Spin glass like behavior in Cd0.42Mn0.58In2S4

The magnetic behavior of the diluted magnetic semiconductor Cd_0.42Mn_0.58In₂S₄ has been study by dc magnetization and ac susceptibility experiments. Zero field cooled and field cooled measurements reveal irreversibility below T_irr=2.60±0.15 K. Ac susceptibility data, performed as a function of the temperature and the frequency, confirm the spin-glass like behavior of the material with T_f=2.75±0.15 K. High temperature susceptibility data follow a typical Curie-Weiss law with θ=−74±1 K which suggests predominant antiferromagnetic interactions. The randomness of the magnetic ions, necessary to explain the magnetic behavior of the material, has been determined by X-ray powder diffraction experiments.     

The magnetic susceptibility of hydrogen-doped partially crystalline (Zr76Ni24)1−xHx metallic glasses

The magnetizations of Zr₇₆Ni₂₄ metallic glass and hydrogen-doped partially crystalline (Zr₇₆Ni₂₄)_1−xH_x metallic glasses have been measured in the temperature range 10-300 K and magnetic fields up to 2 T for various dopant concentrations (x=0, 0.024, 0.043, 0.054). It is found that the samples are paramagnetic and magnetic susceptibility at room temperature, χ(300 K), shows a nonmonotonic behaviour upon hydrogenation. The values of χ(300 K) of the hydrogen-doped partially crystalline (Zr₇₆Ni₂₄)_1−xH_x metallic glasses are reduced with increase in hydrogen content up to x=0.043, whereas for x=0.054, an enhancement of χ(300 K) has been revealed. The magnetic susceptibility is weakly temperature dependent down to 110 K, below which an increase is observed. A shallow minimum exists between 90 and 120 K. The form and magnitude of the observed temperature dependence of the magnetic susceptibility are well accounted for by the sum of the quantum corrections to the magnetic susceptibility. Hydrogen reduces the electronic diffusion constant and influences strongly the quantum interference at defects, slowing down the spin diffusion and enhancing the magnetic susceptibility in the temperature range from 110 down to 10 K.     

Magnetic properties and spin order of Sr7Fe10O22

The magnetic properties of Sr₇Fe₁₀O₂₂ have been investigated by means of magnetic susceptibility and Mössbauer absorption measurements. This compound proved to be antiferromagnetic with a Néel temperature T_N = 425 K; the magnetic susceptibility is constant from the lowest measuring temperature (78 K) up to T_N.The Mössbauer measurements and the analogies with “brownmillerite” type compounds indicate that iron ions occupy one octahedral and two tetrahedral different sites. An antiferromagnetic spin configuration with moments lying in the ab plane appears to be consistent with the experimental results. A small spontaneous magnetic moment was observed at room temperature with features resembling those of strontium hexaferrite; a weak ferromagnetic behavior can not however be excluded taking into account the aforementioned susceptibility behaviour.     

Possible observation of the coexistence of superconductivity and long-range magnetic order in NdRh4B4

The ternary rare earth compound NdRh₄B₄ has been studied by means of critical field, low temperature heat capacity, and static magnetic susceptibility measurements. Features in the upper critical field and heat capacity data at 1.31 K and 0.89 K suggest the occurrence of long-range magnetic order in the superconducting state. The temperature dependence of the static magnetic susceptibility follows a Curie-Weiss law with an effective magnetic moment μ_eff = 3.58 ± 0.05 μ_B and a Curie-Weiss temperature θ_p = ?6.2 ± 1.0 K between 20 K and room temperature. However,, magnetization vs. applied magnetic field isotherms suggest the development of a ferromagnetic component in the Nd³⁺ magnetization at low temperatures.     

Evidence of glassy ferromagnetic phase and kinetic arrest of electronic phase in Sm0.35Pr0.15Sr0.5MnO3 manganites

The effect of doping of rare earth Pr³⁺ ion as a replacement of Sm³⁺ in Sm_0.5Sr_0.5MnO₃ is investigated. Temperature dependent dc and ac magnetic susceptibility, resistivity, magnetoresistance measurements on chemically synthesized (Sm_0.5−xPr_x)Sr_0.5MnO₃ show various unusual features with doping level x=0.15. The frequency independent ferromagnetic to paramagnetic transition at higher temperature (∼191 K) followed by a frequency dependent reentrant magnetic transition at lower temperature (∼31 K) has been observed. The nature of this frequency dependent reentrant magnetic transition is described by a critical slowing down model of spin glasses. From non-linear ac susceptibility measurements it has been confirmed that the finite size ferromagnetic clusters are formed as a consequence of intrinsic phase separation, and undergo spin glass-like freezing below a certain temperature. There is an unusual observation of a 2nd harmonic peak in the non-linear ac susceptibility around this reentrant magnetic transition at low temperature (∼31 K). Arrott plots at 10 and 30 K confirm the existence of glassy ferromagnetism below this low temperature reentrant transition. Electronic- and magneto-transport measurements show a strong magnetic field—temperature history dependence and strong irreversibility with respect to the sweeping of magnetic field. These results are attributed to the effect of phase separation and kinetic arrest of the electronic phase in this phase separated manganite at low temperatures.     

Structural and magnetic properties and hyperfine interaction in La3.5Ru4O13 compound

Structural, magnetic and hyperfine interaction measurements have been carried out on the novel compound La_3.5Ru₄O₁₃ prepared under two different atmospheres (air and oxygen flow). This compound is formed in the orthorhombic structure (space group Pmmm, # 47). The coexistence of the triple-layered perovskite-type planes (quasi-2D structure) and the rutile-like slabs (1D structure) leads to interesting magnetic and electronic properties in this compound. The magnetic susceptibility of this system shows a peak at T~47 K associated with antiferromagnetic interactions. The Curie-Weiss behaviour of the susceptibility provides an effective magnetic moment consistent with Ru ions in low-spin state. Perturbed angular correlation measurements carried out with ¹¹¹Cd probe in the temperature range 10-60 K reveal only quadrupole interactions and indicate the occurrence of structural distortions for T<40 K.     

Superparamagnetic behavior of La0.67Sr0.33MnO3 nanoparticles prepared via sol-gel method

Magnetic nanoparticles of La_0.67Sr_0.33MnO₃ (LSMO) manganite were prepared by sol-gel method. Phase formation and crystal structure of the synthesized powder were examined by the X-ray diffraction (XRD) using the Rietveld analysis. The mean particle size was determined by the transmission electron microscopy (TEM). Infrared transmission spectroscopy revealed that stretching and bending modes are influenced by calcinations temperature. The temperature dependence of the ac magnetic susceptibility was measured at different frequencies and ac magnetic fields in the selected ranges of 40-1000 Hz and 80-800 A/m, respectively. The temperature dependence of ac susceptibility shows a characteristic maxima corresponding to the blocking temperature near room temperature. The frequency dependence of the blocking temperature is well described by the Vogel-Fulcher law. By fitting the experimental data with this law, the relaxation time τ₀=1.7×10⁻¹² s, characteristic temperature T₀=262±3 K, anisotropy energy E_a/k=684±15 K and effective magnetic anisotropy constant k_eff=2.25×10⁴ erg/cm³ have been obtained. dc Magnetization measurement versus magnetic field shows that some of LSMO nanoparticles are blocked at 293 K. The role of magnetic interparticle interactions on the magnetic behavior is also investigated.     

Probing the magnetic state by linear and non-linear ac magnetic susceptibility measurements in under-doped manganite Nd0.8Sr0.2MnO3

We have thoroughly investigated the entire magnetic states of under-doped ferromagnetic-insulating manganite Nd_0.8Sr_0.2MnO₃ through temperature-dependent linear and non-linear complex ac magnetic susceptibility measurements. This ferromagnetic-insulating manganite is found to have frequency-independent ferromagnetic to paramagnetic transition temperature at around 140 K. At around 90 K (≈T_?) the sample shows a second frequency-dependent re-entrant magnetic transition as explored through complex ac susceptibility measurements. Non-linear ac susceptibility measurements (higher harmonics of ac susceptibility) have also been performed (with and without the superposition of a dc magnetic field) to further investigate the origin of this frequency dependence (dynamic behavior at this re-entrant magnetic transition). Divergence of 3rd harmonic of ac susceptibility in the limit of zero exciting field indicates a spin-glass-like freezing phenomena. However, large value of spin-relaxation time (τ₀=10⁻⁸ s) and small value of coercivity (∼22 Oe) obtained at low temperature (below T_?) from critical slowing down model and dc magnetic measurements, respectively, are in contrast with what generally observed in a canonical spin glass (τ₀=10⁻¹²-10⁻¹⁴ s and very large value of coercivity below freezing temperature). We have attributed our observation to the formation of finite size ferromagnetic clusters which are formed as consequence of intrinsic phase separation and undergo cluster glass-like freezing below certain temperature in this under-doped manganite. The results are supported by the electronic- and magneto-transport data.     

High temperature magnetic ordering in La2RuO5

Magnetic susceptibility, heat capacity and electrical resistivity measurements have been carried out on a new ruthenate, La₂RuO₅ (monoclinic, space group P2₁/c) which reveal that this compound is a magnetic semiconductor with a high magnetic ordering temperature of 170 K. The entropy associated with the magnetic transition is 8.3 J/mol K close to that expected for the low spin (S=1) state of Ru⁴⁺ ions. The low temperatures specific heat coefficient γ is found to be nearly zero consistent with the semiconducting nature of the compound. The magnetic ordering temperature of La₂RuO₅ is comparable to the highest known Curie temperature of another ruthenate, namely, metallic SrRuO₃, and in both these compounds the nominal charge state of Ru is 4+.     

Magnetic phase transitions,anisotropic susceptibility and dipolar interactions in antiferromagnetic MnNb2O6

The magnetic properties of MnNb₂O₆ single crystals have been studied in the temperature range 1.6–300 K (T_N = 4.4 K), in fields up to 220 kOe. The high field saturation at low temperature, as well as the paramagnetic susceptibility at high temperature, agree well with a ${}^6\text{S}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}$ state for Mn²⁺ ions. From 1.6 to 3.8 K a spin flop is induced by fields ranging from 17 to 21 kOe, applied in the direction of the a-axis. Elements of the magnetic susceptibility tensors up to rank 12, measured below the spin flop field, are in accordance with a magnetic anisotropy originating mainly from magnetic dipolar interactions.     

Fabrication and magnetic response probed by RF transverse susceptibility in La0.67Ca0.33MnO3 nanowires

The temperature and magnetic field dependence of the radio-frequency (RF) transverse susceptibility (χ_T) of La_0.67Ca_0.33MnO₃ crystalline nanowires has been studied using a very sensitive self-resonant tunnel-diode oscillator (TDO) technique. The nanowires were synthesized using porous templates of anodized alumina by chemical solution deposition technique, and the crystalline nature of the nanowires with the average diameter of 70 nm was confirmed by TEM, SAED, and HREM. RF transverse susceptibility experiments reveal the presence of a double-peak structure at T≤245 K (the Curie temperature) but a single peak at T>245 K. This distinguishes the low temperature ferromagnetic state from the high temperature paramagnetic state. The effective magnetic anisotropy field (H_K), which corresponds to the peak location of χ_T, has been found to increase with decrease in temperature from the Curie temperature.     

Knight shifts and magnetic susceptibilities of the intermetallic compounds CeCu4 and CeCu5

The magnetic susceptibility and Knight shift of the compounds CeCu₄ and CeCu₅ have been measured over the temperature ranges 80–800 and 140–400 K, respectively. The most important contributions to the magnetic susceptibility are the Curie-Weiss term, expressing the paramagnetism of the localized ?-electrons, and a temperature independent term, which have both been determined. The phenomenological exchange integral F_s? between the 4?-electron spins and conduction electron spins was found to be ?10.43× 10^?3 eV for CeCu₄ and 3.9 × 10^?3 eV for CeCu₅. A reversal in the sign of the s?? coupling for CeCu₅ is noted.     

NMR,magnetic susceptibility and specific heat of CrAl7

The temperature dependence of the magnetic susceptibility, Knight shift and specific heat for the compound CrAl₇ have been measured. These measurements point out that, at the temperature around T_N ≈220 K the compound CrAl₇ presents a second order phase transition from the electron itinerant antiferromagnetism state to the paramagnetic state. The NMR and magnetic susceptibility measurements are correlated and the results are discussed in terms of the electron itinerant antifer-romagnetism and rigid band models. For the temperature independent-term of the susceptibility all the contributions are given.     

Cluster glass magnetism in the phase-separated Nd2/3Ca1/3MnO3 perovskite

A detailed study of the low-temperature magnetic state and the relaxation in the phase-separated colossal magnetoresistance Nd_2/3Ca_1/3MnO₃ perovskite has been carried out. Clear experimental evidence of the cluster-glass magnetic behavior of this compound has been revealed. Well defined maxima in the in-phase linear ac susceptibility χ′(T) were observed, indicative of the magnetic glass transition at T_g∼60 K. Strongly divergent zero-field-cooled and field-cooled static magnetizations and frequency dependent ac susceptibility are evident of the glassy-like magnetic state of the compound at low temperatures. The frequency dependence of the cusp temperature T_max of the χ′(T) susceptibility was found to follow the critical slowing down mechanism. The Cole–Cole analysis of the dynamic susceptibility at low temperature has shown extremely broad distribution of relaxation times, indicating that spins are frozen at “macroscopic” time scale. Slow relaxation in the zero-field-cooled magnetization has been experimentally revealed. The obtained results do not agree with a canonical spin-glass state and indicate a cluster glass magnetic state of the compound below T_g, associated with its antiferromagnetic–ferromagnetic nano-phase segregated state. It was found that the relaxation mechanisms below the cluster glass freezing temperature T_g and above it are strongly different. Magnetic field up to about μ₀H∼0.4 T suppresses the glassy magnetic state of the compound.     

Magnetic and transport properties of Nd1.67Sr0.33NiO4

Nd_1.67Sr_0.33NiO₄ polycrystals have been prepared by modified sol–gel method and subsequent annealing. X-ray diffraction analysis, electrical resistivity, magnetic susceptibility and thermal magnetisation have been measured. Rietveld analyses show a tetragonal or pseudo-tetragonal K₂NiF₄-type structure. The resistivity measurements present a change in conduction mode close to 230 K, which corresponds to the charge ordering temperature. Below this temperature, the material adopts a variable range hopping conduction mode; and above, the conduction follows adiabatic thermal activated mode. The magnetic measurements show paramagnetic behaviour in the range of 80–300 K. Moreover, the magnetic susceptibility data show a sign of the charge ordering transition about 230 K.     

Reentrant spin glass behaviour in Nd0.84K0.12MnO3

Polycrystalline Nd_0.84K_0.12MnO₃ was prepared in single phase form with Pbnm space group. The magnetic properties are studied from magnetization, linear and non-linear susceptibility, and thermoremanent magnetization measurements. The sample exhibits paramagnetic to ferromagnetic transition followed by low temperature spin glass like transition. From frequency variation of ac susceptibility measurements, the spin glass transition temperature is found to be 97.6±0.1 K with critical exponents zυ=1.13±0.06. The critical exponent γ corresponding to spin glass transition has been determined from the third harmonic susceptibility analysis and it is found to be 3.09±0.05. The effective number of spins blocked under frustration and their correlation length are determined from the analysis of thermoremanent magnetization.     

Magnetic and structural studies of the alloy system REIn0.5Ag0.5

The structural and magnetic properties of the alloy system REIn_0.5Ag_0.5 [RE = Gd, Tb, Dy, Ho, Er, Tm and Yb] are reported. All these alloys (except that of Yb) crystallize in a cubic CsCl type structure at room temperature. Low temperature X-ray diffraction data does not reveal any structural phase transformation down to 8 K. On the basis of magnetic susceptibility data at a different temperature (3–300 K) and applied magnetic field (2 × 10⁵ to 8 × 10⁶ A m^-1, it has been concluded that GdIn_0.5Ag_0.5 is ferromagnetic (T_c = 118 K), TbIn_0.5Ag_0.5 and DyIn_0.5Ag_0.5 are meta magnetic (T_N = 66 and 30 K, respectively) and alloys involving Ho, Er, Tm and Yb are ferrimagnetic with Néel temperatures (T_N) equal to 24, 22, 21 and 20 K, respectively. The evaluated effective magneton number (p) is found to be slightly larger compared to theoretical values for tripositive ions of Gd, Tb and Dy and a bit smaller for Ho, Er, Tm and Yb. The results have been qualitatively explained using appropriate theories.     

Abnormal magnetic properties of the Ce24Co11 hexagonal phase

The lighter rare earth-cobalt and thorium-cobalt binary systems were revised on the rare earth or thorium side, by metallographic, electron microprobe and X-ray methods. In agreement with previous works, it is confirmed that, in these systems, the first intermetallic compound corresponds to the following stoichiometry: 3:1 for trivalent La, Pr and Nd; 7:3 for tetravalent Th; 24:11 for Ce. The electronic structure of Ce in the hexagonal (P6₃mc) Ce₂₄Co₁₁ phase was investigated via magnetic susceptibility measurements in the 4.2–1300 K temperature range. The results show that the Curie-Weiss law is not followed, no magnetic order occurs down to 4.2 K and a very small change in the thermal behaviour of the magnetic susceptibility appears above the melting point of the phase (750 K). The abnormally low values of the magnetic susceptibility of Ce₂₄Co₁₁ could be understood by assuming Co is a non-magnetic state and Ce in a temperature dependent mixed valence state.     

Influence of temperature on critical fields in ZnCr2Se4

The complex ac dynamic magnetic susceptibility was used to study the influence of temperature on critical fields in polycrystalline ZnCr₂Se₄ spinel. An antiferromagnetic order with a Néel temperature T_N=20.7 K and a strong ferromagnetic exchange evidenced by a positive Curie-Weiss temperature θ_CW=55.1 K were established. An increasing static magnetic field shifts T_N to lower temperatures while a susceptibility peak at T_m in the paramagnetic region—to higher temperatures. The non-zero and negative values both of the second and third harmonics of susceptibility suggest only a parallel spin coupling in ferromagnetic clusters in the range between the Néel and Curie-Weiss temperatures. Below T_N the magnetic field dependence of susceptibility, χ_ac(H), shows two peaks at critical fields H_c1 and H_c2. The values of H_c1 decrease slightly with temperature while the values of H_c2 drop rapidly with temperature. The strong changes of H_c2 temperature induced are mainly responsible for a spin frustration of the re-entrant type in the spinel under study.