Les oxydes modeles de basse dimension, comme les composes de spins 1/2 CuGeO3, SrCu2(BO3)2 ou NaV2O5, soulevent de nombreuses questions sur la nature de l'anti-ferromagnetisme de la phase basse-temperature, desordonne par les fluctuations quantiques. Cette these porte sur la description theorique des proprietes magnetiques de ces composes, en lien avec les nombreux resultats experimentaux. En particulier, des resultats inattendus ont ete observes dans deux experiences originales : effet de rotation de la polarisation dans une experience de diffusion inelastique de neutrons et transitions optiques ``interdites''. Pour expliquer ces effets, nous avons ete amenes a considerer des interactions anisotropes entre spins comme l'interaction de Dzyaloshinski-Moriya. Nous avons etudie les effets de cette interaction dans les systemes quantiques sans ordre magnetique et explique la structure fine de l'excitation triplet observee dans SrCu2(BO3)2. L'effet de rotation de polarisation permet d'etudier les interferences entre excitations magnetiques et phonons et est intimement lie a la presence d'anisotropie. Nous avons etabli les regles de selection dans le cadre d'une theorie perturbative dans le couplage spin-phonon et compare avec les resultats experimentaux. De meme, nous avons etudie les regles de selection des transitions optiques, en examinant non seulement l'effet de l'operateur dipolaire magnetique, mais aussi celui de l'operateur dipolaire electrique en generalisant la theorie de Fleury-Loudon. L'ordre de grandeur de l'interaction de Dzyaloshinski-Moriya - statique et dynamique - a ete reconsidere pour la geométrie de ces composes sur la base de la theorie du superechange. Nous avons montre qu'elle pouvait devenir, de facon etonnante a priori, plus grande que l'echange principal.

Cette thèse traite de composés magnétiques géométriquement frustrés, cristallisant dans la structure pyrochlore, c'est-à-dire un arrangement tri-dimensionnel de tétraèdres reliés entre eux par leurs sommets. Tout d'abord, on montre que le liquide de spins Tb2Ti2O7 pose un certain nombre de difficultés quant à sa fabrication, certaines propriétés physiques mesurées étant très dépendantes des conditions de croissance. Cependant, deux températures caractéristiques, indépendantes des échantillons, à 2 et 50 K, ont pu être mises en évidence par différentes techniques expérimentales, et ce, sur différents échantillons. Ensuite, l'étude de la dynamique de spins dans Tb2Sn2O7, une glace de spins ordonnée, suggère l'existence d'un mécanisme complexe, caractérisé par plusieurs temps de fluctuations, dont l'un est de l'ordre de 10^{-10} s. Pour ces deux composés, il est montré, par des mesures microscopiques mais également macroscopiques, que les niveaux de champ cristallin de plus basse énergie sont deux singulets, séparés d'environ 2 K, et non un doublet comme généralement admis. Concernant l'étude du composé antiferromagnétique Er2Ti2O7 de symétrie XY, certaines mesures suggèrent une dynamique de spins à basse température, conséquence d'excitations. Enfin, l'analyse des résultats obtenus pour le composé antiferromagnétique Heisenberg Gd2Sn2O7 met en évidence des contradictions concernant l'existence ou non d'une dynamique de spins à basse température.

Several magnetic materials, in the first approximation, can be described by idealised theoretical models, such as classical Ising or Heisenberg spin systems, and, to some extent, such models are able to qualitatively expose many experimentally observed phenomena. But often, to account for complex behavior of magnetic matter, such models have to be refined by including more terms in Hamiltonian. The compound LiHo_xY_{1-x}F_4, by increasing concentration of nonmagnetic yttrium can be tuned from a diluted ferromagnet to a spin glass. LiHoF_4 is a good realisation of the transverse field Ising model, the simplest model exhibiting a quantum phase transition. In the pure case the magnetic behaviour of this material is well described by mean-field theory. It was believed that when diluted, LiHo_xY_{1-x}F_4 would also manifest itself as a diluted transverse field Ising model which continue to be well described by mean-field theory, and, at sufficient dilution, at zero temperature, exhibit a quantum spin-glass transition. The experimental data did not support such a scenario, and it was pointed out that, to explain physics of LiHo_xY_{1-x}F_4 in transverse magnetic field, the effect of a transverse-field-generated longitudinal random field has to be considered. We explore this idea further in local mean-field studies in which all three parameters: temperature, transverse field and concentration can be consistently surveyed, and where the transverse-field-generated longitudinal random field is explicitly present in the effective spin-1/2 Hamiltonian. We suggest other materials that are possible candidates for studying quantum criticality in the transverse field Ising model, and in the diluted case, for studying the effects of transverse and longitudinal random fields. The compounds we consider are RE(OH)_3, where RE are the rare earth ions Tb^{3+}, Dy^{3+} and Ho^{3+}. Using mean-field theory, we estimate the values of the transverse magnetic field that, at zero temperature, destroy ferromagnetic order to be B_x^c=4.35 T, B_x^c=5.03 T and B_x^c=54.81 T for Ho(OH)_3, Dy(OH)_3 and Tb(OH)_3, respectively. We confirm that Ho(OH)_3 and Tb(OH)_3, similarly to LiHoF_4, can be described by an effective spin-1/2 Hamiltonian. In the case of Dy(OH)_3 there is a possibility of a first order phase transition at transverse field close to B_x^c, and Dy(OH)_3 cannot be described by a spin-1/2 effective Hamiltonian. While diluted dipolar Ising spin glass has been studied experimentally in LiHo_xY_{1-x}F_4 and in numerical simulations, there are no studies of the Heisenberg case. Example materials that are likely candidates to be realisations of the diluted dipolar Heisenberg spin glass are (Gd_xY_{1-x})_2Ti_2O_7, (Gd_xY_{1-x})_2Sn_2O_7 and (Gd_xY_{1-x})_3Ga_5O_{12}. To stimulate interest in experimental studies of these systems we present results of Monte of Carlo simulations of the diluted dipolar Heisenberg spin glass. By performing finite-size scaling analysis of the spin-glass correlation length and the spin-glass susceptibility, we provide a compelling evidence of a thermodynamical spin-glass transition in the model. Frustrated pyrochlore magnets, depending on the character of single ion anisotropy and interplay of different types of interaction over a broad range of energy scales, exhibit a large spectrum of exotic phases and novel phenomena. The pyrochlore antiferromagnet Er_2Ti_2O_7 is characterised by a strong planar anisotropy. Experimental studies reveal that Er_2Ti_2O_7 undergoes a continuous phase transition to a long-range ordered phase with a spin configuration that, in this thesis, is referred to as the Champion-Holdsworth state. Such results are not in agreement with the theoretical prediction that the ground state of the pyrochlore easy-plane antiferromagnet with dipolar interactions complementing the nearest neighbour exchange interactions, is not the Champion-Holdsworth state but the so-called Palmer-Chalker state. On the other hand, Monte Carlo simulations of the easy-plane pyrochlore antiferromagnet indicate a thermal order-by-disorder selection of the Champion-Holdsworth state. To answer the question of whether order-by-disorder selection can be the mechanism at play in Er_2Ti_2O_7, we performed Monte Carlo simulations of the easy-plane pyrochlore antiferromagnet with weak dipolar interactions. We estimate the range strengths of the dipolar interaction such that order-by-disorder selection of the Champion-Holdsworth state is not suppressed. The estimated value of the allowed strength of the dipolar interactions indicates that the model studied is likely insufficient to explain the physics of Er_2Ti_2O_7 and other types of interactions or quantum effects should be considered.

Several magnetic materials, in the first approximation, can be described by idealised theoretical models, such as classical Ising or Heisenberg spin systems, and, to some extent, such models are able to qualitatively expose many experimentally observed phenomena. But often, to account for complex behavior of magnetic matter, such models have to be refined by including more terms in Hamiltonian. The compound LiHo_xY_{1-x}F_4, by increasing concentration of nonmagnetic yttrium can be tuned from a diluted ferromagnet to a spin glass. LiHoF_4 is a good realisation of the transverse field Ising model, the simplest model exhibiting a quantum phase transition. In the pure case the magnetic behaviour of this material is well described by mean-field theory. It was believed that when diluted, LiHo_xY_{1-x}F_4 would also manifest itself as a diluted transverse field Ising model which continue to be well described by mean-field theory, and, at sufficient dilution, at zero temperature, exhibit a quantum spin-glass transition. The experimental data did not support such a scenario, and it was pointed out that, to explain physics of LiHo_xY_{1-x}F_4 in transverse magnetic field, the effect of a transverse-field-generated longitudinal random field has to be considered. We explore this idea further in local mean-field studies in which all three parameters: temperature, transverse field and concentration can be consistently surveyed, and where the transverse-field-generated longitudinal random field is explicitly present in the effective spin-1/2 Hamiltonian. We suggest other materials that are possible candidates for studying quantum criticality in the transverse field Ising model, and in the diluted case, for studying the effects of transverse and longitudinal random fields. The compounds we consider are RE(OH)_3, where RE are the rare earth ions Tb^{3+}, Dy^{3+} and Ho^{3+}. Using mean-field theory, we estimate the values of the transverse magnetic field that, at zero temperature, destroy ferromagnetic order to be B_x^c=4.35 T, B_x^c=5.03 T and B_x^c=54.81 T for Ho(OH)_3, Dy(OH)_3 and Tb(OH)_3, respectively. We confirm that Ho(OH)_3 and Tb(OH)_3, similarly to LiHoF_4, can be described by an effective spin-1/2 Hamiltonian. In the case of Dy(OH)_3 there is a possibility of a first order phase transition at transverse field close to B_x^c, and Dy(OH)_3 cannot be described by a spin-1/2 effective Hamiltonian. While diluted dipolar Ising spin glass has been studied experimentally in LiHo_xY_{1-x}F_4 and in numerical simulations, there are no studies of the Heisenberg case. Example materials that are likely candidates to be realisations of the diluted dipolar Heisenberg spin glass are (Gd_xY_{1-x})_2Ti_2O_7, (Gd_xY_{1-x})_2Sn_2O_7 and (Gd_xY_{1-x})_3Ga_5O_{12}. To stimulate interest in experimental studies of these systems we present results of Monte of Carlo simulations of the diluted dipolar Heisenberg spin glass. By performing finite-size scaling analysis of the spin-glass correlation length and the spin-glass susceptibility, we provide a compelling evidence of a thermodynamical spin-glass transition in the model. Frustrated pyrochlore magnets, depending on the character of single ion anisotropy and interplay of different types of interaction over a broad range of energy scales, exhibit a large spectrum of exotic phases and novel phenomena. The pyrochlore antiferromagnet Er_2Ti_2O_7 is characterised by a strong planar anisotropy. Experimental studies reveal that Er_2Ti_2O_7 undergoes a continuous phase transition to a long-range ordered phase with a spin configuration that, in this thesis, is referred to as the Champion-Holdsworth state. Such results are not in agreement with the theoretical prediction that the ground state of the pyrochlore easy-plane antiferromagnet with dipolar interactions complementing the nearest neighbour exchange interactions, is not the Champion-Holdsworth state but the so-called Palmer-Chalker state. On the other hand, Monte Carlo simulations of the easy-plane pyrochlore antiferromagnet indicate a thermal order-by-disorder selection of the Champion-Holdsworth state. To answer the question of whether order-by-disorder selection can be the mechanism at play in Er_2Ti_2O_7, we performed Monte Carlo simulations of the easy-plane pyrochlore antiferromagnet with weak dipolar interactions. We estimate the range strengths of the dipolar interaction such that order-by-disorder selection of the Champion-Holdsworth state is not suppressed. The estimated value of the allowed strength of the dipolar interactions indicates that the model studied is likely insufficient to explain the physics of Er_2Ti_2O_7 and other types of interactions or quantum effects should be considered.

This thesis will present research that studies the role of disorder, geometric frustration and the long range dipolar interaction on the collective behaviour of several insulating, rare earth magnets. Experiments were performed at low temperatures to measure the specific heat and magnetic susceptibility of several materials. Susceptibility was measured with a SQUID magnetometer that has been designed and constructed primarily for the study of slow dynamics in glassy systems. Specifically, this thesis will discuss three distinct topics. The first is the series of materials LiHo(x)Y(1-x)F(4), which are manifestations of the dilute, dipolar coupled Ising model. The low-x portion of the phase diagram has become a rather contentious issue in recent years with both theoretical and experimental groups disagreeing on the existence of a spin glass freezing transition and one experimental group arguing for the existence of an exotic "antiglass'' or spin liquid state resulting from quantum entanglement at x=0.045. We present specific heat and dynamical susceptibility measurements on four stoichiometries in this series: x = 0.018, 0.045, 0.080 and 0.012. No evidence of an unusual antiglass state is observed. Instead, our results show evidence, at all dilution levels studied, of a spin glass freezing transition. Interpretation of experimental data is found to be complicated by the anomalously slow dynamics in these materials. The relaxation time scales are found to increase as the concentration of Ho(3+) ions is reduced, an effect which can be attributed to single-ion physics and the importance of the nuclear hyperfine coupling in this system. A second set of materials studied here is a series of several Gd garnet materials, the most famous of which is Gd(3)Ga(5)O(12) (GGG), a material previously argued to be a disorder-free spin glass. Our specific heat experiments reproduce previous experiments on GGG and show that the homologous Gd garnets Gd(3)Te(2)Li(3)O(12) and Ga(3)Al(5)O(12) do not share the same glassy physics but exhibit sharp ordering features. By experimenting with the introduction of random site dilution, it is concluded that a 1-2% off-stoichiometry inherent in GGG is likely a special kind of disorder that is particularly effective in inducing random frustration and the formation of a spin glass. Finally, specific heat measurements on the pyrochlore antiferromagnet Gd(2)Sn(2)O(7) (GSO) are presented. While GSO has generally been found to be a well behaved and well understood model magnet, with long range order developing at around 1 K, like many other geometrically frustrated magnets, it has been discovered to possess persistent spin dynamics down to very low temperatures as measured by μSR and Mössbauer spectroscopy. Measurement of the low temperature limit of the specific heat when compared with linear spin-wave theory, however, presents a consistent picture of gapped magnon excitations that freeze out at low temperatures and make the existence of the proposed dynamic ground state unlikely.

Spin systems with low dimensionality and geometrical frustration have attracted interest because of the possible emergence of novel magnetic phases at low temperatures by suppressing conventional magnetic order, and allow for a novel spin-disordered ground state, such as quantum spin liquid and glass without any apparent structural disorder. In this thesis, we have discussed magnetic and dielectric measurements on the quasi-two-dimensional triangular antiferromagnet NiGa2S3.85, in order to investigate its magnetic state and dielectric property at low temperatures. In the measurement of susceptibility In the measurement of susceptibility £q(T), we found that the freezing temperature is near 6 K. This suggests that the sample with the sulfur deficiency should be close to the stoichiometric NiGa2S3.85. Under 7 T magnetic filed ZFC(zero-field-cooling) and FC(field-cooling) still bifurcate indicating more magnetic order state than spin-liquid. Temperature-dependent dielectric measurement shows an interesting colossal enhancement of dielectric constant with frequency dispersion and is ascribed to the interfacial polarization (termed as Maxwell-Wagner relaxation) at the interface between adjacent layers. Temperature-dependent dielectric measurement under applied magnetic field (up to 9 T) shows negligible magnetodielectric behavior because of the sample is not magneto resistive.

The majority of research tends to focus on the effects of violent video games, and as a result the motivations to play games are understudied. This study used the uses and gratifications theory as a framework for investigating game player’s motivation to play video games for the purpose of catharsis. This study also proposed that in-game variables, such as level of difficulty and content of the video game, all be investigated to see the effects they have on the achievement of catharsis or the development of aggression through other mediating variables such as enjoyment, control, and frustration with the game. It was found that difficulty of the game predicted frustration with the game and that those with more game playing experience reported greater feelings of catharsis, enjoyment, and feelings of control. None of the independent variables were found to attribute to feelings of aggression, including game content. Feelings of control within the game were found to be predicted by game type. Although there were relatively few main effects with the independent variables, correlations show trends in the data between variables that would support the achievement of catharsis through greater feelings of control, enjoyment, and decreased frustration.

This thesis will present research that studies the role of disorder, geometric frustration and the long range dipolar interaction on the collective behaviour of several insulating, rare earth magnets. Experiments were performed at low temperatures to measure the specific heat and magnetic susceptibility of several materials. Susceptibility was measured with a SQUID magnetometer that has been designed and constructed primarily for the study of slow dynamics in glassy systems. Specifically, this thesis will discuss three distinct topics. The first is the series of materials LiHo(x)Y(1-x)F(4), which are manifestations of the dilute, dipolar coupled Ising model. The low-x portion of the phase diagram has become a rather contentious issue in recent years with both theoretical and experimental groups disagreeing on the existence of a spin glass freezing transition and one experimental group arguing for the existence of an exotic "antiglass'' or spin liquid state resulting from quantum entanglement at x=0.045. We present specific heat and dynamical susceptibility measurements on four stoichiometries in this series: x = 0.018, 0.045, 0.080 and 0.012. No evidence of an unusual antiglass state is observed. Instead, our results show evidence, at all dilution levels studied, of a spin glass freezing transition. Interpretation of experimental data is found to be complicated by the anomalously slow dynamics in these materials. The relaxation time scales are found to increase as the concentration of Ho(3+) ions is reduced, an effect which can be attributed to single-ion physics and the importance of the nuclear hyperfine coupling in this system. A second set of materials studied here is a series of several Gd garnet materials, the most famous of which is Gd(3)Ga(5)O(12) (GGG), a material previously argued to be a disorder-free spin glass. Our specific heat experiments reproduce previous experiments on GGG and show that the homologous Gd garnets Gd(3)Te(2)Li(3)O(12) and Ga(3)Al(5)O(12) do not share the same glassy physics but exhibit sharp ordering features. By experimenting with the introduction of random site dilution, it is concluded that a 1-2% off-stoichiometry inherent in GGG is likely a special kind of disorder that is particularly effective in inducing random frustration and the formation of a spin glass. Finally, specific heat measurements on the pyrochlore antiferromagnet Gd(2)Sn(2)O(7) (GSO) are presented. While GSO has generally been found to be a well behaved and well understood model magnet, with long range order developing at around 1 K, like many other geometrically frustrated magnets, it has been discovered to possess persistent spin dynamics down to very low temperatures as measured by μSR and Mössbauer spectroscopy. Measurement of the low temperature limit of the specific heat when compared with linear spin-wave theory, however, presents a consistent picture of gapped magnon excitations that freeze out at low temperatures and make the existence of the proposed dynamic ground state unlikely.

Darbo objektas: stresas, socialinė frustracija, emocinis išsekimas, emocinis atsparumas mokytojų darbe. Tyrimo problema. Daugelis mokslinių tyrinėjimų patikimai identifikuoja specifinius mokymo proceso stresorius ir jų neigiamą poveikį mokytojų sveikatai bei gerovei. Mokytojo darbe svarbu tai, kad dėl socialinės frustracijos keičiasi psichinį stresą išgyvenančio žmogaus elgesys, atsiranda nesąmoningos reakcijos į stresorių (nesąmoningi psichologinės gynybos mechanizmai, dirbtini autoriteto palaikymo būdai ar streso „kaukės“). Mokslinių tyrimų apžvalga leid��ia teigti, kad sąmoningi streso įveikimo būdai turi būti siejami su patiriamo streso atpažinimu – tai leidžia kontroliuoti stresinių įvykių poveikį ir ugdyti atsparumą stresui. Atsparumą stresui darbe didina žmogaus pasitenkinimas darbu, taip pat pakankamas savigarbos lygis. Mokslinėje literatūroje nėra pateikiama kompleksinių tyrimų, susijusių su stresu mokytojų darbe. Šio tyrimo pagalba buvo siekiama mokytojų patiriamo streso lygį analizuoti sąryšyje su socialine frustracija, emociniu išsekimu, taip pat įvertinti tiriamųjų emocinio atsparumo lygį. Tyrimo tikslas - ištirti ir įvertinti Kauno ir Punsko gimnazijose dirbančių mokytojų patiriama stresą, socialinę frustraciją, emocinį išsekimą bei emocinį atsparumą. Tyrimo uždaviniai: 1. Įvertinti Kauno ir Punsko gimnazijose dirbančių mokytojų patiriamo streso lygį, socialinę frustraciją, emocinį išsekimą bei emocinį atsparumą. 2. Palyginti Kauno ir Punsko mokytojų patiriamo... [toliau žr. visą tekstą] / Work’s subject: stress, social frustration, emotional exhaustion, emotional hardiness in teachers’ work. So far there is no nonfiction literature which would present complex research concerning stress at teachers work. Numerous researches helped to explore only the level of stress but not stress itself. While doing this research I was trying to explain what are the reasons of experienced stress levels and what kind of consequences cause it. A lot of scientific researches credibly identify specific teaching process of stressor and there’s negative affection on teachers health and welfare. Psychical process of stress develops syndrome of emotional exhaustion theory. In teachers’ work important is that emotional frustration changes psychical stress at affected person and unmeant reaction to stressor. Deliberate options of overcoming stress concerns with identification of it, which let us to control stressful events effect and training hardiness of stress. On the way of changing people’s behavior reaction to stress in interpersonal relations it is important to form their self-respect. Hardiness of stress at work higher person’s pleasure of his/her job. Purpose of the research – to examine and evaluate teachers of Kaunas and Punskas gymnasiums affected by stress, emotional exhaustion, social frustration and emotional hardiness. 1. Evaluation of teachers working in Kaunas and Punskas gymnasiums affected by different levels of stress, emotional exhaustion, social frustration and... [to full text]

I barnmorskans kompetensområde ingår att främja tidig amningsstart och ge amningsstöd under barnets första vakenhetsperiod strax efter födelsen. Det finns evidens för att tidig amningsstart leder till helamning under en längre tidsperiod. Det är därför viktigt att den första amningen sker inom 120 minuter efter barnets födelse. Förlossningsbarnmorskans stöd i samband med den första amningen har stor betydelse för att detta ska möjliggöras. I föreliggande studie beskrivs en rad faktorer som både stör och främjar den tidiga amningsstarten. Barnmorskor har enligt sin kompetensbeskrivning samt direktiv från WHO och UNICEF ett tydligt ansvar att främja amning inom denna tidsram. Syftet med denna studie är att beskriva förlossningsbarnmorskans stödjande roll i samband med amning inom 120 minuter efter födelsen och identifiera de faktorer som upplevs påverka stödet. Sammanlagt 81 förlossningsbarnmorskor har deltagit i denna enkätstudie som analyserades med en kombinerad kvalitativ och kvantitativ metod. I resultatet framkom att förlossningsbarnmorskor prioriterar ett närvarande och informativt amningsstöd. De involverar partnern och eftersträvar att genom närvaro och dialog vara ett stödjande och stärkande stöd. Stort fokus läggs på främjandet av barnets naturliga amningsbeteende. Barnmorskorna uppmuntrar föräldrarna att vara närvarande och observanta på barnets signaler. Så långt det går undviks störande vårdrutiner och ett handgripligt amningsstöd.  Det mest framträdande i resultatet är att den pressade arbetssituationen inom förlossningsvården tvingar barnmorskor att välja mellan ett handgripligt amningsstöd eller ett uteblivet stöd. Denna resursbrist och stressiga arbetsmiljö leder i sin tur till uppgivenhet hos barnmorskor. Resultaten i denna studie föranleder diskussion kring resursbristens negativa effekter på amning ur ett långtidsperspektiv. Effekterna av en senarelagd amningsstart, ett uteblivet amningsstöd och negativ första amningsupplevelse är troligen en sjunkande amningsfrekvens. Teoretiskt sett är den rådande resursbristen inom svensk förlossningsvård ett direkt hot mot folkhälsan då en eventuell sjunkande amningsfrekvens skulle bidra till en fortsatt ökning av olika metabola sjukdomar, hjärt-kärlsjukdomar och cancer.