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1.
Temperature and field-dependent magnetization measurements on polycrystalline CeMnCuSi2 reveal that the Mn moments in this compound exhibit ordering with a ferromagnetic (FM) component ordered instead of the previously reported purely antiferromagnetic (AFM) ordering. The FM ordering temperature, Tc, is about 120 K and almost unchanged with external fields up to 50 kOe. Furthermore, an AFM component (such as in a canted spin structure) is observed to be present in this phase, and its orientation is modified rapidly by the external magnetic field. The Ce L3-edge X-ray absorption result shows that the Ce ions in this compound are nearly trivalent, very similar to that in the heavy fermion system CeCu2Si2. Large thermomagnetic irreversibility is observed between the zero-field-cooled (ZFC) and field-cooled (FC) M(T) curves below Tc indicating strong magnetocrystalline anisotropy in the ordered phase. At 5 K, a metamagnetic-type transition is observed to occur at a critical field of about 8 kOe, and this critical field decreases with increasing temperature. The FM ordering of the Mn moments in CeMnCuSi2 is consistent with the value of the intralayer Mn–Mn distance RaMn–Mn=2.890 Å, which is greater than the critical value 2.865 Å for FM ordering. Finally, a magnetic phase diagram is constructed for CeMnCuSi2. 相似文献
2.
A. Bhattacharjee P.J. van Koningsbruggen Joel S. Miller 《Journal of Physics and Chemistry of Solids》2008,69(11):2713-2718
The 57Fe Mössbauer spectroscopy of mononuclear [Fe(II)(isoxazole)6](ClO4)2 has been studied to reveal the thermal spin crossover of Fe(II) between low-spin (S=0) and high-spin (S=2) states. Temperature-dependent spin transition curves have been constructed with the least-square fitted data obtained from the Mössbauer spectra measured at various temperatures between 84 and 270 K during a cooling and heating cycle. This compound exhibits an unusual temperature-dependent spin transition behaviour with TC(↓)=223 and TC(↑)=213 K occurring in the reverse order in comparison to those observed in SQUID observation and many other spin transition compounds. The compound has three high-spin Fe(II) sites at the highest temperature of study of which two undergo spin transitions. The compound seems to undergo a structural phase transition around the spin transition temperature, which plays a significant role in the spin crossover behaviour as well as the magnetic properties of the compound at temperatures below TC. The present study reveals an increase in high-spin fraction upon heating in the temperature range below TC, and an explanation is provided. 相似文献
3.
Presently we explored nanosandwich structures with graphite (Gt) and graphene (Gn) nanolayers. We found that in Pt–SiO2–Gt, Pt–BN–Gt and Pt–SiO2–Ni–Gn structures the spectra may be decomposed into several components, each corresponding to a different value of the total spin angular momentum S. Only one component was required to describe the Pt–SiO2–Ni–Gn spectra at 5.3 K, with additional components appearing at higher temperatures. On the other hand, a single component described the Pt–BN–Ni–Gn spectra at all temperatures. Temperature dependence of the spectra of the Pt–SiO2–Ni–Gn system was studied in the 5.3–75.3 K range. Presently we obtained experimental results for novel sandwich systems, with the Gn layer only two monoatomic layers thick. Thus, we compared experimental spectra of a three-nanolayer sandwich system containing a Gt nanolayer with those of a four-nanolayer system containing a diatomic Gn layer. The experimental results were discussed using a theoretical model of the respective physical mechanisms. We propose an exchange anticrossing mechanism, whereby the spin-state polarization of the given Zeeman?s substate in the Pt nanolayer is transported to Gt or Ni–Gn nanolayer by the exchange interaction between the two layers. As long as exchange interaction coupling spin states in different nanolayers is involved, we term the respective spectra the “spin anticrossing exchange-resonance spectra”. This clarifies the physical origins of some of the model parameters, i.e. the growing external magnetic field shifts the Zeeman?s substates in the different layers differently, producing the anticrossing spectrum. In the frameworks of the developed model, we propose spin–orbit (SO) interaction as the main factor inducing the spin–lattice relaxation, which is one of the important factors determining the line shape. We performed ab initio calculations of the SO interaction in carbon and metal nanolayers, finding that the SO interactions monotonously increase with the atomic number. 相似文献
4.
The effect of oxygen/cobalt off-stoichiometry upon magnetism in CaBaCo4O7 has been investigated. It is shown that the oxides CaBaCo4O7+δ and CaBaCo4−xO7−δ (0≤x≤0.20) synthesized below 1100 °C in air exhibit phase separation, where ferrimagnetic regions with TC~56 K to 64 K coexist with regions of magnetic clusters. The latter are detected from ac-susceptibility measurements, which show various frequency dependent peaks at ~14–20 K, 37 K, and 45 K, depending on the stoichiometry. The origin of this phenomenon is attributed to the great sensitivity of the material to oxidation as the synthesis of temperature is lowered, leading to the introduction of additional Co3+ cations, with respect to the ideal formula CaBaCo22+Co23+O7. This excess Co3+ tends to destroy the ferromagnetic zig-zag chains of the ferrimagnetic structure and creates various cobalt spin clusters, leading to the inherent phase separation in the samples. 相似文献
5.
P.B FabritchnyiM.V Korolenko M.I AfanasovM Danot E Janod 《Solid State Communications》2003,125(6):341-346
Mössbauer parameters of 119Sn diamagnetic dopant cations in an antiferromagnetic compound having the ilmenite structure are for the first time reported. The spectra reveal a well resolved hyperfine splitting pattern of combined magnetic and quadrupole interactions (at 5 K, δ=0.19 mm/s, H1=52.5 kOe, eVZZQ3/2=−0.80 mm/s, θ≈0°). This spectral component whose contribution (A1=82%) represents more than four fifths of the total amount of the dopant (Sn/(Mn+Ti)=1/200) is assigned to Sn(IV) ions located in the bulk of MnTiO3, on the Mn(II) site, and with a Mn(II) vacancy in their nearest surrounding. Two spectral components with minor contributions are also observed: one of them (H2≈25 kOe, A2=8%) can be assigned to Sn(IV) ions, in the MnTiO3 lattice as well, on a site where they exhibit a weaker spin polarization (this site could be the Ti(IV) one) and the other (H3=0 kOe, A3=10%) to SnO2 or/and Ti1−xSnxO2 clusters. The Néel temperature of MnTiO3 probed by the 119Sn dopant (TN=69±2 K) agrees well with the values previously provided by ESR and antiferromagnetic resonance measurements. Variation of H1 with temperature follows close the Brillouin function for S=5/2. No perturbation appears in the Mössbauer spectra around T=90 K where a broad peak, characteristic of 2D magnetic interactions, is observed on the static magnetic susceptibility curve. 相似文献
6.
Hongzhi Luo Fanbin MengYanqiang Cai Wangwen HongEnke Liu Guangheng WuXiaoxi Zhu Chengbao Jiang 《Journal of magnetism and magnetic materials》2011,323(17):2323-2327
Quaternary Heusler alloys Fe1.5M0.5CoSi with M=V, Cr, Mn and Fe have been investigated theoretically and experimentally. All of these samples crystallize in the ordered Heusler-type structure. The calculated electronic structure shows a pseudogap around EF in the minority spin states of Fe2CoSi. With the substitution of low-valent atoms for Fe, the majority antibonding peak is shifted to higher energy and a minority gap around the Fermi level is opened. High spin polarization ratio is obtained in Fe1.5M0.5CoSi (M=V, Cr, Mn) alloys. The calculated total spin moments decrease with decreasing number of valence electrons and follow the Slater-Pauling curve, which agree with the experimental results well. The Curie temperature decreases as M atom varies from Fe to V, but is always higher than 650 K, which is suitable for technical applications. 相似文献
7.
Suman Kumar Nath Kazi Hanium Maria Saroaut Noor S.S. Sikder S.Manjura Hoque M.A. Hakim 《Journal of magnetism and magnetic materials》2012
A series of Ni1−xCdxFe2O4 (0.0≤x≤0.8) were prepared by conventional double sintering ceramic method and sintered at 1200 °C for 6 h. X-ray diffraction results confirmed the single-phase spinel structures of all the samples. The Curie temperature decreases linearly with increasing Cd content, which is explained due to the weakening of the A–B exchange interaction. The sample with x=0.7 shows re-entrant type of spin glass phase transitions. The magnetic moment and saturation magnetization at 20 K are found to increase with Cd content up to x=0.5 and then tends to decrease for x>0.5. The increase in magnetic moment with cadmium is attributed to Neel's two sublattice (A- and B-sublattice) collinear models according to which the magnetic moment is the vector sum of the lattice magnetic moment. The decrease in magnetization for x>0.5 obeys the Yafet–Kittel (Y–K) model. The increase in Y–K angles for x>0.3 indicates the increased tendency for triangular spin arrangements on B-sites. This suggests the existence of a canted spin structure in the ferrite system with higher content of Cd. 相似文献
8.
L.J. Gillie A.J. Wright G. Van Tendeloo 《Journal of Physics and Chemistry of Solids》2004,65(1):87-93
The anion-deficient perovskite Y0.8Sr2.2Mn2GaO8−δ (where δ∼0.1) has been synthesised and the crystal and magnetic structures determined by Rietveld analysis of neutron powder diffraction (NPD) data. The material has body-centred tetragonal symmetry (I4/mmm, a=7.6373(3) Å and c=15.6636(10) Å) and consists of alternating layers of octahedral and tetrahedral polyhedra, the layers being perpendicular to [001]. The octahedral layers are preferentially occupied by manganese and the tetrahedral layers are a mixture of manganese and gallium. The precise cation distribution depends critically on preparative conditions. An unusual structural feature of these materials is the arrangement of oxygen vacancies in the tetrahedral layers: in the basic structure, isolated squares of corner-linked tetrahedra are formed instead of the chains that are observed in brownmillerite phases. Additional oxide ions in this layer probably allow the Mn ions to achieve distorted square pyramidal coordination. Low temperature NPD and magnetisation data indicate antiferromagnetic ordering below 100 K. 相似文献
9.
The density-functional theory (DFT) within the full potential linearized augmented plane wave (FPLAPW) method was applied to study the layered organic–inorganic hybrid Fe[CH3(CH2)2PO3(H2O)]. The relative stability of the ground state, the electronic band structure, the magnetic and the conducting properties were investigated. The calculations reveal that the compound has a stable ferromagnetic ground state and the spin magnetic moment per molecule is about 4.0 μB, which is mainly from Fe(II) ion. By analysis of the band structure, we find that the compound has half-metallic properties. 相似文献
10.
Petra Á. Szilágyi Stéphane Dorbes José Antonio Real Christophe Faulmann 《Journal of Physics and Chemistry of Solids》2008,69(11):2681-2686
Thermal and pressure effects have been investigated on the [Fe(sal2-trien)][Ni(dmit)2] spin crossover complex by means of Mössbauer spectroscopic, calorimetric, X-ray diffraction and magnetic susceptibility measurements. The complex displays a complete thermal spin transition between the and spin states of FeIII near 245 K with a hysteresis loop of ca. 30 K. This transition is characterised by a change of the enthalpy, ΔHHL=7 kJ/mol, entropy, ΔSHL=29 J/Kmol, and the unit cell volume, ΔVHL=15.4 Å3. Under hydrostatic pressures up to 5.7 kbar the thermal transition shifts to higher temperatures by ca. 16 K/kbar. Interestingly, at a low applied pressure of 500 bar the hysteresis loop becomes wider (ca. 61 K) and the transition is blocked at ∼50% upon cooling, indicating a possible (irreversible) structural phase transition under pressure. 相似文献
11.
E.S. Demidov B.A. Aronzon S.N. Gusev A.S. Lagutin S.A. Levchuk S.N. Nikolaev V.V. Podolskii M.V. Sapozhnikov 《Journal of magnetism and magnetic materials》2009,321(7):690-694
The paper reports on the results of a study of the synthesis conditions effects on magnetic and transport properties of nanosized layers of high-Tc diluted magnetic semiconductors (DMS), such as Ge:Mn, Si:Mn and Si:Fe, fabricated by laser-plasma deposition over a wide range of the growth temperature, Tg=(20-550) °C on single-crystal GaAs or Al2O3 substrates. Ferromagnetism of the layers was detected by measurement data of the magneto-optical Kerr effect, anomalous Hall effect, negative magnetoresistance and ferromagnetic resonance (FMR) at 5-500 K. The optimum growth temperature, Tg, for Si:Mn/GaAs layers with Tc≈400 K is shown to be about 400 °C. The Si:Mn/Al2O3 layers with 35% of Mn have the metal-type of conductivity with manifestation of magnetization up to room temperature. Different types of uniformly doped structures and digital alloys have been investigated. In contrast to GaSb:Mn films, Si-based ferromagnetic layers have strongly different magnetic and electric properties in case of uniformly doped structures and digital alloys. Positive results of the Fermi level variation effect on the improvement of Si- and Ge-based DMS layers have been gained on the use of additional doping with shallow acceptor Al impurity which contributes to the increase of the hole concentration and the RKKY exchange interaction of 3d-ions. The Ge:(Mn, Al)/GaAs or Ge (Mn, Al)/Si layers grown at 20 °C feature surprising extraordinary angular dependence of FMR. 相似文献
12.
The crystal structure, magnetic and magnetotransport properties of the variation of B′-site transition metal in Sr2FeMO6 (M=Mo, W) with double perovskites structure have been investigated systematically. Measurements of magnetization vs. temperature at H=5 T show that Sr2FeMoO6 is a ferromagnet and Sr2FeWO6 is an antiferromagnet with TN∼35 K. Additionally, the large magnetoresistance ratio (MR) of ∼22% (H=3 T) at room temperature (RT) was observed in the Sr2FeWO6 compound. However, the Sr2FeMoO6 compound did not show any significant MR even at high fields and RT (MR∼1%; H=3 T and 300 K). The implications of these findings are supported by band structure calculations to explain the interaction between the 4d(Mo) and 5d(W) orbitals of transition metal ions and oxygen ions. 相似文献
13.
A.D. Arelaro E. Lima Jr L.M. Rossi P.K. Kiyohara H.R. Rechenberg 《Journal of magnetism and magnetic materials》2008
The influence of different M2+ cations on the effective magnetic anisotropy of systems composed of MFe2O4 (M=Fe, Co and Mn) nanoparticles was investigated. Samples were prepared by the high-temperature (538 K) solution phase reaction of Fe (acac)3, Co (acac)2 and Mn (acac)2 with 1,2 octanodiol in the presence of oleic acid and oleylamine. The final particles are coated by an organic layer of oleic acid that prevents agglomeration. Transmission electron microscopy (TEM) images show that particles present near spherical form and a narrow grain size distribution, with mean diameters in the range of 4.5–7.6 nm. Powder samples were analyzed by ac susceptibility and Mössbauer measurements, and Keff for all samples was evaluated using both techniques, showing a strong dependence on the nature of the divalent cation. 相似文献
14.
Ferromagnetic Ga1−xMnxAs layers (where x≈4.7–5.5%) were grown on (1 0 0) GaAs substrates by molecular beam epitaxy. These p-type (Ga,Mn)As films were revealed to have a ferromagnetic structure and ferromagnetism is observed up to a Curie temperature of 318 K, which is ascribed to the presence of MnAs secondary magnetic phases within the film. It is highly likely that the phase segregation occurs due to the high Mn cell temperature around 890–920 °C, as it is well established that GaMnAs is unstable at such a high temperature. The MnAs precipitate in the samples with x≈4.7–5.5% has a Curie temperature Tc≈318 K, which was characterized from field-cooled and zero-field-cooled magnetization curves. 相似文献
15.
EPR spectroscopy has become an increasingly powerful tool to examine the spin states and dynamics of single-molecule magnets, but has not been exploited to probe bulk magnetically ordered phases of molecular magnets. In this article, we review the EPR spectra of antiferromagnets and canted antiferromagnets below TN with particular reference to our own studies on the canted antiferromagnet, p-NCC6F4CNSSN (TN=36 K). The antiferromagnetic resonance experiment allows the saturation of the sublattice magnetisation to be probed. In addition, the exchange and anisotropy fields (He and Ha), the spin-flop field (Hsf) and for canted antiferromagnets, the Dzyaloshinskii-Moriya field (HDM), which gives rise to the spontaneous moment, can be determined. 相似文献
16.
Antonio Raudino Franco Battaglia 《Journal of Electron Spectroscopy and Related Phenomena》1980,20(3):327-331
The He(II) spectra of the unsubstituted metallocenes {M(η-C5H5)2}, M V, Cr, Mn, Fe, Co, Ni and Ru, and of {Mn(η-C5H4Me)2} are reported; both He(I) and He(II) spectra of some decamethylmetallocenes {M(η-C5Me5)2}, where M Mg, V, Cr, Mn, Fe, Co and Ni, are also given. Intensity changes between the He(I) and He(II) spectra are shown to provide a reliable guide to band assignment. A ligand field treatment of the decamethylmanganocene cation, including limited configuration interaction, gives values for Δ2, B and C; these values are also in good agreement with the photoelectron spectra of {M(η-C5Me5)2} where M V, Cr and Fe. Overlap between the ligand and metal “d” band structures prevents complete assignment in the cases of Co and Ni. 相似文献
17.
Yu.A. Danilov E.S. Demidov Yu.N. Drosdov V.P. Lesnikov V.V. Podolskii M.V. Sapozhnikov A.P. Kasatkin 《Journal of magnetism and magnetic materials》2006
We report on laser synthesis of thin 30–200 nm epitaxial layers with mosaic structure of diluted magnetic semiconductors GaSb:Mn and InSb:Mn with the Curie temperature TC above 500 K and of InAs:Mn with TC no less than 77 K. The concentration of Mn was ranged from 0.02 to 0.15. In the case of InSb:Mn and InAs:Mn films, the additional pulse laser annealing was needed to achieve ferromagnetic behavior. We used Kerr and Hall effects methods as well as ferromagnetic resonance (FMR) spectroscopy to study magnetic properties of the samples. The anisotropy FMR was observed for both layers of GaSb:Mn and InSb:Mn up to 500 K but it takes place with different temperature dependencies of absorption spectra peaks. The resonance field value and amplitude of FMR signal on the temperature is monotonically decreased with the temperature increase for InSb:Mn. In the case of GaSb:Mn, this dependence is not monotonic. 相似文献
18.
Zn-doped nickel ferrite nanoparticles (Zn0.6Ni0.4Fe2O4) have been prepared via a surfactant, polyethylene glycol assisted hydrothermal route. X-ray powder diffractometry (XRD), Fourier transform infrared spectroscopy, transmission electron microscopy (TEM), and vibrating scanning magnetometry (VSM) were used for the structural, morphological, and magnetic characterizations of the product, respectively. TEM analysis revealed that the nanoparticles have a narrow size distribution, with average particle size of 15±1 nm, which agrees well with the XRD based estimate of 14±2 nm. The absence of saturation and remanent magnetization, and coercivity in the high temperature region of the M-H curve and non-zero magnetic moments indicate superparamagnetism of the nanoparticles with a canted spin structure. The appearance of a peak on the temperature-dependent zero-field cooling magnetization curve at ∼190 K indicates the blocking temperature of the sample. 相似文献
19.
Françoise Gilbert Philippe Refait François Lévêque Céline Remazeilles Egle Conforto 《Journal of Physics and Chemistry of Solids》2008,69(8):2124-2130
Magnetic methods are efficient tools in soil and environmental science. But in such natural environments, several magnetic minerals are generally present. So, synthetic standard samples are necessary for calibration of laboratory techniques. The aim of this study was to synthesise goethite free of magnetic impurities (concentration <∼1 μg kg−1) with different crystal sizes. Goethite was prepared by oxidation of aqueous suspensions of Fe(OH)2 precipitates. Final products were characterised by X-ray diffraction, infrared spectroscopy, scanning and transmission electron microscopy and magnetic methods. Goethite could be obtained in the absence of any trace of strong magnetic minerals using FeSO4·7H2O and NaOH as reactants with the following experimental conditions: temperature=45 °C, [FeSO4·7H2O]=0.50 mol L−1, [NaOH]=0.20 mol L−1, stirring speed=760 rpm. The Fe(II) concentration and the stirring speed were varied. It proved possible to modify the size of the goethite crystals by varying the Fe(II) concentration and the stirring speed, but important changes of these parameters induced the formation of other phases, lepidocrocite when the oxidation reaction was drastically accelerated and Fe3O4 when the reaction was slowed down. In any case, for weak magnetic fields, a low-coercivity magnetic mineral saturating at weak magnetic fields was observed. It may correspond to traces of δ-FeOOH or to domains structurally similar to δ-FeOOH inside the multidomainic crystals of δ-FeOOH. 相似文献
20.
X.J. Liu Z.Q. Li A. Yu M.L. Liu W.R. Li B.L. Li P. Wu H.L. Bai E.Y. Jiang 《Journal of magnetism and magnetic materials》2007
We have investigated the magnetic, electrical transport and electron spin resonance (ESR) properties of polycrystalline Fe-doped manganite LaMn0.7Fe0.3O3+δ prepared by sol–gel method. A typical cluster-glass feature is presented by DC magnetization and AC susceptibility measurements and a sharp but shallow memory effect was observed. Symmetrical Lorentzian lines of the Mn/Fe spectra were detected above 120 K, where the sample is a paramagnetic (PM) insulator. When the temperature decreases from 120 K, magnetic clusters contributed from ferromagnetic (FM) interaction between Mn3+ and Mn3+/Fe3+ ions develop and coexist with PM phase. At lower temperature, these FM clusters compete with antiferromagnetic (AFM) ones between Fe3+ ions, which are associated with a distinct field-cooled (FC) effect in characteristic of cluster-glass state. 相似文献