Complex Magnetic Behavior Research Articles

Comparative phase transformation and magnetocaloric effect study of Co and Mn substitution by Cu in MnCoGe compounds

Structural and magnetic phase transformations and magnetocaloric effect of Mn and Co substitutions by Cu in MnCoGe have been investigated using X-ray diffraction, differential scanning calorimetry, and magnetization measurements. Increase in Cu concentration reduces the martensitic structural and magnetic phase transition temperatures. However, nearly doubling of the amount of Co substitution is required compared to Mn for an equivalent change in the structural transition temperature. A giant magnetocaloric effect, -ΔSMmax ≈ 50 J kg−1K−1 for Δμ0H = 5 T, resulting from coupling of concomitant structural and magnetic transformations near room temperature has been obtained for a sample with around 11 at% Mn-substitution. Fine tuning of Cu concentration (20 at%) in the case of Co substitution resulted in concurrent structural and magnetic transitions at around 260 K. However, the absence of a magnetostructural coupling resulted in peak entropy change of less than 4 J kg−1K−1. Samples with 15 at% or higher Co-substitution showed complex magnetic behavior and multiple magnetic transitions. The nature of magnetic phase transitions in both Co- and Mn-substituted samples have been investigated and phase diagrams for both sets of samples have been derived based on calorimetry and magnetometry results.

Griffiths-like phase and charge-spin glass state in La1.5Sr0.5CoO4

Hole-doped antiferromagnetic La2CoO4 has been known to possess intriguing electronic and magnetic phases due to the complex temperature and magnetic field dependent behavior of Co3+ ions. Here, we report on magnetic and dielectric observations in the half hole-doped La1.5Sr0.5CoO4. A Griffiths-like phase has been observed in the high temperature region below TG (∼244 K). At low temperature (∼55 K), a metamagnetic phase has been observed where antiferromagnetic correlations appear. On further cooling, a static weak antiferromagnetic ordering appears at ∼30 K, and a charge-spin glass state has been realized at ∼14 K.

Coercive field enhancement in microstructured (La0.4Pr0.6)0.67Ca0.33MnO3 thin films

The perovskite material (La0.4Pr0.6)0.67Ca0.33MnO3 (LPCMO) has complex electronic and magnetic behavior based on phase competition between ferromagnetic metallic (FMM) and insulating phases with similar free energies. Experimental evidence has indicated that in-plane stress anisotropy influences these phases and can affect electronic and magnetic properties. Here we investigate the roles that both stress and shape anisotropies may play in controlling the coercive field of the material. LPCMO thin films of various thicknesses (20, 25, and 30 nm) were deposited on (110) NdGaO3 (NGO) substrates using pulsed laser deposition and the coercive fields were measured. Photolithography was then used to fabricate microstructured arrays of LPCMO on the NGO substrates for each of the films. The coercive fields of these arrays of LPCMO were compared to the behavior of the corresponding unpatterned LPCMO thin films across a range of temperatures. Microstructure arrays for the thicker (25 and 30 nm) films showed a substantial increase in the coercive field after forming the arrays, whereas a thinner film (20 nm) showed almost no change in the coercive field. Stress anisotropy continues to play a dominant role in the behavior of LPCMO thin films and dimensionality of the magnetic domains also influences the results. The films show 2D behavior when film thickness approaches the size of the critical radius for single-to-multidomain transitions. Making thicker films allows for 3D behavior and a role for shape anisotropy to influence the coercive fields.

Magnetic frustration in low-dimensional substructures of hulsite Ni5.15Sn0.85(O2BO3)2

This paper presents an extensive study of the structural, magnetic, and thermodynamic properties of the hulsite ${\mathrm{Ni}}_{5.15}{\mathrm{Sn}}_{0.85}{({\mathrm{O}}_{2}{\mathrm{BO}}_{3})}_{2}$. The crystal structure of the hulsite has two planar substructures formed by Ni and Sn atoms: one with rectangular configuration and the other with a triangular arrangement. These substructures are linked by the boron ions and by Ni in another site closer to the rectangular arrangement, resulting in a quasi-two-dimensional character. Thus, this system literally adds a new dimension to the study of oxyborates. Our results point to a complex magnetic behavior consistent with these substructures. The planes with rectangular arrangement form a complex magnetic ordering at 180 K (one of the highest magnetic transitions among the oxyborates). The other subsystem, formed by Ni atoms located in a two-dimensional triangular lattice, does not order down to temperatures as low as 3 K. The experimental results suggest a spin-liquid behavior for this subsystem. The magnetic moments of the ions between these planes also freeze at low temperatures. The two magnetic planes coexist as independent subsystems down to the lowest temperatures of our experiments.

A Family of A-Site Cation-Deficient Double-Perovskite-Related Iridates: Ln9Sr2Ir4O24 (Ln = La, Pr, Nd, Sm)

The compositions of the general formula Ln11- xSr xIr4O24 (Ln = La, Pr, Nd, Sm; 1.37 ≥ x ≥ 2) belonging to a family of A-site cation-deficient double-perovskite-related oxide iridates were grown as highly faceted single crystals from a molten strontium chloride flux. Their structures were determined by single-crystal X-ray diffraction. On the basis of the single-crystal results, additional compositions, Ln9Sr2Ir4O24 (Ln = La, Pr, Nd, Sm), were prepared as polycrystalline powders via solid-state reactions and structurally characterized by Rietveld refinement. The compositions Ln9Sr2Ir4O24 (Ln = La, Pr, Nd, Sm) contain Ir(V) and Ir(IV) in a 1:3 ratio with an average iridium oxidation state of 4.25. The single-crystal compositions La9.15Sr1.85Ir4O24 and Pr9.63Sr1.37Ir4O24 contain relatively less Ir(V), with the average iridium oxidation states being 4.21 and 4.09, respectively. The magnetic properties of Ln9Sr2Ir4O24 (Ln = La, Pr, Nd, Sm) were measured, and complex magnetic behavior was observed in all cases at temperatures below 30 K.

Constrained Magnetostratigraphic Dating of a Continental Middle Miocene Section in the Arid Central Asia

The Neogene succession of the Aktau Mountains in the Ili Basin, southeast Kazakhstan, is a terrestrial archive well suited for researching the role of Central Asia in Miocene climate evolution. We present an integrated approach for dating the well-exposed Bastau Formation, based on magnetostratigraphy and constraints from cyclostratigraphy and biostratigraphy. Stepwise demagnetization yielded characteristic remanence directions that are consistent with those expected for the Miocene in Central Asia. The reddish-colored alluvial floodplain deposits and grey lacustrine deposits show partly complex magnetic behavior with magnetite and hematite as the main magnetic carriers, with variable demagnetization behavior and non-dipolar normal and reverse polarity directions. The observed magnetic properties are best explained by depositional variability and magneto-mineralogical alteration effects of both dissolution and neo-formation of magnetite, including significant secondary magnetization. The mean of reverse polarity directions is flatter than the expected Middle Miocene Earth magnetic field, which is an indicator for the existence of inclination shallowing that supports a primary origin. Detailed rock magnetic analyses are used to analyze the nature of the characteristic remanent magnetization and to discriminate primary and secondary remanence directions in order to obtain a reliable magnetostratigraphic result. The proposed age of 15.3 Ma to 13.9 Ma for the Bastau Formation corresponds to the known biostratigraphic setting, matches with typical sedimentation rates of foreland basins in Central Asia, and coincides with spectral analysis of geochemical proxies of that section. The resulting age model serves as a robust framework for paleoclimate reconstruction of Neogene climate dynamics in Central Asia.

Complex magnetic behaviour and evidence of a superspin glass state in the binary intermetallic compound Er5Pd2

The binary intermetallic compound Er5Pd2 has been investigated using dc and ac magnetic susceptibilities, magnetic memory effect, isothermal magnetization, non-linear dc susceptibility, heat capacity and magnetocaloric effect studies. Interestingly, even though the compound does not show geometrical frustration it undergoes glassy magnetic phase transition below 17.2 K. Investigation of dc magnetization and heat capacity data divulged absence of long-ranged magnetic ordering. Through the magnetic memory effect, time dependent magnetization and ac susceptibility studies it was revealed that the compound undergoes glass-like freezing below 17.2 K. Analysis of frequency dependence of this transition temperature through scaling and Arrhenius law; along with the Mydosh parameter indicate, that the dynamics in Er5Pd2 are due to the presence of strongly interacting superspins rather than individual spins. This phase transition was further investigated by non-linear dc susceptibility and was characterized by static critical exponents γ and δ. Our results indicate that this compound shows the signature of superspin glass at low temperature. Additionally, both conventional and inverse magnetocaloric effect was observed with a large value of magnetic entropy change and relative cooling power. Our results suggest that Er5Pd2 can be classified as a superspin glass system with large magnetocaloric effect.

The Smaller the Better: Hosting Trivalent Rare-Earth Guests in Cu–P Clathrate Cages

Summary The most striking difference between the trivalent rare-earth cations and their alkali and alkaline-earth peers is the presence of localized 4 f electrons. Placing trivalent rare-earth cations inside fullerene molecules or in between blocks of intermetallics has given rise to a plethora of fascinating properties and materials. A long-sought-after yet undiscovered material is a semiconducting compound with rare-earth cations situated inside the oversized polyhedral cages of a three-dimensional framework. In this work, we present a synthesis of unconventional clathrates, Ba 8−x R x Cu 16 P 30 , with the smallest pentagonal dodecahedral cages encapsulating La 3+ and Ce 3+ . Their composition and crystal structure were unambiguously determined by a combination of synchrotron powder diffraction, time-of-flight neutron powder diffraction, scanning transmission electron microscopy, and electron energy-loss spectroscopy. Our quantum-mechanical calculations and experimental characterizations show that the incorporation of the rare-earth cations significantly enhances hole mobility and reduces hole concentration, resulting in a drastic (700%) increase in the thermoelectric performance.

Reversible 90-Degree Rotation of Fe Magnetic Moment Using Hydrogen

[Pd/Fe]2 multilayers were deposited on a flat MgO(001) to study the effect of hydrogen on magnetic interlayer coupling. Complex magnetic hysteresis behavior, including single, double, and triple loops, were measured as a function of the azimuthal angle in a longitudinal and transverse direction. With a combination of a 2-fold magnetic anisotropy energy (MAE) in the bottom-Fe and a 4-fold MAE in the top-Fe, the complex magnetic hysteresis behavior could be clearly explained. Two well-split hysteresis loops with almost zero Kerr remanence were measured by choosing a suitable Pd thickness and applying the magnetic field perpendicular to the easy axis of the bottom-Fe. The split double loops originated from the 90°-rotation of the top-Fe moment. On exposure to a hydrogen gas atmosphere, the separation of the two minor loops increased, indicating that Pd-hydride formation enhanced the ferromagnetic coupling between the two Fe layers. Based on these observations, we proposed that, by applying a suitable constant magnetic field, the top-Fe moment could undergo reversible 90°-rotation following hydrogen exposure. The results suggest that the Pd space layer used for mediating the magnetic interlayer coupling is sensitive to hydrogen, and therefore, the multilayer system can function as a giant magnetoresistance-type sensor suitable for hydrogen gas.

Observation of unusual critical region behavior in the magnetic susceptibility of EuSe

The Europium Chalcogenides (EuCh: EuO, EuS, EuSe, and EuTe) have been regarded as model examples of simple, cubic, Heisenberg exchange coupled magnetic systems, with a ferromagnetic nearest-neighbor exchange constant J1 and an antiferromagnetic next-nearest-neighbor constant J2. Unlike the other EuCh, EuSe exhibits a range of complex magnetic behaviors, the latter being attributed to EuSe being near the point where J2=-J1, where its magnetism appears to consist of nearly de-coupled 2D ferromagnetic sheets. Analysis of precision SQUID measurements of the magnetic susceptibility χ in EuSe showed that in the region from ∼Tc to ∼2Tc, a fit of the data to the critical equation χ = χ2Tc(T/Tc-1)-γ gives γ=2.0, an exponent not predicted by any current theory. Additionally, this fit predicts that Tc should be ∼0K. We tentatively interpret this by saying that in the paramagnetic region the system "thinks" EuSe should not order above T=0. Tc=0K is predicted by the Mermin-Wagner theorem (MW) for Heisenberg-coupled 2D magnetic systems, and we can show that when J2=-J1, MW can also be applied to the J1, J2 exchange model of the EuCh to give a rigorous Tc=0 prediction. Under 10 kbar applied pressure EuSe exhibits a different γ and fitted Tc. An additional, and rather strange, critical-region effect was discovered. The EuSe sample was found to exhibit a relaxation effect in a small range of temperatures, just above and just below the actual Tc of 4.7K, with time constants of up to 5 minutes. We cannot yet fully explain this observed macroscopic effect.

The origin of fine structure in magnetization curve of αCoV2O6

Multiple field-induced plateaus in αCoV2O6 at low temperatures were revealed earlier by M. Lenertz et al. [J. Phys. Chem. C 115, 17190 (2011)] and carefully investigated recently by M. Nandi and P. Mandal [J. Appl. Phys. 119, 133904 (2016)]. Four equidistant steps were observed in the magnetization curve. We present a model to describe this phenomenon. A magnetic structure of this substance is formed by highly anisotropic triangular lattice of Ising chains running along the b axis. Due to a three-fold degeneracy of three-sublattice magnetic ordering, domain boundaries appear. Their transformation under magnetic field variation leads to two additional steps in the 1/3 magnetization plateau and gives rise to complex magnetic behavior observed experimentally. The domain structure in αCoV2O6 occurs to be strongly anisotropic because a lifetime of the metastable states depends greatly on the configuration orientation. A strong dependence of the magnetization curve on magnetic field sweep time is predicted.

Substituted group-directed assembly of six coordination compounds based on pyrazole bifunctional ligands

Six new complexes [Mn8(μ4-O)4(phpz)8(MeOH)4]·(MeOH)(H2O) (1) [Co2(HphpzH)(Hphpz)2(phpz)2]·4(MeOH) (2), Ni(Hphpz)2 (3), [Ni(Hphpz)2]·H2O (4), [Zn4(pzpy)4Cl4] (5) and [Cu2(pzpy)2(HCO2)2(H2O)2] (6) have been synthesized by hydrothermal reactions of MCl2·4H2O (M = Mn, Co, Ni, Zn or Cu) with 5-(2-hydroxyphenyl)-3-pyrazole (HphpzH) or 2-(1H-pyrazol-3-yl)pyridine (Hpzpy). The complexes were characterized by elemental analysis, IR spectroscopy and single-crystal X-ray diffraction. Complex 1 is an octanuclear Mn(III) cluster, complexes 2 and 6 are binuclear Co(III) and Cu(II), respectively, complexes 3 and 4 are isomorphous mononuclear species, while complex 5 is a tetranuclear Zn(II) cluster. The magnetic behavior of complex 1 was investigated. Magnetic susceptibility measurements revealed antiferromagnetic exchange interactions between the metal centers in the clusters. The luminescence properties of the complexes were investigated at room temperature in the solid state.

Correlation between structural and transport properties of electron beam irradiated PrMnO3 compounds

The structural, electrical, magnetic, and thermal properties of electron beam (EB) irradiated PrMnO3 manganites were investigated in the present communication. X-ray diffraction data reveals that all samples are single phased with orthorhombic distorted structure (Pbnm). Furthermore, the diffracted data are analyzed in detail using Rietveld refinement technique. It is observed that the EB dosage feebly disturbs the MnO6 octahedra. The electrical resistivity of all the samples exhibits semiconducting behavior. Small polaron hopping model is conveniently employed to investigate the semiconducting nature of the pristine as well as EB irradiated samples. The Seebeck coefficient (S) of the pristine as well as the irradiated samples exhibit large positive values at lower temperatures, signifying holes as the dominant charge carriers. The analysis of Seebeck coefficient data confirms that the small polaron hopping mechanism assists the thermoelectric transport property in the high temperature region. The magnetic measurements confirm the existence of paramagnetic (PM) to ferromagnetic (FM) behavior for the pristine and irradiated samples. In the lower temperature regime, coexistence of FM clusters and AFM matrix is dominating. Thus, the complex magnetic behavior of the compound has been explained in terms of rearrangement of antiferromagnetically coupled ionic moments.

Magnetic properties of (Nd,Ca)(Ba,La)Co2O5+δ tuned by the site-selected charge doping, oxygen disorder, and hydrostatic pressure

Comprehensive study of magnetic properties of the layer-ordered perovskites $\mathrm{N}{\mathrm{d}}_{1--x}\mathrm{C}{\mathrm{a}}_{x}\mathrm{B}{\mathrm{a}}_{1--y}\mathrm{L}{\mathrm{a}}_{y}\mathrm{C}{\mathrm{o}}_{2}{\mathrm{O}}_{5+\ensuremath{\delta}}$ is presented as a function of the site-selected charge doping $\mathrm{[}c=(x--y)/2+\ensuremath{\delta}\ensuremath{-}0.5,x\ensuremath{\le}0.2$ and $y\ensuremath{\le}0.1,0.07l\ensuremath{\delta}l0.84]$, oxygen disorder, and hydrostatic pressure $Pl10\phantom{\rule{0.16em}{0ex}}\mathrm{kbar}$. The single-phase oxygen-ordered orthorhombic phase exhibiting complex ferrimagnetic, antiferromagnetic, and metal-insulator phase transitions was found for a narrow oxygen range around $\ensuremath{\delta}\ensuremath{\sim}0.5\ifmmode\pm\else\textpm\fi{}0.1$. Significant difference between impact of hole $(cg0)$ and electron $(cl0)$ doping was observed depending on the site of cation substitution. Gradual enhancement of the Curie temperature ${T}_{\mathrm{C}}$ was observed over the whole range of $c$ to be unaffected by the local oxygen vacancy disorder. Maximum of the N\'eel temperature ${T}_{\mathrm{N}}$ at $c=0$ was found rapidly disappearing at $c=0.05$ for Ca/Nd substitution while it was maintained for La/Ba substitution, indicating that the oxygen vacancy disorder, especially for $\ensuremath{\delta}g0.5$, has a larger effect on antiferromagnetic phase than the charge doping. The temperature of metal-insulator transition ${T}_{\mathrm{MIT}}$ was found practically unchanged by either charge doping or disorder. The application of hydrostatic pressure slightly suppressed ${T}_{\mathrm{C}}$ and increased ${T}_{\mathrm{N}}$ by stabilization of the antiferromagnetic phase with the largest observed value of $\mathrm{d}{T}_{\mathrm{N}}/\mathrm{d}P=5.75\phantom{\rule{0.16em}{0ex}}\mathrm{K}/\mathrm{kbar}$. Complex magnetic behavior affected by hydrostatic pressure was accounted for by ferro- and antiferromagnetic interactions resulting from the charge separation and spin transitions.

Successive Phase Transitions in Fe2+ Ladder Compounds Sr2Fe3Ch2O3 (Ch = S, Se).

Small single crystals of Sr2Fe3Ch2O3 (Ch = S, Se) have been synthesized by flux methods, and bulk materials have been obtained by solid state reactions. Both compounds are isostructural to the compound Sr2Co3S2O3 (space group Pbam), which contains a novel hybrid spin ladder: a combination of a 2-leg rectangular ladder and a necklace ladder. The 2-leg ladder acts as a well-defined magnetic entity, while intimate magnetic coupling to the necklace ladder induces three successive phase transitions in the range of 40-120 K in each composition (Ch = S or Se), as revealed by Mössbauer spectroscopy, thermodynamics, and magnetometry. The complex magnetic behaviors can be explained by the unique spin-lattice topology.

Magnetic order and phase transition in the iron oxysulfide La2O2Fe2OS2

The Mott-insulating iron oxychalcogenides exhibit complex magnetic behaviour and we report here a neutron diffraction investigation into the magnetic ordering in La2O2Fe2OS2. This quaternary oxysulfide adopts the anti-Sr2MnO2Mn2Sb2-type structure (described by space group I4/mmm) and orders antiferromagnetically below TN=105K. We consider both its long-range magnetic structure and its magnetic microstructure, and the onset of magnetic order. It adopts the multi-k vector “2k” magnetic structure (k=(1/201/2) and k=(01/21/2) and has similarities with related iron oxychalcogenides, illustrating the robust nature of the “2k” magnetic structure.

Five-Fold Ordering in High-Pressure Perovskites RMn3O6 (R = Gd-Tm and Y).

Cation and anion ordering plays an important role in the properties of materials, in particular, in the properties of perovskite materials. Here we report on unusual 5-fold cation/charge ordering in high-pressure-synthesized (at 6 GPa and ∼1670 K) RMn3O6 perovskites with R = Gd-Tm and Y. R3+, Mn2+, and Mn3+ cations are ordered at the A site in two separate chains consisting of R3+ and alternating Mn2+ (in tetrahedral coordination) and Mn3+ (in square-planar coordination), while Mn3+ and mixed-valent Mn3+/Mn4+ are ordered at the B site in layers. The ordering can be represented as [R3+Mn2+0.5Mn3+0.5]A[Mn3+Mn3.5+]BO6. The triple cation ordering observed at the A site is very rare, and the layered double-B-site ordering is also scarce. RMn3O6 compounds crystallize in space group Pmmn with a = 7.2479(2) Å, b = 7.4525(3) Å, and c = 7.8022(2) Å for DyMn3O6 at 213 K, and they are structurally related to CaFeTi2O6. They are prone to nonstoichiometry, R1-δMn3O6-1.5δ, where δ = -0.071 to -0.059 for R = Gd, δ = 0 for R = Dy, δ = 0.05-0.1 for R = Ho and Y, and δ = 0.12 for R = Er and Tm. They show complex magnetic behaviors with several transition temperatures, and their magnetic properties are highly sensitive to the δ values.

Thickness dependence of the magnetic anisotropy and dynamic magnetic response of ferromagnetic NiFe films

We investigate the thickness dependence of the magnetic anisotropy and dynamic magnetic response of ferromagnetic NiFe films. We go beyond quasi-static measurements and focus on the dynamic magnetic response by considering three complementary techniques: the ferromagnetic resonance, magnetoimpedance and magnetic permeability measurements. We verify remarkable modifications in the magnetic anisotropy, i.e. the well-known behavior of in-plane uniaxial magnetic anisotropy systems gives place to a complex magnetic behavior as the thickness increases, and splits the films in two groups according to the magnetic properties. We identify magnetoimpedance and magnetic permeability curves with multiple resonance peaks, as well as the evolution of the ferromagnetic resonance absorption spectra, as fingerprints of strong changes of the magnetic properties associated to the vanishing of the in-plane magnetic anisotropy and to the emergence of non-homogeneous magnetization configuration, local anisotropies and out-of-plane anisotropy contribution arisen as a consequence of the non-uniformities of the stress stored in the film as the thickness is increased and/or to the columnar growth of the film. We interpret the experimental results in terms of the structural and morphological properties, quasi-static magnetic behavior, magnetic domain structure and different mechanisms governing the magnetization dynamics at distinct frequency ranges.

Synthesis, crystal structures, photoluminescent, magnetic and chiroptical properties of two homochiral ErIII complexes with different nuclearity

Employing chiral bis-bidentate N-donor ligand, (+)-2,5-bis(4,5-pinene-2-pyridyl) pyrazine (L), as a bridging ligand for Er(dbm)3H2O, and depending on the ratio control of reactants, two mono- and dinuclear homochiral ErIII complexes with the formulae Er(dbm)3L·2H2O (1) (dbm─ = dibenzoylmethanate) and Er2(dbm)6L·6H2O (2) have been synthesized and structurally characterized. Circular dichroic (CD) spectra verify their chiroptical activities. Investigations on the luminescent properties of complexes 1 and 2 demonstrate that they exhibit characteristic near-infrared (NIR) luminescence of the ErIII ion at around 1533 nm and the emission intensity of the mononuclear complex 1 is much larger than that of dinuclear species 2, the reason of which is elucidated in this work. In addition, the measurements of magnetic properties indicate that the direct-current (dc) magnetic behaviors of complexes 1 and 2 mainly result from the thermal depopulation of the excited MJ sublevels of the ErIII ions. Notablely, complex 2 is the first example of chiral polynuclear lanthanide complexes with NIR-luminescence property.

Synthesis of Metastable Co4N, Co3N, Co2N, and CoO0.74N0.24 from a Single Azide Precursor and Intermediates in CoBr2 Ammonolysis

Metastable cobalt nitrides Co4N, Co3N, Co2N, and cobalt oxide nitride CoO0.74N0.24 were synthesized by ammonolysis of one single metastable azide precursor, [Co(NH3)5N3]Cl2, in high purity by controlled variation of the reaction conditions (temperature, duration, gas atmosphere, and flow rate). The alternative route towards cobalt nitrides by ammonolysis of CoBr2 proceeds via [Co(NH3)6]Br2 and Co(NH3)2Br2 to exclusively yield Co3N. For Co3N1.1 a complex magnetic behavior is observed: dominating ferromagnetic ordering at low temperatures and a small coercive field of 10 mT. Co2N orders antiferromagnetically below 10 K. Electronic structure calculations [DFT, generalized‐gradient approximation (GGA)+U] on CoO0.75N0.25 reveal that the experimentally observed rock‐salt structure is less stable than the sphalerite‐type polymorph by about 30 kJ mol–1 and possesses an antiferromagnetically ordered ground state.