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Details of synthesis and characterization of sol-gel-produced CoFe²O4 nanoparticles embedded in the amorphous SiO² matrix are presented together with results of an extended magnetization study of these materials. The particle size was found to increase from 6 to 15 nm by varying the temperature of a subsequent annealing from 800 to 1100 °C. All samples exhibited superparamagnetic behavior with values of the blocking temperature TB increasing with the particle size. At temperatures above TB the magnetization curves follow the expected Langevin scaling of M vs H/T, which is consistent with the formation of the superparamagnetic state. For T

Focuses on a study which observed giant magnetoresistance (GMR) effects in several classes of bulk magnetic materials. Resistance in metallic systems; Exampls of GMR in bulk materials; Discussion and conclusions.

Polycrystalline samples of UCoGe doped by 1% and 5% of Fe, Ni, and Ru, respectively, have been prepared. Magnetization, ac susceptibility, and electrical resistivity measurements were done on samples in as cast state and annealed at 900 °C for 10 days. The TiNiSi-type orthorhombic crystal structure proved by x-ray powder diffraction was confirmed in the whole series of compounds. Except for the 1% Ni doped sample, all the other samples exhibit clear spontaneous ferromagnetism. The 5% doped compounds have the Curie temperature of TC=6.5 K for U(Co,Fe)Ge, TC=5.0 K for U(Co,Ni)Ge, and TC=7.5 K for U(Co,Ru)Ge. All the studied compounds exhibit only small spontaneous magnetic moments around 0.04μB at 1.8 K. The increasing TC value and stabilization of magnetic moments induced by the transition metals doping are accompanied by a shift in the superconducting transition to lower temperatures with respect to pure UCoGe (TSC≈0.7 K). The 5% doped samples show no sign of superconductivity down to T=0.4 K. [ABSTRACT FROM AUTHOR]

We have studied electrical resistivity anomalies connected with magnetism in RECo[sub 2] (RE=Nd, Tb, Er, Ho) compounds in pressures up to 8 GPa. At ambient pressure the former two compounds exhibit a second order magnetic phase transition (SOMPT) at T[sub C,] whereas a first order magnetic phase transition (FOMPT) is observed in the latter two. Although T[sub C] decreases with pressure in all four compounds, the T[sub C](P) dependence for NdCo[sub 2] and TbCo[sub 2] differs considerably from this for HoCo[sub 2] and ErCo[sub 2]. For the latter two, T[sub c] vs P data deviate dramatically from the initial linear dependence above a critical pressure P[sub c] to become almost pressure independent at higher pressures. We propose that this is reflecting the loss of Co metamagnetism that is also indicated by the vanishing resistivity drop at T[sub c] for P>4 GPa and by the change from a FOMPT to a SOMPT. A scenario is discussed assuming that for P>P[sub c] the projected Co 3d! density of states at E[sub F] decreases. Hence the Co moment collapses because the RE-Co-RE exchange channel becomes ineffective to induce the itinerant 3d electron metamagnetism. The localized RE moments, however, order at a "residual" T[sub C] due to the persisting Ruderman-Kittel-Kasuya-Yosida-type exchange interaction. For NdCo[sub 2] and TbCo[sub 2] the T[sub c] values decrease with pressure by an exponential law but remain rather high in the highest applied pressures. Results of first-principles electronic structure calculations using the full-potential linearized augmented plane wave method are presented for HoCo[sub 2] and NdCo[sub 2] compounds, as well. © 2001 American Institute of Physics. We have studied electrical resistivity anomalies connected with magnetism in RECo[sub 2] (RE=Nd, Tb, Er, Ho) compounds in pressures up to 8 GPa. At ambient pressure the former two compounds exhibit a second order magnetic phase transition (SOMPT) at T[sub C,] whereas a firs! t order magnet... [ABSTRACT FROM AUTHOR]

We report on low-temperature measurements of magnetization, magnetoresistivity, Hall resistivity, magnetostriction, and elastic moduli on a UNiAl single crystal in magnetic fields up to 14 T applied along the c axis of the hexagonal structure. UNiAl is an itinerant 5f-electron antiferromagnet below T[sub N]=19.3 K. At temperatures below 7 K (∼0.3 T[sub N]), it exhibits a first-order metamagnetic transition (MT) at a critical field μ[sub 0]H[sub c]approx. 11.35 T between the low-field antiferromagnetic state and the high-field ferromagnetic one. The transition is accompanied by a sharp anomaly in transport and lattice properties. A striking observation is that the "virgin" curves expressing the field dependence of the various electronic properties clearly differ from those observed on a sample that has once appeared in the high-field state. This irreversibility in bulk properties corresponds to an irreversible change of the magnetic-structure propagation vector wi! thin the basal plane observed by neutron diffraction. The different shapes of M(H), ρ(H), and ρ[sub H](H) curves are strongly suggestive of field-induced changes in the spectrum of spin fluctuations, which play a substantial role in the physics of UNiAl. This seems to be corroborated by the effect of "high-field annealing" on the low-temperature specific-heat data. The irreversibility vanishes at temperatures T>=7 K where the MT loses its first-order character. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Magnetization (M) and specific-heat measurements of a CePtSn single crystal in magnetic fields up to 14 T applied along principal crystallographic axes are reported. CePtSn becomes antiferromagnetic at T[sub N]=7.5 K and undergoes an order-order transition at 5 K (in zero field). In a field applied along the a axis (B//a) a metamagnetic transition (MT) is induced that is manifest by a cusp on the M(B) curve at a critical field B[sub c], an exponential increase of the low-field magnetization, and a linear increase for B>B[sub c](=12.5 T) at 2 K; B[sub c] decreases with increasing temperature. For B//b, qualitatively different M(B) curves are observed in two temperature regimes. For T<3 K, two MTs are found at 4 and 11 T, respectively, the former one irreversible. For T>=3 K only the "11 T" transition remains with modified character and B[sub c] is rapidly decreasing with increasing temperature. These MTs are associated with previously reported GMR effects. Microscopic as! pects of these phenomena are discussed and updated magnetic-phase diagrams for B//a and B//b, respectively, are presented. © 2001 American Institute of Physics. Magnetization (M) and specific-heat measurements of a CePtSn single crystal in magnetic fields up to 14 T applied along principal crystallographic axes are reported. CePtSn becomes antiferromagnetic at T[sub N]=7.5 K and undergoes an order-order transition at 5 K (in zero field). In a field applied along the a axis (B//a) a metamagnetic transition (MT) is induced that is manifest by a cusp on the M(B) curve at a critical field B[sub c], an exponential increase of the low-field magnetization, and a linear increase for B>B[sub c](=12.5 T) at 2 K; B[sub c] decreases with increasing temperature. For B//b, qualitatively different M(B) curves are observed in two temperature regimes. For T<3 K, two MTs are found at 4 and 11 T, respectively, the former one irreversible. For T>=3 K only the "11 T" transition remains with! modified char... [ABSTRACT FROM AUTHOR]

Describes the discovered compounds of the U[sub2]T[sub2]X type, which contribute to heavy fermion research due to a systematic occurrence of gamma enhancement. Factor that affects the magnetic and electronic properties of light actinides in intermetallic compounds; Examples of nonmagnetic compounds that exhibit spin-fluctuation features; Characteristics of the obtained spectra of the compounds.

Focuses on both the temperature and magnetic-field stability of the incommensurate antiferromagnetic phase in the complex magnetic phase diagram of UNiGe. Information on UNiGe; Specific heat of UNiGe; Description of the obtained magnetic phase diagram; Analysis of the magnetic phases in uranium intermetallics.

Presents the results of magnetic, resistivity and specific heat measurements of rare earth NiAl (RENiAl) compounds. Magnetic properties of RENiAl compounds; Metamagnetic transitions observed in RENiAl antiferromagnets; Magnetic ordering temperatures of all compounds.

Deals with a study which examined the magnetism in URhSi crystals through neutron-powder-diffraction. Experiment; Computational formulas for magnetism; Findings of neutron diffraction.

Presents information on the first thermal expansion measurements performed on a single crystal of UNiAl. Schematic representation of the ZrNiAl-type of structure; Temperature dependence of the relative length changes; Magnetocrystalline anisotropy of UNiAl expressed in values of the paramagnetic Curie temperature.

Presents information on a study which investigated the type of the crystal structure, ground state, magnetic, transport and thermal properties of polycrystalline U[sub2]Pt[sub2]Sn. Measurement of low-field magnetization and temperature dependences of the direct current magnetic susceptibility; Description of the magnetization curves of U[sub2]Pt[sub2]Sn; information on two tetragonal crystallographic structures considered.

Presents information on a study which illustrated the magnetic phase diagram of UNiGa that exhibits several antiferromagnetic phases. Details on the magnetic phase diagram of UNiGa; Antiferromagnetic phases observed in zero magnetic field; Measurement of the low-field magnetization using a SQUID magnetometer.

Presents information on a study which investigated the electronic properties and basic bulk properties of UCuSn. Preparation of a polycrystalline sample of UCuSn; Magnetic transitions in UCuSn; Measurement of the temperature dependences of the electrical resistivity, of the specific heat and magnetization.

Presents a study that examined the structure, transport and thermal properties of UCoGa compound. Experimental method; Refined structural parameters for UCoGa at 60 K; Conclusions.

Discusses a study which analyzed the magnetization of a single crystal of the hexagonal antiferromagnet UPdSn in order to examine the energetics associated with antiferromagnetic domains. Result of the fact that the magnetic unit cell is orthorhombic; Condition in which the intensity of the antiferromagnetic peak is doubled; Limitation in conducting bulk magnetization measurements.

Deals with a study which presented magnetization, asynchronous circuits and direct current susceptibility of a UCoGa single crystal. Disadvantage from the complicated magnetization behavior at low temperatures; category in which UCoGa falls; Aspects that explain well the development of magnetism within the large family of UTX compounds; Preparation of UCoGa single crystals.