Low-temperature Magnetization Data Research Articles

Phase behavior of antiferromagnetic ultrathin magnetic films

The phase diagram of a system of classical spins on a square lattice, interacting through a nearest-neighbor antiferromagnetic exchange and a dipolar interaction, is presented. The phase diagram is based on results from aseries of Monte Carlo simulations. The phase diagram shows a parallel antiferromagnetic phase, in which the spins are aligned in the x-y plane, and an antiferromagnetic perpendicular phase, in which the spins are aligned perpendicular to the x-y plane. The critical value of the exchange interaction, J c (T), on the phase boundary separating the two phases shows only a weak dependence on temperature (J c J 0 ), while the transition appears to be first order with an extremely small latent heat. The Monte Carlo data also indicate that the parallel phase separates into two distinct phases, although further work is required to determine the precise nature of the phase boundary separating the two regions. Finally, the low-temperature magnetization data suggest a softening of the spin-wave stiffness close to the phase boundary. The Neel temperature of the perpendicular antiferromagnetic phase is found to be consistent with earlier predictions of spin-wave calculations.

Magnetization behaviour of xEu 2O 3(1− x)Na 2B 4O 7 glasses

Glasses of the xEu 2O 3(1− x)Na 2B 4O 7 system with 0.05⩽ x⩽0.30 were studied by magnetization measurements. Their magnetic behaviour is due to the presence of europium ions in both 2+ and 3+ valence states. Low-temperature (4 K) magnetization data showed the presence of a magnetically ordered phase due to the Eu 2+ ions and permitted an estimation of their amount.

Structural and magnetic behavior of some borate glasses containing europium ions

Glasses of the xEu 2O 3(1− x)Na 2B 4O 7 system with 0.01≤ x≤0.30 were studied by IR spectroscopic, density and magnetic measurements. IR and density data evidenced the network modifier role played by the europium ions in the studied glasses. Low temperature (4 K) magnetization data showed the presence of a magnetic ordered phase due to the Eu 2+ ions and permitted to estimate their amount.

The Ferric Wheel Revisited

We reinvestigate the low temperature magnetic properties of the ferric wheel, a 10 spin (S = 5/2) iron(III) complex. The energy levels for a Heisenberg antiferromagnet with ten S = 5/2 spins are calculated exactly and found to be in excellent agreement with the observed low-temperature experimental data. By comparing the low-temperature magnetic susceptibility data with the exact energy levels, a coupling constant of 9.7 cm-1 is determined.

Non-Linear Magnetic Behavior of a Tetranuclear Copper(II) Cluster

A tetranuclear copper(II) cluster, namely [Cu4OCl6(mor)4], mor—morpholine, has been investigated by the magnetization measurements at the temperature as low as 1.74 and 2.73 K, respectively. A numerical derivative yielded the differential magnetic susceptibility. The low-temperature magnetization data were fitted to a two dimensional function M= f(B,T) and the following set of magnetic parameters has been obtained: g = 2.351, Ja/k = − 6.33 K and Jb/k = − 0.76 K. These parameters determine the spacing of energy levels in a tetranuclear cluster of the C3v symmetry.

Scaling of the magnetization in magnetic fields up to 30 T ofUCu5−xPdx: Evidence for a crossover from correlated to single-ion magnetic interactions upon cooling

Scaling of low-temperature magnetization data for the non-Fermi-liquid systems ${\mathrm{UCu}}_{4}\mathrm{Pd}$ and ${\mathrm{UCu}}_{3.5}{\mathrm{Pd}}_{1.5}$ in fields to 30 T is carried out to help determine the nature of the magnetic interactions above and below 10 K. The size of the scaling exponent \ensuremath{\beta} found from this scaling with fields above 10 K implies that the higher-temperature magnetic excitations in ${\mathrm{UCu}}_{4}\mathrm{Pd}$ are correlated, i.e., $\ensuremath{\beta}g1.0.$ For $Tl~6\mathrm{K},$ $\ensuremath{\beta}l1.0$ for both ${\mathrm{UCu}}_{4}\mathrm{Pd}$ and ${\mathrm{UCu}}_{3.5}{\mathrm{Pd}}_{1.5}$ implying that the excitations may change and assume single-ion character, consistent with recent doping experiments. These results, which contradict a recent neutron-scattering study, may be understood theoretically as a depletion of the occupation of the phase space of magnetic excitations with decreasing temperature ( energy), leading to a decoupling of the excitations.

Crystal growth, thermodynamic and magnetic characterization of the NiIn 2 − 2 xCr 2 xS 4 single crystals

Single crystals of NiIn 2 − 2 x Cr 2 x S 4 compounds were grown by the chemical vapour transport method. A thermodynamic study has been undertaken in order to calculate the optimal parameters of growth conditions. Low-temperature magnetic susceptibility data reveal a spin-glass-like behaviour with a transition temperature around 10 K. The high-temperature data reveal the predominance of antiferromagnetic interactions between the magnetic ions.

Spectroscopic and magnetic properties of two di-copper(II) complexes with macrocyclic schiff bases

Two binuclear copper(II) complexes with macrocyclic Schiff bases Cu 2L I(CH 3COO) 2·5H 2O (complex I) and Cu 2L II(CH 3COO) 2·2H 2O (complex II) were synthesized and then characterized by IR, UV, and thermogravimetric analysis (TGA) measurements. TGA was used to investigate the desolvation of lattice water molecules. IR spectra demonstrated the formation of the cyclic compound and together with chemical elemental analysis were used to propose the structure of the complexes. The UV spectra of both complexes are typical for binuclear copper(II) complexes with Robson-type ligands. Variable-temperature magnetic susceptibility measurements corroborated by EPR and low-temperature isothermal magnetization data confirmed the formation of copper dimers with antiferromagnetic exchange coupling constants of −400 and −1250 cm −1 for complexes I and II, respectively, residing outside the usual range for the phenoxide bridged Cu(II) complexes. This implies the possibility that additional superexchange paths through the macrocyclic ligand may affect the intradimer exchange interaction as well as the phenoxide oxygen bridges.

Anomalous Pr Ordering and Structural Analysis for Oxygenated Tetragonal 1212 Compound Pr1.5Ba1.5Cu3O7.2

Magnetic measurement and powder X-ray Rietveld analysis are performed on oxygenated Pr1.5Ba1.5Cu3O7.2cuprate. This tetragonal compound with lattice parameters a = 0.38916 nm and c = 1.16177 nm is found to form the TlBa2CaCu2O71212-type structure when written as Cu[Ba1.5Pr0.5]PrCu2O7.2. Low temperature magnetic data indicate that anomalous Pr order temperature TN(Pr) decreases from 18 K for orthorhombic PrBa2Cu3O6.9to 10.5 K for Pr1.5Ba1.5Cu3O7.2. The increasing Pr-O bond length with decreasing TNindicates that Pr ordering is closely correlated with the wave function overlap between Pr-4f orbital and O-2pπorbital in the CuO2bi-layers.

Structure, Chemical Bonding, Magnetic Susceptibility, and155Gd Mössbauer Spectroscopy of the Antiferromagnets GdAgGe, GdAuGe, GdAu0.44(1)In1.56(1), and GdAuIn

GdAgGe, GdAuGe, GdAu0.44(1)In1.56(1), and GdAuIn were prepared as single-phase materials from the elements by arcmelting and subsequent annealing at 970 K. The indium compounds were investigated by X-ray diffraction on both powders as well as single crystals. GdAu0.44(1)In1.56(1)adopts the CaIn2structure, a puckered version of the AlB2type:P63/mmc,a=478.9(1) pm,c=740.3(1) pm,V=0.1470(1) nm3,Z=2, wR2=0.0278, for 149F2values, and 8 variables. GdAuIn crystallizes with a ternary ordered variant of the Fe2P type:P62m,a=769.8(3) pm,c=397.8(2) pm,V=0.2042(1) nm3,Z=3, wR2=0.0562, for 505F2values, and 14 variables. GdAgGe crystallizes with the same structure, and GdAuGe adopts the NdPtSb type, a ternary ordered version of the CaIn2structure. Chemical bonding in GdAuIn was investigated by semiempirical band structure calculations. The strongest bonding interactions are found for the Au–In contacts, followed by Gd–Au and Gd–In, while the Gd–Gd interactions are much weaker. The four gadolinium compounds are antiferromagnets with Néel temperatures of 13.0, 16.9, 21.0, and 12.5 K for GdAgGe, GdAuGe, GdAu0.44(1)In1.56(1), and GdAuIn, respectively. No field-induced magnetic transitions are evident from the low-temperature magnetization data. The magnetic hyperfine interactions in these intermetallics were studied in detail by155Gd Mössbauer spectroscopy.

Influence of 90 MeV oxygen ion induced disorder on the magnetotransport in epitaxial La0.7Ca0.3MnO3 thin films

Epitaxial films of La0.7Ca0.3MnO3 have been irradiated with 90 MeV oxygen ions at different dose values ranging from 1011–1014 ions/cm2. The structural, magnetization, and magnetotransport properties have been studied as a function of the ion dose. It is found that the properties change gradually up to a dose of 1013 ions/cm2; however, drastic changes occur when the sample is irradiated at the higher dose of 1014 ions/cm2. Specifically, this sample exhibits a large, nearly temperature independent magnetoresistance in the low temperature regime. The Rutherford backscattering channeling data bring out the presence of defects in the irradiated films. The x-ray diffraction data, the temperature dependence of resistivity and magnetization, and the low temperature magnetic hysterisis data collectively indicate the presence of two different phases in the sample irradiated at 1014 ions/cm2. The surface morphology of this film, observed by atomic force microscopy, exhibits swelling, presumably due to subsurface clustering of point defects. The observed results are analyzed in terms of point defect induced random spin disorder and its effect on the magnetotransport properties.

Spin–flip metamagnetism in the laves phase compounds Dy 0.73Tb 0.27Fe 2− xCo xH n

The results of low temperature magnetization measurements carried out on the Dy 0.73Tb 0.27Fe 2− x Co x system and their hydrogenated compounds are presented. Low temperature (12 K) magnetization data reveals a large increase in anisotropy in the hydrogenated compounds, attributed to a modification in crystalline electric field effects as a result of the orientational ordering of hydrogen atoms in the lattice. The discrete step-wise increase in magnetization upto a field of 2 kOe in the parent alloys and the hydrogenated compounds is attributed to spin–flip metamagnetism.

Giant second-order Zeeman effect in titanium (III) doped caesium gallium alum

Low temperature magnetization data obtained for titanium (III) doped caesium gallium alum show a spectacular deviation from Brillouin behavior with the magnetization highly dependent on the strength of the applied field at a given value of B/T. This arises from unprecedented higher-order contributions to the magnetization and these measurements afford the determination of the Zeeman coefficients to third order. This anomalous magnetic behavior is a manifestation of Jahn-Teller coupling giving rise to low-lying vibronic states which mix into the ground state through the magnetic field.

NMRD studies on phthalate dioxygenase: evidence for displacement of water on binding substrate

Water proton T 1 –1 measurements at magnetic fields between 0.01 and 50 MHz [nuclear magnetic relaxation dispersion (NMRD) measurements] have been performed on solutions of phthalate dioxygenase (PDO) reconstituted at the catalytic iron site with copper(II) or manganese(II). The data show evidence of a weakly coordinated water molecule in CuPDO; in the presence of the substrate, phthalate, this water appears to become even less tightly bound, and an additional tightly coordinated water can be detected. In PDO reconstituted with manganese, one tightly coordinated water is detected in the presence and in the absence of phthalate. An attempt is made to reconcile these data with low-temperature near-IR magnetic circular dichroism and X-ray absorption data, which show that PDO reconstituted with iron or cobalt is six-coordinate in the absence of substrate and five-coordinate in the presence of substrate.

Exchange interactions and magnetism of Co2+ in Zn1-xCoxTe.

A study of cobalt-carrier exchange interactions is carried out in very dilute ${\mathrm{Zn}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Co}}_{\mathit{x}}$Te (x\ensuremath{\le}1%) from correlated magneto-optical and magnetization measurements at T=1.8 K. The resonant magneto-optic Kerr effect is used to complement magnetoreflectance experiments, and determine precisely the exciton Zeeman splittings on single crystals of various Co compositions. Correlated measurements of magnetization performed on the same samples provide a determination of exchange integrals for ${\mathrm{\ensuremath{\Gamma}}}_{6}$ and ${\mathrm{\ensuremath{\Gamma}}}_{8}$ bands within the framework of the exchange model based on the mean-field approximation. In the investigated field and composition range, we find ${\mathit{N}}_{0}$\ensuremath{\alpha}=0.31\ifmmode\pm\else\textpm\fi{}0.03 eV; ${\mathit{N}}_{0}$\ensuremath{\beta}=-3.03\ifmmode\pm\else\textpm\fi{}0.15 eV. This abnormally large value of the p-d exchange constant does not vary with Co concentration in the investigated region. Low-temperature magnetization data obtained in fields up to 15 T are consistently interpreted in a model including the contributions of isolated ions and ${\mathrm{Co}}^{2+}$-${\mathrm{Co}}^{2+}$ pairs of second and third neighbors for the values of exchange constants previously determined. Antiferromagnetic interactions between more distant ions than third neighbors are also taken into account. The long-range exchange parameters obtained by using either a modified Brillouin function or a mean-field approach are in good agreement. \textcopyright{} 1996 The American Physical Society.

Evidence for the high-spin heme iron in both stable and unstable reduced forms of lactoperoxidase: low-temperature magnetic circular dichroism data

The unstable and stable ferrous lactoperoxidase at pH 6.0, 7.0 and 10.2 have been analysed using optical absorption and variable temperature MCD spectroscopy. The evidence is given that two high-spin forms of ferrous LPO are always observed when the enzyme is reduced in a buffer-glycerol mixture at low temperature (ca. −20°C) at which no spectral changes are seen for a long time after the reduction. Form 1 (the absorption band, 450 nm) dominates significantly over form 2 (the absorption band, 435 nm), but a relative content of form 2 increases on lowering the pH value. An annealing of the unstable LPO at high temperatures is followed by complete irreversible conversion of form 1 to form 2. In addition, at least one low-spin ferrous form exists in temperature-dependent equilibrium with the high-spin form(s) in both stable and unstable ferrous LPO. The reversible increase of its content is observed at least down to 140 K, suggesting that minor structural changes are sufficient for reaching the heme iron by a distal amino acid residue (presumably a histidine).

Temperature dependence of the magnetization of glassy and nanocrystalline Fe/sub 82/M/sub 7/B/sub 10/Cu/sub 1/ [M=Zr,Hf,Nb] alloys with high permeability at high frequencies

We report the salient features of the magnetic properties of glassy and nanocrystalline Fe/sub 82/M/sub 7/B/sub 10/Cu/sub 1/ [M=Zr,Hf,Nb] alloys. By controlled annealing, fine 4-6 nm grain size bcc-Fe is formed in a ductile glassy matrix, which gives good soft magnetic properties like permeability and low coercive field. From the low temperature magnetic data and ferromagnetic resonance studies we determine and compare the changes in the spin wave exchange stiffness constants as well as the range of exchange interactions in the glassy and nanocrystalline states.

A Mössbauer study of R6Fe13X (R=Pr, Nd; X=In, Sn, Tl, Pb, Cu, Ag, Au)

Compounds with the composition R6Fe13X (R=Pr, Nd; X=In, Sn, Tl, Pb, Cu, Ag, Au) were studied by57Fe Mossbauer spectroscopy. Attention was focused on the influence of the easy axis of the magnetization on the shape of the hyperfine patterns. The spectra are composed of at least four subpatterns, originating from the different Fe lattice sites. Contrary to the magnetization, a significant dependence of the hyperfine parameters on the specific elements R and X could not be detected. Predominantly, the easy axis of the magnetization was found to lie within the basal plane; only for R=Nd and X=In, Sn, Tl, Pb is an easyc-axis present. Since the low temperature magnetization data obtained for the different compounds show a wide spread, while the57Fe hyperfine fields remain almost constant over the whole series, some kind of antiferromagnetic ordering within the Fe sublattice is anticipated.

The application of high magnetic fields in solid state physics

Frontiers in High Magnetic Fields may induce Frontiers in Materials Engineering and vice versa especially for materials combining semiconductor and magnetic properties in semimagnetic semiconductors. ZnMn 2As 2 is a new material of the class (Zn 1− x Mn x ) 3As 2. For x= 2 3 , however, the usual statistical substitutionof the Zn-ion by Mn 2+ condenses into an ordered layer structure. The different magnetic phases are determined by neutron scattering, compared with low temperature magnetization data and detected directly in the DC-magnetoresistance of the low mobility holes, whose conductivity properties are essentially determined by the internal spin polarization of the material.

Magnetic Properties of the Spin-1/2 Ferromagnetic-Ferromagnetic-Antiferromagnetic Trimerized Heisenberg Chain

The magnetic properties of the ferromagnetic-ferromagnetic-antiferromagnetic trimerized spin-1/2 Heisenberg chain are studied theoretically. The high temperature susceptibilty and the ground state saturation magnetic field are calculated and the exchange energies of the trimer compound 3CuCl${}_2\cdot$2dx are determined. The magnetization curve is obtained by numerical diagonalization of finite size systems. The result explains the low temperature magnetization data for 3CuCl${}_2\cdot$2dx with the exchange energies obtained as above. It is predicted that the magnetization curve has a plateau at 1/3 of the saturation magnetization if the ferromagnetic exchange energy is comparable to or smaller than the antiferromagnetic exchange energy.