The change of some magnetic properties of Cr2O3 in the vicinity of for the paramagnetic state

The observed anomaly of the parallel magnetic susceptibility of Cr₂O₃is discussed as the effect of the changes of the crystal lattice parameters with temperature and the changes of the exchange parameters in some range above T_N connected with it. It is shown that the temperature changes of the crystal parameters have an important influence on the behavior of the magnetic specific heat with temperature too. The results of the calculations based on the correlation theory and the modified Oguchi theory are presented.     

Synthesis, characterization and magnetic properties of complex oxides Ln2Mn2/3Re4/3O7 (Ln = Er, Y) and Y2Zn2/3Re4/3O7

Complex oxides Ln₂Mn_2/3Re_4/3O₇ (Ln = Y, Er) and Y₂Zn_2/3Re_4/3O₇ with a zirkelite structure and hexagonal unit cells (space group P3₁21, z = 6) have been obtained. Static and dynamic magnetic susceptibility measurements show that these oxides possess spin-glass behavior at low temperatures. Valence combinations of d-metals in the oxides are Mn²⁺(Zn²⁺)–Re⁵⁺. It is supposed that the examined specimens Ln₂Mn_2/3Re_4/3O₇ (Ln = Y, Er) contain the second magnetic phase of an unknown composition.     

Influence of low-temperature annealing on magnetic properties of (Nd0.625Ni0.375)85Al15 metallic glass

After a review of the selection process of (Nd_0.625Ni_0.375)₈₅Al₁₅ as a metallic glass with a relatively high glass-forming ability, we investigate the influences of its phase transitions by duplicating the heating process of the isochronal thermal analysis with low-temperature annealings. The structure, thermal stability and magnetic properties are characterized. And the influences on magnetic properties are particularly discussed with emphasis. Both the annealing processes, to the glass-transition temperature and to the onset temperature of crystallization, bring about a higher coercivity of the sample and a higher freezing temperature of the spin-glass-state. For the sample annealed to the onset temperature of crystallization, the influence is quite obvious and is ascribed to the formation of ferrimagnetic Nd₇Ni₃ phase, as detected by XRD. For the sample annealed to the glass-transition temperature, the indistinct influence is further identified with the analysis of the frequency dependence of the spin-glass-state, and it is mainly attributed to the change of the short-range order in the amorphous matrix.     

New RRh5Ge3 compounds of the new SmRh5Ge3 structure type and their magnetic properties (R=Sm, Gd, Tb)

Powder X-ray diffraction results and macroscopic magnetic properties of new ternary RRh₅Ge₃ compounds (R=Sm, Gd, Tb) are reported. The compounds SmRh₅Ge₃ (a=2.2744(4) nm, c=0.3888(1) nm), GdRh₅Ge₃ (a=2.2711(5) nm, c=0.3872(1) nm) and TbRh₅Ge₃ (a=2.2628(7) nm, c=0.3851(1) nm) crystallize in the hexagonal SmRh₅Ge₃-type structure (space group P6₃/m; No. 176). The GdRh₅Ge₃ and TbRh₅Ge₃ compounds are Curie–Weiss paramagnets down to 5 K.     

Magnetic and neutron diffraction studies on potassium uranate KUO3

The magnetic properties of KUO₃ with the cubic perovskite structure have been studied. It shows an antiferromagnetic-type of transition at ca. 17 K in the magnetic susceptibility vs. temperature curve. Magnetic hysteresis is observed at 4.5 K, but not observed at 20 K. Neutron diffraction measurements have been performed on the powdered KUO₃ below and above the transition temperature. The neutron diffraction pattern measured at 10 K shows no appreciable difference from that measured at 50 K. A small ordered magnetic moment of U⁵⁺ ion will make it very difficult to observe magnetic diffractions, even if a magnetic ordering occurs. If the magnetic spin alignment occurs in a small domain, no magnetic diffraction will be found in the neutron experiments. On the other hand, the magnetic phenomena of KUO₃ have been analyzed on the basis of an octahedral crystal field model.     

Structural and magnetic properties of Nd3(Fe,Ti)29Cx carbide

Nd₃(Fe,Ti)₂₉C_x, carbide has been synthesized by gas-solid reaction. An enhancement of the Curie temperature T_c from 437 K to 575 K is observed, reflecting a lattice expansion of 4.1% upon carbonation. The room temperature saturation magnetization M_s of the carbide is 145.5 A m² kg ¹ and the average hyperfine field, H_eff, 24.8 T. The magnetic structure of Nd₃(Fe,Ti)₂₉C_x carbide changes from easy-cone-like in the case of the parent compound to axial-like after carbonation with a room temperature anisotropy field H_A of 8 T.     

Effect of Mn concentration on the spin glass transition temperature of Fe0.70−xMnxAl0.30 alloys

Magnetization measurements on zero field cooled (ZFC) and field cooled (FC) samples as a function of temperature where made on Fe_0.70−xMn_xAl_0.30 alloys with 0≤x≤0.10. Our data show the existence of two regimes of the spin glass temperature T_f when increasing the concentration x of the Mn atoms. We found that T_f decreases slowly with increasing x up to x=0.06 and then shows a rapid linear decrease above this concentration. The existence of two regimes of T_f behavior with x may be attributed to the disappearance of ferromagnetic clusters which exist for low values of x (x<0.06). Compared to the Mn-free alloy, the relative changes in T_f are bigger and exceed 40% at x=0.10. The second regime (x>0.06) is associated with more influence of x on T_f.     

Magnetic properties of a new iron lead vanadate Pb2FeV3O11

Temperature dependence of dc/ac magnetization and electron paramagnetic resonance (EPR) spectra of Pb₂FeV₃O₁₁ iron lead vanadate has been investigated. The dc magnetic measurements have shown the presence of antiferromagnetic interactions with Curie-Weiss temperature, T_CW = −15.2 K, in the high temperatures range while the field cooled (FC) magnetization revealed a maximum at T_N = 2.5 K which coincides with a long range magnetic ordering. Temperature dependence of χ′ has shown a maximum at the same temperature. EPR spectrum of Pb₂FeV₃O₁₁ at room temperature is dominated by nearly symmetrical, very intense and broad resonance line centered at g_eff ∼ 2.0 that could be attributed to the correlated system of iron ions. The temperature dependence of magnetic resonance parameters (amplitude, g-factor, linewidth, integrated intensity) has been determined in the 4-300 K range and it suggests the existence of short range correlated spin system up to high temperatures. The temperature dependence of the amplitude of the resonance line has shown a pronounced maximum at 12.5 K that indicates on the existence of two subsystems of weakly and strongly coupled iron pairs. Comparison of dc magnetic susceptibility and EPR integrated intensity points to the presence of correlated spin agglomerates that play an important role in determination of the magnetic response of Pb₂FeV₃O₁₁.     

Magnetic behaviour of two AlB2-related germanides: CePd0.63Ge1.37 and CeAu0.75Ge1.25

The title compounds were prepared from the elemental components by arc-melting and subsequent annealing at 1020 K and 1170 K. Both CePd_0.63Ge_1.37 and CeAu_0.75Ge_1.25 crystallize in the AlB₂ structure type with a statistical distribution of the transition metal and germanium atoms on the boron site. The structure of CeAu_0.75Ge_1.25 was refined from single crystal X-ray data: P6/mmm, a=433.5(1) pm, c=422.6(1) pm, V=0.0688(1) nm³, Z=1, wR2=0.0504 for 157 F² values and 7 variables. Magnetic susceptibility data for both compounds show a full cerium moment and ferromagnetic ordering at 6.0(5) K for CeAu_0.75Ge_1.25 and 3.0(5) K for CePd_0.63Ge_1.37. The crystal structure and properties of CeAu_0.75Ge_1.25 are compared with those of equiatomic CeAuGe which adopts the NdPtSb structure type, an ordered variant of AlB₂.     

Structural and magnetic properties of a novel compound with Y3(Fe, V)29 stoichiometry and disordered CaCu5-type structure

A novel phase with nominal composition Y₃Fe_27.5V_1.5 has been synthesized by arc melting elemental constituents, followed by annealing at 1123 K. The samples were analyzed by electron microprobe analysis and the stoichiometric composition was Y_3.04Fe_27.56V_1.44. X-ray diffraction from powder samples shows that the structure is of a disordered CaCu₅-type (Space Group: P6/mmm) with lattice parameters a=4.8769(1) Å, c=4.1729(3) Å. This disordered structure, revealed using standard difference Fourier methods, can be considered as a TbCu₇-type, containing iron dumbbell sites. The disorder is not restricted to the rare earth sites and the dumbbell atoms, but is observed at other sites as well. The stoichiometric formula derived by Rietveld analysis is Y_3.00(3)Fe_28.5(3). Magnetic measurements give a Curie temperature of 439(5) K, and a saturation magnetization of 156.4 and 125.5 A m² kg⁻¹ at 5 and 300 K, respectively. The anisotropy field is 4.76 T at 5 K and 2.43 T at 300 K. X-ray powder diffraction patterns of magnetically aligned powder samples indicate that the magnetocrystalline anisotropy is of easy plane type. This result is supported from the analysis of the magnetization measurements on aligned powders which give K₁<0, K₂>0 and K₁+2K₂<0, a result that confirms the easy plane anisotropy. Mössbauer spectra were also obtained and fitted with a model consistent with the disorder. The average hyperfine fields are 28.4 and 21.5 T at 4.2 and 300 K, respectively.     

Crystal structure and magnetic properties of ZnV2O4

We present structural and magnetic data on ZnV₂O₄ single crystals. Single crystal X-ray diffraction shows the measured crystals to be of very high quality, especially with respect to atomic order. The measured magnetic susceptibility resembles to that of a spin glass system, surprising for a translational invariant structure. The results are discussed in the framework of disorder in a magnetically frustrated lattice.     

Structural, magnetic and magnetotransport properties of La0.8Sr0.2MnO3/xLaMnO3 composites

The effect of LMO doping on the structure, magnetic and magnetotransport properties of La_0.8Sr_0.2MnO₃ (LSMO)/xLaMnO₃ (LMO) has been investigated. Two types of LSMO/xLMO composites, named as SL_x (low temperature sintered samples) and SH_x (high temperature sintered samples) samples, were prepared by different sintering temperature and solid-state reaction method. The presence of LMO at the grain boundaries increases the disordered states at the surface of the grains and therefore the magnetization and transition temperature decrease by increasing the amount of LMO doping level. Results show that the rate of decreasing of transition temperature is much more for high temperaure sintered samples. Also the resistivity of samples increases by the increase of LMO doping level. Results also show that the LMO doping has an effect on a low field magnetoresistance (LFMR). The value of LFMR increases for low doping level of 0 ≤ x ≤ 15, for SL_x samples and 0 ≤ x ≤ 10 for SH_x samples. Also LFMR decreases at high doping level. The spin dependent tunneling and scattering at the interfaces of the grain boundaries are responsible for the increase of LFMR at low doping level, while reduction of LFMR at high doping level may result from the grain boundary becoming too thick for electron tunneling.     

Grain size dependent magnetization, electrical resistivity and magnetoresistance in mechanically milled La0.67Sr0.33MnO3

We have studied magnetization, ac susceptibility, resistivity and magnetoresistance in mechanically milled La_0.67Sr_0.33MnO₃. The material with grain size micron to nanometer scale has stabilized in rhombohedral crystal structure with space group R3C. We have found various grain size effects, e.g., decrease of ferromagnetic moment, increase of surface spin disorder, and appearance of insulator/semiconductor type resistivity. In addition to these conventional features, we have identified a magnetic anomaly at 45 K in bulk sample. Ferromagnetic to paramagnetic transition temperature (T_C) is above room temperature for all samples. The samples are typical soft ferromagnet that transformed from multi-domain state to single domain state in nanocrystalline samples. The remarkable observation is that low temperature freezing of ferromagnetic domains/clusters does not follow the conventional spin glass features. Experimental results clearly showed the enhancement of high field magnetoresistance in nanocrystalline samples below 200 K, whereas low field magnetoresistance gradually decreases above 200 K and almost absent at 300 K. We have discussed few more magnetic and electrical changes, highly relevant to the progress of nanomaterial research in ferromagnetic manganites.     

Structure and magnetic properties of Gd3(Fe1−xTix)29 (x=0.011–0.034)

Single-phase compounds Gd₃(Fe_1−xTi_x)₂₉ (x=0.0110.034) have been synthesized. Gd₃(Fe_1−xTi_x)₂₉ crystallises in a monoclinic lattice with space group P2₁/c, and the crystal structure is refined by the Rietveld technique based on X-ray powder diffraction data. Thermomagnetic analysis indicates that the Curie temperature of the compounds ranges from 517 K to 538 K. The saturation magnetizations of the Gd₃(Fe_1−xTi_x)₂₉ (x=0.011, 0.022, 0.034) at 1.5 K are 103.6, 102.0 and 94.3 Am²/kg, and the anisotropy fields at 1.5 K are 6.0, 6.2 and 6.4T, respectively.     

The magnetic ordering in the Ho5Si3 and Ho5Ge3 compounds

A neutron diffraction investigation has been performed on the Ho₅Si₃ and Ho₅Ge₃ compounds (hexagonal Mn₅Si₃-type, hP16, P6₃/mcm) to study their magnetic structure. The results prove that these intermetallic phases show a complex sine-modulated type magnetic ordering, both presenting on cooling two subsequent antiferromagnetic orderings (T_N1 and T_N2).Between T_N1 = 24(2) and T_N2 = 16(4) K Ho₅Si₃ shows a first antiferromagnetic ordering of the sine-modulated type with a propagation vector K₁ = [0, 0, ±0.284(1)]; then, below T_N2 the sine-modulated type ordering is conserved, but by the two propagation vectors K₁ = [0, 0, ±0.2773(7)] and K₂ = [±1/5, ±1/5, 0].For Ho₅Ge₃, between T_N1 = 27(2) and T_N2 = 18(4) K, the sine-modulated ordering is realized through the propagation vectors K₁ = [0, 0, ±3/10] and K₂ = [0, 1/2, 0], whilst below T_N2 the ordering takes place with propagation vectors K₁ = [0, 0, ±3/10], K₂ = [0, 1/2, 0], K₃ = [0, 0, ±2/5] and K₄ = [±1/5, ±1/5, 0]. For both the Ho₅Si₃ and Ho₅Ge₃ compounds, the dimensions of the magnetic unit cell are 5a × 5a × 10c times the crystal unit cell of Mn₅Si₃-type.     

Spin-glass behavior and exchange bias in phase-separated Nd0.85Sr0.15CoO3

The magnetic properties of Nd_0.85Sr_0.15CoO₃ have been systematically investigated by dc magnetization, ac susceptibility and magnetic relaxation. The dynamics scaling analysis of ac susceptibility and magnetic relaxation give sufficient evidence of the existence of a spin-glass phase, which can be ascribed to the complicated interactions among Co³⁺ and Co⁴⁺ ions in this phase-separated compound. The field-cooled magnetic hysteresis loop displays both horizontal and vertical shifts, i.e., the exchange bias effect, while no shifts are present with increase of the measuring field up to ±50 kOe. The results further sustain the picture of the spin-glass phase coexisting with other magnetic regions in the sample.     

Effect of CuO on the sintering temperature and piezoelectric properties of MnO2-doped 0.75Pb(Zr0.47Ti0.53)O3-0.25Pb(Zn1/3Nb2/3)O3 ceramics

The sintering temperature of 0.75Pb(Zr_0.47Ti_0.53)O₃-0.25Pb(Zn_1/3Nb_2/3)O₃ ceramics containing 1.5 mol% MnO₂ was decreased from 930 to 850 °C with the addition of CuO. The CuO reacted with the PbO and formed a liquid phase during the sintering, which assisted the densification of the specimens. Most of the Cu²⁺ ions existed in the CuO second phase, thereby preventing any possible hardening effect from the Cu²⁺ ions. Variations of the k_p, Q_m, ?₃^T/?₀ and d₃₃ values with CuO were similar to that of the relative density. The specimen containing 0.5 mol% CuO sintered at 850 °C showed the good piezoelectric properties of k_p = 0.5, Q_m = 1000, ?₃^T/?₀ = 1750 and d₃₃ = 300 pC/N.     

Transport properties of the YbAl3 compound: On the energy scales of YbAl3 from thermopower data

We report thermopower and resistivity measurements of an YbAl₃ single crystal obtained by the “self-flux” method. Our data reveal Fermi liquid behavior up to T_FL = 35 K. The Kondo temperature, T_K ≈ 450 K, was determined from the high temperature thermopower data. The characteristic temperature, T₀, extracted from the temperature slope of the thermopower in the Fermi liquid regime is higher than the T_K. We discuss a possible explanation of the obtained energy scales of YbAl₃.     

Synthesis and properties of Ba3NaRu2O9−δ and Ba3(Na, R)Ru2O9−δ (R=rare earth) crystals

Crystals of Ba₃NaRu₂O_9−δ (δ≈0.5) and Ba₃(Na, R)Ru₂O_9−δ (R=Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm and Yb) were grown by an electrochemical method, and their crystallographic, magnetic, and electric properties were studied. All crystals have a hexagonal structure of space group P6₃mmc. Ba₃NaRu₂O_9−δ and Ba₃(Na, R)Ru₂O_9−δ (except Ce) have a negative asymptotic Curie temperature suggesting the existence of an antiferromagnetic order; however, they are paramagnetic at temperatures above 1.7 K. Ba₃NaRu₂O_9−δ has an effective magnetic moment P_eff of 0.91 μ_B, while P_eff of Ba₃(Na, R)Ru₂O_9−δ (except Ce) reflects the large free-ion moment of the rare earth ions. Ba₃(Na, Ce)Ru₂O_9−δ shows peculiar magnetic behavior that differs from the magnetism of other Ba₃(Na, R)Ru₂O_9−δ crystals. The resistivity of all crystals exhibits an activation-type temperature dependence with an activation energy in the range of 0.10.2 eV.