This review summarizes recent developments in the theory of spin glasses, as well as pertinent experimental data. The most characteristic properties of spin glass systems are described, and related phenomena in other glassy systems (dielectric and orientational glasses) are mentioned. The Edwards-Anderson model of spin glasses and its treatment within the replica method and mean-field theory are outlined, and concepts such as "frustration," "broken replica symmetry," "broken ergodicity," etc., are discussed. The dynamic approach to describing the spin glass transition is emphasized. Monte Carlo simulations of spin glasses and the insight gained by them are described. Other topics discussed include site-disorder models, phenomenological theories for the frozen phase and its excitations, phase diagrams in which spin glass order and ferromagnetism or antiferromagnetism compete, the Ne\'el model of superparamagnetism and related approaches, and possible connections between spin glasses and other topics in the theory of disordered condensed-matter systems.

Spin glasses: Experimental facts, theoretical concepts, and open questions

In this chapter, we will restrict our attention to the ferrites and a few other closely related materials. The great interest in ferrites stems from their unique combination of a spontaneous magnetization and a high electrical resistivity. The observed magnetization results from the difference in the magnetizations of two non-equivalent sub-lattices of the magnetic ions in the crystal structure. Materials of this type should strictly be designated as “ferrimagnetic” and in some respects are more closely related to anti-ferromagnetic substances than they are to ferromagnetics in which the magnetization results from the parallel alignment of all the magnetic moments present. We shall not adhere to this special nomenclature except to emphasize effects, which are due to the existence of the sub-lattices.

Ferromagnetic materials

The development of novel materials is a fundamental focal point of chemical research; and this interest is mandated by advancements in all areas of industry and technology. A good example of the synergism between scientific discovery and technological development is the electronics industry, where discoveries of new semiconducting materials resulted in the evolution from vacuum tubes to diodes and transistors, and eventually to miniature chips. The progression of this technology led to the development * To whom correspondence should be addressed. B.L.C.: (504) 2801385 (phone); (504) 280-3185 (fax); bcushing@uno.edu (e-mail). C.J.O.: (504)280-6846(phone);(504)280-3185(fax);coconnor@uno.edu (e-mail). 3893 Chem. Rev. 2004, 104, 3893−3946

http://depa.fquim.unam.mx/amyd//archivero/FidelmarLechugaSanabria_4940.pdf

Recent advances in the liquid-phase syntheses of inorganic nanoparticles.

Iron, the most ubiquitous of the transition metals and the fourth most plentiful element in the Earth's crust, is the structural backbone of our modern infrastructure. It is therefore ironic that as a nanoparticle, iron has been somewhat neglected in favor of its own oxides, as well as other metals such as cobalt, nickel, gold, and platinum. This is unfortunate, but understandable. Iron's reactivity is important in macroscopic applications (particularly rusting), but is a dominant concern at the nanoscale. Finely divided iron has long been known to be pyrophoric, which is a major reason that iron nanoparticles have not been more fully studied to date. This extreme reactivity has traditionally made iron nanoparticles difficult to study and inconvenient for practical applications. Iron however has a great deal to offer at the nanoscale, including very potent magnetic and catalytic properties. Recent work has begun to take advantage of iron's potential, and work in this field appears to be blossoming.

Synthesis, Properties, and Applications of Iron Nanoparticles

The resistance switching behaviour of several materials has recently attracted considerable attention for its application in non-volatile memory (NVM) devices, popularly described as resistive random access memories (RRAMs). RRAM is a type of NVM that uses a material(s) that changes the resistance when a voltage is applied. Resistive switching phenomena have been observed in many oxides: (i) binary transition metal oxides (TMOs), e.g. TiO(2), Cr(2)O(3), FeO(x) and NiO; (ii) perovskite-type complex TMOs that are variously functional, paraelectric, ferroelectric, multiferroic and magnetic, e.g. (Ba,Sr)TiO(3), Pb(Zr(x) Ti(1-x))O(3), BiFeO(3) and Pr(x)Ca(1-x)MnO(3); (iii) large band gap high-k dielectrics, e.g. Al(2)O(3) and Gd(2)O(3); (iv) graphene oxides. In the non-oxide category, higher chalcogenides are front runners, e.g. In(2)Se(3) and In(2)Te(3). Hence, the number of materials showing this technologically interesting behaviour for information storage is enormous. Resistive switching in these materials can form the basis for the next generation of NVM, i.e. RRAM, when current semiconductor memory technology reaches its limit in terms of density. RRAMs may be the high-density and low-cost NVMs of the future. A review on this topic is of importance to focus concentration on the most promising materials to accelerate application into the semiconductor industry. This review is a small effort to realize the ambitious goal of RRAMs. Its basic focus is on resistive switching in various materials with particular emphasis on binary TMOs. It also addresses the current understanding of resistive switching behaviour. Moreover, a brief comparison between RRAMs and memristors is included. The review ends with the current status of RRAMs in terms of stability, scalability and switching speed, which are three important aspects of integration onto semiconductors.

https://iopscience.iop.org/article/10.1088/0034-4885/75/7/076502/pdf

Emerging memories: resistive switching mechanisms and current status.

Magnetic and electron paramagnetic resonance measurements were employed to probe magnetic interactions in the single crystal and ceramic of La0.7Ca0.3MnO3 manganite in the vicinity and above their paramagnetic-ferromagnetic phase transition. It is shown that strong differences in the Curie point values and in the temperature dependences of inverse susceptibilities are observed in spite of the same structure and cation composition of both samples. We suggest that the difference between lattice effects in these samples, induced by their different chemical disorder, proves a more realistic description of experimental data than so-called "Griffiths singularity".

Thermodynamics of Paramagnetic-Ferromagnetic Phase Transition in ${\rm La}_{0.7}{\rm Ca}_{0.3}{\rm MnO}_{3}$ Manganite: “Griffiths singularity” versus Chemical Disorder and Lattice Effects

Magnetic and transport properties of polycrystalline ${\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Ca}}_{x}\mathrm{Mn}{\mathrm{O}}_{3}$ $(x=0.8,0.9)$ perovskites were investigated in the temperature range $4.2--300\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, magnetic field up to $16\phantom{\rule{0.3em}{0ex}}\mathrm{kOe}$ and under hydrostatic pressures up to $12\phantom{\rule{0.3em}{0ex}}\mathrm{kbar}$. The ${\mathrm{La}}_{0.1}{\mathrm{Ca}}_{0.9}\mathrm{Mn}{\mathrm{O}}_{3}$ compound exhibits a heterogeneous spin configuration in its ground state [$G$-type antiferromagnetic (AFM) phase with local ferromagnetic (FM) regions and $C$-type AFM]. The $x=0.8$ compound is mostly an orbital ordered $C$-type AFM. In the case of ${\mathrm{La}}_{0.1}{\mathrm{Ca}}_{0.9}\mathrm{Mn}{\mathrm{O}}_{3}$, an applied pressure slightly increases the magnetic transition temperature and significantly enhances the FM component. Pronounced hysteretic effects observed in ${\mathrm{La}}_{0.1}{\mathrm{Ca}}_{0.9}\mathrm{Mn}{\mathrm{O}}_{3}$ may be attributed to the competition between the FM and AFM fractions in the $G$-AFM structure. On the other hand, ${\mathrm{La}}_{0.2}{\mathrm{Ca}}_{0.8}\mathrm{Mn}{\mathrm{O}}_{3}$ is insensitive to applied pressure probably due to a robustness of orbital ordered state. Resistivity data point out that AFM ordering in ${\mathrm{La}}_{0.2}{\mathrm{Ca}}_{0.8}\mathrm{Mn}{\mathrm{O}}_{3}$ occurs at temperatures below orbital ordering.

Pressure effects on magnetic and transport properties of electron-doped La 1-x Ca x Mn O 3 (x=0.8,0.9)

The pressure effect on exchange bias (EB) and coercive fields, ${H}_{\mathrm{E}}$ and ${H}_{\mathrm{C}}$, in phase-separated ferromagnetic/antiferromagnetic (FM/AFM) CaMn${}_{1\ensuremath{-}x}$Ru${}_{x}$O${}_{3}$ manganites with 0.06 \ensuremath{\le} $x$ \ensuremath{\le} 0.15 was studied by magnetization measurements performed in the temperature range 10--200 K and under hydrostatic pressure up to 11 kbar. Both ${H}_{\mathrm{E}}$ and ${H}_{\mathrm{C}}$ exhibit intriguing dependence on Ru doping and on applied pressure. It was found that ${H}_{\mathrm{E}}$ is apparent only at $x$ 0.1 and decreases progressively with increasing doping, while ${H}_{\mathrm{C}}$ depends nonmonotonically on Ru content, reaching a maximum at around $x$ \ensuremath{\sim} 0.09. The ${H}_{\mathrm{E}}$ was found to increase strongly under applied pressure within doping range 0.06 \ensuremath{\le} $x$ \ensuremath{\le} 0.1, while ${H}_{\mathrm{C}}$ exhibits irregular behavior, namely, increases with increasing pressure for $x$ $=$ 0.15, changes nonmonotonically for $x$ $=$ 0.1, decreases for $x$ $=$ 0.08, and is almost invariable for $x$ $=$ 0.06. Complex pressure and Ru-doping effects on ${H}_{\mathrm{E}}$ and ${H}_{\mathrm{C}}$ are explained within a model involving size-variable nanoscale FM regions (droplets) embedded in an AFM matrix. The enhancement of EB with increasing pressure is attributed to the reduction in the FM droplet size, evidenced by both pressure dependence of spontaneous FM moment and ${H}_{\mathrm{E}}$ dependence upon cooling field ${H}_{\mathrm{cool}}$. The impact of FM droplet size on the EB was further evidenced by the magnetic field effect, which, in contrast to the pressure effect, leads to a growth of the FM droplets. The intricate ${H}_{\mathrm{C}}$ dependencies on both pressure and Ru content are understandable in a view of the transition from the multidomain state to the single-domain one, induced by droplet size decrease with increasing pressure or with doping lowering. Concisely, owing to the unique mechanism of valence modification, the external pressure appears to be an effective tool for controlling the EB and the coercivity in Ru-doped CaMnO${}_{3}$ perovskites.

Pressure-tuned exchange bias and coercivity in Ru-doped CaMnO 3

Structural, magnetic, and transport properties in Pr05Ca05Mn1−xNixO3 (x=0, 004, 007, 01) were investigated It is remarkable that low Ni-doping levels at Mn sites induce drastic changes in the physical properties of Pr05Ca05MnO3 due to melting of the charge ordered state and the consequent capability of Ni ions to create ferromagnetic (FM) clusters It was found that oxygen deficient samples (3−δ=284±003) exhibit resistivities higher by four to five orders than that of their stoichiometric counterparts and do not exhibit metal-insulator transition Only a stoichiometric x=004 sample with higher content of the FM phase shows metal-insulator transition at T≈80 K A change in slope in the zero field cooling magnetization curve observed for x=004 and 007 (may be slightly oxygen deficient samples) are indicative of spin-glass-like state Applied hydrostatic pressure of about 10 kbars reduces the temperature of charge ordering in x=0 sample by about 10 K indicating on pressure induced suppression of

G. Gorodetsky

Papers

Thermodynamics of Paramagnetic-Ferromagnetic Phase Transition in ${\rm La}_{0.7}{\rm Ca}_{0.3}{\rm MnO}_{3}$ Manganite: “Griffiths singularity” versus Chemical Disorder and Lattice Effects

Pressure effects on magnetic and transport properties of electron-doped La 1-x Ca x Mn O 3 (x=0.8,0.9)

Pressure-tuned exchange bias and coercivity in Ru-doped CaMnO 3

The effect of Ni doping on the magnetic and transport properties in Pr0.5Ca0.5Mn1-xNixO3 manganites

Surface acoustic wave pressure transducers and accelerometers