Showing papers on "Antiferromagnetism published in 1985"

Dinuclear Complexes with Predictable Magnetic Properties

Abstract: When two paramagnetic transition metal ions are present in the same molecular entity, the magnetic properties can be totally different from the sum of the magnetic properties of each ion surrounded by its nearest neighbors. These new properties depend on the nature and the magnitude of the interaction between the metal ions through the bridging ligands. If both ions have an unpaired electron (e.g. Cu2+ ions), then the molecular state of lowest energy is either a spin singlet or a spin triplet. In the former case, the interaction is said to be antiferromagnetic, in the latter case ferromagnetic. The nature and the order of magnitude of the interaction can be engineered by judiciously choosing the interacting metal ions and the bridging and terminal ligands, and, thus, by the symmetry and the delocalization of the orbitals centered on the metal ions and occupied by the unpaired electrons (magnetic orbitals). The first success in this “molecular engineering” of bimetallic compounds was in the synthesis of a Cu2+VO2+ heterobimetallic complex in which the interaction is purely ferro-magnetic. The same strategy could be utilized for designing molecular ferromagnets, one of the major challenges in the area of molecular materials. Another striking result is the possibility of tuning the magnitude of the interaction through a given bridging network by modifying the nature of the terminal ligands, which, in some way, play the role of “adjusting screws”. By careful selection of the bridging and terminal ligands, a very large antiferro-magnetic interaction can be achieved, even if the metal ions are far away from each other. Some sulfur-containing bridges are especially suitable in this respect.

Theory of magnetic and structural ordering in iron.

Abstract: Using the total-energy general-potential linearized-augmented-plane-wave method, we have tested the adequacy of the local-spin-density approximation for describing the magnetic and structural properties of iron. We find that there are fundamental deficiencies in the local-spin-density approximation, both quantitative and qualitative, in that there are substantial errors in the calculated ground-state volumes and magnetic moments, as well as a prediction of the wrong ground-state crystal structure.

Mictomagnetic, ferromagnetic, and antiferromagnetic transitions in La(FexAl1-x)13 intermetallic compounds.

Abstract: Cubic La(${\mathrm{Fe}}_{\mathrm{x}}$${\mathrm{Al}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${)}_{13}$ intermetallic compounds can be stabilized with iron concentration x between 0.46 and 0.92 in the ${\mathrm{NaZn}}_{13}$-type structure (D${2}_{3}$) with Fm3c (${O}_{h}^{6}$) space-group symmetry. Here the Fe-Fe coordination number can increase up to 12. At low x values, a mictomagnetic regime occurs with distinct cusps in the ac susceptibility. With the increase of the iron concentration, a soft ferromagnetic phase is found which at lower temperatures shows anisotropy effects related to reentrant mictomagnetic behavior. Finally, for xg0.86, antiferromagnetic order appears along with a sharp metamagnetic transition in external fields of a few teslas. The saturation magnetic moment increases linearly with x from 1.4${\ensuremath{\mu}}_{B}$/Fe to 2.1${\ensuremath{\mu}}_{B}$/Fe throughout the ferromagnetic and antiferromagnetic regime. The breakdown of long-range ferromagnetic order at high x values can be explained by modifications of the iron moment and their coupling at a large Fe-Fe coordination number. However, with application of a magnetic field, the ferromagnetic state can be fully recovered. The room-temperature resistivity decreases with increasing x from 200 to 160 \ensuremath{\mu}\ensuremath{\Omega} cm. The low-temperature slope d\ensuremath{\rho}/dT is related to the magnetic order, being negative in the antiferromagnetic state and positive in the ferromagnetic state. The metamagnetic transition causes a decrease of the resistivity of about 20% and a sign change in d\ensuremath{\rho}/dT. This behavior is discussed in terms of the two-current model. The thermal expansion exhibits a strong Invar character and is described by a combined band and local-moment model which allows calculations of corresponding magnetovolume coupling constants. The metamagnetic transition causes a large magnetic striction.

Calculated electronic structure of chromium surfaces and chromium monolayers on iron.

Abstract: A self-consistent calculation of the magnetic and electronic properties of the chromium (100) and (110) surfaces and of a chromium monolayer on the (100) and (110) iron surfaces is presented. It is found that (i) the (100) chromium surface is ferromagnetic with a greatly enhanced spin polarization (3.00 electrons); (ii) a substantial enhancement of the spin imbalance exists several (g5) layers into the bulk; (iii) the (110) chromium surface is antiferromagnetic with a large (2.31) spin imbalance; (iv) the (100) chromium monolayer on ferromagnetic iron is ferromagnetic, with a huge spin imbalance (3.63), and aligned antiferromagnetically with respect to the bulk iron; (v) the (110) chromium monolayer on ferromagnetic iron is also ferromagnetic, with a spin imbalance of 2.25 and antiferromagnetically aligned to the iron. The spin imbalance of chromium on iron (100) is possibly the largest of any transition-metal system.

Phase Transition of the Heisenberg Antiferromagnet on the Triangular Lattice in a Magnetic Field

Abstract: Phase transitions of the two-dimensional classical Heisenberg antiferromagnet on the triangular lattice are studied in the presence of magnetic fields. Three types of ordered phase and successive phase transitions among them are found. Properties of each phase are investigated by means of a Monte Carlo similation.

Experimental Studies of Triangular Lattice Antiferromagnets with S=1/2: NaTiO2 and LiNiO2

Abstract: Real triangular lattice antiferromagnet with S =1/2 has been long-awaited since Anderson pointed out that its ground state might be a quantum liquid-like state rather than the Neel state. In this paper we report that NaTiO 2 and LiNiO 2 are promising candidates for it, the former being near Heisenberg-type and the latter near Ising-type. Our magnetization measurements on LiNiO 2 show a striking linear to nonlinear response transition at T N1 =210 K. A pronounced anomaly appears in ESR at another transition T N2 =∼20 K suggesting a ferrimagnet-like ordered state below. However, neither ferromagnetic nor antiferromagnetic reflections could be observed in zero field neutron scattering between 1.4 and 300 K. The susceptibility of NaTiO 2 is low suggesting a strong antiferromagnetic coupling between the spins but no Brass scattering could be observed at 1.4 K. These are suggestive of the remarkable quantum effects.

Spin fluctuations in itinerant electron magnetism

Abstract: 1 Introduction- 11 Local Magnetic Moment and the Weiss Theory of Ferromagnetism- 12 Magnetic Moments of Atoms- 13 Heisenberg Localized Electron Model- 14 Itinerant Electron Model- 15 Localized vs Itinerant Electron Models- 16 Random-Phase Approximation Theory of Spin Fluctuations in Itinerant Electron Magnets- 17 Local Moments in Metals- 18 Self-Consistent Renormalization Theory of Spin Fluctuations and Weakly Ferro- and Antiferromagnetic Metals- 19 Unified Picture of Magnetism- 110 Organization of the Book- 2 Mean-Field Theory of Itinerant Electron Magnetism- 21 Model Hamiltonians- 22 Ferromagnetism- 23 Antiferromagnetism- 24 Spin-Density Waves- 25 Stability of Various Spin Orderings- 3 Dynamical Mean-Field Theory of Spin Fluctuations- 31 Stoner Excitations and Spin Waves in Ferromagnetic Metals- 32 General Spin Fluctuations and Dynamical Susceptibilities- 33 Critical Spin Fluctuations- 34 Antiferromagnets- 35 Limitations of the Hartree-Fock-RPA Theory- 4 Self-Consistent Renormalization (SCR) Theory of Spin Fluctuations- 41 Expressions for the Free Energy of an Interacting Electron System- 42 Paramagnon Theories- 43 SCR Theory of Ferromagnetic Metals- 431 Curie Temperature and Magnetic Susceptibility Above TC- 432 Analytical Explanation of the New CW Law- 433 Magnetization Below TC- 434 Rotationally Invariant Treatment- 44 Phenomenological Mode-Mode Coupling Theory- 45 SCR Theory of Antiferro- and Helimagnetic Metals- 46 Physical Origin of the New Curie-Weiss Susceptibility- 461 Temperature Variation of the Mean-Square Local Amplitude of Spin Fluctuation- 462 Spatial Spin Correlation- 47 Coexistence of and Phase Transitions Between Ferro- and Antiferromagnetism- 48 Quantitative Aspects of the SCR Theory for Weak Itinerant Ferromagnets- 5 Physical Properties of Weakly and Nearly Ferro- and Antiferromagnetic Metals- 51 Properties of Spin Fluctuations- 52 Thermal Expansion- 53 Specific Heat- 54 Nuclear Spin Relaxation- 541 Weakly and Nearly Ferromagnetic Metals- 542 Weakly and Nearly Antiferromagnetic Metals- 55 Electrical and Thermal Resistivities and Magnetoresistance- 551 Weakly and Nearly Ferromagnetic Metals- 552 Antiferromagnets- 56 Coupling Between Spin and Charge Density Fluctuations- 6 Local Magnetic Moments- 61 Local Moments in Insulator Magnets- 62 Metal-Insulator (Mott) Transition- 63 s-d or s-f Exchange Model- 64 Local Moment Formation in Metals- 641 Virtual Bound State- 642 The Anderson Model- 643 The Wolff-Clogston Tight-Binding Model- 65 Physical Properties of a Single Local Moment in Metals- 66 Interaction Between a Pair of Local Moments in Metals- 67 Local Moment Description of Magnetic Transition Metals- 7 A Unified Theory and Its General Consequences- 71 General Considerations Toward a Unified Theory- 72 A Phenomenological Description of the Unified Theory- 73 General Mechanism for the Curie-Weiss Susceptibility- 731 A Mean Mode-Mode Coupling Theory of Magnetic Susceptibility- 732 General Expressions for the Curie Temperature and Susceptibility- 733 Spin Correlations and Magnetic Susceptibility- 74 Possibility for Systematic Analyses of Experimental Results- 75 Temperature Variation of the Local Amplitude of Spin Fluctuation- 751 General Remarks- 752 Temperature-Induced Local Moments- 76 Limitations of the Adiabatic Approximation- 8 Functional Integral Theory- 81 Basic Formalism- 82 Local Moment in Metals- 83 Band Magnetism - A General Formalism- 84 Methods of Calculating the Free Energy Functional- 841 A Closed-Form Expression for ? [?, ?]- 842 Long-Wavelength Approximations- 85 A Unified Description of Magnetism in Narrow-Band Systems- 86 Approximation Methods of Evaluating the Functional Integrals- 861 Unified Theory- 862 Molecular Field (Single-Site) Approximation- 863 Choice of Forms for the Interaction Hamiltonian- 87 Results of Numerical Calculations- 871 Ferromagnetic Transition Metals ?-Fe, Co, Ni- 872 Antiferromagnetic Transition Metals- 873 FeSi, Nearly Ferromagnetic Semiconductor- 874 Temperature-Induced Local Moments in CoS2, CoSe2- 875 Magnetovolume Effects- 88 Supplementary Discussions on Various Approaches and Physical Pictures- 881 The Hartree-Fock Theory for Excited States with Spatially Varying Spin Density- 882 Local Band Theory- 883 Persistence of Exchange Splitting of the Band Above TC- 9 Spin Fluctuations in d-Electron Systems- 91 Spin Fluctuations and Neutron-Scattering Measurements- 92 Local Moment Systems- 921 Heusler Alloys- 922 EuO- 93 Substances Close to the Local Moment Limit- 931 MnPt3, FePd3- 932 FePt3- 94 Substances Close to the Weakly Ferro- and Antiferromagnetic Limits- 941 MnSi- 942 Cr- 95 Substances in the Intermediate Regime: q-Space Description- 951 Fe3Pt- 952 CeFe2- 953 ?-Mn, ?-(FeMn), ?-Fe- 954 ?-Mn- 96 Ferromagnetic Transition Metals Fe, Co, and Ni- 97 Some Systematic Trends in Paramagnetic Scattering- 10 Toward a Unified Theory of Dynamical Spin Fluctuations- 101 General Considerations- 102 Green's Function Theory of Dynamical Susceptibilities- 103 Effect of Electron Lifetime on RPA-SCR Spin Fluctuations- 11 Concluding Remarks- References

Interaction of magnetic impurities in Cu and Ag

Abstract: Ab initio calculations for the electronic structure of pairs of magnetic impurities like Cr, Mn and Fe in Cu and Ag are presented. The calculations are based on density functional theory and apply the KKR Green function method. The authors calculate the local densities of states and the local moments for both the ferromagnetic and antiferromagnetic pair configurations. In particular, they estimate the energy difference between these configurations for different interatomic impurity distances. They show that this RKKY-type energy can be obtained in first order from the difference between the single-particle energies of these configurations calculated with the same 'frozen' impurity potential. In both hosts, two Fe impurities couple strongly ferromagnetically on nearest-neighbour sites, whereas Cr impurities show a strong antiferromagnetic interaction. Mn impurities are an intermediate case, interacting weakly antiferromagnetically.

CeCu2: a new Kondo lattice showing magnetic order

Abstract: The authors report measurements on the lattice parameter, electrical resistivity, thermal conductivity, thermoelectric power, susceptibility, magnetisation and specific heat as well as preliminary neutron diffraction results for the orthorhombic compound CeCu2. The Ce valence is close to three and the overall crystal-field splitting seems to be approximately=200K. CeCu2 behaves as a Kondo lattice system with a 'Kondo temperature' in the crystal-field ground state being of the order of 10-20K. Below 3.5K CeCu2 shows magnetic order of an anisotropic antiferromagnetic type.

Quantitative Aspects of the Theory of Weak Itinerant Antiferromagnetism

Abstract: The self-consistent renormalization (SCR) theory of spin fluctuations in itinerant electron antiferromagnets is formulated in a rotationally invariant way with four independent parameters associated with the band structure and the exchange enhancement factor. Various physical quantities are expressed in terms of these parameters and possible quantitative comparisons with experiment are discussed. Numerical calculations for some typical examples are performed for the temperature dependences of the staggered magnetic susceptibility above T N and the staggered magnetization below T N .

Electronic structure of MnSb

Abstract: Self-consistent, spin-polarized energy-band calculations have been performed for MnSb, for both ferromagnetic and antiferromagnetic spin alignments. For ferromagnetic MnSb we find a 3d5.5 configuration on the Mn atom, with a magnetic moment of 3.3μB on the Mn sites, and –0.06μB on the Sb sites. The charge transfer of Mn to Sb is very small. A detailed analysis is made of the strong covalent Mn-Mn and Mn-Sb interactions. The coupling between the moments is described in terms of covalent interactions of unoccupied states of the Sb 5p band with the Mn 3d bands. These interactions stabilize the ferromagnetic alignment. The calculated spin density, which agrees very well with experimental data, can be easily understood in terms of a model of covalent bonding. We compare the calculated Fermi surface, total density of states, and joint density of states. with results of transport measurements, x-ray photoelectron spectroscopy, and optical measurements, respectively.

Orbital complementary and countercomplementary effects in superexchange interaction through heterobridges in binuclear copper(ii) complexes

Abstract: Low antiferromagnetism of μ-alkoxo-μ-carboxylatodicopper(II) complexes were reasonably explained in terms of the orbital countercomplementary effect based on Hoffmann’s theory for superexchange interaction.

Magnetic order in ternary compounds RRh2Si2 and RRu2Si2

Abstract: Investigations by neutron diffraction and magnetic measurements are reported on the ternary suicides RRh2Si2 (R  Ce, Nd, Tb) and RRu2Si2 (R  Nd, Tb) with the tetragonal structure of the ThCr2Si2 type. CeRh2Si2 orders antiferromagnetically below 36 K with a wave vector k = [ 1 2 1 2 0] and magnetic moments parallel to the c-axis (m0) = 1.50 μ/Ce). The magnetic structure of TbRh2Si2 is antiferromagnetic (k = [001]) below TN = 94 K, the magnetic moments (8.5 μB/Tb at T = 15 K) are also parallel to the c-axis. NdRh2Si2 has the same magnetic structure below TN = 57 K, with m0 = 2.80 μB/Nd parallel to the c-axis. NdRu2Si2 exhibits a more complicated magnetic structure: below TN = 24 K it develops a sine-wave modulation (k = [0.130.130]) of the magnetic moments always parallel to the c-axis, with an amplitude Ak = 3.23 μB/Nd; a squaring of the magnetic structure occurs at about 15 K (m0 = 2.84 μB), and at T

High Field Magnetization of Solid Oxygen

Abstract: High field magnetization of solid oxygen is measured in the pulsed field up to 500 kOe. The spin flop field H c in the antiferromagnetic α-phase is investigated in detail and exchange and anisotropy fields are evaluated. The obtained data are compared with previously determined parameters and magnetic properties of three solid phases are satisfactorily explained. The α-phase is two-dimensional antiferromagnet with intrinsic Neel temperature of 30 K and the β-phase consists of the triangular spin short range order while the one-dimensional short range order exists in the A-15 type γ-phase. The corresponding exchange constants in these phases are determined by using the theory of low-dimensional magnetism and a systematic change is obtained throughout three phases.

Spin glass behaviour in an antiferromagnetic non-frustrated lattice: Sr2FeNbO6 perovskite

Abstract: From magnetic susceptibility and hysteresis loop measurements on the cubic perovskite Sr2FeNbO6, it is shown that a spin glass transition does exist in this compound which has a non-frustrated lattice, and only antiferromagnetic interactions. This experimental results allows the authors to conclude that lattice frustration is not an essential feature for the spin glass transition in antiferromagnetic insulators. Moreover, it is argued that short-range atomic correlations, which modify the magnetic phase diagrams of the diluted compounds, make this spin glass transition possible.

Optical determination of the antiferromagnetic exchange constant between nearest-neighbor Mn2+ ions in Cd0.95Mn0.05Te.

Abstract: The optical splitting of the A-exciton in Cd0.95 Mn 0.05 Sehas been measured at 1.45 K with dc magnetic fields B up to 20 T applied along the c-axis. Magnetization measurements have been made at 1.8 K with pulsed magnetic fields up to 2 8 T. The A-exciton splitting vs. B curve as well as the magnetization vs. B curve show a temperature- broadened step-like increase at B1= 13.0± 0.5 T which is attributed to the magnetic field induced alignment of the antiferromagnetically coupled nearest-neighbor Mn++ion pairs, and yields a value J = -8.7 ± 0.3 K for the antiferromagnetic exchange constant. The magnetization curve shows a second step at B2≃ 25 T; three additional steps are expected before a complete ferromagnetic alignment of the pairs is achieved at B ≃ 65 T.

Orbital Antiferromagnetism in CeB6

Abstract: It is definite from recent theoretical and experimnental works that a quartet \(\varGamma_{8}\) is the ground multiplet of f levels in CeB 6 Because the degeneracy of the quartet is composed of the orbital degeneracy as well as the Kramers degeneracy, its degree of freedom can be expressed by two kinds of Pauli matrices, which are called orbital spins and magnetic spins, respectively It is proposed that the low temperature phase II is an antiferromagnetic state of orbital spins caused by the exchange interaction Our model can explain various mysterious experimental results of phase II such as the increase of the transition temperature with increasing magnetic fields and the appearance of antiferromagnetic motments in the presence of fields, which vanish in the absence of fields Therefore it can be concluded that the ordering in phase II of CeB 6 is the first example of the orbital ordering realized by the exchange interaction

Theory of the low-temperature phases in boracites: Latent antiferromagnetism, weak ferromagnetism, and improper magnetostructural couplings.

Abstract: A phenomenological theory of the magnetic and magnetoelectric properties of boracites is developed, using the Landau-Dzialoshinskii approach. An interpretation is proposed for the main distinctive features characterizing 11 members of this family of compounds. Three subclasses of materials are distinguished corresponding to 2 essentially different phys. situations. In Ni-I boracite the simultaneous ferromagnetic-ferroelectric-ferroelastic transition results from a nonlinear (improper) coupling of the magnetization, polarization, and strain components, to the primary order parameter identified as a "latent" antiferromagnetic ordering. Monoclinic Ni-I can be viewed as the 1st exptl. example of a new class of magnetic materials, which should be recognized macroscopically by an M .apprx. (Tc - T)3/2 variation law, the existence of a spontaneous structural ordering occurring simultaneously with the magnetic ordering, and a weak value of the magnetization despite its exchange origin. In the 2 other classes of trigonal and orthorhombic boracites, the transitions are purely magnetic, the order parameter having a 1- or 2-dimensional antiferromagnetic order, bilinearly coupled to a weak magnetization of relativistic origin. The dielectric and elastic anomalies, and the magnetoelectric properties in these 2 groups of boracites are explained by secondary couplings of the order parameter with the relevant nonspontaneous polar tensors. The complementarity of the 2 additional Landau-type approaches of structural and magnetic transitions is illustrated.

Magnetic Structure of (Ba1-xSrx)2Zn2Fe1 2O22 (x=0-1.0)

Abstract: Neutron and X-ray diffraction studies and magnetization measurements were carried out on single crystals of (Ba 1- x Sr x ) 2 Zn 2 Fe 12 O 22 . The substitution of Ba by Sr produces two effects on the crystal structure: a lattice deformation around the Sr ions and a redistribution of the Zn and Fe ions in the tetrahedral sites. The magnetic structure is analyzed in consideration of these effects: Spins are bunched in the form of ferrimagnet in the every (T 1/2 ST 1/2 ) block and the bunched spins make an angle φ 0 between the adjacent (T 1/2 ST 1/2 ) blocks. At 294 K, the turn angles φ 0 's are found to be 0^° (ferromagnetic), 0^°<φ 0 <180^° (helical) and 180° (antiferromagnetic) for 0≤ x ≤0.5, 0.5< x <0.8 and \(0.8{\lesssim}x{\leq}1.0\), respectively. A brief discussion on the exchange interaction of this spin system is given.

Magnetic Property of a Dense Kondo Substance: CeCu2

Abstract: We have measured the electrical resistivity, specific heat, magnetoresistance, magnetic susceptibility and magnetization of CeCu 2 single crystal in the temperature region of 14 K to room temperature CeCu 2 is found to be a so-called dense Kondo substance with a large specific heat coefficient of 180 mJ/mole·K 2 around 10 K The magnetic susceptibility and the negative magnetoresistance are extremely anisotropic, reflecting the orthorhombic crystal structure The antiferromagnetic ordering is suggested below 30 K

Magnetic Structures in the Sc 1-x Ti x Fe 2 System —Magnetic Phase Transitions in Itinerant Electron Systems

Abstract: The magnetic structure and magnetic phase transitions of Sc 1- x Ti x Fe 2 with x ≧0.5 were studied from measurements of Mossbauer effect and magnetization. A coexistent state of ferro- and antiferromagnetism appears at low temperatures in samples with x ≧0.7. A magnetic phase transition from the ferromagnetic to the coexistent state is observed with decreasing temperature for 0.7≦ x 0.8. These transitions can be explained as phase transitions in an itinerant electron system with weakly coupled ferromagnetic and antiferromagnetic components of spin fluctuation modes.

Magnetic behaviour of tetrakis[(2-diethylaminoethanolato)isocyanatocopper(II)], a complex with an antiferromagnetic ground state; the crystal and molecular structure of the triclinic modification

Abstract: The crystal and molecular structure and magnetic behaviour of [{Cu(NCO)(OCH2CH2NEt2)}4](B) from benzene have been determined. The crystal structure determination was carried out by single-crystal X-ray diffraction methods and refined to R= 0.066 for 4 379 independent reflections: triclinic, space group P, with unit-cell dimensions a= 13.478(3), b= 12.873(3), c= 11.542(3)A, α= 84.020(5), β= 80.263(5), and γ= 86.863(5)°. Each copper atom is five-co-ordinated by three oxygen and two nitrogen atoms. The magnetic susceptibility measured over the temperature range 5.0–302.5 K shows a maximum at 94 K and thus indicates that antiferromagnetic spin coupling is dominant. The magnetic behaviour can be explained on the basis of the isotropic Heisenberg–Dirac–van Vleck model. The results are compared with the structural and magnetic properties of the tetragonal form (A) of this complex. No phase transition between the two modifications could be found up to the melting point.

Specific Heat Measurements of Ce1-xLaxB6

Abstract: Specific heat measurements have been done on the samples of Ce 1- x La x B 6 ( x =0, 0.03, 0.10 and 0.25) at low temperatures down to 0.1 K under the magnetic field of 0, 6 and 36 kOe. In the ordered state specific heat consists of a T 3 -term and a large γ T -term. The former originates from the excitation of antiferromagnetic spin wave and the latter is common in the dense Kondo systems. The γ-value is insensitive to the La-doping and the applied magnetic field as well as the type of magnetic ordering. The result is consistent with the \(\varGamma_{8}\) ground level model but with a substantial distortion. The present result is also consistent with the temperature dependence of resistivity in the same temperature range.

A calculation of elastic constants of ferromagnetic iron at finite temperatures

Abstract: The temperature dependence of the elastic constants C'=1/2(C11-C12),C44 and B of BCC iron is calculated within the tight-binding approximation using the single-site spin-fluctuation theory of band magnetism. The theory reproduces the observed anomalous 'softening' of the tetragonal shear constant C', relating it to the contribution of the eg orbitals. The negative slope with temperature of the trigonal shear constant C44 and bulk modulus B is shown to arise from the lattice expansion. The influence of magnetic moments on the elastic constants of ferromagnetic and antiferromagnetic, BCC transition metals is discussed in general.