Substitution Of Fe For Mn Research Articles

Large magnetocaloric effect and negative thermal expansion of Mn-Ni-Si-Fe-Co-Ge high-entropy alloys

Magnetocaloric high-entropy alloys (HEAs) with a vast compositional space have attracted significant interest for some time due to their great potential in multifunctional application. However, magnetocaloric HEAs generally exhibit modest magnet-entropy change as their undergo second-order phase transition. This work focuses on designing MM'X (M, M′ = transition metals, X = main group elements) HEAs undergoing magnerostructural transition to achieve great magnetocaloric response. For this purpose, MnxFe1-xNi0.6Co0.4Si0.62Ge0.38 (x = 0.43, 0.45, 0.48, 0.50) with intriguingly crystallographic texture are successfully synthesized and their magnetocaloric effect and negative thermal expansion (NTE) are investigated. The substitution of Fe for Mn reduces the transition temperature (Tt) so that weakens the first-order transition of MM'X HEAs. Besides, Mn0.55Fe0.45Ni0.6Co0.4Si0.62Ge0.38 undergoing first-order transition from Ni2In-paramagnetic-austenitic phase to TiNiSi-ferromagnetic-martensitic phase exhibits a great magnetic entropy change of 16 J∙kg−1K−1 at 206 K for 2 T. Moreover, an obviously NTE is observed through phase transition with liner NTE coefficient of −6.77×10−6 K−1. In addition, Mn0.55Fe0.5Ni0.6Co0.4Si0.62Ge0.38 displays an intriguing NTE with liner NTE coefficient of −1401.7×10−6 K−1 (220–270 K) along the direction parallel to field in a temperature range from 220 K to 270 K, which is much higher than typical NTE materials. Therefore, the present work demonstrates that MM'X HEAs exhibit potential to achieve some magnetocaloric and NTE multifunctional application.

Pivotal Role of Intersite Hubbard Interactions in Fe-Doped α-MnO2

We present a first-principles investigation of the structural, electronic, and magnetic properties of the pristine and Fe-doped $\alpha$-MnO$_2$ using density-functional theory with extended Hubbard functionals. The onsite $U$ and intersite $V$ Hubbard parameters are determined from first principles and self-consistently using density-functional perturbation theory in the basis of L\"owdin-orthogonalized atomic orbitals. For the pristine $\alpha$-MnO$_2$ we find that the so-called C2-AFM spin configuration is the most energetically favorable, in agreement with the experimentally observed antiferromagnetic ground state. For the Fe-doped $\alpha$-MnO$_2$ two types of doping are considered: Fe insertion in the $2 \times 2$ tunnels and partial substitution of Fe for Mn. We find that the interstitial doping preserves the C2-AFM spin configuration of the host lattice only when both onsite $U$ and intersite $V$ Hubbard corrections are included, while for the substitutional doping the onsite Hubbard $U$ correction alone is able to preserve the C2-AFM spin configuration of the host lattice. The oxidation state of Fe is found to be $+2$ and $+4$ in the case of the interstitial and substitutional doping, respectively, while the oxidation state of Mn is $+4$ in both cases. This work paves the way for accurate studies of other MnO$_2$ polymorphs and complex transition-metal compounds when the localization of $3d$ electrons occurs in the presence of strong covalent interactions with ligands.

Feasibility and Limitations of High-Voltage Lithium-Iron-Manganese Spinels

Positive electrodes with high energy densities for Lithium-ion batteries (LIB) almost exclusively rely on toxic and costly transition metals. Iron based high voltage spinels can be feasible alternatives, but the phase stabilities and optimal chemistries for LIB applications are not fully understood yet. In this study, LiFexMn2-xO4 spinels with x = 0.2 to 0.9 were synthesized by solid-state reaction at 800 °C. High-resolution diffraction methods reveal gradual increasing partial spinel inversion as a function of x and early secondary phase formation. Mössbauer spectroscopy was used to identify the Fe valences, spin states and coordination. The unexpected increasing lattice parameters with Fe substitution for Mn was explained considering the anion-cation average bond lengths determined by Rietveld analysis and Mn3+ overstoichiometries revealed by cyclic voltammetry. Finally, galvanostatic cycling of Li-Fe-Mn-spinels shows that the capacity fading is correlated to increased cell polarization for higher upper charging cut-off voltage, Fe-content and C-rate. The electrolyte may also contribute significantly to the cycling limitations.

Effect of iron substitution in cryptomelane on the heterogeneous reaction with isoprene

Biogenic isoprene is an important pollutant for regional air quality. Being ubiquitously distributed on the earth surface, manganese (hydr)oxides should play a vital role in the transformation of isoprene. Cryptomelane is a typical manganese oxide with isomorphous substitution of Fe for Mn, but less attention has been paid to its heterogeneous reaction with isoprene. When Fe3+ replaces Mn3+, K+ is depleted and Mn3+ is oxidized to Mn4+. In contrast, oxygen vacancies are formed when Fe3+ substitutes Mn4+. Fe substitution creates weak crystallites and abundant mesopores, resulting in the increase of isoprene adsorption. As found by theoretical calculations, the Mn4+–O2- bonds at the cross sections of the tunnels is more active than that on the outer wall of the tunnels. After the adsorption of isoprene, bridging carboxylate species and hydrogen-bonding water are produced and the surface octahedra are distorted, i.e., Mn4+O6 → Mn3+O6-δ. As the heat facilitates the breakage of Mn4+–O2-, the increase of environmental temperature enhances the oxidation of isoprene. The above findings shed light on the effect of Fe substitution in cryptomelane to enhance the oxidation of isoprene, and illustrates that heterogeneous reaction with isoprene impairs the transformation of other environmental substances on cryptomelane.

Fe substitution for Mn in Rhombohedral La0.8Sr0.2Mn1−xFexO3 — the Structural, Magnetic, and Magnetocaloric Properties

Fe substitution for Mn in Rhombohedral La0.8Sr0.2Mn1−xFexO3 — the Structural, Magnetic, and Magnetocaloric Properties

Synthesis, structural, and magnetic properties of Heusler-type Mn2-xFe1+xGe (0.0 ≤ x ≤ 1.0) alloys

Bulk Mn2-xFe1+xGe (0.0 ≤ x ≤ 1.0) alloys have been synthesized by arc-melting followed by a low temperature homogenization thermal annealing, whereas for comparison purposes the Mn2FeGe alloy was also produced in ribbon form by rapid solidification. A study of the structural and magnetic properties is presented. Contrary to theoretical predictions, Mn2FeGe crystallizes in a hexagonal DO19 crystal structure (space group P63/mmc) and orders ferromagnetically with a saturation magnetization (MS) value of ~1.7 µB/f.u. in the ground state. With the substitution of Fe for Mn in bulk Mn2-xFe1+xGe, we observed an increase in the FM interactions with a maximum MS value of 5.1 µB/f.u. for x = 1.0, and a significant progressive increase in the Curie temperature (TC) in a wide range spanning ~200 K to over 400 K.

Enhanced multiferroic characteristics in hexagonal ScMn1−xFexO3 ceramics

In the present study, enhanced antiferromagnetic characteristics and room temperature magnetoelectric coupling are achieved by Fe-substitution for Mn in h-ScMnO3. The antiferromagnetic Néel temperature (TN) increases from 131 K for ScMnO3 up to 140 K for ScMn0.8Fe0.2O3. Electric field controlled magnetism is confirmed for ScMn0.8Fe0.2O3 at room temperature, combining with the short-range magnetic spin ordering. The Rietveld structural refinement and selected area electron diffraction confirm the noncentrosymmetric P63cm structure for the present ceramics. The ferroelectric domain walls at the atomic scale are determined by the aberration-corrected high-angle annular dark-field scanning transmission electron microscopy; meanwhile, the spontaneous polarization of 5.6 μC/cm2 is determined. The noticeable magnetoelectric coefficient αME ∼ 0.78 mV/cm Oe (measured under a magnetic field up to 3000 Oe) is obtained in ScMn0.8Fe0.2O3, which is quite stable with the applied magnetic field, reflecting coupling of the short-range spin ordering with the ferroelectric ordering. The enhanced antiferromagnetic behaviors are discussed with the effect of Fe-substitution, which reduce the magnetic frustration and enhance the exchange interaction.

Influence of magnetic field, chemical pressure and hydrostatic pressure on the structural and magnetocaloric properties of the Mn–Ni–Ge system

The magnetic, structural and thermomagnetic properties of the MM’X material system of MnNiGe are evaluated with respect to their utilization in magnetocaloric refrigeration. The effects of separate and simultaneous substitution of Fe for Mn and Si on the Ge site are analysed in detail to highlight the benefits of the isostructural alloying method. A large range of compounds with precisely tunable structural and magnetic properties and the tuning of the phase transition by chemical pressure are compared to the effect of hydrostatic pressure on the martensitic transition.We obtained very large isothermal entropy changes of up to J based on magnetic measurements for (Mn,Fe)NiGe in moderate fields of 2 T. The enhanced magnetocaloric properties for transitions around room temperature are demonstrated for samples with reduced Ge, a resource critical element. An adiabatic temperature change of 1.3 K in a magnetic field change of 1.93 T is observed upon direct measurement for a sample with Fe and Si substitution. However, the high volume change of 2.8% results in an embrittlement of large particles into several smaller fragments and leads to a sensitivity of the magnetocaloric properties towards sample shape and size. On the other hand, this large volume change enables to induce the phase transition with a large shift of the transition temperature by application of hydrostatic pressure (72 K ). Thus, the effect of 1.88 GPa is equivalent to a substitution of 10% Fe for Mn and can act as an additional stimulus to induce the phase transition and support the low magnetic field dependence of the phase transition temperature for multicaloric applications.

Effect of substitution of Fe for Mn on the structural, magnetic properties and magnetocaloric effect of LaNdSrCaMnO 3

Abstract We have studied the structural, magnetic and magnetocaloric properties of La0.6Nd0.1Sr0.15Ca0.15Mn1−xFexO3 (LNSCMFex) perovskite samples. The samples were synthesized using the solid-state reaction at high temperature and were analyzed by XRD data based on the Rietveld refinement technique. LNSCMFex samples crystallized in orthorhombic symmetry with Pnma space group. Besides, the curves of magnetization reveals that all samples exhibit a magnetic transition from the paramagnetic to ferromagnetic phase at the Curie temperature TC, which decreases from 327 K to 296 K with the increase of the Fe doping level from x=0 to x=0.1. The thermal evolution of magnetization in the ferromagnetic phase at low temperature varies as T3/2 in accordance with Bloch's law. The magnitude of the isothermal magnetic entropy, (− Δ S M max ), at the FM Curie temperature increases from 3.79 J/kg K for x=0 composition to 5.8 J/kg K for x=0.1, under a magnetic field of 5 T. For an applied magnetic field of 5 T, the relative cooling power (RCP) values are found to vary between 173.66 and 231.76 J/kg. These results suggest that these materials could be used as an active magnetic refrigerant around room temperature.

Electronic structure and magnetic properties of Mn, Co, and Ni substitution of Fe in Fe4N

The magnetic properties of Mn, Co and Ni substituted Fe4N are calculated from first principles theory. It is found that the generalized gradient approximation reproduces with good accuracy the magnetic moment and equilibrium volume for the parent Fe4N structure, with the atomic moment largest for the Fe atom furthest away from the N atom (Fe I site), approaching a value of 3 muB/atom, whereas the Fe atom closer to the N atom (Fe II site) has a moment closer to that of bcc Fe. Substitution of Fe for Mn, Co or Ni, shows an intricate behavior in which the Mn substitution clearly favors the Fe II site, Ni favors substitution on the Fe I site and Co shows no strong preference for either lattice site. Ni and Co substitution results in a ferromagnetic coupling to the Fe atoms, whereas Mn couples antiferromagnetically on the Fe II site and ferromagnetically on the Fe I site. For all types of doping, the total magnetic moment is enhanced compared with Fe4N only in the energetically very unfavorable case of Mn doping at the Fe I site.

Suppression of the long-range magnetic order in Pb3(Mn1−xFex)7O15 upon substitution of Fe for Mn

Structure and magnetic properties of Pb3(Mn1−xFex)7O15 single crystals with х=0–0.2 grown by spontaneous crystallization from solution in melt have been investigated. All the crystals belong to the hexagonal space group P63/mcm. The magnetic properties appeared to be strongly dependent on the iron doping level. At small (х=0.05) dopant concentrations, the value of magnetization and Neel temperature TN decrease insignificantly (TN=70K). With increasing х, the three-dimensional magnetic ordering does not occur and temperature dependences of magnetization at х≥0.1 exhibit spin-glass-like features in the low-temperature region.

Magnetic properties of NdMn1-xFexO3+δsystem

Magnetization, AC susceptibility and specific heat measurements were performed on polycrystalline NdMn1-xFexO3+δ compounds (x = 0.0, 0.1 and 0.2). Substitution of Fe for Mn reduces the Néel temperature TN, which is associated with magnetic ordering of Mn sublattice, from 85.5 K to 57.0 K. The temperature dependence of magnetization for x = 0.2 exhibits the compensation temperature and the pole inversion below Tcomp = 26.7(5) K. Initial magnetization curves present a remnant magnetization in the ordered region with the sign of remnant magnetization depending on temperature. The substitution of Fe for Mn changes hysteresis loop of NdMnO3+δ from the ferromagnetic-like one (μ0Hc = 0.09 T) by expanding the width of the loop (μ0Hc = 0.55 T) for x = 0.1 and then shrinking the central part of the loop to “butterfly” type (μ0Hc = 0.35 T) for x = 0.2.

Dualistic distribution coefficients of elements in the system mineral-hydrothermal solution. II. Gold in magnetite

The system magnetite-Au-hydrothermal solution was employed to continue studying the distribution coefficients of trace elements in system with real crystals. The role of surface nonautonomous phase (NP) is elucidated. The distribution coefficient of an Au structural admixture between magnetite and hydrothermal solution at the experimental conditions [450°C, 1 kbar (100 MPa), and fluid sampling by a trap] is, according to the most representative data, 1.0 ± 0.3, and Au is thus not an incompatible element in magnetite, in contrast to pyrite and arsenopyrite [1], minerals for which this coefficient is much lower than one. The NP is enriched in Au with respect to the rest of the crystal by a factor of more than 4000, and this results in an one order of magnitude increase in the bulk distribution coefficient. Similar to pyrite, the reason for the dualistic nature of the distribution coefficient is the presence of an NP, which contains ∼2000 ± 500 ppm Au. The NP occupies the approximately 330-nm surface layer of the crystal, and the chemically bound Au [Au(III), according to XPS data] admixture is evenly distributed with depth within the layer, which is the reason for the strongly determinate dependences of the concentrations of the evenly distributed Au admixture on the size and specific surface area of the crystal. The occurrence of an NP is controlled by the chemistry of the system. The partial substitution of Fe for Mn and the synthesis of a phase close to jacobsite MnFe2O4 results in the disappearance of both the NP itself and the size dependence of the Au concentration. The XPS spectra of O 1s and Fe 2p are used to analyze two models: (i) a single goethite-like (O2−/OH−∼ 1) phase of variable composition and Fe in more than one valence state and (ii) a heterogeneous structure of alternating domains of wuestite- and goethite-like NP. The reason for the “excess” admixture in the former instance can be vacancies at Fe sites, whereas that in the latter one is the interaction of the admixture with nanometer-in-size nanometer in-size strained domains on the surface of the crystal.

Metallurgical origin of the effect of Fe doping on the martensitic and magnetic transformation behaviours of Ni 50Mn 40-xSn 10Fe x magnetic shape memory alloys

This study investigated the metallurgical origin of the effects of Fe substitution for Mn on the martensitic and the magnetic transformation behaviours of Ni 50Mn 40-xSn 10Fe x ( x = 0, 3, 4, 5, 6) alloys. Substitution of Fe for Mn at above 3 at% introduced an fcc γ phase in the microstructure. Formation of the γ phase influenced the composition of the bcc/B2 matrix, leading to decrease in martensitic transformation temperatures and transformation entropy change. The Curie temperature of the parent phase increased slightly, whereas the Curie temperature of the martensite increased rapidly with increasing Fe addition. Changes in the temperatures of the martensitic and magnetic transformations are confirmed to directly relate to the e/a ratio of the matrix caused by formation of γ phase. The minimum e/a ratio value for the occurrence of the martensitic transformation is estimated to be 8.045 for the alloy system studied. A narrow e/a ratio range of 8.113–8.137 is estimated for the occurrence of metamagnetic transformation M ( p a r a ) ⇔ A ( f e r r o ) . This metamagnetic reverse transformation was induced by a magnetic field at 225 K within a range of 3–7 T in the Ni 50Mn 35Sn 10Fe 5 alloy. The magnetic work required to induce the transformation is estimated to be ∼176 J/kg, comparable to the thermodynamic energy deficit for the transformation at the testing temperature estimated from thermal measurement. These findings clarify the origin of the effects of Fe doping in Ni 50Mn 40-xSn 10 alloys and provides reference on alloys design for this system.

Martensitic transition and magnetocaloric properties in Ni 45Mn 44− xFe xSn 11 alloys

The structural, martensitic transition and magnetocaloric effect in Heusler alloys Ni 45Mn 44− x Fe x Sn 11 ( x = 0, 2, 5 and 8) have been studied by means of XRD, SEM/EDS and magnetization measurements. The alloys with x = 2 and 5 exhibit the co-existence of orthorhombic (S.G. Pmma) martensite phase and cubic L2 1 structure (S.G. Fm-3m) austenite phase at room temperature. The martensitic transition temperature, M s , shows a non-monotonic dependence on the Fe content. M s increases from 265 K in the undoped alloy to 310 K with the addition of 2 at.% Fe, whereas further increase in Fe content to 5 and 8 at.% leads to the decrease of M s to 290 and 207 K. Substitution of Fe for Mn slightly increases the Curie temperature of austenite phase and the thermal hysteresis. Associated with the martensitic transition, the maximum magnetic entropy changes under a magnetic field change of 20 kOe are 10.6, 6.4 and 5.6 J/kg K for x = 0, 5 and 8, respectively.

EXAFS, XANES, and DFT study of the mixed-valence compoundYMn2O5: Site-selective substitution of Fe for Mn

In ${\text{YMn}}_{2}{\text{O}}_{5}$, the Mn atoms occupy two nonequivalent Wyckoff sites within the unit cell exhibiting different oxygen coordinations, i.e., the system can be characterized as a mixed-valence compound. For the formation of the orthorhombic crystal structure, Jahn-Teller distortions are assumed to play an important role. In this study, we aimed at the investigation of the crystal structure changes upon the substitution of Mn by the non-Jahn-Teller cation ${\text{Fe}}^{3+}$. Therefore, we synthesized a series of ${\text{YMn}}_{2\ensuremath{-}x}{\text{Fe}}_{x}{\text{O}}_{5}$ powder samples with $x=0$, 0.5, and 1 by a citrate technique. We utilized extended x-ray absorption fine structure (EXAFS) and x-ray absorption near-edge structure (XANES) analysis as well as density-functional theory (DFT) to investigate the two nonequivalent Wyckoff sites within the orthorhombic crystal structure (confirmed for all compositions) occupied by transition-metal atoms. For quantitative determination of structural short-range order, all plausible options of substitution of Fe for Mn are discussed. On the basis of these evaluations, the EXAFS and XANES behavior is analyzed and appropriate crystallographic weights are assigned to the subset of structural models in accordance with the experimental data. From EXAFS analysis, using multiple-scattering theory, we conclude only the $4h$ Wyckoff site to be occupied by Fe [occupancy refined is $(100\ifmmode\pm\else\textpm\fi{}3)\mathrm{%}$ in case of $x=1$]. Furthermore, taking the XANES spectra into account, we are able to verify the EXAFS results and additionally explain the differences in the $\text{Mn}\text{ }K$ XANES spectra in dependence on $x$ to be caused by changes in the dipole transitions to $4p$ final states. From quantitative pre-edge analysis an oxidation number of $+4$ for the Mn atom for $x=1$ is determined whereas the Fe valence is shown to be unchanged. Since the substitution process only involves one Wyckoff site, the experimentally observed limit to a maximum amount of $x=1$ is explained. Additionally, a possible disorder, discussed in the literature, is not proven for our samples. With DFT calculations, the experimental findings are verified on the basis of the total energy of the different possible electronic configurations. Crystal-field effects are identified to be responsible for the site-selective substitution of Fe for Mn.

Magnetic and magnetotransport properties of the (La 0.67Pb 0.33)(Mn 1− xFe x)O 3 (0 ≤ x ≤ 0.1) compounds

A study of magnetic and electrical transport properties of Fe-doped colossal magnetoresistive manganese perovskites (La 0.67Pb 0.33)(Mn 1− x Fe x )O 3 ( x = 0, 0.01, 0.03, 0.06 and 0.1) is presented. Polycrystalline compounds were prepared by the sol–gel low-temperature method. The dc magnetization measured in the fields 50 Oe and 1 kOe and hysteresis loops up to 89 kOe were measured from 4 K up to 400 K. Four-probe magnetoresistance measurements have been performed in the same temperature range at the applied magnetic fields up to 80 kOe. It was found that the substitution of Fe for Mn results in a reduction of the saturation magnetic moment, an increase of the resistivity, as well as a decrease of the Curie ( T C) and metal–insulator ( T M–I) transition temperatures. The x = 0.1 compound exhibits the largest magnetoresistance effect of about 300% around its T M–I temperature in the applied field of 80 kOe. The resistivity above T C for the compounds follows the thermally activated behaviour with the activation energy of about 0.12 eV. The results confirm that Fe substitutes for Mn 3+, forming Mn 4+/Fe 3+ pairs which do not support the double exchange interaction. This strongly affects the magnetic and magnetotransport properties as compared with those of the Fe undoped compound.

The structural and magnetic properties of Mn2−xFexNiGa Heusler alloys

The effect of Fe substitution on the phase transformation and magnetic properties of Mn2NiGa has been studied. A single bcc phase was obtained in Mn2−xFexNiGa (x=0–0.6). With the substitution of Fe for Mn, the lattice constant decreases gradually. The martensitic transformation can be observed when x=0–0.3. Both the martensitic transformation and austenitic transformation temperatures decrease monotonically with increasing Fe content, which is different from common electron concentration dependence in Ni–Mn–Ga system. The saturation magnetizations Ms of Mn2−xFexNiGa in both austenitic and martensitic phases increase obviously with the doping of Fe, while the variation of TC shows an opposite tendency. Theoretical calculations indicate that both austenitic and martensitic phases are ferrimagnets. The Fe moment varies from positive to negative after the tetragonal distortion, which leads to the decrease of the saturation magnetization.

Crystal structure and magnetic properties of Nd(Mn1–xFex)2Si2 compounds

X-ray powder diffraction, resistivity and magnetization studies have been performed on polycrystalline Nd(FexMn1–x)2Si2 (0 ≤ x ≤ 1) compounds which crystallize in a ThCr2Si2-type structure with the space group I4/mmm. The field-cooled temperature dependence of the magnetization curves shows that, at low temperatures, NdFe2Si2 is antiferromagnetic, while the other compounds show ferromagnetic behaviour. The substitution of Fe for Mn leads to a decrease in lattice parameters a, c and unit-cell volume V. The Curie temperature of the compounds first increases, reaches a maximum around x = 0.7, then decreases with Fe content. However, the saturation magnetization decreases monotonically with increasing Fe content. This Fe concentration dependent magnetization of Nd(FexMn1–x)2Si2 compounds can be well explained by taking into account the complex effect on magnetic properties due to the substitution of Mn by Fe. The temperature's square dependence on electrical resistivity indicates that the curve of Nd(Fe0.6Mn0.4)2Si2 has a quasi-linear character above its Curie temperature, which is typical of simple metals.

Magnetic properties and magnetocaloric effect of Nd(Mn 1− xFe x) 2Ge 2 compounds

Polycrystalline Nd(Mn 1− x Fe x ) 2Ge 2 (0 ≤ x ≤ 1) compounds have been prepared by arc-melting. X-ray powder diffraction analysis shows that all samples crystallize in the ThCr 2Si 2-type structure with the space group I4/ mmm. The substitution of Fe for Mn results in decreases of the lattice constants a, c and the unit-cell volume V. Magnetic properties and magnetocaloric effect of the compounds Nd(Mn 0.9Fe 0.1) 2Ge 2 and Nd(Mn 0.8Fe 0.2) 2Ge 2 have been studied by magnetic measurements. A spin reorientation transition at about 188 K is observed for Nd(Mn 0.9Fe 0.1) 2Ge 2. The Nd(Mn 0.8Fe 0.2) 2Ge 2 compound shows more complicated magnetic behavior, which is characterized by four magnetic ordering states below room temperature. The maximum values of the magnetic entropy change are 2.35 and 1.84 J kg −1 K −1 for x = 0.1 and 0.2, respectively, under the applied field changing from 0 to 5 T. The relative cooling powers of Nd(Mn 0.9Fe 0.1) 2Ge 2 and Nd(Mn 0.8Fe 0.2) 2Ge 2 are 145.9 and 133.8 J kg −1 under an applied field change of 5 T.