Single Magnetic Transition Research Articles

Structural, dielectric and magnetic study of double perovskite La2CoMnO6

Polycrystalline double perovskite La2CoMnO6 sample was prepared via solid state reaction route and its structural, dielectric and magnetic properties were investigated. XRD confirmed the phase formation without any impurity. Rietveld refinement analysis suggested the presence of monoclinic (P21/n, ordered) as well as rhombohedral and orthorhombic (R3c &Pbnm, disordered) structures. Microstructural analysis using FESEM confirmed that average grain size lies in micrometer range. Dielectric constant (log ε′) and loss tangent (tanδ) both exhibited large values at lower frequencies as well as in higher temperature range. Nyquist impedance plot proposed NTCR (negative temperature coefficient of resistance) nature of double perovskite sample. DC conductivity showed increasing trend with increase in temperature and also, the conductivity is of the order of 10−2 S/m, which represent semiconducting behavior of prepared sample. Also, the analysis suggested the co-existence of thermal activation (TA), small polaron hopping (SPH) and variable range hopping (VRH) conduction mechanisms. Temperature dependent magnetic measurements (M-T) suggested that sample exhibit single magnetic transition at 226 K. Field dependent magnetic measurements (M-H) confirmed the ferromagnetic nature of the prepared sample. M-H loop is not well saturated even at 60 kOe which suggested the presence of anti-site disorder. Multi-domain magnetic structure of the prepared sample suggests its suitability for memory device applications.

Improved magnetic properties of Fe substituted La2CoMnO6 for spintronic applications

A detailed study of magnetic behaviour of double perovskites was carried out by developing La2Co1-xFexMnO6; (x = 0.0, 0.2, 0.5, 0.8 and 1.0) via sol–gel technique. All samples showed single magnetic transition except pure LCMO (x = 0.0) and LCFMO2 (x = 0.5). Temperature dependent inverse magnetic susceptibility (χ-1) was fitted in accordance with Curie-Weiss law. μeff (effective magnetic moment) was determined for all the developed samples. Pure LCMO showed a downward divergence from Curie-Weiss law below 230 K but above transition temperature which indicates the characteristics of Griffiths phase. Saturation magnetization (Ms) increased initially and then decreased, whereas coercive field (Hc) was found to be monotonous decreased with increase in Fe content. LCFMO1 (x = 0.2) was noticed to have maximum Ms (38.87 emu/g) which indicated that the magnetic properties of pure LCMO were improved with Fe substitution, but for lower substitution only. Magnetization vs. field (M−H) curves were not well saturated even at a magnetic field of 60 kOe, therefore, values of Ms for all the samples were estimated using law of approach to saturation. With increase in Fe content, an increased anti-site disorder among Mn and Co strengthened antiferromagnetic (AFM) super exchange interactions and weakened ferromagnetism (FM). Therefore, substitution of Fe on Co-site was responsible for systematic decrease in saturation magnetization when × exceeded 0.2.

Sizable magnetic entropy change in bismuth-substituted La0.75Bi0.1Na0.15MnO3 manganite.

The bismuth (Bi)-substituted La0.85-xBixNa0.15MnO3 (x = 0 and x = 0.1) manganites have been investigated for achieving room temperature magnetic entropy change at low magnetizing intensities. A 10% Bi ion substitution at the La site has led to the relatively higher symmetry R3̄c rhombohedral structure showing improvement in Mn-O-Mn bond angles. The chemical additive Bi2O3 has assisted in grain growth to form densified specimens even at low sintering temperatures. The sample has a soft ferromagnetic nature with a single magnetic transition occurring at 275 K. Phenomenal improvement in magnetic sensitivity at low magnetic fields was achieved with TC close to room temperature. Nearly 100-500 percent increases in magnetic entropy change was realised over existing parent compounds and the entropy changes are greater than the prototype, Gd of active magnetic refrigeration. The magnetic interactions are governed by the Tri-Critical Mean Field model with emphasis on the coexistence of long-range and short-range interactions. The characteristics, viz. soft ferromagnet of second-order phase transition, abrupt phase change at TC, the resultant large magnetic entropy change of 4.4 J kg-1 K-1 and temperature averaged entropy change of 3.914 J kg-1 K-1 (10 K) at the low magnetic field of 1.5 T are expected to facilitate application prospects as a magnetic refrigerants for room temperature working range.

Role of electronegativity on the crystal field splitting of Eu3+ manifold in pyrochlore-type oxides, Ca3M3Nb2O14 (M = Ti and Sn)

In this work, the influence of partial substitution of tetravalent cations like Ti and Sn on both A and B sites of the pyrochlore type Ca3M3Nb2O14:0.15Eu3+ (M = Ti and Sn) red phosphors on the photoluminescence properties was studied. In this attempt, the compositions of the formula Ca3Sn3-xTixNb2O14:0.15Eu3+ (x = 0, 1.5 and 3) and Ca3Ti3Nb2O14:xEu3+ (x = 0.05–0.20) phosphors were prepared via the conventional ceramic route and characterized for their structure, morphology and photoluminescence properties through various advanced techniques. Powder XRD analysis of these phosphors confirm the formation of the pyrochlore-type structure with partial occupation of Ti/Sn cations on the A site. Thus the mixing of Ti/Sn ions on the A site revealed the role of electronegativity of these ions on the photoluminescence properties of these phosphors. The full width half maximum (fwhm) of the charge transfer band in titanate phosphor is more compared to that of stannates and charge transfer band is relatively located at longer wavelength (333 nm) in titanate phosphors compared to stannate system The splitting of characteristic Eu3+ manifold is smaller in titanates relative to the stannate phosphors. Further, the fwhm of 5D0-7F2 electric dipole transition is observed to be narrow for titanium substituted compositions which is ascribed to the difference in bonding environment of Ti and Sn in the host lattice. The titanate phosphors exhibit intense sharp narrow red emissions due to 5D0–7F2 transitions of Eu3+ ions with higher asymmetric ratio. The presence of the single sharp 5D0-7F1 magnetic dipole transition in both systems without splitting confirms the loss of pyrochlore D3d symmetry around the Eu3+ ions. These results imply that displaced pyrochlore system offers a lot of opportunities to manipulate the luminescence properties.

Enhanced electrical and magnetic properties of post-annealed plasma-activated-sintered La2CoMnO6 ceramics

Double perovskite La2CoMnO6 (abbreviated as LCMO) ceramics with compact structure and excellent properties were synthesized by plasma-activated-sintering followed by post-annealing. The effect of post-annealing on microstructure as well as electrical and magnetic properties was investigated. The LCMO ceramics were found to be single-phased with a tightly-bonded structure in the monoclinic space group (P21/n), and Co3+ and Mn3+ were converted into Co2+ and Mn4+ after post-annealing. As a result, the magnetic performance of the post-annealed LCMO ceramics was enhanced remarkably, although the annealing process had little effect on electrical properties due to the variable-range-hopping mechanism. The post-annealed plasma activated sintered LCMO ceramics exhibited a single magnetic transition point at 225.1 K, whose saturation magnetization and coercivity were 46.85 emu/g and 7.96 kOe, respectively.

Tungsten-substituted double perovskite Ba2FeMo1-xWxO6 for enhanced magnetocaloric effects

Abstract Double perovskite materials Ba2FeMo1-xWxO6 (0.0 ≤ x ≤ 0.4) partially substituted with Tungsten (W) at the Molybdenum (Mo) site were prepared by the solid state reaction method and thoroughly investigated for structural, magnetic and magnetocaloric properties. Rietveld refined X-ray diffraction profiles were used to confirm the formation of cubic structure with Fm-3m space group in both the pristine as well as W-substituted samples. Upon increasing temperature, a single magnetic transition from ferromagnetic to paramagnetic phase was observed in each sample at its Curie temperature around which maximum magnetic entropy change could be obtained. A second order nature of the magnetic phase transition was established in all the samples with the help of Arrott plots and the universal master curve investigations and the magnetocaloric effect was obtained from the magnetic isotherms. Magnetocaloric effects estimated in terms of the maximum magnetic entropy change and temperature averaged entropy change (TEC) were enhanced with controlled W-substitution. Among the various compositions, sample with (x = 0.3) i.e., Ba2FeMo0.7W0.3O6 demonstrated a magnetic entropy change of 1.483 J/kgK and a TEC value of 2.74 J/kgK over a temperature span of 10 K under an applied magnetic field of 2.5 T. The results obtained in the present work clearly suggest that the investigated compounds can be customized for use in magnetic refrigeration technology.

Critical behavior and magnetocaloric effect in the multiferroic double perovskite Lu2NiMnO6

A systematic investigation on the structure, magnetism, magnetocaloric effect, and critical behaviors of multiferroic Lu2NiMnO6 synthesized by sol-gel method are reported. This compound crystallizes in a monoclinic structure with the space group P21/n. Upon decreasing temperature, a single magnetic transition from paramagnetic to ferromagnetic phase has been observed, around which considerable magnetic entropy changes can be obtained. Besides, evaluation of the critical exponents are performed using various techniques, like the modified Arrott plot, Kouvel-Fisher method and critical isotherm analysis based on the magnetic data around magnetic transition temperature. The obtained critical exponent values are found to be coincided and comparable with those predicted by the mean-field model, which are also confirmed by the single scaling equation: m = f±(h), where m and h are the renormalized magnetization and field, respectively by observation of isotherm M(H) curves below and above the critical temperatures collapsing into two independent universal branches. The exponents determined in this study are in good agreement with those calculated from the renormalization group approach for a three-dimensional system coupled with the attractive long-range interactions between spins that decay as J(r)∼r−(3+σ) with σ = 1.325.

Triclinic–monoclinic–orthorhombic (T–M–O) structural transitions in phase diagram of FeVO4-CrVO4 solid solutions

Phase diagram of FeVO4-CrVO4 solid solutions pertinent with structural and magnetic phases is presented with unambiguous experimental evidences. Solid solutions Fe1–xCrxVO4 (0 ≤ x ≤ 1.0) were synthesized through the standard solid state route and studied by X-ray diffraction, scanning electron microscopy, energy dispersive spectra of X-rays, Raman spectroscopy, d.c. magnetization, and 57Fe Mössbauer spectroscopic studies. FeVO4 and CrVO4 were found to be in triclinic (P-1 space group) and orthorhombic structures (Cmcm space group), respectively. Cr incorporation into the FeVO4 lattice leads to the emergence of a new monoclinic phase dissimilar to the both end members of the solid solutions. In Fe1–xCrxVO4 up to x = 0.10, no discernible changes in the triclinic structure were found. A new structural monoclinic phase (C2/m space group) emerges within the triclinic phase at x = 0.125, and with the increase in Cr content, it gets stabilized with clear single phase signatures in the range of x = 0.175–0.25 as evidenced by the Rietveld analysis of the structures. Beyond x = 0.33, orthorhombic phase similar to CrVO4 (Cmcm space group) emerges and coexists with a monoclinic structure up to x = 0.85, which finally tends to stabilize in the range of x = 0.90–1.00. The Raman spectroscopic studies also confirm the structural transition. FeVO4 Raman spectra show the modes related to three nonequivalent V ions in the triclinic structure, where up to 42 Raman modes are observed in the present study. With the stabilization of structures having higher symmetry, the number of Raman modes decreases and the modes related to symmetry inequivalent sites collate into singular modes from the doublet structure. A systematic crossover from two magnetic transitions in FeVO4, at 21.5 K and 15.4 K to single magnetic transition in CrVO4, at 71 K (antiferromagnetic transition), is observed in magnetization studies. The intermediate solid solution with x = 0.15 shows two magnetic transitions, whereas in the compound with x = 0.33 one of the magnetic transitions disappears. 57Fe Mössbauer spectroscopic studies show a finger print evidence for disappearance of non-equivalent sites of Fe as the structure changes from Triclinic–Monoclinic–Orthorhombic phases with the increasing Cr content in Fe1–xCrxVO4. Comprehensive studies related to the structural changes in Fe1–xCrxVO4 solid solutions lead us to detailed phase diagrams which shall be characteristic for room temperature structural and temperature dependent magnetic transitions in these solid solutions, respectively.

Large low-field magnetocaloric effect in directionally solidified Ni55Mn18+xGa27−x (x = 0, 1, 2) alloys

The magnetostructural transformation and magnetocaloric effect of directionally solidified polycrystalline Ni55Mn18+xGa27−x (x=0, 1, 2) alloys were studied. It is shown the directionally solidified alloys form coarse columnar-shaped grains with strong 〈001〉A (the subscript A refers to austenite) preferred orientation along the solidification direction. Through Mn substitution for Ga, a coupled magnetostructural transformation was realized in Ni55Mn19Ga26 and Ni55Mn20Ga25 alloys. Large adiabatic temperature variation (ΔTad) of 1.47K and 1.57K under the low field change of 1.5T were achieved in these two alloys, respectively. Such ΔTad values are obviously higher than that obtained from a single martensitic transformation and magnetic transition. The present results demonstrate that proper composition tuning to achieve magnetostructural transformation as well as increasing the grain size and preferential orientation degree through directional solidification could be an economical processing route to optimize magnetocaloric properties in polycrystalline Ni-Mn-Ga based alloys.

Magnetism and charge order in the ladder compound Co3O2BO3

There are two known ludwigites containing a single transition metal element, ${\text{Fe}}_{3}{\text{O}}_{2}{\text{BO}}_{3}$ and ${\text{Co}}_{3}{\text{O}}_{2}{\text{BO}}_{3}$. The structure of these materials has low-dimensional units in the form of three-legged ladders (3LL) that confer to each of them unique magnetic and electronic properties. ${\text{Fe}}_{3}{\text{O}}_{2}{\text{BO}}_{3}$ presents a staggered charge density wave (CDW) transition in the ladders near room temperature and two magnetic transitions. It has remained a mystery why the other compound ${\text{Co}}_{3}{\text{O}}_{2}{\text{BO}}_{3}$ behaves so conventionally, with a single magnetic transition and no CDW in spite of similar structural and electronic configurations. Neutron diffraction results presented here in this system finally unravel these differences. Far from a trivial explanation, we uncover a coexistence of low and high spin Co ions in well-defined octahedral sites. Our results allow one to solve the contrasting behavior of the Fe and Co ludwigites in terms of a subtle and unique charge ordering mechanism occurring at the microscopic level of the rungs of the 3LL.

Monoclinic crystal structure ofα−RuCl3and the zigzag antiferromagnetic ground state

The layered honeycomb magnet alpha-RuCl3 has been proposed as a candidate to realize a Kitaev spin model with strongly frustrated, bond-dependent, anisotropic interactions between spin-orbit entangled jeff=1/2 Ru4+ magnetic moments. Here we report a detailed study of the three-dimensional crystal structure using x-ray diffraction on untwinned crystals combined with structural relaxation calculations. We consider several models for the stacking of honeycomb layers and find evidence for a crystal structure with a monoclinic unit cell corresponding to a stacking of layers with a unidirectional in-plane offset, with occasional in-plane sliding stacking faults, in contrast with the currently-assumed trigonal 3-layer stacking periodicity. We report electronic band structure calculations for the monoclinic structure, which find support for the applicability of the jeff=1/2 picture once spin orbit coupling and electron correlations are included. We propose that differences in the magnitude of anisotropic exchange along symmetry inequivalent bonds in the monoclinic cell could provide a natural mechanism to explain the spin gap observed in powder inelastic neutron scattering, in contrast to spin models based on the three-fold symmetric trigonal structure, which predict a gapless spectrum within linear spin wave theory. Our susceptibility measurements on both powders and stacked crystals, as well as neutron powder diffraction show a single magnetic transition at TN ~ 13K. The analysis of the neutron data provides evidence for zigzag magnetic order in the honeycomb layers with an antiferromagnetic stacking between layers. Magnetization measurements on stacked single crystals in pulsed field up to 60T show a single transition around 8T for in-plane fields followed by a gradual, asymptotic approach to magnetization saturation, as characteristic of strongly anisotropic exchange interactions.

Critical phenomena and estimation of the spontaneous magnetization from a mean field analysis of the magnetic entropy change in La0.65Eu0.05Sr0.3Mn0.95Cr0.05O3

We have studied the magnetic and magnetocaloric properties of the La0.65Eu0.05Sr0.3Mn0.95Cr0.05O3 manganite prepared by using a soft chemical method (Pechini method). This compound presents a single magnetic transition from ferromagnetic (FM) to paramagnetic (PM) phase at TC=338K. To investigate the nature of the magnetic phase transition, found to be of second-order, a detailed critical exponent study has been performed by dc-magnetization M (H,T) measurements around the Curie temperature TC. Modified Arrott plot method has been adopted to study the critical behavior of the compound around its transition region. The values deduced for the critical exponents β, γ and δ are close to the theoretical prediction of the mean-field model, indicating that the magnetic interactions are long-range. Moreover, we have investigated the validity and usefulness of the theoretical modeling in our compound La0.65Eu0.05Sr0.3Mn0.95Cr0.05O3 based on the mean-field analysis of the magnetic entropy change (−ΔSM) versus the magnetization data. Results obtained through this approach are compared to those obtained from extrapolation of the Arrott curves. An excellent agreement is found between the experimental (−ΔSM) and the one estimated by Landau theory.

Spatial control of functional properties via octahedral modulations in complex oxide superlattices

Control of atomic structure, namely the topology of the corner-connected metal-oxygen octahedra, has emerged as an important route to tune the functional properties at oxide interfaces. Here we investigate isovalent manganite superlattices (SLs), [(La(0.7)Sr(0.3)MnO(3))n/(Eu(0.7)Sr(0.3)MnO(3))n] × m, as a route to spatial control over electronic bandwidth and ferromagnetism through the creation of octahedral superstructures. Electron energy loss spectroscopy confirms a uniform Mn valence state throughout the SLs. In contrast, the presence of modulations of the MnO(6) octahedral rotations along the growth direction commensurate with the SL period is revealed by scanning transmission electron microscopy and X-ray diffraction. We show that the Curie temperatures of the constituent materials can be systematically engineered via the octahedral superstructures leading to a modulated magnetization in samples where the SL period is larger than the interfacial octahedral coupling length scale, whereas a single magnetic transition is observed in the short-period SLs.

Age splitting of the La(Fe1−xSix)13Hy first order magnetocaloric transition and its thermal restoration

The La(Fe1−xSix)13Hy system has a first order ferromagnetic phase transition with a large magnetocaloric effect for 0.11 < x < 0.13. Such materials produced the highest currently published cooling power of a magnetic refrigerator. Adjusting the H content, y allows selection of any Curie point Tc from ∼200 K to 330 K, but hydrogen-unsaturated material (y < 1.6) with a first order transition exhibits an unusual instability. If La(Fe1−xSix)13Hy is held within a few K of its initial Tc, an initially single magnetic transition, with a sharp differential scanning calorimetry peak, gradually splits into two transitions separated by a large temperature interval. The ultimate splitting interval depends almost linearly on (1.6-y) and Tc. If the material is held more than 10 K above or below Tc, an initially sharp transition is retained, and a split transition is restored to its original sharp single transition. The recovery rate increases with temperature. For temperatures above 320 K, the recovery rate is rapid enough to allow overnight recovery of magnetocaloric material that is in a split state. This method was employed to maintain high performance of La(Fe1−xSix)13Hy in a magnetic refrigerator. In order to verify that the recovery process involves the macroscopic movement of hydrogen within the solid, a portion of 0.2 mm diameter particle material with a split transition was ground into particles of 0.05 mm diameter. The unground 0.2 mm particles and the ground 0.05 mm particles were held at 13 K above Tc. The 0.3 mm particles recovered their initial single transition, but the 0.05 mm particles, when examined as a group, retained their split line, presumably because they had been separated into particles with differing total hydrogen fraction y.

Magnetic properties of double perovskite La2BMnO6 (B = Ni or Co) nanoparticles

Double perovskite La2BMnO6 (B = Ni and Co) nanoparticles with average particle size of ~50 nm were synthesized using a facile, environmentally friendly, and scalable molten-salt reaction at 700 °C in air. Their structural and morphological properties were characterized by X-ray diffraction and transmission electron microscopy. Their magnetic properties were evaluated and compared using dc magnetic M-T and M-H, and ac magnetic susceptibility versus frequency, temperature, and field for the first time. The dc magnetization curves show paramagnetic-ferromagnetic transitions at TC∼ 275 and 220 K for La2NiMnO6 (LNMO) and La2CoMnO6 (LCMO) nanoparticles, respectively. ac susceptibility revealed that the LCMO nanoparticles had a single magnetic transition indicative of Co(2+)-O(2-)-Mn(4+) ordering, whereas the LNMO nanoparticles showed more complex magnetic behaviors suggesting a re-entrant spin glass.

Structural studies and magnetic and transport properties of Cr-substituted La0.67Ba0.33Mn1−xCrxO3 (0 ≤ x ≤ 0.15) perovskites

We have investigated the structural, magnetic and electrical transport properties of a series of ABO3-type perovskite compounds, La0.67Ba0.33Mn1−xCrxO3 (0≤x≤0.15), which strongly depend on the doping level x. The slight difference between the ionic radii of Cr3+ and Mn3+ causes no change in the structure when x≤0.1, remaining rhombohedral (space group R-3C), while for x=0.15 the structure becomes cubic (space group Pm-3m). Energy dispersive X-ray analysis (EDAX) confirms the expected stoichiometry of all samples. Upon Cr doping on the Mn site, the lattice parameters, the unit cell volume and the BOB bond angle are reduced. All samples present a single magnetic transition from ferromagnetic to paramagnetic phase, showing a decrease of the Curie temperature Tc and the magnetization M when x increases (x≤0.15). However, Cr doping makes the saturation magnetization at 5K to decrease, which indicates that the Cr3+ moments tend to be antiparallel to the Mn3+ moments at low temperature.The Cr-doped manganites exhibit a large variation in resistivity values. The increase of Cr doping (x≤0.15) leads to an increase of the electrical resistivity. Below 10at.% of Cr3+, the electrical resistivity shows a metallic behavior, which is well fitted by the relation ρ=ρ0+ρ2T2+ρ4.5T4.5, indicating the importance of the grain/domain boundary, the electron–electron scattering effects and, to a lesser extent, the electron–(magnon, phonon) scattering effects in the mechanism of conduction. On the other hand, the 15at.% of Cr3+ doping makes the material to exhibit a semiconductor behavior, for which the electronic transport can be explained by a variable range hopping (VRH) and small polaron hopping (SPH) models. Results are consistent with a reduction of the number of available hopping sites for the Mn eg (↑) electron due to the substitution of Mn3+ by Cr3+, which suppresses the double exchange (DE) interactions.

Nematic phase without Heisenberg physics in FeAs planes

We use Monte Carlo simulations and analytical arguments to analyze a frustrated Ising model with nearest-neighbor antiferromagnetic coupling ${J}_{1}$ and next-nearest-neighbor coupling ${J}_{2}$. The model is inspired on the physics of pnictide superconductors and to some extent we argue that it can be more representative of this physics than the Heisenberg counterpart. Parameters are chosen such that the ground state is a columnar or striped state, as observed experimentally, but is close to the transition to the simple N\'eel ordered antiferromagnetic state $R={J}_{2}/|{J}_{1}|\ensuremath{\gtrsim}0.5$. We find that a nematic phase is induced close to $R=0.5$ by finite-size effects and argue that this explains experiments in imperfect samples that find a more robust nematic state as the quality of the sample decreases [A. Jesche et al., Phys. Rev. B 81, 134525 (2010)]. Including the effect of a weak coupling with the lattice, we find that a structural transition occurs associated with a nematic phase, with a magnetic transition occurring at a lower temperature. These two transitions merge into a single structural and magnetic transition with a stronger first-order character for larger spin-lattice couplings. These two situations are in agreement with the different phenomenologies found in different families of pnictides.

Effects of the Mn/Co ratio on the magnetic transition and magnetocaloric properties of Mn1+xCo1−xGe alloys

We have investigated the magnetic transition and magnetocaloric effects of Mn1+xCo1−xGe alloys by tuning the ratio of Mn/Co. With increasing Mn content, a series of first-order magnetostructural transitions from ferromagnetic to paramagnetic states with large changes of magnetization are observed at room temperature. Further increasing the content of Mn (x = 0.11) gives rise to a single second-order magnetic transition. Interestingly, large low-field magnetic entropy changes with almost zero magnetic hysteresis are observed in these alloys. The effects of Mn/Co ratio on magnetic transition and magnetocaloric effects are discussed in this paper.

Modified magnetic ground state inNiMn2O4thin films

We demonstrate the stabilization of a magnetic ground state in epitaxial ${\text{NiMn}}_{2}{\text{O}}_{4}$ (NMO) thin films not observed in their bulk counterpart. Bulk NMO exhibits a magnetic transition from a paramagnetic phase to a collinear ferrimagnetic moment configuration below 110 K and to a canted moment configuration below 70 K. By contrast, as-grown NMO films exhibit a single magnetic transition at 60 K and annealed films exhibit the magnetic behavior found in bulk. Cation inversion and epitaxial strain are ruled out as possible causes for the new magnetic ground state in the as-grown films. However, a decrease in the octahedral ${\text{Mn}}^{4+}:{\text{Mn}}^{3+}$ concentration is observed and likely disrupts the double exchange that produces the magnetic state at intermediate temperatures. X-ray magnetic circular dichroism and bulk magnetometry indicate a canted ferrimagnetic state in all samples at low temperature. Together these results suggest that the collinear ferrimagnetic state observed in bulk NMO at intermediate temperatures is suppressed in the as grown NMO thin films due to a decrease in octahedral ${\text{Mn}}^{4+}$ while the canted moment ferrimagnetic ordering is preserved below 60 K.

FeCoBSiNb bulk metallic glasses with Cu additions

AbstractThe effect of Cu additions (1, 2 and 3 at.%) on the glass forming ability (GFA) and magnetic properties of [(Fe0.5Co0.5)0.75Si0.05B0.20]96Nb4 is studied. As the Cu content increases, the GFA deteriorates. The structure of the samples, as well as the crystallization behavior was in‐situ studied by means of synchrotron beam. The as‐cast 1 mm diameter rods are characterized by a mixture of (nano)‐crystals and amorphous matrix. Upon heating, the pre‐existing nuclei grow, without forming new crystalline phases. The magnetic properties are characteristic for soft magnetic materials. Despite that several crystalline magnetic phases can be identified in the as‐cast samples, only one single magnetic transition prior to complete crystallization could be identified upon heating. The values for saturation magnetization and for Curie temperature are relatively close for all samples. The initial permeability of the Cu containing samples seems to be higher than that for the fully amorphous [(Fe0.5Co0.5)0.75Si0.05B0.20]96Nb4 alloy (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)