Showing papers on "Antiferromagnetism published in 1973"
TL;DR: In this paper, a simple expression for the magnetoresistance of the antiferromagnetic metals due to the electron-spin scattering by the s -d interaction is obtained using the molecular field approximation for the spin system.
Abstract: A simple expression for the magnetoresistance of the antiferromagnetic metals due to the electron-spin scattering by the s - d interaction is obtained using the molecular field approximation for the spin system The expression includes the ferromagnetic case It is shown that in the antiferromagnetic case the positive magnetoresistance appears below the transition point, in contrast to the negative-magnetoresistance in the case of the para or ferromagnetic case In the ferromagnetic case the negative magnetoresistance shows a deep and finite valley at the transition point, which is consistant with the experiments of the ferromagnetic rare-earth metals such as Gd and Tb
178 citations
TL;DR: In this article, the crystal structures of the rhombohedral compounds ACrX 2 (A = Na, Ag, Cu; X = S, Se) at 300 and 4 K have been refined from neutron-diffraction powder data.
171 citations
TL;DR: In this article, the statistical mechanics of a two-dimensionalally infinite set of Ising spins are worked out for the case in which they form either a triangular or a honeycomb arrangement.
Abstract: In this paper the statistical mechanics of a two-dimensionally infinite set of Ising spins is worked out for the case in which they form either a triangular or a honeycomb arrangement. Results for the honeycomb and the ferromagnetic triangular net differ little from the published ones for the square net (Curie point with logarithmically infinite specific heat). The triangular net with antiferromagnetic interaction is a sample case of antiferromagnetism in a non-fitting lattice. The binding energy comes out to be only one-third of what it is in the ferromagnetic case. The entropy at absolute zero is finite; it equals $S(0)=R\frac{2}{\ensuremath{\pi}}\ensuremath{\int}{0}^{\frac{\ensuremath{\pi}}{3}}\mathrm{ln}(2cos\ensuremath{\omega})d\ensuremath{\omega}=0.3383R$The system is disordered at all temperatures and possesses no Curie point.
156 citations
TL;DR: The transition metal phosphorus trisulfide compounds with the general formula MPS3, with M = Mn, Fe, Ni, have been prepared by chemical vapor transport, vapor sublimation and direct combination of the elements.
120 citations
TL;DR: In this paper, an ordered state where spins are coupled with their directions statistically distributed within a very fine particle was found, and the spin structure is quite different from normal antiferromagnetism.
Abstract: AMORPHOUS materials have no preferred crystal axes, but it might be thought that shape or strain could define an antiferromagnetic axis in a compound containing a large concentration of magnetic ions with negative nearest-neighbour exchange interactions. We have studied such an amorphous compound, and find an ordered state where spins are coupled with their directions statistically distributed within a very fine particle. This spin structure is quite different from normal antiferromagnetism, although there are some similarities in the magnetic properties.
103 citations
85 citations
TL;DR: In this article, a general theory of spin-dependent phonon Raman scattering in magnetic crystals is developed, where the integrated Raman intensity as a function of temperature is expressed as S (T )=( n 0 + 1)| R + M | 2, where the first term represents the spin independent part and the second one the spin- dependent part which is proportional to the nearest neighbor spin correlation function.
Abstract: A general theory of the spin-dependent phonon Raman scattering in magnetic crystals is developed. The integrated Raman intensity as a function of temperature is expressed as S ( T )=( n 0 +1)| R + M | 2 , where the first term represents the spin-independent part and the second one the spin-dependent part which is proportional to the nearest neighbor spin correlation function . Three types of temperature variation of intensity are predicted in ferromagnetic and antiferromagnetic cases, depending on values of R / M . Two microscopic mechanisms, variation of the d electron transfer with lattice vibrations and that of the non-diagonal exchange, contribute to the spin-dependent part, and it is shown that the former is essentially important in producing the large temperature variation. The theory is applied to explaining the observed temperature variation of various Raman active phonon modes in CdCr 2 S 4 and the experimental results are explained successfully.
83 citations
TL;DR: In this article, the difference between the magnitudes and thermal evolutions of the magnetic susceptibilities are explained in terms of ferromagnetic vs antiferromagnetic superexchange enhancement and large vs small spin polarons associated with excited states.
75 citations
TL;DR: Li2MnO3 as mentioned in this paper is a variant of the NaCl-type structure family and crystallizes monoclinic, a = 4.928 A, b = 8.533 A, c = 9.604 A, β = 99.5°, Z = 8; as a version of the Li2SnO3 type of structure.
Abstract: Li2MnO3 kristallisiert nach Guinier-Daten monoklin, a = 4,928 A, b = 8,533 A, c = 9,604 A, β = 99,5Deg;, Z = 8, in einer Variante des Li2SnO3-Typs. Parameter siehe Text. Unterhalb der Neel-Temperatur (≈50°K) liegt Antiferromagnetismus, oberhalb Paramagnetismus, μ = 3,83, μB, θ = −33°K (Curie-Weiss) vor. Der Madelung-Anteil der Gitterenergie, MAPLE, wird berechnet und diskutiert.
On the Knowledge of the NaCl-Type Structure Family: New Investigations on Li2MnO3
According to Guinier photographs Li2MnO3 crystallizes monoclinic, a = 4.928 A, b = 8.533 A, c = 9.604 A, β = 99.5°, Z = 8; as a variant of the Li2SnO3 type of structure. Parameters see text. Below the Neel temperature (≈50°K) we find antiferromagnetism, above paramagnetism with μ = 3.83 μB, θ = −33°K (Curie-Weiss Law). The Madelung Part of Lattice Energy, MAPLE, is calculated and discussed.
69 citations
TL;DR: In this paper, the spectrum of the ruthenium-99 Mossbauer γ transition has been obtained for the ternary oxides SrRuO3, CaRuO2O3 and Y2Ru2O7.
Abstract: Ruthenium-99 Mossbauer spectra have been obtained for the ternary oxides SrRuO3, CaRuO3, BaRuO3, and Y2Ru2O7 and for the quaternary oxides Sr(Ru1–xIrx)O3(x= 0·1 and 0·2) and Sr(Ru0·7Mn0·3)O3. The spectrum of SrRuO3 reveals the first example of a hyperfine magnetic field in a ruthenium compound; the internal field of 352 kG at 4·2 K is compatible with the ferromagnetic moment derived from neutron-diffraction data, and confirms the collective-electron magnetism model for this perovskite. A more precise value for the E2/M1 mixing ratio of 2·72 ± 0·17 has been obtained for the 99Ru Mossbauer γ transition. The oxide CaRuO3 shows only a single line and hence no magnetic ordering even at 4·2 K; it is not antiferromagnetic as previously reported but is Curie-Weiss paramagnetic. The oxide BaRuO3 also gives a singlet; there is no long-range antiferromagnetic ordering, but within each cluster of three face-sharing RuO6 units localised pairing of the 4d electrons takes place. The oxide Y2Ru2O7 is magnetically ordered at 4·2 K, with a hyperfine field of 126 kG. Substitution of ruthenium by iridium in the oxide SrRuO3 reduces the field at ruthenium by approximately 60 kG for each iridium nearest neighbour, whereas in the case of manganese substitution the reduction for each manganese neighbour is only 22 kG.
62 citations
TL;DR: The static magnetic susceptibility and the ESR spectra from 1.6 to 300 K have been measured on a powder sample of the titled free radical and the broad maximum in the susceptibility which indicates an antiferromagnetic interaction has been observed at 6.9 K as discussed by the authors.
Abstract: The static magnetic susceptibility and the ESR spectra from 1.6 to 300 K have been measured on a powder sample of the titled free radical. The broad maximum in the susceptibility which indicates an antiferromagnetic interaction has been observed at 6.9 K. The broadening of the ESR absorption line and the shift of the g-value have been found in the temperature region below Tmax, in which the susceptibility reached its round maximum. There appeared anomalies in the slope of the susceptibility, the linewidth, and the g-value versus temperature curves in the vicinity of 1.7 K. These anomalies may imply a magnetic-phase transition from the short-range ordered state to the long-range ordered state at about 1.7 K. The existence of a ferromagnetic interaction between the magnetic chains in the triphenylverdazyl radical solid is discussed on the basis of the susceptibility, the spin distribution, and the crystal structure. It is understood qualitatively that the radical with a negative spin density has a latent fe...
TL;DR: The magnetic properties of rare earth-magnesium compounds with the CsCl structure have been determined in the temperature range 4.2-300 K with applied magnetic fields up to 18 kOe.
Abstract: The magnetic properties of rare earth-magnesium compounds with the CsCl structure have been determined in the temperature range 4.2–300 K with applied magnetic fields up to 18 kOe. There is a change in sign of the asymptotic Curie temperatures in going from compounds with light rare-earth elements to those with heavy rare-earth elements. The temperature dependence of the magnetization in the magnetically ordered region points to antiferromagnetism for the former compounds and to ferromagnetism for the latter compounds. For all compounds investigated the lattice constants have been determined.
TL;DR: In this article, the derivation of series expansions appropriate for low temperatures or high applied magnetic fields for the two-dimensional Ising model of a ferromagnetic and antiferromagnet was studied as a field grouping.
Abstract: The derivation of series expansions appropriate for low temperatures or high applied magnetic fields for the two‐dimensional Ising model of a ferromagnet and antiferromagnet is studied as a field grouping. New results are given for the high field polynomials for the triangular lattice to order 10, the simple quadratic lattice to order 15, and the honeycomb lattice to order 21.
TL;DR: In this paper, the orthorhombic phases of YMnO3, HoMnNO3 and YbNOM3 were made by transformation of the normal hexagonal phases at 1000°C and 35-40 kbar.
TL;DR: In this article, the effect of the crystal field anisotropy on the transition temperature has been interpreted and the results seem to indicate that the molecular field theory gives a better approximation than do the Green's-function techniques.
Abstract: Magnetic-susceptibility and heat-capacity measurements on single crystals of Ni${\mathrm{Cl}}_{2}$ \ifmmode\cdot\else\textperiodcentered\fi{} 4${\mathrm{H}}_{2}$O, which is isomorphic to Mn${\mathrm{Cl}}_{2}$ \ifmmode\cdot\else\textperiodcentered\fi{} 4${\mathrm{H}}_{2}$O and Mn${\mathrm{Br}}_{2}$ \ifmmode\cdot\else\textperiodcentered\fi{} 4${\mathrm{H}}_{2}$O, indicate an antiferromagnetic-paramagnetic transition at (2.99\ifmmode\pm\else\textpm\fi{}0.01) \ifmmode^\circ\else\textdegree\fi{}K. The large zero-field splitting of the ${\mathrm{Ni}}^{2+}$ ion in this material results in an 11 \ifmmode^\circ\else\textdegree\fi{}K doublet-singlet splitting of its ground state with the doublet lying lower. A molecular-field model has been used to obtain an exchange-parameter value of $\frac{\mathrm{zJ}}{k}=\ensuremath{-}5.25$ \ifmmode^\circ\else\textdegree\fi{}K. The effect of the crystal field anisotropy on the transition temperature has been interpreted and the results seem to indicate that the molecular-field theory gives a better approximation than do the Green's-function techniques.
TL;DR: In this paper, the derivation of series expansions appropriate for low temperatures or high applied magnetic fields for the two-dimensional Ising model of a ferromagnet and antiferromagnetic magnet was studied as a temperature grouping.
Abstract: The derivation of series expansions appropriate for low temperatures or high applied magnetic fields for the two‐dimensional Ising model of a ferromagnet and antiferromagnet is studied as a temperature grouping. New results are given for the ferromagnetic polynomials for the triangular lattice to order 16, for the ferromagnetic and antiferromagnetic polynomials for the simple quadratic lattice to order 11, and for the honeycomb lattice to order 16.
TL;DR: In this paper, one-dimensional dilute systems with nearest neighbor interactions were studied in terms of the power series of the concentration of magnetic atoms, and the specific heats, the susceptibilities and the magnetizations of the ferro magnets and antiferromagnets were obtained.
Abstract: One-dimensional dilute systems with nearest neighbor interactions are studied in terms of power series of the concentration of magnetic atoms. Recurrence relations between coefficients of the power series of the Ising systems are obtained. The Ising systems of S = 1/2 are studied. The specific heats, the susceptibilities, and the magnetizations of the ferro magnets and antiferromagnets are obtained. At low temperatures, three steps in the magnetization of antiferromagnetic systems are found. An Ising system of S = 1/2 with nearest and second nearest neighbor interactions is also studied by extending the method, and the specific heats are obtained when the magnetic field is zero.
TL;DR: The total dilatation of CeAl2 from 2.5 to 300 K was found to be similar to that of LaAl2, thus making the assumption of a Ce4+→Ce3+ transition unlikely as discussed by the authors.
Abstract: The total dilatation of CeAl2 from 2.5 to 300 K was found to be similar to that of LaAl2, thus making the assumption of a Ce4+→Ce3+ transition unlikely. A negative peak in the dilatation curve of CeAl2 coincides with the specific-heat peak at 3.36 K. A second transition occurs at 4.5–4.8 K. Magnetization measurements confirm the antiferromagnetism of CeAl2.
TL;DR: In this paper, a semi-infinite two-dimensional Ising model with its spins on the boundary row having a different interaction energy E′1 from the ferromagnetic bulk was considered, and it was shown that the boundary specific heat has two divergent terms: one of which diverges linearly at the bulk critical temperature Tc, and the other, logaritmically.
Abstract: We consider a semi‐infinite two‐dimensional Ising model with its spins on the boundary row having a different interaction energy E′1 from the ferromagnetic bulk. We find that the boundary specific heat has two divergent terms: one of which diverges linearly at the bulk critical temperature Tc, and the other, logaritmically. The linearly divergent term is independent of E′1, and the coefficient of the logaritmically divergent term is a decreasing function of E′1. There is a boundary latent heat at Tc, which is identical to McCoy and Wu's result. The boundary spins, which can be either ferromagnetic or antiferromagnetic, are aligned for temperature lower than Tc. The boundary spontaneous magnetization approaches zero in the form of A(E′1)(1−T/Tc)1/2, and the boundary zero field magnetic susceptibility diverges at Tc in the form −B (E′1)ln|1−T/Tc|, where A(E′1) and B(E′) are increasing functions of E′1.
TL;DR: By neutron diffraction and susceptibility measurements the crystallographic and magnetic structures of (CH3NH3)2MnCl4 and (CD3ND3) 2mcl4 have been investigated as mentioned in this paper.
TL;DR: In this paper, a theory for spin waves in a dilute antiferromagnet has been developed which uses the coherent potential approximation (CPA) to treat the randomly varying Ising interactions between nearest Antiferromagnetic neighbours but treats the off-diagonal parts of the Heisenberg interactions in a more approximate fashion.
Abstract: For pt. I see abstr. A78044 of 1972. A theory for spin waves in a dilute antiferromagnet has been developed which uses the coherent potential approximation (CPA) to treat the randomly varying Ising interactions between nearest antiferromagnet neighbours but treats the off-diagonal parts of the Heisenberg interactions in a more approximate fashion that is consistent with the Goldstone theorem. Although similar to the theory that was found to be successful for K(Co, Mn)F3 and (Co, Mn)F2 in paper I, the problem of the magnetic vacancy requires special treatment. A fictitious spin is placed on the Zn atoms but large potentials are introduced there to prevent the spin waves from propagating via these sites. The Green functions, neutron scattering and Raman scattering have been calculated.
TL;DR: In this paper, a density of states for hexagonal NiS is presented which is, in accord with all presently known data, in many ways that of White and Mott and attributes the conductivity change to a splitting and narrowing of the Ni(eg) bands below a certain threshold.
Abstract: Measurements of the conductivity, magnetic susceptibility, and specific heat have been made on single crystals of hexagonal NiS (NiAs structure) of controlled purity and stoichiometry. Above the transition temperature NiS is found to be a metal having a density of states at the Fermi surface of approximately 26.5×1022 states/cm3 eV and displaying only Pauli paramagnetism. Below the transition temperature NiS is found to be a semimetal with a density of carrier states at the Fermi surface roughly half that of the metallic state. Below the transition temperature NiS is an antiferromagnet with a Neel temperature of approximately 1600°K. The data are interpreted and a density of states for hexagonal NiS is presented which is, we believe, in accord with all presently known data. This model resembles in many ways that of White and Mott and attributes the conductivity change to a splitting and narrowing of the Ni(eg) bands below the conductivity transition.
TL;DR: In this paper, the specific heat of an Fe 0.49 Rh 0.51 alloy over the temperature range 100-500 K was measured and the entropy change at the antiferromagnetic to ferromagnetic phase transition was found to be 13±1 J kg -1 K -1.
TL;DR: The thermal conductivities of the resulting magnetoelastic modes can reasonably account for the experimental results: in particular, the anomalous behaviors of the mixed modes between 5 and 17 \ifmmode^\circ\else\textdegree\fi{}K are explained by the effect of a large magnon scattering on the mixed mode as discussed by the authors.
Abstract: The thermal conductivities ${K}_{\ensuremath{\perp}}$ and ${K}_{\ensuremath{\parallel}}$ in the $c$ plane and along the $c$ axis, respectively, have been measured in Fe${\mathrm{Cl}}_{2}$ between 1.2 and 80 \ifmmode^\circ\else\textdegree\fi{}K. Both ${K}_{\ensuremath{\perp}}$ and ${K}_{\ensuremath{\parallel}}$ are found to exhibit, in a wide temperature range, an unusual behavior which reveals the presence of a strong spin-phonon coupling. The experimental results in the antiferromagnetic phase are interpreted on the basis of the magnon-phonon resonant interaction arising from single-ion magnetostriction. It is shown that the thermal conductivity of the resulting magnetoelastic modes can reasonably account for the experimental results: In particular, the anomalous behaviors of ${K}_{\ensuremath{\perp}}$ and ${K}_{\ensuremath{\parallel}}$ between 5 and 17 \ifmmode^\circ\else\textdegree\fi{}K are explained by the effect of a large magnon scattering on the mixed modes. This large scattering leads to a negligible contribution of the spin waves to heat transport. From the ${K}_{\ensuremath{\perp}}$ results, the magnetoelastic coupling constant ${G}_{44}$ is found to be 3.5 meV.
TL;DR: In this paper, two antiferromagnetic structures were observed simultaneously in a series of mixed crystals (Fex, Mn1−x)WO4 over a miscibility range of about twenty per cent.
TL;DR: The magnetic superlattice reflections for the two structures can be indexed on a tetragonal magnetic cell which has basal plane edges twice that of the chemical cell and the same dimension in the unique c-axis direction (cm = c0).
Abstract: Neutron diffraction data from a powder sample of ErAg show two antiferromagnetic transitions at temperatures of 18 ± 1 K and 9.5 ± 0.5 K. The magnetic superlattice reflections for the two structures can be indexed on a tetragonal magnetic cell which has basal plane edges twice that of the chemical cell (am = 2a0) and the same dimension in the unique c‐axis direction (cm = c0). Between 18 and 9.5 K the magnetic ordering is similar to HoAg and conforms to a sinusoidally modulated magnetization wave propagating in the 〈100〉 direction with the moments tilted from the c axis at angles ranging from 40° (at 18 K) to 80° (at 10 K). The modulation wavelength of 53 ± 2 A (7.4am) is incommensurate with the unit chemical cell and is temperature independent. In this incommensurate ordering region the ordered moment increases with decreasing temperature to a maximum value of 6.8μB at T = 10 K. Below 9.5 K, the antiferromagnetic ordering is a commensurate (+ − + −) layer‐type structure similar to that of DyAg and TbAg, ...
TL;DR: In this paper, the c-axis resistivity of dysprosium in the vicinity of the Neel temperature T/sub n/ has been verified using phonon-smeared superzone-induced band gaps.
Abstract: Results are presented for the c-axis resistivity of dysprosium in the vicinity of the Neel temperature T/sub n/, which provide the first quantitative verification of the theory of scattering of electrons by spin fluctuations above TN in an antiferromagnet. Immediately below the transition the resistivity can be described by including the effects of phonon-smeared superzone-induced band gaps. (auth)
TL;DR: In this article, the authors examined the properties of a model which exhibits this behavior from a theoretical point of view and showed that the model can explain some aspects of recent observations of spin polarized photoemission from the surface of EuO.
TL;DR: A neutron diffraction study on the powder samples of FeMnP has been made in order to determine the magnetic structure as well as the ordering of iron and manganese atoms as mentioned in this paper.
Abstract: A neutron diffraction study on the powder samples of FeMnP has been made in order to determine the magnetic structure as well as the ordering of iron and manganese atoms. It is ascertained that iron and manganese atoms occupy the tetrahedral and pyramidal sites, respectively. FeMnP is antiferromagnetic with the Neel temperature at 340 K. The magnetic unit cell is twice as large as the chemical unit cell, being doubled along the c -axis. The magnetic structure as derived on the basis of Bertaut's method is such that A x and G z modes are simultaneously present in this compound. In combination with the Mossbauer effect measurement, the magnetic moments of the iron and manganese atoms at 128 K are found to be 0.5 and 2.6µ B , respectively.