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1.
The exchange interactions and the magnetic exchange energies are calculated by using the mean field theory and the probability law of Zn1−xMnxCr2O4 nanoparticles. The high-temperature series expansions have been applied in the spinels Zn1−xMnxCr2O4 systems, combined with the Padé approximants method, to determine the magnetic phase diagram, i.e. TC versus dilution x. The critical exponent associated with the magnetic susceptibility (γ) is deduced. The obtained value of γ is insensitive to the dilution ratio x and may be compared with other theoretical results based on the 3D Heisenberg model.  相似文献   

2.
By using mean field theory, we have evaluated the nearest-neighbour and the next-neighbour super-exchange J1(x) and J2(x), respectively, for Zn1−xCuxCr2Se4 in the range 0?x?1. The intraplanar and the interplanar interactions are deduced. High-temperature series expansions are derived for the magnetic susceptibility and two-spin correlation functions for a Heisenberg ferromagnetic model on the B-spinel lattice. The calculations are developed in the framework of the random phase approximation. The magnetic phase diagram is deduced. A spin glass phase is predicted for intermediate range of concentration. The results are comparable with those obtained by magnetic measurements. The critical exponents associated with the magnetic susceptibility (γ) and the correlation lengths (ν) have been deduced. The values are comparable to those of the 3D Heisenberg model, and are insensitive to the dilution x.  相似文献   

3.
X-ray powder diffraction and magnetization measurements were done on the magnetic shape memory alloys Ni2Mn1+xIn1−x. On the basis of the results, the magnetic phase diagram was determined for Ni2Mn1+xIn1−x alloys. Magnetization measurements make clear that the excess Mn atoms, which substitute for In sites, are coupled ferromagnetically to the ferromagnetic manganese sublattices. A magnetic phase diagram of Ni2Mn1+xIn1−x alloys is discussed qualitatively on the basis of the interatomic dependence of the exchange interactions.  相似文献   

4.
The magnetic properties of the Ca1−xMnxO systems in the range 0?x?1 have been studied by mean field theory and high-temperature series expansions (HTSEs). By using the first theory, we have evaluated the nearest neighbour and the next-neighbour super-exchange interaction J1(x) and J2(x) respectively, in the range 0.45?x?1. The corresponding classical exchange energy for magnetic structure is obtained for the Ca1−xMnxO systems. The HTSEs combined with the Padé approximants (PA) method is applied to the Ca1−xMnxO systems; we have obtained the magnetic phase diagrams (TN or TSG versus dilution x) in the range 0?x?1. The obtained theoretical results are in agreement with experimental ones obtained by magnetic measurements. The critical exponents associated with the magnetic susceptibility (γ) and the correlation lengths (ν) are deduced in the range 0?x?1.  相似文献   

5.
Magnetization curves of Tb1−xGdxMn6Sn6 compounds (0?x?1) have been measured for aligned powder samples in the temperature range 4.2–300 K in pulsed magnetic fields up to 30 T. Temperature and concentration dependences of the magnetocrystalline anisotropy constants K1 and K2 and concentration dependence of the temperature of spontaneous spin-reorientation transition have been determined. Using these data, we estimated the contribution of the manganese and terbium atoms to the magnetic anisotropy of Tb1−xGdxMn6Sn6 and analyzed the origin of the appearance of field-induced first-order magnetic phase transition in these compounds.  相似文献   

6.
Magnetic properties of the Ce2Fe17−xMnx, x=0–2, alloys in magnetic fields up to 40 T are reported. The compounds with x=0.5–1 are helical antiferromagnets and those with 1<x?2 are helical ferromagnets or helical antiferromagnets at low and high T, respectively. Mn ions in the system carry average magnetic moment of 3.0±0.2 μB that couple antiparallelly to the Fe moments. Easy-plane magnetic anisotropy in the Ce2Fe17−xMnx compounds weakens upon substitution of Mn for Fe. The absolute value of the first anisotropy constant in the Ce2Fe17−xMnx helical ferromagnets decreases slower with increasing temperature than that calculated from the third power of the spontaneous magnetization. Noticeable magnetic hysteresis in the Ce2Fe17−xMnx, x=0.5–2, helical magnets over the whole range of magnetic fields reflects mainly irreversible deformation of the helical magnetic structure during the magnetization of the compounds. A contribution from short-range order (SRO) magnetic clusters to the magnetic hysteresis of the helical magnets has been also estimated.  相似文献   

7.
Cerium-doped Y1−xCexMnO3 compounds have been prepared in single-phase form for x=0 to 0.10. X-ray diffraction (XRD) patterns could be analyzed by using P63cm space group. Temperature variations of ac susceptibility and magnetization measurements show that these Ce-doped materials exhibit weak ferromagnetic transition. The observed ferromagnetic transition is attributed to the double exchange ferromagnetic interaction between Mn2+ and Mn3+ ions due to electron doping. The MH loops exhibit hysteresis along with linear contribution and were analyzed based on bound magnetic polaron (BMP) model. Increase in saturation magnetization and decrease in BMP concentrations have been observed with increase in Ce doping.  相似文献   

8.
A series of Ni43Mn46Sn11−xSbx (x=0, 1, and 3) alloys were prepared by an arc melting method. The martensitic transition shifts to higher temperature with the increasing Sb content. The isothermal magnetization curves and Arrott plots around martensitic transition temperatures show a typical metamagnetic behavior. Under a low applied magnetic field of 10 kOe, large magnetic entropy changes around the martensitic transition temperature are 10.4, 8.9, and 7.3 J/kg K, for x=0, 1, and 3, respectively. The origin of the large magnetic entropy changes and potential application for Ni43Mn46Sn11−xSbx alloys as working substances in magnetic refrigeration are discussed.  相似文献   

9.
We have examined magnetizations as a function of temperature and magnetic field in layered perovskite manganites La2−2xSr1+2xMn2O7 single crystals (x=0.313, 0.315, 0.318, 0.320 and 0.350) in order to determine the phase boundary between two ferromagnets (one is an uniaxial ferromagnet whose easy axis is parallel to the c-axis and the other is a planar ferromagnet whose easy axis is within the ab-plane) and following results are obtained: (i) all the present manganites exhibit magnetic transitions from a ferromagnet to a paramagnet at 76, 107, 116, 120 and 125 K for x=0.313, 0.315, 0.318, 0.320 and 0.350, respectively; (ii) for x=0.318, 0.320 and 0.350, the magnetic structure is a planar ferromagnet below Curie temperature; (iii) for x=0.313 and 0.315, the magnetic structure changes from an uniaxial to a planar ferromagnet at 66 and 85 K, respectively. From the results described above we have constructed the magnetic phase diagram of layered perovskite manganite La2−2xSr1+2xMn2O7 (0.313?x?0.350).  相似文献   

10.
Single-phase polycrystalline samples of La0.67Ca0.33Mn1−xO3 (x=0.00, 0.02, 0.04, 0.06) have been prepared using the sol-gel method. The structure, magnetocaloric properties and the Curie temperature of the samples with different Mn vacancy concentrations have been investigated. The experimental results show that vacancy doping at the Mn-sites has a significant influence on the magnetic properties of La0.67Ca0.33Mn1−xO3. The Curie temperature decreases monotonically with increasing the Mn-site vacancy concentration x. A remarkable enhancement of the magnetic entropy change has been obtained in the La0.67Ca0.33Mn0.98O3 sample. The entropy change reaches |ΔSM|=3.10 J kg−1 K−1 at its Curie temperature (264 K) under an applied magnetic field H=10 kOe, which is almost the same value as that of pure Gd.  相似文献   

11.
12.
In attempt to characterise the magnetic ordering in the whole composition range of the Cd1−xZnxCr2Se4 system, various magnetic measurements were performed on both crystalline and polycrystalline samples with 0?x?1. The magnetic properties of the system are typical of a ferromagnet below x=0.4 and of a complex antiferromagnet one above x=0.6. In this work the intermediate region was carefully studied. The variations of both M(T) and χac at low fields suggest that transitions from ferromagnetic to Gabay–Toulouse ferromagnetic-spin-glass mixed phase at low temperature occur in the range 0.41?x?0.58. The high-temperature susceptibility measurements show that for the whole concentration range the system obeys Curie–Weiss laws. The results can be explained by the coexistence of competing interactions (ferromagnetic between nearest neighbours and antiferromagnetic between higher order neighbours) and disorder due to the random substitution between zinc and cadmium ions in the tetrahedral sites of the spinel lattice. An experimental magnetic phase diagram of the system is established.  相似文献   

13.
Magnetization curves with various magnetic field orientations and nanowire diameters were measured at room temperature. The measured coercivity as a function of angle (θ) between the field and wire axis reveals that the coercivity decreases with increasing value of θ for various nanowires. Theoretically, based on Monte Carlo simulation we investigated the magnetization reversal modes of the Co1−xCux nanowires and obtained also the θ dependence of the coercivity. Comparing the simulated with the experimental results, we find that the magnetocrystalline anisotropy plays an important role on the magnetic properties of Co1−xCux nanowires, and the magnetization reversal process in the Co1−xCux nanowires could not be understood by the classical uniform rotation mode in the chain-of-sphere model.  相似文献   

14.
In this study, magnetic and magnetocaloric properties of Pr0.68Ca0.32−xSrxMnO3 (x=0, 0.1, 0.18, 0.26 and 0.32) compounds were investigated. X-ray results indicated that all the samples have a single phase of orthorhombic symmetry. The orthorhombic unit cell parameters increase with the increase in Sr content. Large negative magnetic entropy changes (−26.2 J/kg K at 38 K and 5 T for x=0 and −6.5 J/kg K at 83 K and 6 T for x=0.1) were attributed to ultrasharp metamagnetic transitions. The peak value of ΔSm decreased from −4.1 J/kg K for x=0.18 sample to −2.4 J/kg K for x=0.32 at 1 T magnetic field.  相似文献   

15.
Amorphous soft magnetic ribbons Fe73.5−xCrxSi13.5B9Nb3Cu1 (x=1–5) have been fabricated by rapid quenching on a single copper wheel. The differential scanning calorimetry (DSC) patterns showed that the crystallization temperature of α-Fe(Si) phase is ranging from 542 to 569 °C, a little higher than that of pure Finemet (x=0). With the same annealing regime, the crystallization volume fraction as well as the particle size of α-Fe(Si) crystallites decreased with increasing Cr amount substituted for Fe in studied samples. Especially, the interesting fact is that the laminar structure of heat-treated ribbons on the surface contacted to copper wheel in the fabricating process has been firstly discovered and explained to be related to the existence of Cr in studied samples. The hysteresis loop measurement indicated that there is the pinning of displacement of domain walls. The giant magnetocaloric effect (GMCE) has been found in amorphous state of the samples. After annealing, the soft magnetic properties of investigated nanocomposite materials are desirably improved.  相似文献   

16.
The effect of Na doping and annealing time on the structure, electrical properties, magnetoresistance and thermopower properties has been investigated in perovskite La1−xNaxMnOy (x=0.025, 0.075 and 0.1) systems. La1−xNaxMnOy crystallizes in a single-phase rhombohedral structure. It is observed a simultaneous occurrence of the ferromagnetic to paramagnetic state and metallic to insulating state. In the meanwhile, a large negative magnetoresistance with low applied magnetic field is observed. In addition, ρ(T) curves for Na-doped samples exhibit another broad transition Tms2 below Tms. Such double peak behavior in the ρ(T) curve interpreted by the electronic inhomogeneity in the samples. The sign of S changes from positive to negative depending on composition. The values of Seebeck coefficient are small (in the microvolt range).  相似文献   

17.
In this paper we report a systematic study of Mn-site substitution by M=Co, Cr and Al in La0.85Ag0.15MnO3 series to understand the magnetic interactions between Mn and other transition metals. The long-range ferromagnetic (FM) ordering of the parent compound was significantly affected by Mn-site substitution. The measured magnetic properties of Co-doped samples have been explained on the basis of FM interactions in Mn3+-O-Mn4+, Co2+-O-Mn4+, Co3+-O-Mn4+ networks and simultaneous antiferromagnetic (AFM) interactions in Mn4+-O-Mn4+, Co2+-O-Mn3+ networks. The magnetic properties of Cr-doped compounds could be understood on the basis of double exchange FM interactions in Mn3+-O2−-Mn4+ networks and competing AFM in Cr3+-O-Mn4+, Mn4+-O-Mn4+, Cr3+-O-Mn3+ networks. However, it is found that the doping of Al ions play a role of magnetic dilution, without contributing any other competing magnetic interaction. The field variations of magnetization of all the above three series could be analysed by fitting to Brillouin function model and the effective spin contribution for FM has been determined. The measured saturation magnetization has been explained quantitatively.  相似文献   

18.
Magnetic and transport properties of (La0.7Pb0.3MnO3)1−xAgx composites are explored in this study. Ferromagnetism is gradually attenuated due to the magnetic dilution with increase of Ag content percentage. Clearly irreversible behavior in the zero-field cooling and field cooling curves at a low field caused by the competition between the magnetization and magnetic domain orientation processes has been observed as x increases. Saturation magnetization decreases as x increases, while ferromagnetic transition temperature remains around 346 K for all composites. The resistivity decreases significantly for (La0.7Pb0.3MnO3)1−xAgx composites. It is suggested that introduction of Ag into the niche of grain boundaries forms artificial conducting network and improves the carriers to transport. However, enhancement of magnetoresistance has been observed for the system.  相似文献   

19.
It is expected that joint existence of ferromagnetic properties and ferroelectric structural phase transition in diluted magnetic semiconductors IV-VI leads to new possibilities of these materials. Temperature of ferroelectric transition for such crystals can be tuned by the change of Sn/Ge ratio. Magnetic susceptibility, Hall effect, resistivity and thermoelectric power of Ge1−xySnxMnyTe single crystals grown by Bridgeman method (x=0.083-0.115; y=0.025-0.124) were investigated within 4.2-300 K. An existence of FM ordering at TC∼50 K probably due to indirect exchange interaction between Mn ions via degenerated hole gas was revealed. A divergence of magnetic moment temperature dependences at T?TC in field-cooled and zero-field-cooled regimes is obliged to magnetic clusters which are responsible for superparamagnetism at T>TCTf (freezing temperature) and become ferromagnetic at TC arranging spin glass state at T<TfTC. Phase transition of ferroelectric type at T≈46 K was revealed. Anomalous Hall effect which allows to determine magnetic moment was observed.  相似文献   

20.
The study of the structural and magnetic phase diagram of the manganites La1−xAgxMnO3 shows similarity with the La1−xSrxMnO3 series, involving a metallic ferromagnetic domain at relatively high temperature (≈300 K). The Ag-system differs from the Sr-one by a much smaller homogeneity range (x≤1/6) and the absence of charge ordering. But the most important feature of the Ag-manganites deals with the exceptionally high magnetoresistance (−25%) at room temperature under 1.2 T, that appears for the composition x=1/6. The latter is interpreted as the coincidence of the optimal double exchange condition (Mn3+:Mn4+=2) with Tmax=300 K (maximum of the ρ(T) curve in zero field).  相似文献   

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