Paramagnetic Region Research Articles

Crystallization and magnetic hardening behaviour of Fe-rich FeSiBNb(Cu) melt-spun alloys

The sequential, multi-stage crystallization and magnetic hardening behaviour of Fe82B14Si2Nb2, Fe83B13Si2Nb2, Fe83B12Si2Nb2Cu1 and Fe85B13Nb2 melt-spun alloys have been investigated. The microstructure-crystallization-magnetic property relationship was established using X-ray diffractometry (XRD), differential scanning calorimetry (DSC), magnetometry, transmission electron microscopy (TEM) and magneto-optical Kerr effect microscopy (MOKE) techniques. The increase of Fe content (>82 at%) of as-quenched ribbons imparts microstructural heterogeneity across the ribbon cross–section; i.e., textured α-Fe crystals at the free surface to hetero-amorphous microstructure in the bulk matrix. The isochronal annealing of hetero-amorphous alloys depicts simultaneous surface and bulk crystallization process occurring before and after the crystallization onset temperature (Tx1) temperature. The annealing temperature range (Ta < Tx1) coinciding with the paramagnetic region of the thermo-magnetic plot, induces irreversible magnetic hardening due to simultaneous coarsening of pre-existing crystal nuclei and exchange de-coupling between nanocrystal and intergranular matrix. The onset of primary crystallization in the pre-crystallized ribbons results in bimodal nanocrystallite distribution having an average crystallite size exceeding the ferromagnetic exchange length of Fe-based alloys. The minor Cu addition alters the growth morphology of pre-existing nuclei from dendrite-like to equiaxed, assisting heterogeneous nucleation and improving intergranular amorphous stability by delaying boride precipitation. The soft-magnetic property deterioration of partially crystallized ribbons is discussed within the framework of Extended-Random Anisotropy models.

Observation of unusual Griffith’s phase behavior in quadruple perovskite oxide CaCu3Mn4O12 (CCMO) synthesized through chemical route

The CaCu3Mn4O12 (CCMO) ceramic was successfully synthesized through the chemical route. The phase formation was confirmed by the X-ray diffraction pattern. Thermogravimetric (TGA), FT-IR, SEM, TEM, EDX, and XPS analysis were performed for investigation of the thermal behavior, phase identification, microstructural analysis, elemental analysis and oxidation state of the CCMO ceramic respectively. FT-IR spectra confirmed the existence of MnO6 octahedral in body-centered cubic (BCC) complex perovskite oxide that resembles the CaCu3Ti4O12 structure. The average particle size was observed by TEM in the range between 100 and 200 nm. AFM shows the average roughness of the surface was found to be in the range of 30 ± 5 nm. XPS and EDX studies confirmed the purity and oxidation state of the CCMO ceramic. The synthesized material shows very interesting unique Griffith’s phase (TG) results that arise disorder in magnetic susceptibility in which ferromagnetic transition was to be observed in the paramagnetic region.

Electrical transport properties of RCr6Ge6 (R = Y, Gd, Tb, Dy, Lu) compounds

Electrical transport properties of the RCr 6 Ge 6 (R = Y, Gd, Tb, Dy, Lu) compounds with the MgFe 6 Ge 6 structure type (space group P 6/ mmm ) were studied. Polycrystalline samples were prepared by arc melting of the stoichiometric amounts of the constituent elements (nominal purities: Y, Gd, Tb, Dy, Lu − 99.9 wt. %, Cr − 99.99 wt. %, Ge − 99.999 wt. %) on a water-cooled copper hearth under a protective Ti-gettered argon atmosphere. Subsequently the buttons were annealed at 1070 K for 720 h in evacuated silica tubes, followed by quenching in cold water. Quality of the prepared samples was tested by X-ray powder diffraction (diffractometer DRON-2.0M, Fe K α -radiation) and Scanning Electron Microscopy (REMMA 102-02 electron microscope equipped with an energy-dispersive spectroscopy X-ray analyser). XRPD data were collected in the transmission mode on a STOE STADI P diffractometer, Cu K α 1 radiation. The crystal structure refinement of LuCr 6 Ge 6 was performed using X-ray powder diffraction method (structure type MgFe 6 Ge 6, space group P 6/ mmm , Pearson symbol hP 13, a = 5.1617(1), c = 8.2745(1) A). The atomic parameters are: Lu in (1 a ): 0 0 0, B iso = 0.6(0) (hereafter A 2 ); site occupations G = 0.64(4), Cr in (6 i ): 1/2 0 z , z = 0.2518(3); B iso = 0.6(0); Ge1 in (2 d ): 1/3 2/3 1/2, B iso = 0.6(0); Ge2 in (2 c ): 1/3 2/3 0; B iso = 0.6(0); Ge3 in (2 e ): 0 0 z; z = 0.3491(4); site occupations G = 0.86(1), R Bragg = 0.0660, R f = 0.0590. The temperature dependencies of electrical resistivity were measured in the temperature range 11−300 K employing two-probe method on millimeter-scale, well-shaped pieces cut by spark erosion from the polycrystalline samples using the helium cooler with closed cycle (Advanced Research systems, USA). Electrical resistivity measurements showed that the resistivity values of the all studied compounds increase with temperature indicating metallic type of conductivity. The slope change of the resistivity at low temperature part of r ( T ) dependencies for the GdCr 6 Ge 6 and TbCr 6 Ge 6 compounds is connected with their magnetic ordering. Change of the resistivity caused by magnetic ordering was not observed for the DyCr 6 Ge 6 compound in the studied temperature interval. In the paramagnetic region, the resistivity data of RCr 6 Ge 6 can be approximated by the Bloch–Gruneissen–Mott (BGM) formula and values of the Debye temperature Θ D were calculated. Keywords: intermetallics, electrical resistivity, X-ray diffraction, crystal structure.

Structure, microstructure, electrical transport mechanism and magnetoresistance in La0.8Ag0.2MnO3

Bulk polycrystalline sample of La0.8Ag0.2MnO3 has been successfully synthesized by the sol gel method. Structural, morphology, electrical properties and magnetoresistance has been investigated. Refinement results from XRD at room temperature showed a single-phase material with a rhombohedral crystal structure and R-3c space group. Electrical transport showed by comparison of experimental data with theoretical model, the sample undergo a metal-insulator transition at TM-I accompanying the ferromagnetic-paramagnetic transition. Data for temperature dependence of resistivity has been fitted using the formula ρ(T) = ρFMf + (1 − f)ρPM, ρPM is resistivity of the ferromagnetic region, ρPM is resistivity of the paramagnetic region and f is the volume fraction of ferromagnetic phase. Result of fitted data is in good agreement with experimental data. MR measurements in the range of magnetic field 0-1 T, measurements were carried out at temperatures of 15 K, 100 K, 200 K and 285 K, the results showed a decrease in resistivity.

Spin fluctuations of the uranium 5f-electrons in UN according to 14N-NMR data

The results of the study of the paramagnetic region of uranium mononitride by the method of nuclear magnetic resonance (NMR)of 14N nuclei are presented.The 14N NMR spectra, the Knight shifts K, the spin-lattice relaxation times T1 have been obtained within the temperature range T = 60 – 375 K and at magnetic fields 92.8 kOe and 117.5 kOe. The temperature dependence of the Knight shift of the 14N line is proportional to the spin susceptibility χ of 5f-electrons of uranium. The ratio of the experimentally determined value TT1K2 to the theoretically calculated value of the Korringa contribution is 21.5 (at T = 295 K), which is significantly more than for common metals. This suggests that nuclear relaxation is based on the same mechanism as the Knight shift, namely, the indirect connection between the 14N nuclei and the localized magnetic moments of uranium through conduction electrons. The experimental results on the T-dependence of the spin-lattice relaxation rate of 14N also do not contradict the assumption that uranium mononitride is a concentrated Kondo system.

Magnetic state and magnetic hysteresis in the molybdenum diselenide intercalated with chromium atoms

In this work intercalated compounds in the Cr-MoSe2 system were synthesized for the first time. Their magnetic properties are studied at various intercalant concentrations, temperatures and magnetic fields. The temperature dependences of effective magnetic moments and positive paramagnetic Curie temperatures in the paramagnetic region evidence the feasible ferromagnetic interactions between intercalated atoms. The existence of low-temperature ferromagnetic state in CrxMoSe2 is confirmed by hysteresis phenomena in temperature dependences magnetic susceptibility and field dependences of magnetization. The change in the magnetic state affects the character of the temperature dependences of the resistivity.

Crystal structure and magnetic properties of TmV0.17Ge2 and LuV0.15Ge2 ternary germanides

In this study, the new germanides TmV0.17Ge2 and LuV0.15Ge2 were synthesized from elements by arc-melting, before annealing at 870 K, and investigating using powder X-ray diffractometry and energy-dispersive X-ray spectroscopy analysis. The new ternary phases crystallized in the CeNiSi2 structure type (space group Cmcm) and they were characterized by the partial occupation of one of the 4c sites by vanadium atoms. The magnetic properties were measured in the temperature range from 1.9 to 390 K. The magnetic susceptibility of TmV0.17Ge2 obeys the Curie–Weiss law in the paramagnetic region at high temperatures, whereas the low temperature data indicated cluster-glass behavior. Almost temperature-independent magnetic susceptibility was found for LuV0.15Ge2 in the high temperature region, whereas an anomaly was present at low temperatures.

Large magnetocaloric effect in [formula omitted] (RE = Gd, Tb and Dy) series of compounds

We report on the low-temperature physical properties of RE8Pd24Ga (RE = Gd, Tb and Dy) compounds studied by means of thermodynamic and electronic transport measurements. The three compounds exhibit a putative antiferromagnetic ordering. In the paramagnetic region, their magnetic susceptibility follows the Curie-Weiss relation with effective magnetic moments close to those expected for the respective RE3+ ions. Gd8Pd24Ga and Dy8Pd24Ga undergo another magnetic phase transitions in the ordered state. In fairly small magnetic fields, the magnetization of Tb8Pd24Ga and Dy8Pd24Ga reveals a metamagnetic-like transition that bears a first-order character. All three compounds studied exhibit magnetocaloric effect of the magnitude similar to those reported for materials applicable as magnetic refrigerants.

Magnetic excitations in hole-doped Sr2IrO4 : Comparison with electron-doped cuprates

We have studied the evolution of magnetic and orbital excitations as a function of hole-doping in single crystal samples of Sr2Ir(1-x)Rh(x)O4 (0.07 < x < 0.42) using high resolution Ir L3-edge resonant inelastic x-ray scattering (RIXS). Within the antiferromagnetically ordered region of the phase diagram (x < 0.17) we observe highly dispersive magnon and spin-orbit exciton modes. Interestingly, both the magnon gap energy and the magnon bandwidth appear to increase as a function of doping, resulting in a hardening of the magnon mode with increasing hole doping. As a result, the observed spin dynamics of hole-doped iridates more closely resemble those of the electron-doped, rather than hole-doped, cuprates. Within the paramagnetic region of the phase diagram (0.17 < x < 0.42) the low-lying magnon mode disappears, and we find no evidence of spin fluctuations in this regime. In addition, we observe that the orbital excitations become essentially dispersionless in the paramagnetic phase, indicating that magnetic order plays a crucial role in the propagation of the spin-orbit exciton.

Magnetoelectric Effect in a Paramagnetic Region in Gd0.15Mn0.85Se

The electric polarization in a zero magnetic field and in a magnetic field of 12 kOe is measured in a GdxMn1 – xSe solid solution in the percolation concentration region in the temperature range 80–380 K. For composition x = 0.15, the polarization hysteresis and the dependence of the remanent polarization on magnetic field and temperature are determined. The hysteresis is explained in the model of migration polarization and the magnetoelectric effect is explained in the Maxwell–Wagner model.

Evolution of structural and magnetic behavior of SrRuO3 by Ga doping at Ru site

Here, we report the study of structural and magnetic behavior of SrRuO3 by Ga doping at Ru site. SrRuO3 has an orthorhombic structure of Pbnm symmetry that has not changed by Ga doping, however, lattice parameters has decreased. The SrRuO3 is the one and only example of 4d based itinerant ferromagnet (FM) in oxides with transition temperature (Tc) ∼ 160 K. Below Tc, SrRuO3 shows large bifurcation between Zero-field-cooled (ZFC) and field-cooled (FC) magnetization, which decreases by Ga doping. The inverse susceptibility (χ−1) in paramagnetic (PM) and high-temperature region shows that the Curie temperature (θp) as well as effective moment decreases by Ga doping. The isothermal magnetization at 5 K shows hysteresis, which retain by Ga doping though the moment decreases. The Arrott plot confirms the FM nature and gives spontaneous magnetization (MS) that decreases by Ga doping.

Comparative study of La0.6R0.1Ca0.3Mn0.9Cr0.1O3 (R = La, Eu and Ho) nanoparticles: effect of A-cation size and sintering temperature

A systematic study of nanocrystalline La0.6R0.1Ca0.3Mn0.9Cr0.1O3 (R = La, Eu and Ho) manganites has been undertaken to analyse the effect of sintering temperature and A-site cation radius on the structural and magnetic properties. In order to acquire a series of samples with different particle sizes, the samples were prepared by a solution combustion method and were subjected to annealing at four different temperatures. Rietveld analysis of X-ray diffraction (XRD) data confirmed the presence of orthorhombic symmetry with Pbnm space group for all the samples. The grain size retrieved from the TEM analysis is greater than the noted crystallite size calculated from XRD by the Scherrer’s equation. A paramagnetic-ferromagnetic transition is shown by all our investigated compounds at low temperature. With increasing sintering temperature or particle size, the Curie temperature (Tc) was found to increase, which is attributed to the magnetically disordered surface layer. All the phases obey Curie–Weiss law in the high temperature region and the effective magnetic moment calculated from the high temperature paramagnetic region shows an increase with sintering temperature.

Charge density wave in a doped Kondo chain

We report the existence of the charge density wave (CDW) in the ground state of 1D Kondo lattice model at the filling of n=0.75 in the weak coupling region. The CDW is driven by the effective Coulomb repulsion mediated by the localized spins. Based on our numerical results using the density matrix renormalization group method, we show that the CDW phase appears in the paramagnetic region previously known as the Tomonaga-Luttinger liquid. The emergence of this phase serves as an example of CDW phase induced without bare repulsive interactions, and enriches the phase diagram of the 1D Kondo lattice model.

Effect of titanium substitution on the structural, magnetic and magnetocaloric properties of La0.67Ba0.25Ca0.08MnO3 perovskite manganites

We have studied the effect of Mn substitution by Ti on the structural, magnetic and magnetocaloric properties of La0.67Ba0.25Ca0.08MnTiO3 samples. All samples were synthesized using the flux method. X-ray powder diffraction showed that our samples crystallize in the rhombohedral phase $$R\overline{3} c$$ space group. According to the magnetic properties, our samples present a transition from a paramagnetic to a ferromagnetic phase upon decreasing temperature. The deviation of the inverse curve of the magnetic susceptibility from Curie–Weiss law indicates the existence of a Griffiths phase. This reveals the presence of ferromagnetic clusters in paramagnetic region. Regarding the positive slopes of Arrott’s plots, the universal theory and the Landau B(T) coefficient value sign demonstrate the second-order magnetic phase transition. The magnetic entropy change was determined based to Maxwell’s relations and Landau’s theory. Near room temperature, our samples exhibited an important magnetic entropy change with maxima of 3.21 and 2.76 J kg−1 K−1, under an applied magnetic field of 5 T, respectively, for La0.67Ba0.25Ca0.08MnO3 and La0.67Ba0.25Ca0.08Mn0.95Ti0.05O3. Relative cooling power was estimated as well. It was found to reach 168 and 187 J/kg for La0.67Ba0.25Ca0.08MnO3 and La0.67Ba0.25Ca0.08Mn0.95Ti0.05O3, respectively. From the hysteresis cycles, our studied sample showed a typical soft ferromagnetic behavior with a low coercive field at 10 K. These results make our samples promising candidates for magnetic refrigeration.

Diamagnetism versus paramagnetism of charged ideal spin-1/2 fermions in a harmonic trap under a uniform magnetic field

Magnetic properties of harmonically trapped charged ideal spin-1/2 fermions in a uniform magnetic field are studied. It is shown that the magnetism of charged spin-1/2 fermions can be explained by a competition between the diamagnetic and paramagnetic effects, where a variable spin factor is introduced to describe the strength of paramagnetic effect. As the spin factor increases, a crossover from diamagnetic region to paramagnetic region appears. Moreover, the critical values of spin factor are obtained at low-temperature and under weak magnetic field, respectively. Spin-1/2 fermions display distinct magnetic behaviors from spinless case.

Magnetic Properties and Nature of Magnetic State of Intercalated CrxMoSe2 Compounds

This is a pioneering work on the synthesis of molybdenum diselenides intercalated by chromium atoms. Their magnetic properties are studied at various intercalant concentrations, temperatures, and magnetic fields. The temperature dependences of effective magnetic moments and positive paramagnetic Curie temperatures in the paramagnetic region evidence the feasible ferromagnetic interactions between intercalated atoms. The existence of low-temperature ferromagnetic state in CrxМоSe2 is confirmed by hysteresis phenomena in temperature and field dependences of magnetization and magnetic susceptibility.

Correlation between critical behavior and magnetocaloric effect for La0.8-x·xNa0.2-x·xMnO3 (x=0 and 0.1) compounds

The critical behavior of manganite perovskite type La0.8-x·xNa0.2-x·xMnO3 (with x = 0 and 0.1) was studied based on the experimental magnetic measurements in the paramagnetic ferromagnetic transition region using different techniques such as the modified Arrott plot, the Kouvel-Fisher method and critical isothermal analysis. Experimental results revealed that the two samples show a second-order magnetic phase transition. The deduced critical exponents are close to a 3D Ising model for La0.8Na0.2MnO3 and a 3D tricritical mean field model for La0.7·0.1Na0.1·0.1MnO3. The reliability of these critical exponents was confirmed by the Widom scaling relation and the universal scaling hypothesis. Moreover, an excellent agreement was found between the spontaneous magnetization determined from the entropy change and from the extrapolation of the modified Arrott plots, confirming the universal behavior of the magnetocaloric effect in these systems.

Magnetic and eletronic transport properties in n-type diluted magnetic semiconductor Ge&lt;sub&gt;0.96–x&lt;/sub&gt;Bi&lt;sub&gt;x&lt;/sub&gt;Fe&lt;sub&gt;0.04&lt;/sub&gt;Te film

The epitaxial thin films of Ge&lt;sub&gt;0.96−&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt;Bi&lt;sub&gt;&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt;Fe&lt;sub&gt;0.04&lt;/sub&gt;Te are deposited on BaF&lt;sub&gt;2&lt;/sub&gt; substrates by using pulsed laser deposition technique. The thin films with three different compositions i.e. Ge&lt;sub&gt;0.8&lt;/sub&gt;Bi&lt;sub&gt;0.2&lt;/sub&gt;Te, Ge&lt;sub&gt;0.76&lt;/sub&gt;Bi&lt;sub&gt;0.2&lt;/sub&gt;Fe&lt;sub&gt;0.04&lt;/sub&gt;Te, and Ge&lt;sub&gt;0.64&lt;/sub&gt;Bi&lt;sub&gt;0.32&lt;/sub&gt;Fe&lt;sub&gt;0.04&lt;/sub&gt;Te are prepared in this wok. Their high-quality epitaxy and crystallinity are confirmed by X-ray diffraction and atomic force microscopy. According to the measurements of Hall effect variation, we find that each of all curves exhibits a negative slope for the different films as the temperature varies from low temperature to room temperature, indicating that Ge&lt;sub&gt;0.96−&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt;Bi&lt;sub&gt;&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt;Fe&lt;sub&gt;0.04&lt;/sub&gt;Te films are n-type material because the substitution of Bi for Ge makes the carriers change from holes into electrons. Temperature dependence of resistivity confirms that the electronic transport behavior for each of Ge&lt;sub&gt;0.96−&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt;Bi&lt;sub&gt;&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt;Fe&lt;sub&gt;0.04&lt;/sub&gt;Te thin films exhibits a typical semiconductor characteristic. From the measurements of temperature dependence of electronic transport under various external magnetic fields, we find that the Ge&lt;sub&gt;0.64&lt;/sub&gt;Bi&lt;sub&gt;0.32&lt;/sub&gt;Fe&lt;sub&gt;0.04&lt;/sub&gt;Te thin film shows some magnetoresistive effect while other composition films do not possess such a property. Based on the linear fitting of temperature dependence of magnetic susceptibility in high temperature and low temperature region, the magnetic property of Ge&lt;sub&gt;0.64&lt;/sub&gt;Bi&lt;sub&gt;0.32&lt;/sub&gt;Fe&lt;sub&gt;0.04&lt;/sub&gt;Te thin film changes from 253 K. Together with the study of magnetic susceptibility curve in the paramagnetic region, the Curie-Weiss temperature is determined to be 102 K. At a low temperature of 10.0 K, we observe an obvious ferromagnetic hystersis loop in Ge&lt;sub&gt;0.64&lt;/sub&gt;Bi&lt;sub&gt;0.32&lt;/sub&gt;Fe&lt;sub&gt;0.04&lt;/sub&gt;Te instead of in Ge&lt;sub&gt;0.76&lt;/sub&gt;Bi&lt;sub&gt;0.2&lt;/sub&gt;Fe&lt;sub&gt;0.04&lt;/sub&gt;Te thin film. These results imply that the increase of Bi dopant is main reason for the establishment of ferromagnetic ordering state. The carrier concentration increases and thus promotes the carriers transporting the Ruderman-Kittel-Kasuya-Yoshida interaction, thereby leading to the separated Fe ions producing the magnetic interaction and forming an n-type diluted magnetic semiconductor.

Магнитные свойства и природа магнитного состояния интеркалированных соединений Cr-=SUB=-x-=/SUB=-MoSe-=SUB=-2-=/SUB=-

AbstractThis is a pioneering work on the synthesis of molybdenum diselenides intercalated by chromium atoms. Their magnetic properties are studied at various intercalant concentrations, temperatures, and magnetic fields. The temperature dependences of effective magnetic moments and positive paramagnetic Curie temperatures in the paramagnetic region evidence the feasible ferromagnetic interactions between intercalated atoms. The existence of low-temperature ferromagnetic state in Cr_ x МоSe_2 is confirmed by hysteresis phenomena in temperature and field dependences of magnetization and magnetic susceptibility.

Dynamics of the magnetoelastic phase transition and adiabatic temperature change in Mn1.3Fe0.7P0.5Si0.55

The adiabatic temperature change ΔTad of a Mn1.3Fe0.7P0.5Si0.55 Fe2P-type alloy was measured under different magnetic field-sweep rates from 0.93 Ts−1 to 2870 Ts−1. We find a field-sweep-rate independent magnetocaloric effect due to a partial alignment of magnetic moments in the paramagnetic region overlapping with the magnetocaloric effect of the first-order phase transition. Additionally, the first-order phase transition is not completed even in fields up to 20 T leading to a non-saturating behavior of ΔTad. Measurements in different pulsed fields reveal that the first-order phase transition cannot follow the fast field changes as previously assumed, resulting in a distinct field-dependent hysteresis in ΔTad.