Cluster-glass Phase Research Articles

Relaxation phenomena of remanent magnetizations in spin- and cluster-glasses of itinerant magnetic FexTiS2 crystals studied by hall effect

Abstract Relaxation phenomena of isothermal remanent magnetization (IRM) and field-cooled thermoremanent magnetization (TRM) in spin- and cluster-glass phases of intercalation compound FexTiS2 have been studied using the anomalous Hall effect. After an applied magnetic field is switched off, the time decay of Hall resistivity (or remanent magnetization) follows a power law of the form ϱH(t) = At−m, where A is a constant and m an exponent. In both IRM and TRM, the exponent m depends appreciably on the applied magnetic field intensity and temperature, for which we have obtained a universal relationship with a newly introduced quantity of “relative relaxed magnetization”.

Resistivity minima in concentrated gamma -Cu100-xMnx alloys (36

High-resolution electrical resistivity data of concentrated \ensuremath{\gamma}-${\mathrm{Cu}}_{100\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Mn}}_{\mathit{x}}$ alloys with x=36, 60, 73, 76, and 83 have been presented here in the temperature range 1.2\ensuremath{\le}T\ensuremath{\le}30 K. They show resistivity minima at ${\mathit{T}}_{\mathrm{min}}$ lying between 2.5 and 24.5 K. In this temperature range the alloys with x=36, 60, and 73 are cluster glasses while those with x=76 and 83 show a mixed cluster-glass and long-range antiferromagnetic phase. Resistivity below the minima follows a \ensuremath{\surd}T type of behavior and has been interpreted in terms of the electron-electron (e-e) interaction effects in the presence of weak localization. The e-e interaction effects have dominant contributions to the resistivity in the temperature range of 2 K\ensuremath{\le}T\ensuremath{\le}${\mathit{T}}_{\mathrm{min}}$/3. The contributions from magnetic and phonon scattering are found to be negligible in this range. A good estimation of the density of states at the Fermi level, made from the coefficient of the \ensuremath{\surd}T term, gives further support to the interpretation. In the higher temperature range of ${\mathit{T}}_{\mathrm{min}}$/3\ensuremath{\le}T\ensuremath{\le}30 K, besides the e-e interaction effects, magnetic contribution of the type ${\mathit{T}}^{3/2}$ and phonon contribution given by the standard Bloch-Gr\uneissen relation have been observed. From our present findings and the earlier reports on other systems, we conclude that the ${\mathit{T}}^{3/2}$ type of magnetic contribution to the resistivity arises due to the low-temperature spin diffusive modes in spin/cluster glasses. The above analysis is insensitive to the magnetic state of the alloys. \textcopyright{} 1996 The American Physical Society.

Neutron powder diffraction study of intercalation compound Fe xTiS 2

The crystal structures of the intercalation compounds Fe x TiS 2 ( x = ⅓, ¼), which show a behavior characteristic of a cluster-glass phase at low temperature, were refined by means of Rietveld analysis of neutron powder-diffraction data. When x = ⅓, the space group is P3̄1 and a √3 a × √3 a × 2 c superlattice is formed. When x = ¼, the space group becomes C2/m and a 2√3 a × 2 a × 2 c superlattice is formed. For both concentrations, the occupancy at the Fe sites is less than 1.0.

Time decay of thermoremanent magnetization in cluster-glass phase of intercalation compound Fe xTiS 2 studied by use of anomalous Hall effect

Time decay of Hall resistivity ρ H after field-cooling under magnetic fields H FC = 0.035–0.14 T for a cluster-glass phase of Fe x TiS 2 ( x = 1 4 , T g = 53 K ) has been measured over the temperature range 4.2–35 K and time range 10 −1–10 3 s. After the magnetic field is switched off to zero at time t = 0, the Hall voltage decays with time obeying the power law ρ H( t) = At − m in a short time range up to t d, beyond which the decay becomes faster than a power law. The temperature and magnetic field dependences of the exponents m are analyzed to obtain a universal relation for the thermoremanent magnetization (TRM), m = Dξ, where ξ is a characteristic quantity, defined by ξ = 1 − M(0)/ M FC( T → 0); M FC( T → 0) is the magnetization at H = H FC extrapolated to T = 0 and M(0) the remanent magnetization at time t = 0. Comparison with the present field-cooled and the zero-field case (isothermal remanent magnetization, IRM) is made to emphasize the dependence of relaxation behavior on the magnetic history.

Hole-doping effect on magnetic properties of La1−xSrxCoO3 (0 ≤ x ≤ 0.5)

We performed magnetization, neutron scattering and NMR measurements to reveal the hole-doping effect on magnetic properties of La1−xSrxCoO3 (0 ≤ x ≤ 0.5). A magnetic phase diagram which includes spin-glass (0 ≤ x ≤ 0.18) and cluster-glass (0.18 ≤ x ≤ 0.5) phases is proposed.

Relaxation behaviors in cluster-glass phase of itinerant magnetic FexTiS2 crystals studied by magnetotransport measurements using pulsed magnetic fields

Time decays of Hall resistivities ϱH using pulsed magnetic fields up to 20 T for a cluster-glass phase of FexTiS2 (x = 14, Tg = 53 K) have been measured over the temperature ranges 4.2–45 K and time ranges 10-1–103 s. The temperature and peak field dependences of ϱH are analyzed to obtain a universal relationship, mTα = Cφβ, for the parameters characterizing the dynamical properties, where m is an exponent for the power law ϱH(t) = At-m after a field is switched off, α = - 12, and φ a newly introduced quantity, φ = [M(Hp) - Mr(0)]/M(Hp) [M( Hp) is the magnetization at the peak field Hp and Mr(0) the remanent magnetization at time t = 0]. The exponent β has different values 0.60 and 2.9 for φ < φc and φ > φc, respectively; φc = 0.34, which corresponds to a three-dimensional ‘critical volume fraction’ in a site-percolation picture.

Magnetic phase transition of stage-2 CucCo1-cCl2-graphite intercalation compounds.

Stage-2 ${\mathrm{Cu}}_{\mathit{c}}$${\mathrm{Co}}_{1\mathrm{\ensuremath{-}}\mathit{c}}$${\mathrm{Cl}}_{2}$-graphite intercalation compounds (GIC's) (0\ensuremath{\le}c\ensuremath{\le}1) provide ideal two-dimensional random spin systems with a spin frustration effect arising from competing ferromagnetic and antiferromagnetic interactions. The magnetic properties of these compounds have been studied by dc and ac magnetic susceptibility, and superconducting quantum interference device magnetization. The sign of the Curie-Weiss temperature changes from positive to negative with increasing concentration around c=0.80 to 0.85. The intraplanar exchange interaction J(Cu-Co) between ${\mathrm{Cu}}^{2+}$ and ${\mathrm{Co}}^{2+}$ spins is ferromagnetic and depends on the Cu concentration. These systems with c0.9 undergo a ferromagnetic phase transition at the critical temperature ${\mathit{T}}_{\mathit{c}}$. The irreversible effect of magnetization is observed below ${\mathit{T}}_{\mathit{c}}$. The low-temperature phase below ${\mathit{T}}_{\mathit{c}}$ may correspond to a cluster glass phase where the spin direction of ferromagnetic clusters is frozen because of frustrated interisland interactions which include a dipole-dipole interaction and an interplanar antiferromagnetic interaction. The critical temperature ${\mathit{T}}_{\mathit{c}}$ increases as c increases and exhibits a broad maximum around c=0.5. This enhancement of ${\mathit{T}}_{\mathit{c}}$ is partly due to the ferromagnetic interaction J(Cu-Co). No magnetic phase transition is observed for 0.9c1 partly because of the spin frustration effects arising from (i) the competition between ferromagnetic J(Cu-Co) and antiferromagnetic J(Cu-Cu) interactions, and (ii) the fully frustrated nature of the antiferromagnet on the triangular lattice.

Magnetic Properties of Random-Mixture Graphite Intercalation Compounds

Abstract Random-mixture GICs such as stage-2 NicMn1-cCl2 GICs and stage-2 CocMn1-cCl2 GICs provide model systems for studying 2D random spin systems with spin frustration effects. The magnetic properties of these compounds have been studied by dc and ac magnetic susceptibility, and low field SQUID magnetization measurements. An irreversible effect of magnetization for stage-2 NicMni1-cCl2 GICs (0.8 ≤ c ≤ 1) and stage-2 CocNi1-cCl2 GICs (0 ≤ c ≤ 1) indicates an occurrence of cluster glass phase below a critical temperature where the spin directions of ferromagnetic clusters are frozen because of frustrated interisland interactions.

Low-Field Magnetization and AC Magnetic Susceptibility of Spin- and Cluster-Glasses of Itinerant Magnet FexTiS2

Magnetizations and ac magnetic susceptibilities at low magnetic fields using a SQUID magnetometer have been measured for spin-glass (SG; x =0.1 and 0.2) and cluster-glass (CG; x =1/4 and 1/3) phases of Fe x TiS 2 over the frequency range 0.5–100 Hz and temperature range 4.2–80 K. The frequency and temperature variations of the ac magnetic susceptibilities have different behaviors for SG and CG; in particular, the estimated distribution function of relaxation time g (ω, T ) for x =1/4 has a double-peaked shape. The dimensionality and criticality of the CG phases are also discussed. Monte Calro simulations using a site-percolation model with a two-dimensional triangular lattice are made by taking into account the 1st, 2nd, and 3rd nearest neighbors to obtain the percolation probability P .

Effects of structure on exchange interactions in crystalline and amorphous alloys Gd xY 50−xAg 50

Magnetic interactions and effects of dilution with nonmagnetic Y on the magnetic properties of crystalline and amorphous alloys Gd x Y 50− x Ag 50 (10 ≤ x ≤ 50) have been investigated by measurements of bulk magnetization and susceptibility and by Mössbauer spectroscopy with 155Gd. The crystalline alloys order antiferromagnetically for all Gd concentrations with a noncollinear arrangement of Gd moments induced by negative biquadratic exchange interactions. In amorphous alloys, ferromagnetic order is found for large Gd concentrations ( x ≥ 40). Below the critical concentration x cr, in the range 30< x cr<40, properties typical for magnetic cluster glasses are observed. Magnetic hyperfine fields B hf at 155Gd nuclei vary with x in opposite directions in amorphous and in crystalline alloys. In crystalline alloys, the variation is due to a positive transferred hyperfine field. In amorphous alloys, a reduction of | B hf| with decreasing Gd concentration is caused by a reduction of the frozen Gd moments in the cluster glass phase.

Anisotropic Spin-Glass and Cluster-Glass of Layered FexTiS2Crystals

Zero-field cooled (ZFC) and field cooled (FC) magnetizations have been measured on the spin- and cluster-glasses of iron intercalation compound Fe x TiS 2 ( x =0.1-1/3) over the temperature range 4.2-150 K. We have found appreciable field cooling effects in both spin- and cluster-glass phases. From the observed ZFC and FC curves, strong anisotropies in the paramagnetic Curie temperature and effective magnetic moments are found, for which a qualitative discussion is given.

Ferromagnetic resonance and magnetic ordering in amorphous (FeMn)CP alloys

The magnetic properties of a series of amorphous (FexMn1−x)80P16C4 metallic glasses have been studied via ferromagnetic resonance and zero field ac susceptibility measurements. We find that the Fe ferromagnetism is rapidly destroyed by the competition with the antiferromagnetic coupling of the Mn moment, leading to a cluster glass or spin glass phase in the concentration range x≲70%. Alloys with x greater than 70% show a transition to ferromagnetism with well defined critical behavior. In addition, both the susceptibility and the magnetic resonance reveal a marked anomaly at lower temperatures which can be attributed to the coexistence of ferromagnetism and spin glass order. These anomalies become weaker as the alloys become more strongly ferromagnetic. No resonance signals were detected in alloys with x≲20%.

Magnetic field effects on Mössbauer spectra ofAuFe

Zero and applied field Mossbauer spectra onAuFe alloys with 5, 10 and 20 at % Fe have provided information on the spin glass, cluster glass and long range ferromagnetic phases which are present in this system. The mean hyperfine parameters for these phases are presented.