Magnetic Properties Of Intermetallic Compounds Research Articles

Epitaxy, exfoliation, and strain-induced magnetism in rippled Heusler membranes

Single-crystalline membranes of functional materials enable the tuning of properties via extreme strain states; however, conventional routes for producing membranes require the use of sacrificial layers and chemical etchants, which can both damage the membrane and limit the ability to make them ultrathin. Here we demonstrate the epitaxial growth of the cubic Heusler compound GdPtSb on graphene-terminated Al2O3 substrates. Despite the presence of the graphene interlayer, the Heusler films have epitaxial registry to the underlying sapphire, as revealed by x-ray diffraction, reflection high energy electron diffraction, and transmission electron microscopy. The weak Van der Waals interactions of graphene enable mechanical exfoliation to yield free-standing GdPtSb membranes, which form ripples when transferred to a flexible polymer handle. Whereas unstrained GdPtSb is antiferromagnetic, measurements on rippled membranes show a spontaneous magnetic moment at room temperature, with a saturation magnetization of 5.2 bohr magneton per Gd. First-principles calculations show that the coupling to homogeneous strain is too small to induce ferromagnetism, suggesting a dominant role for strain gradients. Our membranes provide a novel platform for tuning the magnetic properties of intermetallic compounds via strain (piezomagnetism and magnetostriction) and strain gradients (flexomagnetism).

Synthesis, processing and characterization of FeMnGa nanoparticles for permanent magnet applications

In recent years, there is a great demand in materials suitable for permanent magnets which led to shortages in the supply of rare earth elements, a basic ingredient of high performance magnets. Research for rare earth free magnetic materials is considered as a viable alternative. Various Heusler alloys are investigated as possible candidates. Among them, the binary compound MnXGa has gained interest. A method of improving the magnetic properties of intermetallic compounds is the introduction of a magnetic atom like Fe in replacement of a 3d metal, in our case, by replacing a quantity of Mn with Fe. In this study Mn0.4Fe0.3Ga0.3 alloys were prepared in a high purity Ar atmosphere with the arc-melting technique followed by melt-spinning in order to get nanostructured ribbons. The samples were further treated (annealing, ball milling) in order to tune the microstructure and obtain single phase samples with optimum magnetic properties. Magnetization measurements were performed by using a Vibrating Sample Magnetometer (VSM), versus temperature and field. The structure of the samples was observed with the X-Ray Diffraction Patterns (XRD). The L12 structure was observed for the first time, among the other ones D019 and L21 which are already observed in Mn3Ga studies. A deeper observation was performed with a Scanning Electron Microscope (SEM). Saturation magnetization of the basic material was measured at 81.4 Am2/kg while remanence and coercive field were low. The effect of the grain size on the magnetic properties, due to ball milling, is presented.

Magnetic anisotropy in intermetallic compounds containing both uranium and 3d-metal

Magnetic properties of intermetallic compounds containing both uranium and a 3d metal (Fe, Co) are summarized and discussed. It was shown that the ordered magnetism of the U and 3d-metal sublattices can coexist in the same compound (e.g. with 2–17 and 1–12 stoichiometries) even at room and elevated temperatures.

Crystalline electric field parameters for RTX2 compounds

The RTxX2(x≤1) type metallic compounds where R is a rare-earth element, T is a d-electron element and X is a p-electron element (X = Si, Ge, Sn) crystallize in different orthorhombic crystal structures. The systems exhibit complex magnetic behaviour. Their magnetism arises from the long range interaction of the magnetic moments localized on the rare-earth ions, described by RKKY model. The magnetic ordering in these systems is not purely of the RKKY-type but is modified by the crystalline electric field effect, which can significantly influence the magnitude of the Néel temperature and decrease the rare-earth magnetic moments as compared with the free ion values. The determination of the CEF parameters is important for understanding the nature of magnetic properties of intermetallic compounds. The Bnm parameters were calculated for RTX2 compounds using the so-called point-charge model. The quadrupole splitting observed in the Mössbauer spectra of GdTxSn2 compounds (T = Fe, Co, Ni, Cu) allow to determined the experimental values of B20 parameters for RTX2 compounds.

Structure and magnetic properties of intermetallic compounds (Gd1-xRx)3Fe28Nb (R = Ce, Nd, Sm)

The effect of the substitution of Sm, Nd and Ce for Gd on the structure and magnetic properties of (Gd1-xRx)3Fe28Nb (R = Sm, Nd and Ce) compounds have been studied. The single-phase regions for R = Sm, Nd and Ce correspond to the composition range of 0 x0.2, 0 x0.5 and 0 x0.4, respectively. All of the compounds crystallize in the Nd3Fe29-xTix-type structure. The lattice parameters a, b, c and V increase with the increase of the Sm and Nd content, while decrease with an increase of the Ce content. Substitution of Sm, Nd and Ce for Gd leads to a decrease of Curie temperature (TC) and an increase of the saturation magnetization (MS). The compounds (Gd1-xSmx)3Fe28Nb and (Gd1-xNdx)3Fe28Nb exhibit planar anisotropy perpendicular to the [102] direction, the anisotropy field HA increases with the substitution content, while in compounds (Gd1-xCex)3Fe28Nb, the planar anisotropy field HA decreases with an increase of the Ce content. (Gd0.6Ce0.4)3Fe28Nb exhibits an intermediate easy axis behaviour.

Structure and magnetic properties of intermetallic compounds (La1−xRx)2Co16Ti (R=Sm, Nd)

The influence of R substitution in (La 1− x R x ) 2 Co 16 Ti compounds (R=Sm, Nd; x =0.0–1.0) on structural and magnetic properties has been investigated. The lattice parameters of the (La 1− x R x ) 2 Co 16 Ti compounds decrease with increasing x in the range 0≤ x ≤1.0. With x increasing, the saturation magnetic moment increases for (La 1− x Nd x ) 2 Co 16 Ti while remains unaffected for (La 1− x Sm x ) 2 Co 16 Ti. The Curie temperature increases with increasing Sm or Nd substitution. The uniaxial magnetocrystalline anisotropy of (La 1− x Sm x ) 2 Co 16 Ti becomes enhanced with increasing Sm substitution. The anisotropy of (La 1− x Nd x ) 2 Co 16 Ti changes from easy-axis ( x <0.4) to easy-plane anisotropy ( x >0.4).

Structure and magnetic properties of intermetallic compounds of the composition Gd3(Fe,Ni)28(Nb,Mo)

The effect of the substitution of Ni for Fe on the magnetic and structural properties of Gd-3(Fe28-xNix)(Nb1-y,Mo-y) (x less than or equal to 4, y=0.3 and 0.7) compounds have been studied. All of the compounds crystallize in the Nd3Fe29-xTix-type structure and the lattice parameters a, b, c and the unit cell volume V decrease with increasing Ni content. Substitution of Ni for Fe leads to a clear increase of the Curie temperature (T-C) and to a small decrease of the saturation magnetization (M-S). The compounds exhibit planar anisotropy perpendicular to the [102] direction. The anisotropy field H-A decreases with increasing Ni content. The effect of Ni substitution on the Curie temperature and the saturation magnetization are discussed. (C) 1999 Elsevier Science S.A. All rights reserved.

Relationship between the structural and the magnetic properties of ErMN 12 − xFe x compounds

The crystal and magnetic properties of intermetallic compounds of formula ErMn 12− x Fe x with x = 0, 2, 4, 6, 8, have been analyzed versus the relative distribution of the transition metal (Mn or Fe) on the different d-metal sites of the tetragonal structure. Neutron diffraction and magnetisation measurements allow better understanding of the relationships between the atom ordering and the (Mn,Fe)-(Mn,Fe), (Mn,Fe)-Er and Er-Er magnetic couplings.

Ups and Downs of Magnetic Properties of Intermetallic Compounds during Mechanical Milling

Ups and Downs of Magnetic Properties of Intermetallic Compounds during Mechanical Milling

Effect of carbon on the structural and magnetic properties of intermetallic compounds with the ThMn12 structure

Carbon was introduced by arc melting to RTiFe11, where R=Sm, Gd, Th, Dy, Ho, Er, and Y, and its effects on the crystallographic and magnetic properties of these compounds have been investigated by x-ray and magnetic measurements. The experimental results show that the carbon atoms occupy 8i sites in ThMn12 structure. It is found that the substitution does not have an effect on the Curie temperature, but instead increases both saturation magnetization and magnetocrystalline anisotropy. The intrinsic magnetic properties of SmTiFe11 are improved with the addition of the carbon atoms, indicating that SmTiFe11−xCx is a better candidate for permanent magnetic applications than SmTiFe11.

Thermodynamic, electronic and magnetic properties of intermetallic compounds through statistical models

Local and average electronic and magnetic properties of transition metal alloys are strongly correlated to the distribution of atoms on the lattice sites. The ability of some systems to form long range ordered structures at low temperature allows to discuss their properties in term of well identified occupation operators as those related to long range order (LRO) parameters. We show that using theoretical determinations of these LRO parameters through statistical models like the cluster variation method (CVM) developed to simulate the experimental phase diagrams, we are able to reproduce a lot of physical properties. In this paper we focus on two points: (i) a comparison between CVM results and an experimental determination of the LRO parameter by NMR at 59Co in a CoPt3 compound, and (ii) the modelling of the resistivity of ferromagnetic and paramagnetic intermetallic compounds belonging to Co-Pt, Ni-Pt and Fe-Al systems. All experiments were performed on samples in identified thermodynamic states, implying that kinetic effects are thoroughly taken into account.

Effect of nitrogen on the structural and magnetic properties of intermetallic compounds with the ThMn12 structure

The effects of nitrogen uptake on the structural and magnetic properties of RFe12−xTx alloys have been studied. Several interstitial nitrides with composition RFe12−xTxNy (R=Nd and Sm and T=Ti and V) were prepared by heat treating fine powders of RFe12−xTx alloys in N2 gas. Preliminary results show the following observations: (1) The ThMn12 structure of the original compounds is retained with the addition of nitrogen but with increased lattice constants (a and c). (2) The Curie temperature is greatly enhanced by about 150–175 K. (3) The character of magnetic anisotropy is changed from ‘‘weak uniaxial’’ type to ‘‘strong uniaxial’’ type for NdFe12−xTxNy and from ‘‘uniaxial’’ to ‘‘planar’’ for SmFe12−xTxNy.

Apparatus for in situ measurements of influence of hydrogen absorption on the magnetic properties of intermetallic compounds

A laboratory apparatus for studying in situ change of magnetic properties of the intermetallic compounds upon hydrogen absorption was constructed. Both magnetization and Pressure Temperature Concentration (PTC) relations are determined simultaneously by using a combination of the extraction magnetometer and PTC-measuring unit. Absorbed or desorbed amounts of hydrogen are measured volumetrically.

Effect of carbon take-up on the crystal-field effects in rare-earth compounds R 2Fe 17

The 155Gd Mössbauer effect and the magnetic properties of intermetallic compounds of the type Gd 2Fe 17C x were studied. From the quadrupole splitting of the Mössbauer spectra we determined the signs and the magnitudes of the electric field gradients present at the gadolinium nuclei in these compounds. The second-order field parameter A 2 0 estimated from these field gradients was shown to be in agreement with an easy magnetization direction parallel to the c axis, as found in Sm 2Fe 17C 0.6.

Half-metallic ferromagnets. I. Structure and magnetic properties of NiMnSb and related inter-metallic compounds

The authors present investigations of the crystal structure the microstructure and the magnetic properties of the inter-metallic compounds XMnSb (X=Pt, Ni, Co, Au, Cu) and PtMnSn. It was found that several of these materials contain precipitates of other phases and/or large atomic disorder, which can be influenced by heat treatment. The magnetic properties show an effective paramagnetic moment which differs from the value corresponding to the saturation moment at 0 K. This effect is attributed to a decrease of the conduction electron spin polarisation at high temperature.

ChemInform Abstract: Hydrogen Induced Change of the Magnetic Properties of Intermetallic Compounds

ChemInform Abstract: Hydrogen Induced Change of the Magnetic Properties of Intermetallic Compounds

Magnetic properties of intermetallic compounds studied by 169Tm Mössbauer spectroscopy

In this paper a review is given of the most recent investigations of intermetallic thulium compounds using 169Tm Mössbauer spectroscopy. The magnetic properties are described in terms of a Hamiltonian, which comprises the exchange interaction and the crystal field interaction.

Mössbauer spectroscopy and x-ray diffraction studies of neptunium intermetallics under high pressure†

The magnetic properties of intermetallic compounds of the light actinides vary from primary local moment behaviour through itinerant electron magnetism to non-magnetic behaviour. A dominant parameter separation of the actinide ions which experimentally can be varied by the microscopic magnetic behaviour we performed Mössbauer experiments on NpAl 2, NpOs 2, NpCo 2Si 2, and NpAs using the 60 keV transition in 237Np. The magnetic hyperfine field B hf and the isomer shift S, which are a measure of the ordered magnetic moment and the s-electrondensity at the nucleus, respectively, as well as the magnetic ordering temperatures have been determined at various pressures up to 70 kbar and in the temperature range from 1.6 K to 77 K. In addition, the lattice parameter variation of NpAl 2 was measured up to 100 kbar at room temperature by X-ray diffraction. We obtained the following results: 1. In the cubic Laves phase compounds NpAl 2 and NpOs 2 with a NpNp distance at ambient pressure of 3.371 Å and 3.258 Å, respectively, we observed a strong decrease to B hf and Curie temperature with pressure indicating a progressive delocalization of the 5f electrons. This is markedly confirmed by the isomer shift. In addition , line broadenings are observed which point towards fluctuations phenomena and show that the delocalization process is of a dynamical nature [1–3]. 2. The X-ray measurements demonstrate an increase of the compressibility of NpAl 2 by a factor of 5 when a pressure of 80 kbar is applied. This behaviour further supports the picture of 5f delocalization with reduced atomic volume. A collapse of volume on account of 5f delocalization 3. has been predicted theoretically for Am metal [4], but could not yet be experimentally verified for this element. 4. In NpCo 2Si 2 which has a tetragonal structure and a nearest neighbour distance of 3.877 Å the magnetic hyperfine field remains constant under pressure. It indicates that in this compound the 5f electrons are well localized. The Néel temperature T N increases with smaller volume. The variation of T N can be explained quantitatively in terms of the rigid spin model of Ruderman-Kittel-Arrott [5, 6] 5. NpAs which has an even larger NpNp separation of 4.128 Å shows a complex hyperfine pattern at 70 kbar consisting of several subspectra. Two different lattice structures coexist: The NaCl type structure and unknown high pressure phase. The hyperfine field belonging to the former is only slightly (∼4%) reduced when pressure (70 kbar) is applied and illustrates its highly localized property. The subspectrum of the latter structure gives a reduction of B hf of ∼16% with respect to the values of the NaCl phase.

Hydrogen absorption and magnetic properties of intermetallic compounds based on 3d elements

Hydrogen absorption and magnetic properties of intermetallic compounds based on 3d elements

NEUTRON DIFFRACTION STUDY OF THE Ho-Fe SYSTEM

The magnetic properties of intermetallic compounds in the Ho-Fe system have been investigated. Neutron diffraction analyses have been carried out on HoFe2, Ho6Fe23 and Ho2Fe17 over a large range of magnetic reflections. The magnetic moments of the Fe atoms are found to be localized and not dependent on the rare earth amount in the alloys as has been found previously in Co or Ni intermetallic compounds. The moment values of Ho and Fe are in good agreement with the measured spontaneous magnetization assuming a ferrimagnetic model. The decrease of Curie temperature, 610 °K, 560 °K and 325 °K respectively, with increasing iron concentration is discussed in terms of coordination number and interatomic distances between the Fe atoms, according to the Neel-Slater theory.