Mn_5Ge_3C_x films with x>0.5 were experimentally shown to exhibit a strongly enhanced Curie temperature T_C compared to Mn_5Ge_3. In this letter we present the results of our first principles calculations within Green's function approach, focusing on the effect of carbon doping on the electronic and magnetic properties of the Mn_5Ge_3. The calculated exchange coupling constants revealed an enhancement of the ferromagnetic Mn-Mn interactions mediated by carbon. The essentially increased T_C in Mn_5Ge_3C is well reproduced in our Monte Carlo simulations and together with the decrease of the total magnetisation is found to be predominantly of an electronic nature.
This work reports on structural and magnetic investigations of the Heusler compound Co$_2$FeSi. X-Ray diffraction and Mößbauer spectrometry indicate an ordered $L2_1$ structure. Magnetic measurements by means of X-ray magnetic circular dichroism and magnetometry revealed that this compound is, currently, the material with the highest magnetic moment ($6 μ_B$) and Curie-temperature (1100K) in the classes of Heusler compounds as well as half-metallic ferromagnets.
A concept is presented serving to guide in the search for new materials with high spin polarization. It is shown that the magnetic moment of half-metallic ferromagnets can be calculated from the generalized Slater-Pauling rule. Further, it was found empirically that the Curie temperature of Co$_2$ based Heusler compounds can be estimated from a seemingly linear dependence on the magnetic moment. As a successful application of these simple rules, it was found that Co$_2$FeSi is, actually, the half-metallic ferromagnet exhibiting the highest magnetic moment and the highest Curie temperature meas…
We investigate the effects of various dopants (M = K--Br) on the Curie temperature of the magnetic compound NdFe12 through first-principles calculations. Analysis by the Korringa--Kohn--Rostoker method with the coherent potential approximation reveals that doping the Fe sites with optimal concentrations of Ge and As is a promising strategy for increasing the Curie temperature. To search over a wider space, we also perform Bayesian optimization. Out of over 180,000 candidate compositions, co-doped systems with Co, Ge, and As are found to have the highest Curie temperatures.
The Curie temperature ($T_C$) of binary alloy compounds consisting of 3$d$ transition-metal and 4$f$ rare-earth elements is analyzed by a machine learning technique. We first demonstrate that nonlinear regression can accurately reproduce $T_C$ of the compounds. The prediction accuracy for $T_C$ is maximized when five to ten descriptors are selected, with the rare-earth concentration being the most relevant. We then discuss an attempt to utilize a regression-based model selection technique to learn the relation between the descriptors and the actuation mechanism of the corresponding physical ph…
The local atomic environments and magnetic properties were investigated for a series of Co(1+x)Fe(2-x)Si (0<x<1) Heusler compounds. While the total magnetic moment in these compounds increases with the number of valance electrons, the highest Curie temperature (Tc) in this series was found for Co1.5Fe1.5Si, with a Tc of 1069 K (24 K higher than the well known Co2FeSi). 57Fe Mössbauer spectroscopy was used to characterize the local atomic order and to estimate the Co and Fe magnetic moments. Consideration of the local magnetic moments and the exchange integrals is necessary to understand the tr…
The generalized Heusler compounds Mn2CoZ (Z = Al, Ga, In, Si, Ge, Sn, Sb) with the Hg2CuTi structure are of large interest due to their half-metallic ferrimagnetism. The complex magnetic interactions between the constituents are studied by first principles calculations of the Heisenberg exchange coupling parameters, and Curie temperatures are calculated from those. Due to the direct Mn-Mn exchange interaction in Mn2CoZ, the Curie temperature decreases, while the total moment increases when changing Z from one group to another. The exchange interactions are dominated by a strong direct exchange…
The exchange interactions of Cr4N, Mn4N, Fe4N, Co4N, and Ni4N compounds with perovskite structure were calculated to obtain the Curie temperatures for these compounds from Monte Carlo calculations. Contrary to naive expectation, the exchange interactions vary markedly among these five compounds. In Fe4N, the intra-sublattice interaction of the Fe 3c atoms is strongly negative, leading to a significant reduction of the Curie temperature. The calculated Curie temperatures are 291K (Cr4N), 710K (Mn4N), 668K (Fe4N), 827K (Co4N), and 121K (Ni4N), in good agreement with experimental observations whe…
Combining density-functional theory calculations with a classical Monte Carlo method, we show that for B2-type FeCo compounds tetragonal distortion gives rise to a strong reduction of the Curie temperature $T_{\mathrm{C}}$. The $T_{\mathrm{C}}$ monotonically decreases from 1575 K (for $c/a=1$) to 940 K (for $c/a=\sqrtwo$). We find that the nearest neighbor Fe-Co exchange interaction is sufficient to explain the $c/a$ behavior of the $T_{\mathrm{C}}$. Combination of high magnetocrystalline anisotropy energy with a moderate $T_{\mathrm{C}}$ value suggests tetragonal FeCo grown on the Rh substrat…
The Heusler compounds Mn$_2$TiZ (Z = Al, Ga, In, Si, Ge, Sn, P, As, Sb) are of large interest due to their potential ferrimagnetic properties and high spin polarization. Here, we present calculations of the structural and magnetic properties of these materials. Their magnetic moment follows the Slater-Pauling rule $m = N_V - 24$. None of them is actually a perfect half-metallic ferrimagnet, but some exhibit more than 90% spin polarization and Curie temperatures well above room temperature. The exchange interactions are complex, direct and indirect exchange contributions are identified. The Cur…
We study the interatomic exchange interactions and Curie temperatures in half-metallic semi Heusler compounds NiCrZ (Z=P, Se, Te) and NiVAs. The study is performed within the framework of density functional theory. The calculation of exchange parameters is based on the frozen-magnon approach. It is shown that the exchange interactions in NiCrZ vary strongly depending on the Z constituent. The Curie temperature, Tc, is calculated within the mean field and random phase approximations. The difference between two estimations is related to the properties of the exchange interactions. The predicted …
Based on first-principles electron structure calculations and employing the frozen-magnon approximation we study the exchange interactions in a series of transition-metal binary alloys crystallizing in the zinc-blende structure and calculate the Curie temperature within both the mean-field approximation (MFA) and random-phase approximation (RPA). We study two Cr compounds, CrAs and CrSe, and four Mn compounds: MnSi, MnGe, MnAs and MnC. MnC, MnSi and MnGe are isovalent to CrAs and MnAs is isoelectronic with CrSe. Ferromagnetism is particular stable for CrAs, MnSi and MnGe: All three compounds s…
We report Curie temperatures up to 150 K in annealed Ga1-xMnxAs epilayers grown with a relatively low As:Ga beam equivalent pressure ratio. A variety of measurements (magnetization, Hall effect, magnetic circular dichroism and Raman scattering) show that the higher ferromagnetic transition temperature results from an enhanced free hole density. The data also indicate that, in addition to the carrier concentration, the sample thickness limits the maximum attainable Curie temperature in this material - suggesting that the free surface of Ga1-xMnxAs epilayers is important in determining their phy…
The structural and magnetic properties of Mn5Ge3Cx films prepared at elevated substrate temperatures TS are investigated. In particular, films with x >= 0.5 and TS = 680 K exhibit a strongly enhanced Curie temperature TC = 440 K compared to Mn5Ge3 with TC = 304 K. Structural analysis of these films suggests that the carbon is interstitially incorporated into the voids of Mn octahedra of the hexagonal Mn5Si3-type structure giving rise to a lattice compression. The enhanced ferromagnetic stability in connection with the lattice compression is interpreted in terms of an Mn-Mn interaction mediated…
Heusler alloys are promising for several applications, including magnetic refrigeration, due to high magnetocaloric and magnetovolume effects. One way to optimize this potential is by increasing the magnetovolume effect. Using density functional theory with the Korringa-Kohn-Rostoker method, we calculate the effective exchange interaction energies and corresponding mean field Curie temperature as a function of the volume (hydrostatic pressure) in several L2 1 -type Co 2 YZ Heusler alloys. Different qualitative trends and signs of the pressure derivatives of the Curie temperature and moments ar…
Magnetic materials have a plethora of applications ranging from informatics to energy harvesting and conversion. However, such functionalities are limited by the magnetic ordering temperature. In this work, we performed machine learning on the magnetic ground state and the Curie temperature (TC), using generic chemical and crystal structural descriptors. Based on a database of 2805 known intermetallic compounds, a random forest model is trained to classify ferromagnetic and antiferromagnetic compounds and to do regression on the TC for the ferromagnets. The resulting accuracy is about 86% for …
In this work the theoretical and experimental investigations of Co2TiZ (Z = Si, Ge, or Sn) compounds are reported. Half-metallic ferromagnetism is predicted for all three compounds with only two bands crossing the Fermi energy in the majority channel. The magnetic moments fulfill the Slater-Pauling rule and the Curie temperatures are well above room temperature. All compounds show a metallic like resistivity for low temperatures up to their Curie temperature, above the resistivity changes to semiconducting like behavior. A large negative magnetoresistance of 55% is observed for Co2TiSn at room…
In this work a simple concept was used for a systematic search for new materials with high spin polarization. It is based on two semi-empirical models. Firstly, the Slater-Pauling rule was used for estimation of the magnetic moment. This model is well supported by electronic structure calculations. The second model was found particularly for Co$_2$ based Heusler compounds when comparing their magnetic properties. It turned out that these compounds exhibit seemingly a linear dependence of the Curie temperature as function of the magnetic moment. Stimulated by these models, Co$_2$FeSi was revisi…
wo-dimensional (2D) materials unique properties and their promising applications in post-silicon microelectronics have attracted significant attention in the past decade. Recently, ferromagnetic order with out-of-plane easy axis in a monolayer of CrI3 has been observed and reported, with a Curie temperature of 45 K. Here we study, using density functional theory (DFT) calculations, how hydrogen and oxygen adsorption affects the structural, electronic, and magnetic properties of a CrI3 monolayer. Our results show that while the structure remains almost unchanged by the adsorption of hydrogen, a…
Co$_2$FeSi crystallizes in the ordered L2$_1$ structure as proved by X-ray diffraction and Mößbauer spectroscopy. The magnetic moment of Co$_2$FeSi was measured to be about $6μ_B$ at 5K. Magnetic circular dichroism spectra excited by soft X-rays (XMCD) were taken to determine the element specific magnetic moments of Co and Fe. The Curie temperature was measured with different methods to be ($1100\pm20$)K. Co$_2$FeSi was found to be the Heusler compound as well as the half-metallic ferromagnet with the highest magnetic moment and Curie temperature.
Among the recently widely studied van der Waals layered magnets CrX3 (X=Cl, Br, I), CrCl3 monolayer (ML) is particularly puzzling as it is solely shown by experiments to have an in-plane magnetic easy axis and, furthermore, all of previous first-principles calculation results contradict this. Through systematical first-principles calculations,we unveil that its in-plane shape anisotropy that dominates over its weak perpendicular magnetocrystalline anisotropy is responsible for the in-plane magnetic easy axis of CrCl3 ML. To tune the in-plane ferromagnetism of CrCl3 ML into the desirable perpen…
We present a data set of calculated Curie temperatures for the main-phase compounds of rare-earth permanent magnets. We employ ab initio electronic structure calculations for the itinerant ferromagnetism and an effective spin model for the finite-temperature magnetism. Curie temperatures are derived on the basis of a classical Heisenberg model mapped via Liechtenstein's formula for atomic-pair-wise exchange couplings. Relative trends with respect to the species of rare-earth elements in calculated Curie temperatures for R2Fe14B are in agreement with experimental trends. Quantitative comparison…
Employing first-principles electronic structure calculations in conjunction with the frozen-magnon method we study the effective exchange interactions and spin waves in local moment ferromagnets. As prototypes we have chosen three L2$_1$-type full Heusler alloys Cu$_2$MnAl, Ni$_2$MnSn and Pd$_2$MnSn, and the L1$_2$-type XPt$_3$ compounds with X= V, Cr and Mn. We have also included CoPt$_3$ which is a usual ferromagnet. In all compounds due to the large spatial separation ($\sim 4$ Å) of the magnetic transition metal atoms, the 3\textit{d} states belonging to different atoms overlap weakly and …
Single crystals of a new ternary aluminide ErV$_2$Al$_{20}$ were grown using a self-flux method. The crystal structure was determined by powder X-ray diffraction measurements and Rietveld refinement, and physical properties were studied by means of electrical resistivity, magnetic susceptibility and specific heat measurements. These measurements reveal that ErV$_2$Al$_{20}$ is a Curie-Weiss paramagnet down to 1.95 K with an effective magnetic moment $μ_{eff}$ = 9.27(1) $μ_B$ and Curie-Weiss temperature $Θ_{CW}$ = -0.55(4) K. The heat capacity measurements show a broad anomaly at low temperatur…
Magnetic susceptibility $χ$ of Bi$_{2-x}$Mn$_{x}$Se$_3$ ($x = 0.01-0.2$) was measured in the temperature range $4.2-300$ K. For all the samples, a Curie-Weiss behaviour of $χ(T)$ was revealed with effective magnetic moments of Mn ions corresponding to the spin value S=5/2, which couple antiferromagnetically with the paramagnetic Curie temperature $Θ\sim -50$ K. In addition, for the samples of nominal composition $x$ = 0.1 and 0.2 the effect of a hydrostatic pressure $P$ up to 2 kbar on $χ$ has been measured at fixed temperatures 78 and 300 K that allowed to estimate the pressure derivative of …
(Ga,Mn)As and related diluted magnetic semiconductors play a major role in spintronics research because of their potential to combine ferromagnetism and semiconducting properties in one physical system. Ferromagnetism requires ~1-10% of substitutional Mn_Ga. Unintentional defects formed during growth at these high dopings significantly suppress the Curie temperature. We present experiments in which by etching the (Ga,Mn)As surface oxide we achieve a dramatic reduction of annealing times necessary to optimize the ferromagnetic film after growth, and report Curie temperature of 180 K at approxim…
We demonstrate the manipulation of the Curie temperature of buried layers of the ferromagnetic semiconductor (Ga,Mn)As using nanolithography to enhance the effect of annealing. Patterning the GaAs-capped ferromagnetic layers into nanowires exposes free surfaces at the sidewalls of the patterned (Ga,Mn)As layers and thus allows the removal of Mn interstitials using annealing. This leads to an enhanced Curie temperature and reduced resistivity compared to unpatterned samples. For a fixed annealing time, the enhancement of the Curie temperature is larger for narrower nanowires.
We report the parameter-free, density functional theory calculations of interatomic exchange interactions and Curie temperatures of half-metallic ferrimagnetic full Heusler alloys Mn2VZ (Z=Al, Ge). To calculate the interatomic exchange interactions we employ the frozen-magnon approach. The Curie temperatures are calculated within the mean-field approximation to the classical Heisenberg Hamiltonian by solving a matrix equation for a multi-sublattice system. Our calculations show that, although a large magnetic moment is carried by Mn atoms, competing ferromagnetic (inter sublattice) and antifer…
Mn_2V_1-xCo_xZ (Z=Ga,Al and x=0, 0.25, 0.5, 0.75, 1) Heusler compounds have been synthesized to investigate the effect of Co substitution at the V site on the magnetic moment and Curie temperatures of half-metallic ferrimagnets Mn_2VGa and Mn_2VAl. The Co substituted compounds show a non linear decrease in lattice parameter without altering the crystal structure of the parent compounds. The end members Mn_2VGa and Mn_2CoGa have the saturation magnetization of 1.80 μ_B/f.u and 2.05 μ_B/f.u respectively whereas for the Mn_2V_0.5Co_0.5Ga compound, a near total magnetic moment compensation (0.10 μ…
Diluted magnetic semiconductors (DMSs) based on group-IV materials are desirable for spintronic devices compatible with current silicon technology. In this work, amorphous Mn-doped SiGe thin films were first fabricated on Ge substrates by radio frequency magnetron sputtering and then crystallized by rapid thermal annealing (RTA). After the RTA, the samples became ferromagnetic (FM) semiconductors, in which the Curie temperature increased with increasing Mn doping concentration and reached 280 K with 5% Mn concentration. The data suggest that the ferromagnetism came from the hole-mediated proce…
SmCo5 permanent magnets exhibit enormous uniaxial magnetocrystalline anisotropy energy and have a high Curie temperature. However, a low energy product presents a significant drawback in the performance of SmCo5 permanent magnets. In order to increase the energy product in SmCo5, we propose substituting fixed amount of cobalt with iron in a new magnet, SmFe3CoNi, where inclusion of nickel metal makes this magnet thermodynamically stable. We further discuss some basic theoretical magnetic properties of the SmCo5 compound.
Enhanced Curie temperature and room-temperature 50-nm skyrmions achieved in hexagonal ferromagnet Mn5Ge3+x synthesized via a high-pressure method
Anhui University（安徽大学）；Institutes of Physical Science and Information Technology, Anhui University（安徽大学物理科学与信息技朮研究所）；High Magnetic Field Laboratory, HFIPS, Chinese Academy of Sciences（中国科学院合肥物质科学研究院强磁场科学中心）；Hefei Normal University（合肥师范学院）
We have used single crystal X-ray diffraction methods to establish the crystal structures of a compound in the Pd-Mn-Si system and in the Pd-Mn-Ge system. The title compounds have structures related to the Fe$_2$P structure type and are ferromagnetic with Curie temperatures above the room temperature. Density functional electronic structure calculations help to understand the nature of the local moment ferromagnetism in these compounds. However neither the electronic structure calculations nor the magnetic measurements provide any evidence of half-metallic behavior.
By means of high resolution neutron powder diffraction at low temperature we have characterized the structural details of $\rm La_{x}Sr_{2-x}FeMoO_6$ ($0\leq {\rm x}\leq 0.5$) and $\rm Ca_{x}Sr_{2-x}FeMoO_6$ ($0\leq {\rm x}\leq 0.6$) series of compounds. This study reveals a similar variation of the mean bond-angle \FeOMo in both series. In contrast, the mean bond-distance \FeMoO\ increases with La but not with Ca substitution. Both series also present a different evolution of the Curie temperature ($T_C$), which raises in the La series and slightly decreases in the Ca one. We thus conclude th…
Using \textit{ab-initio} methods we study structural, electronic and magnetic properties of two dimensional compounds with stoichiometry M$_2$N$_3$ (M-metal, N=S,Se,Te). Our study shows that structures with Cr, Ti, and Mn are stable, with significant binding energy. Also, such structures are semiconductors with narrow band gaps. We also show that Cr$_2$Se$_3$, Cr$_2$Te$_3$ and Mn$_2$Te$_3$ have considerable magnetic moments. The negative values of magnetic anisotropy energy suggest, that these materials can maintain ferromagnetic ordering in non-zero temperatures with estimated Curie temperatu…
The reaction of Sr2CuO3 with air and liquid water was studied to address the origin of the reported variable Curie-Weiss impurity contribution to the magnetic susceptibility X of this compound at low temperatures. Sr2CuO3 was found to decompose upon exposure to either of these environments. The compound Sr2Cu(OH)6 was identified as the primary reaction product. A pure sample of Sr2Cu(OH)6 was then prepared separately. Electron paramagnetic resonance (EPR), isothermal magnetization versus magnetic field M(H) and X versus temperature T measurements demonstrate that Sr2Cu(OH)6 contains weakly int…
In this report the Co2 based Heusler compounds are discussed as potential materials for spin voltage generation. The compounds were synthesized by arcmelting and consequent annealing. Band structure calculations were performed and revealed the compounds to be half-metallic ferromagnets. Magnetometry was performed on the samples and the Curie temperatures and the magnetic moments were determined. The Seebeck coefficients were measured from low to ambient temperatures for all compounds. For selected compounds high temperature measurements up to 900 K were performed.
Tuning topological and magnetic properties of materials by applying an electric field is widely used in spintronics. In this work, we find a topological phase transition from topologically trivial to nontrivial states at an external electric field of about 0.1 V/A in MnBi$_2$Te$_4$ monolayer that is a topologically trivial ferromagnetic semiconductor. It is shown that when electric field increases from 0 to 0.15 V/A, the magnetic anisotropy energy (MAE) increases from about 0.1 to 6.3 meV, and the Curie temperature Tc increases from 13 to about 61 K. The increased MAE mainly comes from the enh…
The discovery of monolayer MA$_2$Z$_4$ (M = transition metals; A = IVA elements; Z = VA elements, Science 369, 2020, 670-674) family has led another advance for facilitating and harnessing magnetism in low-dimensional materials. However, only Cr and V based MA$_2$N$_4$ compounds exhibit intrinsic magnetism yet with unsatisfied magnetic ordering temperature. Herein, we identify a stable ferromagnetic number of this family, i.e., VGe$_2$Z$_4$ monolayer, by means of first-principles calculations. It is found that the magnetic configuration sustains under both compression and tensile uniaxial in-p…
Two-dimensional (2D) ferromagnets with high Curie temperature have long been the pursuit for electronic and spintronic applications. CrI3 is a rising star of intrinsic 2D ferromagnets, however, it suffers from weak exchange coupling. Here we propose a general strategy of self-intercalation to achieve enhanced ferromagnetism in bilayer CrI3. We showed that filling either Cr or I atoms into the van der Waals gap of stacked and twisted CrI3 bilayers can induce the double exchange effect and significantly strengthen the interlayer ferromagnetic coupling. According to our first-principles calculati…
In two-dimensional (2D) magnetic systems, large magnetic anisotropy is needed to stabilize the magnetic order according to Mermin-Wagner theorem. Based on density functional theory (DFT) calculations, we propose that the magnetic anisotropic energy (MAE) of 2D ferromagnetic (FM) semiconductors can be strongly enhanced in van der Waals heterostructures by attaching a nonmagnetic semiconductor monolayer with large spin-orbit coupling. We studied Cr2Ge2Te6/PtSe2 bilayer heterostructures, where each layer has been realized in recent experiments. The DFT calculations show that the MAE of Cr2Ge2Te6/…
The static magnetic and dynamic properties of the compound (NH3)2(CH2)3CoCl4 are investigated in the temperature interval 0.5-50 K. It is shown that at TN =2.05 K this compound undergoes a transition to a magnetically ordered antiferromagnet state. A distinctive feature of this compound is the presence of temperature hysteresis at the transition to the ordered state (corresponding to a first order magnetic phase transition) and of a spontaneous magnetic moment along the x axis. The paramagnetic Curie temperatures are determined. The frequency-field curves of the AFMR spectrum in the xy plane a…
The caloric effect in Gd5Si2Ge2 compound is studied experimentally and theoretically. The first-order phase transition is sensitive to both magnetic field and pressure. It indicates that the influences of magnetic field and pressure on the phase transition are virtually equivalent. Moreover, the theoretical analyses reveal that the total entropy change is almost definite at a certain Curie temperature whether the applied external field is magnetic field or pressure. On the basis of theoretical analyses, the entropy change simultaneously induced by magnetic field and hydrostatic pressure can be…
The aim of this paper is to investigate the magnetic properties of the M_n B_i magnetic systems by using the Monte Carlo simulation. Indeed, we analyzed the effect of the number of layers on the magnetic properties of the compound M_n B_i. The magnetization, the binder cumulant, the Curie temperature and the hysteresis cycle are also calculated in this work. We used the free boundary conditions to simulate the properties of the studied system, and we presented the effect of multilayer numbers on the magnetic properties of M_n B_i films. Meanwhile, there are clear indications that coercive fiel…
We report CrISe monolayer as a room temperature ferromagnetic semiconductor with the Curie temperature ($T_C$), magnetic anisotropy energy (MAE) and band gap being 322 K, 113 $μ$eV and 0.67 eV, respectively. The $T_C$ and MAE can be further enhanced up to 385 K and 313 $μ$eV by tensile strain. More interestingly, the magnetic easy axis can be switched between off-plane and in-plane by compressive strain. Particularly, due to the broken inversion symmetry and strong spin-orbit coupling of Se atoms, a large Dzyaloshinskii-Moriya interaction (DMI) of 2.40 meV is obtained. More importantly, by mic…
We have studied the electronic structure of hexagonal MnAs, as epitaxial continuous film on GaAs(001) and as nanocrystals embedded in GaAs, by Mn 2p core-level photoemission spectroscopy. Configuration-interaction analyses based on a cluster model show that the ground state of the embedded MnAs nanocrystals is dominated by a d5 configuration that maximizes the local Mn moment. Nanoscaling and strain significantly alter the properties of MnAs. Internal strain in the nanocrystals results in reduced p-d hybridization and enhanced ionic character of the Mn-As bonding interactions. The spatial conf…
We present theoretical results for the underscreened Kondo lattice model with localized S=1 spins coupled to a conduction band through a Kondo coupling, $J_K$, and interacting among them ferromagnetically. We use a fermionic representation for the spin operators and expand the Hamiltonian in terms of bosonic fields. For large values of $J_K$, we obtain a ferromagnetically ordered solution and a Kondo regime with a Kondo temperature, $T_K$, larger than the Curie temperature, $T_C$. This finding suggests a scenario for a coexistence of Kondo effect and ferromagnetic order. In some uranium compou…
We have used low energy implanted muons as a volume sensitive probe of the magnetic properties of EuO_{1-x} thin films. We find that static and homogeneous magnetic order persists up to the elevated T_C in the doped samples and the muon signal displays the double dome feature also observed in the sample magnetization. Our results appear incompatible with either the magnetic phase separation or bound magnetic polaron descriptions previously suggested to explain the elevated T_C, but are compatible with an RKKY-like interaction mediating magnetic interactions above 69 K.
The magnetic properties of a material are determined by a subtle balance between the various interactions at play, a fact that makes the design of new magnets a daunting task. High-throughput electronic structure theory may help to explore the vast chemical space available and offers a design tool to the experimental synthesis. This method efficiently predicts the elementary magnetic properties of a compound and its thermodynamical stability, but it is blind to information concerning the magnetic critical temperature. Here we introduce a range of machine-learning models to predict the Curie te…
The influence of antisite disorder occupancies on the magnetic properties of the half-metallic Co$_2$MnSi compound was studied by experimental techniques and first-principles calculations. The neutron diffraction studies show almost identical amount of Mn and Co disorders of 6.5\% and 7.6\%, which was found to be in good agreement with density functional theory (DFT) calculations of the stable Co$_2$MnSi system with the corresponding disorders. DFT studies reveal that antiferromagnetic interactions introduced by Mn disorder lead to a reduction of the net magnetic moment. The results are discus…
Hill plot is a well-known criterion of the f-electron element interatomic threshold-distance separating the nonmagnetic state from the magnetic one in actinides or lanthanides. We have reinvestigated the Hill plot of Ce compounds using a commercial crystallographic database CRYSTMET, focusing on a relationship between the Ce-Ce distance and the magnetic ordering temperature, because a Ce compound with no other magnetic elements scarcely has a magnetic ordering temperature higher than 20 K. The Hill plot of approximately 730 compounds has revealed that a Ce compound, especially for ferromagnet,…
We compute the magnetocaloric effect (MCE) in the GdTX (T=Sc, Ti, Co, Fe; X=Si, Ge) compounds as a function of the temperature and the external magnetic field. To this end we use a density functional theory approach to calculate the exchange-coupling interactions between Gd$^{3+}$ ions on each compound. We consider a simplified magnetic Hamiltonian and analyze the dependence of the exchange couplings on the transition metal T, the p-block element X, and the crystal structure (CeFeSi-type or CeScSi-type). The most significant effects are observed for the replacements Ti $\to$ Sc or Fe $\to$ Co …
A partial substitution of Sm by Ce can have drastic effects on the magnetic performance, because it will introduce strain in the structure and breaks the lattice symmetry in a way that enhances the contribution of the Co atoms to magnetocrystalline anisotropy. However, Ce substitutions, which are benefit to improve the magnetocrystalline anisotropy, are detrimental to enhance the Curie temperature (TC). With the requirements of wide operating temperature range of magnetic devices, it is important to quantitatively explore the relationship between the TC and ferromagnetic exchange energy. In th…
Rutile CrO$_2$ is an important half-metallic ferromagnetic material, which is also widely used in magnetic recording. In an attempt to find the conditions, which lead to the increase the Curie temperature ($T_{\rm C}$), we study theoretically the band-filling dependence of interatomic exchange interactions in the rutile compounds. For these purposes, we use the effective low-energy model for the magnetic $t_{2g}$ bands, derived from the first-principles electronic structure calculations in the Wannier basis, which is solved by means of dynamical mean-field theory. After the solution, we calcul…
Recent studies have reported an interesting class of semiconductor materials that bridge the gap between semiconductors and halfmetallic ferromagnets. These materials, called spin gapless semiconductors, exhibit a bandgap in one of the spin channels and a zero bandgap in the other and thus allow for tunable spin transport. Here, a theoretical and experimental study of the spin gapless Heusler compound Mn2CoAl is presented. It turns out that Mn2CoAl is a very peculiar ferrimagnetic semiconductor with a magnetic moment of 2 μB and a high Curie temperature of 720 K. Below 300 K, the compound exhi…
Van der Waals magnetic materials are building blocks for novel kinds of spintronic devices and playgrounds for exploring collective magnetic phenomena down to the two-dimensional limit. Chromium-tellurium compounds are relevant in this perspective. In particular, the 1$T$ phase of CrTe$_2$ has been argued to have a Curie temperature above 300~K, a rare and desirable property in the class of lamellar materials, making it a candidate for practical applications. However, recent literature reveals a strong variability in the reported properties, including magnetic ones. Using electron microscopy, …
