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15 May 2005

Volume 97, Issue 10, Articles (10xxxx)

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back to top Critical Phenomena and Spin Glasses

Inhibition of Nd magnetic order in NdFe1−xCoxO3 by magnetic vacancies

F. Bartolomé and J. Bartolomé

J. Appl. Phys. 97, 10A501 (2005); http://dx.doi.org/10.1063/1.1848354 (3 pages) | Cited 1 time

Online Publication Date: 28 April 2005

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The low-temperature specific heat of NdFe1−xCoxO3 (x = 0, 0.03, 0.1, 0.25, and 0.5) has been measured to study the magnetic ordering of the Nd sublattice as a function of Co content. The results, satisfactorily explained by a mean-field model, show the inhibition of the Nd cooperative ordering for x ≥ 0.1.
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75.50.Dd Nonmetallic ferromagnetic materials
75.40.Cx Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.)
61.72.J- Point defects and defect clusters

Experimental investigation of superspin glass dynamics

D. Parker, F. Ladieu, E. Vincent, G. Mériguet, E. Dubois, V. Dupuis, and R. Perzynski

J. Appl. Phys. 97, 10A502 (2005); http://dx.doi.org/10.1063/1.1850333 (3 pages) | Cited 13 times

Online Publication Date: 28 April 2005

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Magnetic nanoparticle assemblies in high concentrations can exhibit spin glass like properties in the low temperature phase due to the influence of strong dipolar interactions. To address the question of the extent to which the properties of these “superspin” glasses mimic those of an atomic spin glass, several homogeneously dispersed γ‐Fe2O3 nanoparticle assemblies of varying volume fraction have been studied. In a concentrated sample, the main features of atomic spin glasses have been observed including aging phenomena for which we have proposed a rescaling.
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75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Lk Spin glasses and other random magnets
75.20.Ck Nonmetals
75.75.-c Magnetic properties of nanostructures
75.30.Cr Saturation moments and magnetic susceptibilities
75.30.Gw Magnetic anisotropy

Element-specific magnetometry on negatively magnetized NdMnO3+δ

F. Bartolomé, J. Herrero-Albillos, L. M. García, J. Bartolomé, N. Jaouen, and A. Rogalev

J. Appl. Phys. 97, 10A503 (2005); http://dx.doi.org/10.1063/1.1850810 (3 pages) | Cited 5 times

Online Publication Date: 28 April 2005

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Field-cooled x-ray magnetic circular dichroism experiments at several temperatures at the Mn K and Nd L2,3 edges on nonstoichiometric NdMnO3.11 have been performed. Our results show that Nd and Mn net magnetizations are parallel along the whole range of temperatures, ruling out the competition between the Nd and Mn sublattices as the origin of negative magnetization in NdMnO3+δ.
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75.50.Ee Antiferromagnetics
78.20.Ls Magneto-optical effects
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Electronic and magnetic properties of SmFe1−xMnxO3 orthoferrites (x = 0.1, 0.2, and 0.3)

K. Bouziane, A. Yousif, I. A. Abdel-Latif, K. Hricovini, and C. Richter

J. Appl. Phys. 97, 10A504 (2005); http://dx.doi.org/10.1063/1.1851406 (3 pages) | Cited 1 time

Online Publication Date: 28 April 2005

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The electronic and magnetic properties of the orthoferrites SmFe1−xMnxO3 (x = 0.1, 0.2, and 0.3) have been investigated. The Mössbauer data show that the iron ions at different nonequivalent octahedral sites have essentially a trivalent state. Resonant inelastic x-ray emission measurements performed at Fe L3 edge and Mn L3 edge show clearly that Fe ions and Mn ions have the same electronic structure. The temperature-dependent magnetization shows that the Curie temperature of the weak-ferromagnetic SmFeO3 decreases as Fe ions are substituted by Mn ions. A spin-reorientation transition from weak-ferromagnetism to antiferromagnetism seems to take place at low temperature, and the corresponding transition temperature essentially decreases as the Mn content increases. The effect of the substitution of Fe ions by Mn ions in SmFeO3 on the double exchange and the critical temperatures is analyzed and discussed.
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75.50.Gg Ferrimagnetics
71.20.Ps Other inorganic compounds
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.30.Et Exchange and superexchange interactions
76.80.+y Mössbauer effect; other γ-ray spectroscopy
78.70.En X-ray emission spectra and fluorescence

Thermal expansion anomalies of R(Fe,M)12 (R = Y, Nd; M = Mo and Si)

Honglin Du, Benpei Cheng, Jingzhi Han, Shunquan Liu, Jinbo Yang, Yingchang Yang, Yanjie Xue, Bo Chen, and Guangai Sun

J. Appl. Phys. 97, 10A505 (2005); http://dx.doi.org/10.1063/1.1851422 (3 pages) | Cited 1 time

Online Publication Date: 28 April 2005

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Structural and thermal-expansion anomaly studies on R(Fe,M)12 (R = Nd and and Y, M = Mo and Si) compounds were performed by x-ray diffraction. Mo atoms occupy the 8i site. While Si atoms occupy the 8f and 8j sites but not the 8i site. Thermal-expansion anomaly shows only in ab plane in the Mo compounds, while becomes very weak and along with only the c axis in the Si compounds. The anomaly was attributed to the contribution of the interactions of short Fe–Fe distances similar to the previous explanation on other R–Fe intermetallics and that of other strongly positive interactions such as 8j-8j.
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75.50.Bb Fe and its alloys
65.40.De Thermal expansion; thermomechanical effects
61.66.Dk Alloys

Ferromagnetic phase boundary in the bond frustrated Heisenberg model

A. D. Beath and D. H. Ryan

J. Appl. Phys. 97, 10A506 (2005); http://dx.doi.org/10.1063/1.1851916 (3 pages) | Cited 4 times

Online Publication Date: 28 April 2005

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We determine the ferromagnetic phase boundary for the short range ±J bond frustrated Heisenberg model in three dimensions using a very efficient Monte Carlo algorithm which eliminates the critical slowing down usually experienced at a second order phase transition. The phase boundary is identified by measuring the correlation length directly, a method which we show to be superior to more conventional methods such as the crossing of the Binder cumulant. The critical concentration of antiferromagnetic bonds beyond which ferromagnetism is lost is xc = 0.208(2).
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75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.10.Jm Quantized spin models, including quantum spin frustration
75.40.Mg Numerical simulation studies

Influence of a nonmagnetic dilution on the magnetic properties of a ZnxCd1−xCr2S4 system by means of microwave magnetic resonance

G. A. Mendoza, O. Guzmán, H. Ariza–Calderón, and P. Prieto

J. Appl. Phys. 97, 10A507 (2005); http://dx.doi.org/10.1063/1.1852854 (3 pages)

Online Publication Date: 28 April 2005

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The influence of a nonmagnetic dilution on the magnetic properties of a ZnxCd1−xCr2S4 system (0.1<x<0.9) has been studied by means of microwave magnetic resonance at temperatures between 10 and 293 K. Experimental results for the peak-to-peak linewidth ΔHpp and the slope dΔHpp/dT have been discussed by the reduction of the exchange interaction between magnetic ions through the Zn substitution. For 0.6<x<0.9 at T<50 K, the electron-paramagnetic-resonance line tends toward the Lorentzian shape, indicating a medium with competing interactions with strong exchange coupling. For x<0.4 at T<50 K the line shapes have a rich Gaussian line indicating an increment of the interaction cluster medium.
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75.50.Dd Nonmetallic ferromagnetic materials
75.50.Ee Antiferromagnetics
76.30.Lh Other ions and impurities
75.30.Et Exchange and superexchange interactions
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.30.Cr Saturation moments and magnetic susceptibilities

Electronic and magnetic phase diagram of La0.5Sr0.5Co1−xFexO3(0 ⩽ x ⩽ 0.6) perovskites

The-Long Phan, Seong-Cho Yu, Nguyen Van Khiem, Manh-Huong Phan, Jang Roh Rhee, and Nguyen Xuan Phuc

J. Appl. Phys. 97, 10A508 (2005); http://dx.doi.org/10.1063/1.1855197 (3 pages) | Cited 7 times

Online Publication Date: 28 April 2005

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Spin dynamics and magnetic frustration effects in La0.5Sr0.5Co1−xFexO3 (0 ⩽ x ⩽ 0.6) compounds were systematically studied by means of resistivity, dc magnetization, ac susceptibility, and electron-spin-resonance spectra. The Fe substitution caused a metal-semiconductor transition for x ⩽ 0.3 compositions whereas the only semiconducting state behaved for x>0.3 compositions. With increasing Fe-doping levels, the ferromagnetic–paramagnetic transition temperature, TC, decreased from 250 (x = 0) to 166 K (x = 0.4). A spin-glass behavior was observed for x>0.4 compositions and is attributed to the frustration of random competing exchange interactions, namely, the ferromagnetic Co3+–Co4+ double-exchange interaction and the antiferromagnetic interactions such as Co–O–Fe and Fe–O–Fe. The internal dynamic properties of the samples were elucidated by the electron-paramagnetic-resonance spectra. An electronic and magnetic phase diagram of La0.5Sr0.5Co1−xFexO3 is drawn up.
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75.50.Dd Nonmetallic ferromagnetic materials
75.50.Lk Spin glasses and other random magnets
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
71.30.+h Metal-insulator transitions and other electronic transitions
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
75.30.Cr Saturation moments and magnetic susceptibilities
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Et Exchange and superexchange interactions
72.80.Sk Insulators
76.30.Fc Iron group (3d) ions and impurities (Ti-Cu)

Spin dynamics and magnetic frustration effects in La1−xSrxCoO3 (0<x ⩽ 0.5) compounds

Nguyen Van Khiem, Nguyen Xuan Phuc, The-Long Phan, Seong-Cho Yu, and Manh-Huong Phan

J. Appl. Phys. 97, 10A509 (2005); http://dx.doi.org/10.1063/1.1855199 (3 pages) | Cited 4 times

Online Publication Date: 28 April 2005

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La1−xSrxCoO3 (0<x ⩽ 0.5) have been thoroughly studied by means of dc magnetization, ac susceptibilities, and electron-spin-resonance (ESR) spectra. Spin-glass behavior and its transition process for x<0.2 compositions appeared to occur at temperature Tg ranging from 14.6 to 68 K, whereas for further strontium substitution the system was characterized by growing ferromagnetic clusters. The frequency dependence of the spin-glass freezing temperature Tf has been analyzed using the conventional critical slowing-down scaling law. The temperature dependence of Ta with respect to the external magnetic field Hex obeyed an exponential function of θa = Ta/TC∝−Hexn. A complete magnetic phase diagram of La1−xSrxCoO3 is drawn up. Besides, the internal dynamics in the samples are elucidated by the ESR spectra. The results obtained provide more insights into the nature of spin dynamics and so-called magnetic frustration phenomena in such a cobaltate system.
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75.50.Lk Spin glasses and other random magnets
75.50.Dd Nonmetallic ferromagnetic materials
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
75.30.Cr Saturation moments and magnetic susceptibilities
76.30.-v Electron paramagnetic resonance and relaxation
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
64.70.P- Glass transitions of specific systems
64.70.Q- Theory and modeling of the glass transition

Absence of Kondo lattice coherence effects in Ce0.6La0.4Pb3: A magnetic-field study

Richard Pietri, Costel R. Rotundu, Bohdan Andraka, Bryan C. Daniels, and Kevin Ingersent

J. Appl. Phys. 97, 10A510 (2005); http://dx.doi.org/10.1063/1.1855456 (3 pages) | Cited 1 time

Online Publication Date: 28 April 2005

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The specific heat of polycrystalline Ce0.6La0.4Pb3 has been measured in magnetic fields ranging from 0 to 14 T. After subtraction of a lattice contribution, the specific heat between 1 K and 10 K is well described by the S = ½ single-impurity Kondo model with just one adjustable parameter: the zero-field Kondo temperature. In particular, the variation in the temperature and the height of the peak in C vs T is captured with good accuracy. This fit suggests that lattice coherence effects play no significant role in the magnetic-field response of this concentrated Kondo system.
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75.50.Ee Antiferromagnetics
75.30.Mb Valence fluctuation, Kondo lattice, and heavy-fermion phenomena
75.40.Cx Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.)
71.55.Ak Metals, semimetals, and alloys
75.40.Mg Numerical simulation studies

Universal scaling functions and multi-critical points in the site frustrated Heisenberg model

A. D. Beath and D. H. Ryan

J. Appl. Phys. 97, 10A511 (2005); http://dx.doi.org/10.1063/1.1855551 (3 pages) | Cited 1 time

Online Publication Date: 28 April 2005

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Recently, the ordering scenario of three-dimensional site frustrated Heisenberg models has been challenged. The existence of a decoupled tetracritical point (DTP) where ferromagnetic (FM) and antiferromagnetic (AF) order occur simultaneously has been modified to include a line of multicritical points where both FM and AF occur simultaneously. In addition, numerous studies claim that, within the mixed phase, critical exponents are altered from Heisenberg values. Here we show that within the narrow region of proposed multicritical points, the transition temperatures away from the tetracritical point are indeed distinct, confirming the occurrence of a DTP. In addition, we show a universal scaling collapse of the magnetization both away from, and within, the mixed phase using Heisenberg exponents, demonstrating that the stable fixed points are within the Heisenberg universality class.
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75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.10.Jm Quantized spin models, including quantum spin frustration
75.40.Mg Numerical simulation studies
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Magnetic frustration in the spinel compounds GeNi2O4 and GeCo2O4

Sébastien Diaz, Sophie de Brion, Gérard Chouteau, Pierre Strobel, Benjamin Canals, Juan Rodriguez Carvajal, Harison Rakoto, and Jean Marc Broto

J. Appl. Phys. 97, 10A512 (2005); http://dx.doi.org/10.1063/1.1863113 (2 pages) | Cited 7 times

Online Publication Date: 28 April 2005

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In the spinel compounds AB2O4, the B sites form a pyrochlore lattice. GeCo2O4 and GeNi2O4 have been investigated using high magnetic field magnetization as well as neutron diffraction measurements. Both compounds become antiferromagnetic at low temperature (around 23 and 12 K, respectively) with the same propagation vector. The magnetization then presents two spin flop fields and one huge saturation field (above 50 T). The Curie–Weiss temperature is positive for the Co spinel and negative for the Ni one. A model taking into account the first neighbor interaction J1 together with two different third neighbor interactions J2 and J3 is able to account for the common observed magnetic behavior. J1 is ferromagnetic while J2 and J3 are antiferromagnetic, in agreement with Goodenough–Kanamori–Anderson rules. These competing interactions are responsible for the frustration in these compounds.
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75.50.Ee Antiferromagnetics
75.20.Ck Nonmetals
75.30.Et Exchange and superexchange interactions
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Cr Saturation moments and magnetic susceptibilities
75.50.Cc Other ferromagnetic metals and alloys
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