PZT demonstrates drastic modifications of the in-plane magnetic anisotropy, with an almost ${90}^{\ensuremath{\circ}}$ rotation of the preferential anisotropy axis in thinner films under an electric field $E=10.8\phantom{\rule{0.2em}{0ex}}\mathrm{kV}\phantom{\rule{0.1em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$. Also, the influence of thermal strain on the bilayer's magnetic coercivity is compared with that for a reference $\mathrm{Fe}\text{\ensuremath{-}}\mathrm{Ga}$/glass bilayer at cryogenic temperatures. A different evolution is observed as a function of temperature, revealing a thermomechanical influence of the substrate which has not yet been reported in $\mathrm{Fe}\text{\ensuremath{-}}\mathrm{Ga}$ thin films coupled to a piezoelectric material.

The compounds with the general chemical formula RCrTiO5 (R = rare-earth ions) possess an orthorhombic crystal structure having Pbam space group. However, there are limited works carried out on this group of materials, primarily in bulk to explore their structural and magnetic properties. The exploration of structural and magnetic properties of RCrTiO5 compounds in the nano dimension has not been reported to date. This report focuses on the synthesis of DyCrTiO5 nanoparticles using a simple, time saving and cost-effective sol-gel technique to investigate the role of size on structural as well as magnetic properties. The synthesized sample is calcined at 800 °C for three hours. The crystal structure is confirmed from the Le-Bail profile fitting of the x-ray diffraction (XRD) pattern. The DyCrTiO5 nanoparticles are crystallized in an orthorhombic structure with lattice parameters, a, b, c of 7.321 ± 0.001, 8.644 ± 0.002 and 5.840 ± 0.001 A, respectively. The average particle size is found to be 53 ± 3 nm from transmission electron microscopy (TEM). From the temperature-dependent magnetization measurement, the obtained Neel temperature ( T N ) is 147 ± 2 K. In contrast to the bulk form, DyCrTiO5 nanoparticles do not show spin reorientation (SR) which is observed below 37 K or the magnetic compensation because of the dominating contribution of Dy3+ moment. In addition, the irreversibility in magnetization is suppressed when measured as a function of temperature in the heating and cooling cycle of the measurement with increasing the probing magnetic field. This indicates a feature similar to kinetic arrest. In isothermal magnetization measurements, exchange bias effect is observed because of interaction between the uncompensated spins on the surface of the nanoparticles.

The temperature dependence of magnetic susceptibility, χ(T), of the (Cr84Re16)100−xVx alloy system is reported in this contribution. Anomalies are observed at the Neel temperature (TN), associated with the onset of the antiferromagnetic (AF) spin-density-wave (SDW) state, with these anomalies becoming more pronounced as x increases. The TN values determined from χ(T) measurements are in close agreement with that obtained from the measurement of temperature dependence of electrical resistivity, ρ(T). Prominent broad deep minima are observed in χ(T) upon cooling below 100 K which are followed by low temperature peaks in x = 10.4, 10.9 and 12.4 samples. A second anomaly, not associated with TN, is observed at a temperature TO TN.

Previous electrical resistivity ( ρ ) and specific heat ( C P ) studies on the ternary (Cr100-xAlx)95Mo5 alloy system suggested that it harbours two quantum critical points (QCPs). This study reports comprehensive investigations of this alloy system through Seebeck coefficient ( S ) , thermal conductivity ( κ ) , magnetic susceptibility ( χ ) and neutron diffraction ( N D ) measurements in the concentration range 0 ≤ x ≤ 8.6. The results of S and χ show that spin-density-wave (SDW) antiferromagnetism is suppressed to temperatures below 2 K for concentrations in the range 1.4 ≤ x ≤ 4.4. Plots of d S / d T in the limit as T → 2 K depict two minima, i.e. just above x = 1.4 and 4.4. This parameter has been used as a key indicator of quantum critical behaviour (QCB) in Cr alloys. Analyses against the Nordheim-Gorter relationship demonstrates a positive slope for the incommensurate (I) SDW alloys and a negative slope for the commensurate (C) SDW alloys. Extrapolations of these two slopes intercept at a concentration of 3.2 at.% Al indicating the occurrence of band structure modifications when Al is added into the Cr95Mo5 base alloy. The Lorenz number ( L ) for the alloys with x = 0 and 0.5 shows interesting anomalous behaviour associated with band structure effects and SDW magnetic ordering. N D measurements as a function of temperature confirm that alloys with x 4.4 show commensurate (C) SDW order. Power law fits of the form T N ∝ 1.40 − x 0.35 ± 0.05 for the ISDW to P phase transition and T N ∝ x − 4.40 0.63 ± 0.03 for the P to CSDW phase transition rendered the critical exponents 0.35 ± 0.05 and 0.63 ± 0.03 respectively. Overall the results of S , κ , χ and N D corroborate the existence of two QCPs at x ≈ 1.4 and 4.4.

A series of spinel-type MnxNi1-xCo2O4 (x = 0, 0.3, 0.5, 0.7, 1) oxides were synthesized by using a citrate sol-gel technique. The structural, magnetic and electronic properties of the oxides with different Mn content were investigated using X-Ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), vibrating sample magnetometer (VSM) and X-ray photoelectron spectroscopy (XPS). The XRD and FTIR studies revealed that MnxNi1-xCo2O4 formed in a cubic structure for all the compositions synthesized. Transmission electron microscopy (TEM) studies show cubic nano-plates for x = 0 and on increasing Mn concentration, agglomerated nanoparticles with sphere-like shape are observed with a particle size in the range of 11.7 nm–22.1 nm. This is in close agreement with the results of XRD analysis. The Mn 2p, Ni 2p, and Co 2p XPS spectra reveal the coexistence of Mn2+, Mn3+, Ni2+, Ni3+, Co2+, and Co3+ species on the surface of MnxNi1-xCo2O4 samples in differing proportions. The measurements of magnetic properties at room temperature show that the samples have some ferromagnetic behaviour. The saturation magnetization, remnant magnetization, and coercivity of the nanoparticles vary significantly with a concentration of Mn, which tends to be distributed in both tetrahedral and octahedral positions of the spinel lattice.

The study describes the preparation of graphene oxide based silica coated magnetic nanoparticles (Fe3O4@SiO2@GO) functionalized with 2-phenylethylamine (PEA) as an adsorbent for selected organophosphorus pesticides (OPPs) namely chlorpyrifos, parathion, and malathion from aqueous solution. The synthesised (Fe3O4@SiO2@GO-PEA) adsorbent was characterised using Fourier transform-infrared (FT-IR) spectroscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD), Zeta potential, Nitrogen adsorption/desorption at 77 K, and a Vibrating Sample Magnetometer (VSM). The maximum adsorption was found at 15 min, with 15 mg adsorbent dosage using 1 μg/mL concentration. There was no significant difference in the pH condition used highlighting the potential to use the material on a variety of samples. Using non-linear methods, the sorption isotherm data were fitted to Langmuir, Freundlich, Temkin, Dubinin–Radushkevich, Sips, and Redlich and Peterson models. All three pesticides were best fit with the Sips model. Pseudo-first and pseudo-second order kinetics models were fitted to the experimental data using non-linear methods, and pseudo-second-order kinetics gave the best fit to the data for all three pesticides. The absorbent was tested for its reusability, and there was little loss in the recovery of OPPs after 10 cycles. Finally, the adsorbent was tested using real world samples from the Vaal River and Dam (South Africa), and showed greater than 86.9% recovery. The results obtained showed that the synthesised Fe3O4@SiO2@GO-PEA is an efficient adsorbent for recovery and analysis of pesticides.

Mixed ternary spinel-type oxides MnxNi1-xCo2O4 (x = 0, 0.5, 1) were synthesized using a citrate sol-gel route. The morphologies and structures of the mixed oxide nanoparticles were characterized using Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD) and Fourier-Transform Infrared Spectroscopy (FTIR). Structural analysis from XRD and FTIR confirm the formation of single phase cubic spinels. TEM and SEM images show the formation of interconnected nanoparticles. The particle sizes obtained from TEM and XRD are consistent with each other. It was observed that the lattice constant increases with increasing Mn concentration from x=0 to x=0.5 and then decreases with further increase in Mn concentration to x=1. Magnetization measurements were carried out using Vibrating Sample Magnetometery (VSM), which showed that the oxides have weak ferromagnetic behavior with the presence of an antiferromagnetic component. The oxide with the highest Mn substitution was observed to be superparamagnetic at room temperature.

Mn substituted MnxZn1−xCo2O4 (x = 0, 0.3, 0.5, 0.7, 1) oxides were synthesized by a facile co-precipitation method followed by calcination at 600 °C. The presence of manganese ions causes appreciable changes in the structural and magnetic properties of the Mn-substituted ZnCo2O4. The morphologies, structures, and electronic properties of Mn–Zn–Co oxide microspheres were characterized using scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The X-ray diffraction and Fourier transform infrared spectroscopy results confirmed the formation of spinel MnxZn1−xCo2O4. It was shown that the Mn–Zn–Co oxide microspheres increase in size and become regular in shape with increasing Mn concentration with the crystal size lying in the range from 19.1 nm to 51.3 nm. Magnetization measurements were carried out using a vibrating sample magnetometer at room temperature and 10 K. The saturation magnetization is observed to increase with increasing Mn concentration from x = 0 to x = 1.

Spinel ferrimagnetic compounds of the form MCr2O4, where M is a divalent metal cation are of great interest due to the structural and magnetic phase transitions. In this class of materials, NiCr2O4 and CoCr2O4 are well studied in bulk or single crystals. NiCr2O4 demonstrates low temperature magnetic phase transitions together with structural phase transitions. However, CoCr2O4 displays only magnetic phase transitions at low temperature retaining stable cubic phase across the magnetic phase transition temperatures. Exchange interaction between the magnetic cations situated at the tetrahedral or octahedral site determines the net magnetic properties of the material. By site mixing with different cations, drastic changes in the magnetic exchange interaction leading to change in magnetic properties are observed. The present work focuses on the structural and magnetic properties of (Ni0.5Co0.5)(Cr0.75Fe0.25)2O4 nanoparticles. Co2+ and Fe3+ have been substituted at Ni and Cr sites, respectively, to modify the magnetic interactions. Rietveld refinement of the x-ra diffraction (XRD) data confirmed the cubic Fd3¯m space group of the samples. In addition to the site substitution the size of the particles was exclusively in the nano range. Transmission electron microscopy (TEM) analyses showed the average particle size DTEM = 82 ± 2 nm. MZFC and MFC demonstrate irreversibility at low temperature. Energy dispersive X-ray spectroscopy (EDS) confirmed the presence of Co, Ni, Cr, Fe and O without trace of any impurities in the samples. TC of the sample was found to be 138 ± 2 K by differentiating the MZFC data with respect to temperature measured with a probing magnetic field of 0.1 T. Hysteresis loops measured at 3 K demonstrated kinks around zero field range.

International audience; A temperature-dependent coherent magnetization reversal model is proposed for size-distributed assemblies of ferromagnetic nanoparticles (NPs). NPs are assumed to be of uniaxial and cubic anisotropies. The thermal dependence is included by considering thermal fluctuations, implemented through the Néel-Arrhenius theory. Theoretically calculated thermal and angular dependences of magnetization reversal loops are obtained. There are similar behaviors for a single NP and an assembly of NPs. In particular, it is shown that the fourfold anisotropy results in double slope loops along the hard axis in both cases. Also, the azimuthal dependence of coercive fields is similar in both cases and with or without the presence of a fourfold anisotropy. There are also important differences in the behaviors observed for asingle NP and that of an assembly of NPs. Firstly, the blocking temperature is barely enhanced by the presence of a fourfold anisotropy but is greatly enhanced in the assembly of NPs relative to a single NP. Secondly, along the easy axis, for a single size particle, the shape of the M-H loops is neither temperature dependent nor fourfold anisotropy dependent, as it is always rectangular. However, the shape of the M-H loops for an assembly of NPs is temperature dependent, but this shape is weakly dependent on the anisotropy ratio. Simulations of M-H loops using the model presented here would allow the quantitative determination of the anisotropy constants for either single sized NPs or an assembly with different sizes

$M\phantom{\rule{0}{0ex}}a\phantom{\rule{0}{0ex}}g\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}e\phantom{\rule{0}{0ex}}t\phantom{\rule{0}{0ex}}o\phantom{\rule{0}{0ex}}s\phantom{\rule{0}{0ex}}t\phantom{\rule{0}{0ex}}r\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}c\phantom{\rule{0}{0ex}}t\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}o\phantom{\rule{0}{0ex}}n$ is a key property used in devices such as sensors, actuators, and energy harvesters, particularly in spintronics and straintronics. Here the authors perform an exhaustive magnetization-reversal study of galfenol films ranging from 5 to 60 nm in thickness, to tie the magnetic properties to film structure. The thinnest film possesses the best characteristics for potential applications: highest magnetostriction coefficient, lowest coercive and saturation fields, and pronounced anisotropy. These results should inform strain-engineering solutions for voltage control of magnetism in extrinsic multiferroics that combine piezoelectric and magnetostrictive materials.

The magnetic phase diagram of (Cr90Ir10)100-yVy alloy system has been constructed using the TN values obtained from the electrical resistivity, ρ, Seebeck coefficient, S, and magnetization, M, as function of temperature measurements. The present study furthermore proposes a V induced commensurate (C) spin-density-wave (SDW) to incommensurate (I) SDW phase transition on cooling, at a transition temperature TCI, in certain samples in the series investigated. M T measurements on the sample with y = 2.4 shows only one transition associated with the Neel transition at TN, with no additional transition that can be associated with TCI and is accepted to be in the CSDW phase at all temperatures. It is hypothesized that the addition of V destabilizes the CSDW phase and introduces an ISDW phase at lower temperatures in the samples with y = 3.4, y = 3.6 and y = 5.4, as the χ(T) curves of these samples show two transitions. It is suggested that all the samples with y ≤ 5.4 show magnetic phase transitions at TN on cooling from the paramagnetic (PM) to CSDW phase. On further addition of V the samples with y > 5.4 the obtained χ(T) curves show only one transition that suggest that these samples are in the ISDW phase at all temperatures below TN. Results suggest a quantum critical behavior at V concentration of yc = 9.033.

Measurements of the temperature dependence of electrical resistance (R) and neutron powder diffraction (NPD) of a Cr84.7Re15.3 alloy is reported. The magnetism originates from the formation of a spin-density-wave (SDW) as a result of nesting between the electron and hole sheets at the Fermi surface (FS). NPD revealed the magnetic character of the SDW to be commensurate (C) with the lattice with a Neel temperature (TN) of 560 ± 5K that correlates to TN = 585 ± 5K determined from the saddle point in the R(T) results. A power law fit Iα(1−TTN)2β of the neutron data gave β = 0.36(1), indicating that the AF ordering follows the 3D Heisenberg model. An additional antiferromagnetic magnetic contribution, associated with Cr2O3, was observed to co-exist in the alloy. Quantification analyses revealed that the Cr2O3 content was less than 2 wt.%. A β value of 0.30(1) was determined for the magnetic phase transition of Cr2O3 in correspondence with the 3D Ising model.

Rare-earth orthochromites (RCrO3) with orthorhombically distorted perovskite (ABO3) structure exhibit a wealth of magnetic phenomena including temperature-induced magnetization reversal (TMR), spin-reorientation (SR), spin-flipping (SF) and exchange-bias (EB). These occur as a result of magnetic interactions among the cations such as Cr3+–Cr3+, Cr3+–R3+ and R3+–R3+, where R is the rare earth element. In the present work, GdCrO4 samples were prepared using the sol-gel technique. The as-synthesized samples are amorphous in nature. Calcination of the samples at 600 °C for 1 h leads to the formation of the GdCrO4 phase whereas increasing the calcination temperature to 1000 °C for 1 h triggers the decomposition of GdCrO4 into GdCrO3. The role of thermal decomposition of GdCrO4 to GdCrO3 on crystal structure and magnetic transitions are discussed in this paper. Microstructure analyses show that the GdCrO4 powders have an intercalated porous structure that comprises a core-shell like construction with undistinguishable grain boundaries, whereas the morphology of the GdCrO3 demonstrates bulk nature with particles having micrometer size. Magnetization measurements as a function of temperature (M-T) with different probing magnetic fields show the ferromagnetic Curie temperature, (TC), of the GdCrO4 sample to be 24 K. GdCrO3 orders antiferromagnetically with a Neel temperature, TN (Cr), ascribed to the Cr magnetic moment at 171 K. A spin-flip transition (TSF) occurred at 22 K indicating the flipping of Cr3+ and Gd3+ spins and the spin-reorientation (TSR) transition is located at 5 K. The hysteresis loops measured across the transition temperatures validate the magnetic transitions as observed in the M-T curves.

In this report, x-ray photoelectron spectroscopy data for three types of Cu-doped nickel chromite nanoparticles are presented. CuCr2O4, Cu0.5Ni0.5Cr2O4, and NiCr2O4 were prepared using the citric acid-assisted sol-gel method. All samples were amorphous after the initial gel preparations were dried, but after calcination at temperatures higher than 700 °C, the samples crystallized in a spinel structure. X-ray diffraction patterns for the samples were well fitted with the I41/amd space group. Survey scans were conducted as well as detailed scans of Cu 2p, Ni 2p, Cr 2p, and O 1s levels. The O 1s core level was well-fitted with three components, including lattice oxygen (low binding energy) and two higher binding energy components, which corresponded to surface-absorbed hydroxyl groups originating from water and alcohol used in the synthesis of the particles. The line shape of the Cu 2p core level was compatible with mixed 2+ and 1+/0+ oxidation states for Cu ions in these nanoparticles. The strong intensity of the high binding energy satellite indicated that the majority of the Cu 2p ions were in 2+ oxidation state. Finally, Ni 2p showed a mixed 3+/2+ oxidation state for Ni ions in these nanoparticles.

Ni doped CoCr2O4, (Co1–xNix)Cr2O4 with x=0.5 and 0.25, nanoparticles were synthesized through sol-gel technique. The as synthesized samples were calcined at 600 °C for 1h. The phase identification of the samples was carried out using X-ray diffraction (XRD) techniques. The Davg for (Co0.5Ni0.5)Cr2O4 and (Co0.75Ni0.25)Cr2O4 were found to be 33 (1) nm and 22 (1) nm, respectively, from the transmission electron microscopy (TEM). Magnetic properties of the nanoparticles were measured down to 2 K using a vibrating sample magnetometer (VSM). Magnetization as a function of temperature measured under 0.1, 0.5 and 1 T applied magnetic field show a hump like feature at the peak temperature, Tp, similar to the superparamagnetic blocking feature observed in many nanoparticle systems. With increasing applied magnetic field the Tp shifts towards lower temperature. Magnetization as a function of applied magnetic field (μ0H= 0.1 T) showed an exchange bias like feature for x= 0.5, whereas no shifting of the loop was observed for x=0.25 sample. The transition related to spiral ordering at temperature TS was observed for both the samples, whereas no lock-in transition at temperature TL was noticed.

Cubic spinel CoCr2O4 has recently attained attention due to its multiferroic properties. However, the Co site substitution effect on the structural and magnetic properties has rarely been studied in thin film form. In this work, the structural and magnetic properties of Co1-x Ni x Cr2O4 (x= 0, 0.5) epitaxial thin films deposited on MgAl2O4 (100) and MgO (100) substrates to manipulate the nature of strain in the films using pulsed laser deposition (PLD) technique are presented. The epitaxial nature of the films was manifested through x-ray diffraction (XRD), reciprocal space mapping (RSM) and Rutherford backscattering spectrometry (RBS) measurements. Raman measurements revealed a disappearance of characteristic A 1g and F 2g modes of the CoCr2O4 with increase in the Ni content. Atomic force microscopy (AFM) and field emission scanning electron microscopy (FE-SEM) studies show a modification of the surface morphology upon Ni substitution. Magnetic measurements disclose that the ferrimagnetic Curie temperature (T C) of the CoCr2O4 in thin film grown on MgAl2O4 (100) and MgO (100) substrates were found to be 100.6 ± 0.5 K and 93.8 ± 0.2 K, respectively. With Ni substitution the T C values were found to be enhanced to 104.5 ± 0.4 K for MgAl2O4 (100) and 108.5 ± 0.6 K for MgO (100) substrates. X-ray photoelectron spectroscopy (XPS) suggests Cr3+ oxidation states in the films, while Co ions are present in a mixed Co2+/Co3+ oxidation state. The substitution of Ni at Co site significantly modifies the line shape of the core level as well as the valence band. Ni ions are also found to be in a mixed 2+/3+ oxidation state. O 1s core level display asymmetry related to possible defects like oxygen vacancies in the films.

Three spinel compounds, namely CoCr2O4, (Co0.75Ni0.25)Cr2O4, and (Co0.5Ni0.5)Cr2O4 were investigated using x-ray photoelectron spectroscopy techniques. These compounds were synthesized using sol-gel techniques. The gel was dried and subsequently calcined at 600 °C to achieve crystallinity and the correct cubic phase. The survey scans of the analyzed samples with detailed spectra of the Co 2p, Ni 2p, Cr 2p, O 1s, and the valence band were collected. The core levels are found to be asymmetric and have multiple components. Ni and Co have 2+/3+ oxidation states, whereas Cr prefers 3+ oxidation state. The O 1s core level demonstrates three components. The low binding energy component refers to the lattice oxygen atoms, whereas the two high binding energy components correspond to the surface adsorbed hydroxyl groups resulting from water and the alcohol used for the synthesis of these nanoparticles. The data emanating from this study are reported.

NiCr2O4 and CoCr2O4 are two distinct members of the chromite family (ACr2O4) having unique structural and magnetic properties. This paper is a continuation of previous work [Mohanty et al., J. Magn. Magn. Mater. 451(2018)20] and is focused on the modification of ferrimagnetic properties in NiCr2O4 by substituting Co ions at Ni sites. In order to do so (Ni1−xCox)Cr2O4 (x = 0, 0.50, 0.75, 1.00) powder samples were synthesized using chemical co-precipitation techniques. Interest is primarily on (Ni0.5Co0.5)Cr2O4 and (Ni0.25Co0.75)Cr2O4 as characterization results on the end members have been reported. It was determined with in-situ temperature dependent X-ray diffraction measurements that these compositions become fully crystallized cubic spinels with space group Fd 3 - m above 700 °C. All samples were subsequently calcined at 900 °C to ensure phase purity and uniform crystallinity. Transmission electron microscopy showed non-uniform distribution of particle sizes with the majority of the particles having bi-pyramidal structures with flat tops for both samples. A comparative account of different ferrimagnetic Curie temperature, θ f or TC, estimations are presented as determined from measured temperature dependences of the following techniques: Fits of the magnetic susceptibility data indicated a minimum value for the (Ni0.5Co0.5)Cr2O4 sample at 56.1 ± 0.9 K, followed by an increase to 76.8 ± 0.4 K for the (Ni0.25Co0.75)Cr2O4 sample; Neutron diffraction measurements gave values of 80 ± 1 K and 87 ± 1 K; Their paramagnetic Curie points, θ p , were determined to be 73.3 and 84.9 K, respectively. The magnetic frustration index f = ΘCW/TC was found to decrease continuously over the series from 11.9 for NiCr2O4 to 7.1 and 6.5 for x = 0.5 and 0.75 respectively with (Ni0.5Co0.5)Cr2O4 being more frustrated than (Ni0.25Co0.75)Cr2O4. Magnetization as a function of applied magnetic field measured at 3 K demonstrates unusually high coercivity for (Ni0.5Co0.5)Cr2O4, supporting the notion for the higher degree of magnetic frustration in this sample. No exchange bias was observed for M (μ0H) in the (Ni0.25Co0.75)Cr2O4 sample measured at 3 K, but did however show a significant anomaly in its hysteresis loop at this temperature. The anomaly in hysteresis behaviour disappeared when measured at 1.7 K and also at higher temperatures. Frequency dependent ac-susceptibility measurements revealed no shift in the peak position with frequency refuting the existence of spin-glass like behavior in both these samples.

International audience; The temperature dependence of exchange bias properties are studied in polycrystalline BiFeO3/Ni81Fe19 bilayers, for different BiFeO3 thicknesses. Using a field cooling protocol, a non-monotonic behavior of the exchange bias field is shown in the exchange-biased bilayers. Another thermal protocol, the Soeya protocol, related to the BiFeO3 thermal activation energies was carried out and reveals a two-step evolution of the exchange bias field. The results of these two different protocols are similar to the ones obtained for measurements previously reported on epitaxial BiFeO3, indicating a driving mechanism independent of the long-range crystalline arrangement (i.e. epitaxial or polycrystalline). An intrinsic property of BiFeO3 is proposed as being the driving mechanism for the thermal dependent magnetization reversal: the canting of the BiFeO3 spins leading to a biquadratic contribution to the exchange coupling. The temperature dependence of the magnetization reversal angular behavior agrees with the presence of such a biquadratic contribution for exchange biased bilayers studied here

It was recently suggested that for the Cr 1 − x Al x alloy system the Sommerfeld specific heat coefficient ( γ ) as a function of x may peak at the triple point (TP) concentration ( x t ) of the x– T magnetic phase diagram. The TP at ( x t , T t ) represents the intersection point of three magnetic phase transition lines at which incommensurate (I) and commensurate (C) spin-density-wave (SDW) phases are expected to coexist with the paramagnetic (P) phase. A comprehensive experimental study on the physical properties of single crystalline Cr 1 − x Al x alloys in the concentration range 0 ⩽ x ⩽ 0.034, that encloses x t , is reported here for further investigations of the above conjecture and possible anomalous behaviour in other physical properties near x t . The measurements include the electrical resistivity ( ρ ), Seebeck coefficient ( S ), specific heat ( C p ), Hall coefficient ( R H ), magnetic susceptibility ( χ ) and thermal conductivity ( κ ). All these properties, except for κ , depict anomalous temperature and concentration dependencies of SDW origin for x close to x t . The present study indicates a value of x t rather close to x = 0.022. The x -dependence of γ exhibits an extraordinary large and sharp peak near this concentration. This observation is interpreted as indication that the temperature of the TP is likely situated at 0 K. A new magnetic phase diagram is therefore proposed for the Cr 1 − x Al x alloy system for x in the region of x t . This study presents novel experimental evidence of exceptional anomalous magnetic behaviour around the TP concentration of the Cr 1 − x Al x system. It should incite similar studies on other Cr alloy systems with a TP on their magnetic phase diagrams.

Coupled ferromagnetic and antiferromagnetic bilayers are an important class of materials that allow manipulating magnetic properties, including the interfacial exchange bias phenomenon. Bismuth ferrite, BiFeO 3, is the most studied single-phase magnetoelectric multiferroic due to its unique ferroelectric and antiferromagnetic orderings well above room temperature. We report on a systematic experimental study regarding the direct correlation between the Bi 2O 3 parasitic phase concentration in the BiFeO 3 and the magnetic properties of the polycrystalline heterostructure BiFeO 3/Ni 81Fe 19 deposited via magnetron sputtering. It was found that the macroscopic exchange field, that arises from exchange bias coupling, is zero for phase-pure BiFeO 3 and increases up to 18 Oe on increasing the concentration of Bi 2O 3. This trend is in agreement with the azimuthal behavior of the magnetization reversal. The structural characterization also indicates that phase-pure BiFeO 3 has a disordered mesoporous structure. The influence of the Bi 2O 3 parasitic phase and mesoporous state, that is known to exist and introduce defects in the polycrystalline bilayers of BiFeO 3/Ni 81Fe 19, on the magnetization reversal and exchange bias coupling is reported for the first time in this study.Coupled ferromagnetic and antiferromagnetic bilayers are an important class of materials that allow manipulating magnetic properties, including the interfacial exchange bias phenomenon. Bismuth ferrite, BiFeO 3, is the most studied single-phase magnetoelectric multiferroic due to its unique ferroelectric and antiferromagnetic orderings well above room temperature. We report on a systematic experimental study regarding the direct correlation between the Bi 2O 3 parasitic phase concentration in the BiFeO 3 and the magnetic properties of the polycrystalline heterostructure BiFeO 3/Ni 81Fe 19 deposited via magnetron sputtering. It was found that the macroscopic exchange field, that arises from exchange bias coupling, is zero for phase-pure BiFeO 3 and increases up to 18 Oe on increasing the concentration of Bi 2O 3. This trend is in agreement with the azimuthal behavior of the magnetization reversal. The structural characterization also indicates that phase-pure BiFeO 3 has a ...

Nanoparticles of (Co1–xNix)Cr2O4, with x = 0.5 and 0.25, were prepared utilizing the sol-gel technique, in order to investigate the effect of Ni substitution at the Co site. The crystal structure of the prepared samples was identified using X-ray diffraction. Transmission electron microscopy images indicate a non-uniform distribution in particle sizes. Temperature dependent magnetization measurements as a function of probing field demonstrate different magnetic transition temperatures to that of both the parent compounds. The magnetization as a function of applied magnetic field shows a wasp-waist like feature for (Co0.5Ni0.5)Cr2O4 nanoparticles measured at 10 K, which is absent in both NiCr2O4 and CoCr2O4. This feature diminished for other measurement temperatures below the Curie temperature and was also absent at all temperatures for the (Co0.75Ni0.25)Cr2O4 nanoparticles. X-ray photoemission spectroscopy results show that the Ni cations prefers the 3+ and Co the 2+ oxidation states, while that of Cr was found to be 3+. However, mixed oxidation states were observed for Ni and Co in both samples, which can influence the magnetic properties.

Dimensionality effects on epitaxial and polycrystalline Cr 1− x Ru x alloy thin films and in Cr/Cr–Ru heterostructures are reported. X-ray analysis on Cr 0.9965 Ru 0.0035 epitaxial films indicates an increase in the coherence length in growth directions (1 0 0) and (1 1 0) with increasing thickness ( d ), in the range 20≤ d ≤300 nm. Atomic force microscopy studies on these films shows pronounced vertical growth for d >50 nm, resulting in the formation of columnar structures. The Neel temperatures ( T N ) of the Cr 0.9965 Ru 0.0035 films show anomalous behaviour as a function of d at thickness d ≈50 nm. It is interesting to note that this thickness corresponds to that for which a change in film morphology occurs. Experiments on epitaxial Cr 1− x Ru x thin films, with 0≤ x ≤0.013 and d =50 nm, give T N – x curves that correspond well with that of bulk Cr 1− x Ru x alloys. Studies on Cr/Cr 0.9965 Ru 0.0035 superlattices prepared on MgO(1 0 0), with the Cr layer thickness varied between 10 and 50 nm, keeping the Cr 0.9965 Ru 0.0035 thickness constant at 10 nm, indicate a sharp decrease in T N as the Cr separation layers reaches a thickness of 30 nm; ascribed to spin density wave pinning in the Cr layers for d