In-situ time-resolved small-angle neutron scattering (SANS) experiments were conducted on homogenised coldrolled ternary Fe-Au-W alloys during aging for 12 h at temperatures of 650 to 700 degrees C in order to study the kinetics of the nanoscale precipitation. For comparison the precipitation kinetics in the binary counterparts Fe-Au and Fe-W alloys were also studied. In the ternary Fe-Au-W alloy nanoscale Au-rich precipitates were observed by both transmission electron microscopy (TEM) and SANS, while no significant W-rich precipitation was observed. The SANS pattern of the cold-rolled Fe-Au-W alloy clearly reveals a preferred orientation for the plate-shaped nanoscale Au-rich precipitates. As these Au-rich precipitates have a fixed orientation relation with the matrix lattice this preferred orientation originates from the texture of the bcc matrix grains, as confirmed by X-ray diffraction (XRD) pole figure measurements. The effect of texture on the nuclear and the magnetic SANS signal during the precipitation kinetics was included in the data analysis. This enables us to monitor the temperature dependence of the precipitation kinetics for the Au-rich precipitates in the Fe-Au-W alloy during aging at temperatures of 650, 675 and 700 degrees C. It is found that an increase in aging temperature results in a faster kinetics and a lower final precipitate fraction.

Phosphorus recovery via vivianite extraction from digested sludge has recently gained considerable interest. The separation of vivianite was demonstrated earlier at the pilot scale, and operational parameters were optimized. In this study, we tested the robustness of this technology by changing the sludge characteristics, such as dry matter, and via that, sludge viscosity, and vivianite particle size. It was proven that the main factor influencing recovery was the concentration of vivianite in the feed. The technology can extract vivianite even when the sludge has higher dry matter (1.8% - 3.3%) and, therefore, higher viscosity. Smaller vivianite sizes (< 10 µm) can still be recovered but at a lower rate. This made magnetic separation applicable to a wide range of wastewater treatment plants.

The transition-metal based alloy system YNi4-xCoxSi shows a second-order ferromagnetic-to-paramagnetic transition near room temperature. Here, the magnetic structure, the magnetocaloric properties and the magnetic anisotropy of YNi4-xCoxSi (x = 0-4) are investigated. For x = 3.5, 3.75 and 4.0 a Curie temperature near room temperature is observed with TC = 250, 283 and 310K, respectively. In orientated YNi4-xCoxSi powder samples the c axis of the hexagonal crystal structure is found to be the easy magnetic axis, with a large dominant K2 anisotropy constant (K2 > K1 > 0). The magnetic structure and the preferred atomic position for Ni are demonstrated by neutron diffraction measurements. We have found a dramatic decrease in the magnetic moment at the 3g site in the CaCu5-type structure (space group P6/mmm), the saturation magnetization and the Curie temperature with increasing Ni concentration.

Iron oxide-based adsorbents showed potential to reach ultra-low phosphorus (P) concentrations to prevent eutrophication and recover P. High affinity, high capacity at low P concentrations (<1 mg L-1), good stability, and reusability of the adsorbent are key factors for economic viability. In this study, nanoparticles of goethite (alpha-FeOOH), a highly stable phase, have been synthesized with increasing Zn2+-doping, 0-20 %at. Zn/Fe, to manipulate the surface properties, following the results of a previous work. M & ouml;ssbauer spectroscopy showed preserved goethite phase and increased point of zero charge (pzc) at low Zn-doping percentages, while at higher percentages (>5%at.) co-existing phases with increased specific surface area formed. Low concentrations (0.1-10 mg L-1) batch adsorption tests showed increased P removal per unit mass with increasing doping. However, the highest pzc, affinity and P removal per unit area were observed for the 5%at. doped sample, suggesting this dopant concentration to provide the most effective surface. A regeneration test, performed at a lower pH than usual, showed preserved, even improved P desorption with increasing doping. M & ouml;ssbauer spectroscopy showed that the nanoparticle phase and composition, up to 5%at., doping was preserved throughout the process. These results are promising to develop a stable effective Zn-doped goethite-based adsorbent for P recovery at ultra-low concentrations.

Structural, magnetic and magnetocaloric properties of Mn3Sn1-xZnxC antiperovskite carbides have been studied. With increasing Zn content the first-order magnetic transition (FOMT) is weakened. The Curie temperature (T-C) reduces first from 273 to 197 K and when x > 0.3, T-C increases, reaching its maximum of 430 K for x = 1.0. An increase in T-C is accompanied by pronounced changes in magnetic behaviour and a significant rise in magnetization from 21.82(4) to 76.2(2) Am(2)kg(-1) for x = 0.8 in the maximum applied magnetic field of 5 T. Neutron powder diffraction (NPD) was employed to study the magnetic structure of Mn3Sn1-xZnxC compounds. The refinement of the NPD data for x = 0.3 revealed a magnetic structure with propagation vector k = (1/2,1/2,0) with a decrease in the canted antiferromagnetic (AFM) moment, which results in a reduction of the negative volume change at the magnetic transition and a decrease in the magnetocaloric effect (MCE). For x = 0.4, the magnetic structure is described by a propagation vector k = (1/2,1/2,1/2) for the AFM moment which dominates at low temperature, with the presence of a minor ferromagnetic (FM) component with a k = (0, 0, 0) propagation vector, which confirms the presence of the ferrimagnetic (FiM) state. For a higher Zn content (x = 0.6), the magnetic moment originates mainly from the FM component found on three independent Mn positions and an additional AFM moment oriented in the a-b plane. The results presented confirm the presence of competing AFM-FM interactions in Mn3Sn1-xZnxC antiperovskite carbides.

The effect of the heat treatment on the magnetism, magnetocaloric effect and microstructure formation has been systematically studied in Fe-rich (Mn,Fe) y (P,Si) melt-spun ribbons (1.80 ≤ y ≤ 2.00). XRD, SEM and EDS measurements demonstrate that a metal deficiency prompts the stable (Mn,Fe)Si phase, whereas in the metal-rich region the (Mn,Fe)3Si phase is formed. It is found that the annealing temperature influences the composition and lattice parameters of the (Mn,Fe) y (P,Si) alloys, which greatly affects the Curie temperature (TC). For the optimal metal/non-metal ratio y the magnetic entropy change (|ΔSm|) is found to increase from 5.5 to 15.0 Jkg-1K-1 in a magnetic field change of 2 T by varying the annealing temperature from 1313 to 1433 K, indicating an enhancement of the first-order magnetic transition (FOMT). The presented results reveal that the secondary phase and magnetic properties in the (Mn,Fe) y (P,Si) system can be tuned by varying the annealing temperature and by adjusting the metal/non-metal ratio y.

Hybrid anion exchange adsorbents (HAIX) seem promising to prevent eutrophication and recover phosphate (P). HAIX consist of an anion exchange resin (AIX) backbone, promoting anion physisorption (outer-sphere complex), impregnated with iron (hydr)oxide nanoparticles (NPs), for selective P chemisorption (inner-sphere complex). In this work, for the first time, as far as we know, Zn-doped iron (hydr)oxide NPs were embedded in AIX, and the performances compared with conventional HAIX, both commercial and synthesized. Zn-doped HAIX displayed improved P adsorption performances. Mo center dot ssbauer spectroscopy (MS) revealed the goethite nature of the NPs, against the "amorphous hydrous ferric oxide" claimed in literature. The P adsorption comparisons, made in synthetic solution and real wastewater, underlined the crucial role of the NPs for selective P adsorption, while improving the understanding on the competition between physisorption and chemisorption. In pure P synthetic solutions, especially at high P concentrations, physisorption can "hide" chemisorption. This depends also on the anion form of the AIX, due to their higher affinity for multivalent anions, which affects HAIX adsorption selectivity and P desorption. In fact, a mild alkaline regeneration over three adsorption-desorption cycles revealed a complex interaction between the regenerant OH  and the adsorbed P. OH  molecules are consumed to transform phosphate speciation, causing (stronger) P re-adsorption and preventing desorption. Finally, Mo center dot ssbauer spectroscopy revealed NPs agglomeration/growth after the three cycles plus final regeneration at pH 14. This study provides further understanding on the P adsorption-desorption mechanism in HAIX, drawing attention on the choice of experimental conditions for reliable performance assessment, and questioning HAIX consistent P removal and efficient P recovery in the long-term.

Phosphorus (P) removal from freshwater bodies to ultra-low concentrations is fundamental to prevent eutrophication, while its recovery is necessary to close the P usage cycle. Iron oxide-based adsorbents seem promising candidates, being abundant, cheap, and easy to synthesize compounds, with good affinity for P. Affinity is the key parameter when targeting ultra-low concentrations. Also, adsorbent regeneration and re-use is fundamental for the economic viability, hence the adsorbent stability is important. Goethite, (α-FeOOH), is one of the most stable iron (Fe3+) (hydr)oxide species, with higher affinity, but lower adsorption capacity (per kg) compared to other species. Doping could change goethite surface properties, to boost the adsorption capacity, while preserving the high stability and affinity for P. In this work, pure goethite was compared to goethite doped (5%at.) with different elements of different preferential oxidation states: Zn2+, Mn3+, and Zr4+. Doping was successfully achieved for all elements, albeit Zr showed a lower Fe substitution than targeted. Zn doping increased the goethite point of zero charge and adsorption capacity (per mass and per surface area), preserving the high affinity, while Mn- and Zr- doping displayed a decrease in all the parameters. These could be explained with surface protonation as a charge compensation mechanism in Zn2+-for-Fe3+ substitution. The regeneration test showed improved P recovery for Zr- and Zn-doped goethite. All samples remained stable throughout the whole process. This work provides promising insights on doping as a strategy to manipulate iron oxides surface properties and for developing a highly performing and long-lasting goethite-based adsorbent.

The influence of chromium and aluminium doping on the over-reduction during activation of iron-oxide-based water-gas shift catalysts was investigated using Mössbauer spectroscopy for the first time. In situ Mössbauer spectra of catalysts exposed to industrially relevant gas compositions were recorded with increasingly reducing R factors R = [CO]*[H2]/[CO2]*[H2O]. Whereas α-Fe and cementite formed during exposure of a non-doped iron-oxide catalyst to process conditions with an R factor of 2.09, such phases were only observed at R = 4.60 for a chromium-doped catalyst, showing that chromium stabilizes the catalyst. Over-reduction was enhanced to R = 2.88 in a chromium-copper co-doped catalyst. α-Fe was already observed at R = 1.64 in an aluminium-doped catalyst, while cementite formation occurred at R = 2.09, showing that over-reduction was enhanced, the presence of aluminium delaying carburization. Co-doping copper in the aluminium-doped catalyst showed cementite formation at R = 2.09, the same as a non-doped catalyst.

The all-d-metal $\mathrm{Ni}\text{\ensuremath{-}}(\mathrm{Co})\text{\ensuremath{-}}\mathrm{Mn}\text{\ensuremath{-}}\mathrm{Ti}$-based Heusler alloys are found to show a giant magnetocaloric effect near room temperature and are thereby potential materials for solid-state refrigeration. However, the relative large thermal hysteresis and the moderate ferromagnetic magnetization provides limitations for real applications. In the present study, we demonstrate that introducing interstitial B atoms within ${\mathrm{Ni}}_{36.5}{\mathrm{Co}}_{13.5}{\mathrm{Mn}}_{35}{\mathrm{Ti}}_{15}$ alloys can effectively decrease the thermal hysteresis \ensuremath{\Delta}${T}_{\mathrm{hys}}$ (down to 4.4 K), and simultaneously improve the saturation magnetization (maximum 40% enhancement) for low concentrations of B doping (up to 0.4 at. %). In comparison to the undoped reference material, the maximum magnetic entropy change (\ensuremath{\Delta}${S}_{m}$) for the ${\mathrm{Ni}}_{36.5}{\mathrm{Co}}_{13.5}{\mathrm{Mn}}_{35}{\mathrm{Ti}}_{15}{\mathrm{B}}_{0.4}$ alloy shows a remarkable improvement from 9.7 to 24.3 J ${\mathrm{kg}}^{\ensuremath{-}1}\phantom{\rule{0.25em}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}$ for an applied magnetic field change (\ensuremath{\Delta}${\ensuremath{\mu}}_{0}H$) of 5 T (30.2 J ${\mathrm{kg}}^{\ensuremath{-}1}\phantom{\rule{0.25em}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}$ for \ensuremath{\Delta}${\ensuremath{\mu}}_{0}H$ = 7 T). Additionally, due to the obtained low thermal hysteresis \ensuremath{\Delta}${T}_{\mathrm{hys}}$, the maximum reversible \ensuremath{\Delta}${S}_{m}^{\mathrm{rev}}$ amounts to 18.9 J ${\mathrm{kg}}^{\ensuremath{-}1}\phantom{\rule{0.25em}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}$ at 283 K for \ensuremath{\Delta}${\ensuremath{\mu}}_{0}H$ = 5 T (22.0 J ${\mathrm{kg}}^{\ensuremath{-}1}\phantom{\rule{0.25em}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}$ at 281 K for \ensuremath{\Delta}${\ensuremath{\mu}}_{0}H$ = 7 T), which is competitive to the traditional $\mathrm{Ni}\text{\ensuremath{-}}\mathrm{Mn}$-$X$-based Heusler alloys (X = $\mathrm{Ga}$, $\mathrm{In}$, $\mathrm{Sn}$, $\mathrm{Sb}$). The enhancement of the magnetic moments by B doping is also observed in first-principles calculations. These calculations clarify the atomic occupancy of B and the changes in the electronic configuration. Our current study indicates that interstitial doping with a light element (boron) is an effective method to improve the magnetocaloric effect in these all-d-metal $\mathrm{Ni}\text{\ensuremath{-}}\mathrm{Co}\text{\ensuremath{-}}\mathrm{Mn}\text{\ensuremath{-}}\mathrm{Ti}$-based magnetic Heusler compounds.

Constant stress creep experiments at 550 degrees C were performed on a high-purity Fe-3Au-4W (wt.%) ternary alloy with about 1 at.% supersaturation for Au and W in order to study self healing of grain-boundary cavities by both Au-rich and W-rich precipitates. Using synchrotron X-ray nano-tomography, the development of the creep cavities and the healing precipitates at different stages of creep was visualised using two spatial resolutions (30 and 100 nm voxel size) for separate samples taken after different loading times. The healing kinetics was found to strongly depend on the nucleation time of the cavities. Cavities nucleated at an early stage of creep could be fully healed, while the healing of the late-nucleated cavities is much slower due to a decrease in the diffusional flux of the healing supersaturated solutes over time, as a result of ( i ) a decrease in inter-cavity spacing caused by cavity nucleation and ( ii ) a gradual depletion of the supersaturated solutes near the grain boundaries. The interaction between the competing healing mechanisms for creep cavities by Au-rich and W-rich precipitates is discussed. It was found that Au-rich precipitates are formed much faster than the W-rich precipitates, and thereby effectively provide creep damage healing on different time scales.(c) 2022 The Author(s). Published by Elsevier Ltd on behalf of Acta Materialia Inc. This is an open access article under the CC BY license ( http://creativecommons.org/licenses/by/4.0/ )

In view of the interest that (Fe,Co)2(P,Si) compounds have as potential permanent magnets, their structural and magnetic phase diagrams are explored focusing on establishing the range where the hexagonal Fe2P-type structure is observed. In Fe1.93-xCoxP1-ySiy, the highest Si content prior entering a mixed phase domain is y ≈ 0.5. At high Si content but low Co for Fe substitutions, a structural distortion leading to a body-centered orthorhombic structure occurs. At high Co contents, when the Fe2P unit cell reaches a critical volume of about 102.4 Å3, the samples crystallize in a Co2P-type orthorhombic structure. Within the Fe2P-type structural range, the evolution of the unit-cell volume appears to follow the Vegard's law, but this hides strongly anisotropic changes. Simultaneous Co for Fe and Si for P substitutions increase the range where the hexagonal structure is observed in comparison to ternary Fe2(P,Si) and (Fe,Co)2P. The samples are ferromagnetic, but with Curie temperatures showing an unusual evolution, uncorrelated to the c/a ratio of the lattice parameters. At low Si content, TC increases with Co for Fe substitutions. For y = 0.2, the evolution is not significant, while at high Si content TC systematically decreases with the increase in Co. Large Si and Co substitutions lead to a swift weakening of the magnetocrystalline anisotropy until the easy axis anisotropy turns from the c axis toward the a-b plane. This study guides future investigations by restricting the range where desirable properties for permanent magnetic applications can be expected to 0.1 ≲ x ≲ 0.3 and 0.1 ≲ y ≲ 0.3.

A set of doped iron oxides (chromium, aluminum, gallium, indium, manganese, zinc, niobium) were prepared by a one-step coprecipitation/calcination approach evaluated for their WGS activity under industrially relevant conditions and characterized in detail. The WGS activity after ageing the doped catalyst for 4 days at 25 bar follows the order chromium approximate to aluminum > gallium > indium > manganese > zinc > niobium for copper-codoped catalysts. The activated catalysts predominantly consist of magnetite, irrespective of the dopant. Mo''ssbauer spectra of aged catalysts showed that aluminum and zinc occupy both tetrahedral and octahedral sites of magnetite, while chromium, gallium, indium, manganese, and niobium preferentially substitute octahedral iron. The incorporation of trivalent metal ions of similar size to octahedral Fe3+ (i.e., chromium, aluminum, gallium) results in moderate to high CO conversion, irrespective of incorporation in tetrahedral or octahedral sites. The substitution of Fe2+ with Mn2+ results in an increased Fe3+/Fe2+ ratio. Incorporation of Zn2+ in tetrahedral sites (replacing Fe3+ ions) leads to a complex structure where the charge balance is compensated from the octahedral sites. Separate dopant metal oxide phases were observed in indium-and niobium-doped catalysts. XPS shows that copper is present as a separate phase in activated copper-codoped catalysts. Aluminum is identified as the most promising promoter for substituting chromium in commercial high-temperature WGS catalysts on the basis of their similar high CO conversion although incorporation of these dopants into the magnetite structure differed substantially.

While rare-earth magnets exhibit unchallenged hard-magnetic properties, looking for alternatives based on inexpensive elements of non-critical supply remains of utmost interest. Here, we demonstrate that (Fe,Co)(2)(P,Si) single crystals combine a large magnetocrystalline anisotropy ( K-1 approximate to 0.9 MJ m(-3) at 300 K), high Curie temperatures (TC up to 560 K) and an appreciable saturation specific magnetization (101 A m(2) kg(-1)) leading to a theoretical |BH|(max) approximate to 165 kJ m(-3) , making them promising candidate materials as rare-earth-free permanent magnets. Our comparison between (Fe,Co)(2)P and (Fe,Co)(2)(P,Si) single crystals highlights that Si substitution reduces the low-temperature magnetocrystalline anisotropy, but strongly enhances T-C, making the latter quaternary alloys most favorable for room temperature applications. Submicron-sized particles of Fe1.75Co0.20P0.75Si0.25 were prepared by a top-down ball-milling approach. While the energy products of bonded particles are to this point modest, they demonstrate that perma-nent magnetic properties can be achieved in (Fe,Co)(2)(P,Si) quaternary alloys. This work correlates the de-velopment of permanent magnetic properties to a control of the microstructure. It paves the way toward the realization of permanent magnetic properties in (Fe,Co)(2)(P,Si) alloys made of economically competi-tive Fe, P and Si elements, making these materials desirable for applications. (c) 2021 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

The precipitation of supersaturated solutes at free surfaces in ternary Fe–3Au–4W and binary Fe–3Au and Fe–4W alloys (composition in weight percentage) for different ageing times was investigated at a temperature of 700 °C. The time evolution of the surface precipitation is compared among the three alloys to investigate the interplay between the Au and W solutes in the ternary system. The Au-rich grain-interior surface precipitates show a similar size and kinetics in the Fe–Au–W and Fe–Au alloys, while the W-rich grain-interior surface precipitates show a smaller size and a higher number density in the Fe–Au–W alloy compared to the Fe–W alloy. The kinetics of the precipitation on the external free surface for the ternary Fe–Au–W alloy is compared to the previously studied precipitation on the internal surfaces of the grain-boundary cavities during creep loading of the same alloy. Graphical abstract

The physical properties of the extensively studied Fe2P material family, well-known for its promising magnetocaloric qualities are greatly influenced by the unit-cell parameters of this hexagonal system. This sensitivity of the various magnetocaloric properties to structural parameters is particularly important for developing a material suitable for room-temperature magnetic refrigeration. A change in the unit cell, due to added elements can induce pronounced changes in the Curie temperature and the nature of the magnetic phase transition. Li belongs to a yet unexplored group of possible dopant elements - alkali metals, and exhibits an unusual behavior upon introduction to Fe2P. We observe a preference to replace iron atoms, as opposed to the common tendency of nonmagnetic dopants to replace phosphorus, leading to a strong influence on the magnetic structure. The addition of Li introduces a deformation of the unit cell with a small change in volume and a decrease in c/a ratio, while the same crystallographic phase is maintained over a relatively wide concentration range. We show that lithium has an exceptionally strong effect on the Curie temperature of Fe2P reaching 800 K at 20% Li compared to 240 K for the undoped material.

Autonomous healing of creep-induced grain boundary cavities by Au-rich and W-rich precipitates was studied in a Fe-3Au-4W (wt pct) alloy at a fixed temperature of 823 K (550 °C) with different applied stresses. The ternary alloy, with two supersaturated healing solutes, serves as a model system to study the interplay between two separate healing agents. The creep properties are evaluated and compared with those of the previously studied Fe-Au and Fe-W binary systems. The microstructures of the creep-failed samples are studied by electron microscopy to investigate the cavity filling behavior and the mass transfer of supersaturated solute to the defect sites. Compared to the Fe-Au and Fe-W alloys, the new Fe-Au-W alloy has the lowest steady-state strain rate and the longest lifetime. The site-selective filling of the creep-induced cavities is attributed to two different categories of precipitates: micron-sized Au-rich precipitates and nano-sized W-rich precipitates. The Au-rich precipitates are found capable to fully heal the cavities, while the W-rich precipitates show only a limited degree of healing. The two types of precipitates show a reluctance to coexistence, and the formation of W-rich precipitates is suppressed strongly. A model is proposed to describe the competitive healing behavior of the Au-rich and W-rich precipitates.

We report on a study on a representative set of Fe$_{2}$P-based MnFePSi samples by means of $^{55}$Mn NMR in both zero and applied magnetic field. The first-order nature of the magnetic transition is demonstrated by truncated order parameter curves with a large value of the local ordered moment at the Curie point, even at compositions where the transition appears second order from magnetic measurements. No weak ferromagnetic order could be detected at Si-poor compositions showing the kinetic arrest phenomenon, but rather the phase separation of fully ferromagnetic domains from volume fractions where Mn spins are fluctuating. The more pronounced decrease of the ordered moment at the $3f$ sites on approaching $T_C$, characteristic of the mixed magnetism of these materials, is demonstrated to be driven by a vanishing spin density rather than enhanced spin fluctuations at the $3f$ site. An upper limit of 0.03~$\mu_B$ is set for the fluctuating Mn moment at the $3f$ site by the direct detection of a $^{55}$Mn NMR resonance peak in the Mn-rich samples above $T_C$, showing nearly temperature-independent frequency shifts. A sharper secondary peak observed at the same compositions reveals however the disproportionation of a significant $3f$-Mn fraction with negligible hyperfine couplings, which retains its diamagnetic character across the transition, down to the lowest available temperatures. Such a diamagnetic fraction qualitatively accounts for the reduced average $3f$ moment previously reported at large Mn concentrations.

We report on a study on a representative set of FeP-based MnFePSi samples by means of Mn NMR in both zero and applied magnetic field. The first-order nature of the magnetic transition is demonstrated by truncated order parameter curves with a large value of the local ordered moment at the Curie point, even at compositions where the transition appears second order from magnetic measurements. No weak ferromagnetic order could be detected at Si-poor compositions showing the kinetic arrest phenomenon, but rather the phase separation of fully ferromagnetic domains from volume fractions where Mn spins are fluctuating. The more pronounced decrease of the ordered moment at the $3f$ sites than at the $3g$ sites on approaching ${T}_{C}$, characteristic of the mixed magnetism of these materials, is shown to be driven by the drop of the $3f$ spin density instead of enhanced spin fluctuations. The temperature-driven $3f$ spin extinction is demonstrated to evolve into a truly nonmagnetic state of the $3f$ Mn ions well above ${T}_{C}$, in agreement with theoretical models and in contrast with previous experiments who detected just a partial moment quenching. Besides ``normal'' $3f$ Mn ions undergoing a magnetic to spinless state transition, NMR in Mn-rich compositions detects the disproportionation at $3f$ sites of a significant minority Mn fraction with negligible hyperfine couplings, which retains its diamagnetic character independent of temperature. Such a diamagnetic fraction qualitatively accounts for the reduced average $3f$ moment previously reported at large Mn concentrations.