Ferrimagnetism in CsMn1−xNixF3 and CsMn1−xCoxF3

CsMn_1?xNi_xF₃ with 0.3≦x≦0.5 and CsMn_1?xCo_xF₃ with 0.4≦x≦0.65 have been found to be ferrimag with a Curie temperature 50±1K. The magnetic moment at 4.2 K is 1.42μ_B per formula-unit for CsMn_0.65Ni_0.35F₃, and 1.77μ_B for CsMn_0.6Co_0.4F₃. The crystal structure has been determined to be rhombohedral; it probably has a stacking of twelve CsF₃-layers in the unit cell in hexagonal representation. Magnetic properties have been explained on the assumption that a Ni(Co) ion has a strong preference for occupying one of three inequivalent sites in the structure. It has been suggested that the magnetic moments of one-quarter of the magnetic ions couple antiparallel to those of the other three-quarters so that ferrimagnetism appears. The Curie temperature has been discussed in the molecular field approximation.     

Neutron diffraction study of magnetic order in TbRh2Ge2 and TbRu2Ge2

TbRh₂Ge₂ orders antiferromagnetically in the AFI type structure with a magnetic moment of 9.4(3)μ_B at 4.2 K localized on the Tb³⁺ ion. TbRu₂Ge₂ exhibits a square modulated magnetic structure with moments aligned along the c-axis of the crystallographic unit cell. The magnitude of the magnetic moment localized on the Tb³⁺ ion is 9.1(1)μ_B at 4.2 K.     

Magnetism of single-walled silicon carbide nanotubes doped by boron,nitrogen and oxygen

We calculated, using spin polarized density functional theory, the electronic properties of zigzag (10,0) and armchair (6,6) semiconductor silicon carbide nanotubes (SiCNTs) doped once at the time with boron, nitrogen, and oxygen. We have looked at the two possible scenarios where the guest atom X (B, N, O), replaces the silicon X_Si, or the carbon atom X_C, in the unit cell. We found that in the case of one atom B @ SiCNT replacing a carbon atom position annotated by B_C exhibits a magnetic moment of 1 μ_B/cell in both zigzag and armchair nanotubes. Also, B replacing Si, (B_Si), induce a magnetic moment of 0.46 μ_B/cell in the zigzag (10,0) but no magnetic moment in armchair (6,6). For N substitution; (N_C) and (N_Si) each case induce a magnetic moment of 1 μ_B/cell in armchair (6,6), while N_Si give rise to 0.75 μ_B/cell in zigzag (10,0) and no magnetic moment for N_C. In contrast the case of O_C and O_Si did not produce any net magnetic moment in both zigzag and armchair geometries.     

Magnetic properties of Mn doped BN compound

Electronic and magnetic properties of diluted B_1−xMn_xN alloys are calculated by means of the full potential linearized augmented plane wave (FP-LAPW) method and the generalized gradient approximation (GGA). A half-metallic state is predicted for a composition of 6.25%. The spin majority being metallic and minority being semiconducting. We found a total magnetic moment of 2 μ_B (Bohr-magnetons) per supercell, in agreement with the half-metallic behaviour. The main contribution of the cell magnetic moment is localized at the transition metal site Mn, with a local moment of 1.24 μ_B.     

Magnetic structure of YMn12

YMn₁₂ crystallizes in the I₄/mmm tetragonal body-centred structure. Neutron diffraction experiments give evidence for an antiferromagnetic structure (T_N = 120 K) in the tetragonal cell. The magnetic structure has been determined with the help of group theory. The mean Mn magnetic moment is 0.4μ_B. In spite of the non-colinear arrangement of magnetic moments strong negative anisotropic interactions are evidenced. As it is observed in pure Mn and in rare earth-Fe compounds, these interactions are strongly distance dependent.     

Influence of Ni-concentration on the magnetic structure in Tb(Cu,Ni)2 system

A powder sample of orthorhombic Tb(Cu_0.7Ni_0.3)₂ has been studied by neutron diffraction at T = 4.2 K and above the Curie temperature. It is found that this compound is ferromagnetically ordered at 4.2 K. The magnetic moment of Tb in this compound is (9.2 ± 0.2)μ_B, with components (2.2 ± 0.2, 0, 8.9 ± 0.1)μ_B. The influence of the Ni-concentration on the magnetic structure is discussed in the whole Tb(Cu, Ni)₂ system.     

The magnetic structure of the monoclinic modification of ErOOH

The magnetic structure of ErOOH has been investigated. The compound is antiferromagnetic. The spins are in the [010] direction. A magnetic moment of 7.14μ_B for Er³⁺ is determined from the neutron diffraction data.     

Comparison of the structural and magnetic properties of ground-state SrTcO3 and CaTcO3 from first principles

The generalized gradient approximation (GGA) plus on-site Coulomb interaction corrections (GGA+U) method is employed for the total energies and electronic structure calculations of SrTcO₃ and CaTcO₃. G-type antiferromagnetic (G-AFM) is found to be ground state for both compounds, in consistence with the previous experimental results. The mechanism of Neel temperature of SrTcO₃ being higher than that of CaTcO₃ is explored. The insulating band gaps of SrTcO₃ and CaTcO₃ are found to be 1.71 eV and 1.74 eV, respectively. The magnetic moment of Tc1 is found to be 2.237μ_B in SrTcO₃ unit cell and 2.266μ_B in CaTcO₃ unit cell. Structural parameters and electronic structure of the two compounds are examined to explore the origin of their different electrical and magnetic characters.     

Magnetic properties of Europium-graphite intercalation compound C6Eu

An ordered state with a complex magnetic structure has been observed below 4CK. The magnetization for H ⊥ c (c; the c-axis) shows a field-induced phase transition from a small magnetic moment state ( ～ 0.6μ_B) at lower fields to a larger moment one ( 2.2 - 2.5μ_B) above 25kG. The transition field depends on temperature and is found to be 5 - 2kG. The magnetization for H//c has only a sublinear field dependence. Above 40K the magnetic susceptibility obeys the Curie-Weiss law with θ = +1.3K and the molar Curie constant C_m = 6.78, which suggests that Eu ion is divalent in C₆Eu.     

Ab-initio investigation of electronic properties and magnetism of half-Heusler alloys XCrAl (X=Fe, Co, Ni) and NiCrZ (Z=Al, Ga, In)

The electronic structures and magnetism of the half-Heusler alloys XCrAl (X=Fe, Co, Ni) and NiCrZ (Z=Al, Ga, In) have been investigated to search for new candidate half-metallic materials. Here, we predict that NiCrAl, and NiCrGa and NiCrIn are possible half-metals with an energy gap in the minority spin and a completely spin polarization at the Fermi level. The energy gap can be attributed to the covalent hybridization between the d states of the Ni and Cr atoms, which leads to the formation of bonding and antibonding peaks with a gap in between them. Their total magnetic moments are 1μ_B per unit cell; agree with the Slater-Pauling rule. The partial moment of Cr is largest in NiCrZ alloys and moments of Ni and Al are in antiferromagnetic alignment with Cr. Meanwhile, it is also found that FeCrAl is a normal ferromagnetic metal with a magnetic moment of 0.25μ_B per unit cell and CoCrAl is a semi-metal and non-magnetic.     

Neutron diffraction study of β-UD3 and β-UH3

The results of a neutron powder diffraction study on β-UD₃ and β-UH₃ are reported. Diffraction patterns have been obtained both above (220 K) and below (10 K) the Curie temperature, in order to refine the crystal structure on the basis of a large number of resolved Bragg peaks and to obtain the ordered magnetic moment. The two kinds of uranium atoms present in the structure appear to be magnetically equivalent. The observed magnetic moment for β-UD₃ at T = 10 K is μ_ord = (1.45 ? 0.11) μ_B/U_atom     

A new measurement of the magnetic moment of the neutron

The magnetic moment of the neutron has been measured with a factor of one hundred improvement in accuracy. In terms of the Bohr magneton and proton magnetic moment, respectively, the result is μ_n/μ_B= ?1.041 875 79 (26) × 10^?3, μ_n/μ_p = ?0.684 979 45 (17).     

Magnetic ordering above room temperature in the sigma-phase of Fe66V34

Magnetic properties of four sigma-phase Fe_100−xV_x samples with 34.4?x?55.1 were investigated by Mössbauer spectroscopy and magnetic measurements in the temperature interval 4.2-300 K. Four magnetic quantities, viz. hyperfine field, Curie temperature, magnetic moment and susceptibility, were determined. The sample containing 34.4 at% V was revealed to exhibit the largest values found up to now for the sigma-phase for average hyperfine field, 〈B〉=12.1 T, average magnetic moment per Fe atom, 〈μ〉=0.89 μ_B, and Curie temperature, T_C=315.3 K. The quantities were shown to be strongly correlated with each other. In particular, T_C is linearly correlated with 〈μ〉 with a slope of 406.5 K/μ_B, as well as 〈B〉 is so correlated with 〈μ〉, yielding 14.3 T/μ_B for the hyperfine coupling constant.     

High spin polarization in ordered Cr3Co with the DO3 structure: A first-principles study

The electronic structure of the highly ordered alloy Cr₃Co with the DO₃ structure has been studied by FLAPW calculations. It is found that the ferrimagnetic state is stable and that the equilibrium lattice constant of Cr₃Co equals 5.77 Å. A large peak in majority spin density of states (DOS) and an energy gap in minority spin DOS are observed at the Fermi level, which results in a high spin polarization of 90% in the ordered alloy Cr₃Co. The total magnetic moment of Cr₃Co is 3.12μ_B, which is close to the ideal value of 3μ_B derived from the Slater-Pauling curve. An antiparallel alignment between the moments on the Cr (A, C) sites and the Cr (B) sites is observed. Finally, the effect of lattice distortion on the electronic structure and on magnetic properties of Cr₃Co compound is studied. A spin polarization higher than 80% can be obtained between 5.55 and 5.90 Å. With increasing lattice constant, the magnetic moments on the (A, C) sites increase and the moments on the (B, D) sites decrease. They compensate each other and make the total magnetic moment change only slightly.     

The magnetic structure of cubic ErAl3

The magnetic structure of cubic or β-ErAl₃ has been investigated by neutron diffraction from powder samples. ErAl₃ undergoes a transition at 5·1°K, to an antiferromagnetic state with an enlarged tetragonal unit cell. The moments are directed perpendicular to the tetragonal c-axis. Crystal field effects are large and dominant in this compound. The extrapolated saturation moment is 5·1/μ_B, which corresponds to the Γ₈ ground state.     

Cr-Co-Ga Heusler合金新材料探索和物性研究

通过实验和计算研究了从Co₂CrGa到Cr₂CoGa一系列渐变成分合金(Co_50-xCr_x+25Ga₂₅,x=0—25) 的结构、磁性及输运性质.当Cr不断替代A位Co时,晶体结构逐渐从典型的L2₁结构过渡到Hg₂CuTi结构,晶格常数线性地增大0.69%.合金的磁性从Co_{2 关键词： CrCoGa Hesuler合金 KKR-CPA-LDA计算}     

The change in the character of phase transition with nickel in the Ho(Co,Ni)2 compounds

The series Ho(Co_1-cN_c)₂ has been investigated in the composition range c?0.15 by spin-echo NMR of ¹⁶⁵Ho and by magnetic measurements. From NMR data a value of (9.5±0.1)μ_B is estimated for holmium in HoCo₂. Magnetisation measurements on the same compound give (7.9±0.1)μ_B/fu. An assumption of 0.8μ_B for the cobalt moment aligned antiparallel to that of holmium leads to a value of 9.5μ_B for holmium in agreement with the value estimated from NMR. The substitution of nickel for cobalt causes a rapid fall in both the hyperfine field, and the ordering temperatures, while the molecular moment shows a simultaneous rise. These are attributed to a rapid fall in the cobalt moment which leads to a bootstrap process involving the strength of the exchange field and the magnitude of the cobalt moment. Nickel substitution also leads to a change in the character of the magnetic phase transition. Initially first order, this transition becomes second order on exceeding ≈ 9 at% Ni.     

Magnetic moment of 57Ni

An extra neutron added to a doubly magic nuclear core should give a nuclear magnetic moment, μ, in close agreement with the Schmidt value. However, the magnetic moment of ⁵⁷Ni, measured through nuclear alignment at 3–20 mK, is equal to ∣μ∣ = 0.88±0.06 μ_N which is only 45% of the Schmidt value. Comparison with several nuclear structure calculations is made.     

Investigations of cobalt and carbon codoping in gallium nitride for spintronic applications

Extensive theoretical investigations have been carried out to study the ferromagnetic properties of transition metal doped wurtzite GaN using the Tight Binding Linear Muffin-tin Orbital (TBLMTO) method within the density functional theory. The present calculation reveals ferromagnetism in cobalt doped GaN when one gallium is replaced by cobalt in a 3×3×2 supercell of GaN, which gives rise to a cobalt concentration of 2.77%. The system is half-metallic with a magnetic moment of 4.0 μ_B. When Co is bonded with one carbon, there is a drastic decrease in magnetic moment and the system becomes metallic. When Co dimer is introduced via nitrogen which corresponds to the Co concentration of 5.5% the magnetic moment is 3.99 μ_B and the system is half-metallic. Same trend is observed when Co is bonded via nitrogen with unequal distance. When cobalt dimer is formed via carbon, the moment becomes 2.95 μ_B and it shows metallic character. For dimer via carbon with unequal distance, the moment is 3.0 μ_B and the system becomes semiconductor. For higher percentage of cobalt dopant the system shows metallic character. C and Co doped GaN samples have been synthesized experimentally and characterized with X-ray diffraction, transmission electron microscopy, micro-Raman and superconducting quantum interface device measurements. The observed results are correlated with the theoretical studies.