Evolution of spin correlations in SrDy2O4 in an applied magnetic field

The development of short- and long-range magnetic order induced in a frustrated zig-zag ladder compound SrDy2O4 by an applied field is studied using neutron diffraction techniques. In zero field, SrDy2O4 lacks long-range magnetic order down to temperatures as low as 60 mK, and the observed powder neutron diffraction (PND) patterns are dominated by very broad diffuse scattering peaks. Single crystal neutron diffraction reveals that the zero-field magnetic structure consists of a collection of antiferromagnetic chains running along the c axis and that there is very little correlation between the chains in the ab plane. In an applied magnetic field, the broad diffuse scattering features in PND are gradually replaced by much sharper peaks, however, the pattern remains rather complex, reflecting the highly anisotropic nature of SrDy2O4. Single crystal neutron diffraction shows that a moderate field applied along the b axis induces an up-up-down magnetic order associated with a 1/3-magnetisation plateau, in which magnetic correlation length in the ab plane is significantly increased, but it nevertheless remains finite. The resolution limited k = 0 peaks associated with a ferromagnetic arrangement appear in powder and single crystal neutron diffraction patterns in fields of 2.5 T and above.Comment: 10 pages, 11 figure

Magnetic phase diagram of the antiferromagnetic pyrochlore Gd2Ti2O7

Gd2Ti2O7 is a highly frustrated antiferromagnet on a pyrochlore lattice, where apart from the Heisenberg exchange the spins also interact via dipole-dipole forces. We report on low-temperature specific heat measurements performed on single crystals of Gd2Ti2O7 for three different directions of an applied magnetic field. The measurements reveal the strongly anisotropic behaviour of Gd2Ti2O7 in a magnetic field despite the apparent absence of a significant single-ion anisotropy for Gd3+. The H-T phase diagrams are constructed for H//111], H//[110] and H//[112]. The results indicate that further theoretical work beyond a simple mean-field model is required.Comment: 4 figure

GRAPHO-ANALYTICAL MODELING OF PROCESSES OF INTERACTION OF ELEMENTARY COMPONENTS OF A MANAGEMENT PAIR

In order to analyze and justify the choice of the recommended modes of interaction of people in organizational entities, the article covers the main possibilities of increasing the effectiveness of human interaction on the basis of interpreting a typical management pair in the form of two elementary components that can interact in the "subject-object", "subject-subject”, “object-subject” and “object-object” modes, taking into account the fact that each component is characterized by a certain level of subjectivity. At the same time, the authors take into account the fact that during the life of a person and its life cycle in an organizational formation the level of subjectivity of any person varies within the boundary of the linear continuum object - subject, and its subjectity in organizational formation is defined by no means other, as the current state of the ratio of the number of formal and informal influences of the individual as a subject to other members of the organization to the number of the same effects on it as an object from other members of the organization. Due to the fact that the life cycles of the elementary components are characterized by the presence of each of the periods of increase in subjectivity with the achievement of each peak value and the subsequent gradual loss after release or retirement, it is demonstrated that the joint and equally effective activity of the components is possible only provided that they maintain the subject-subject mode of interaction, which corresponds to the dialogue of the two parties, rather than management of or management by one side of the other. Using the superposition of graph- analytic dependencies of Dunig-Kruger and changes in subjectivity throughout life, it is proved that the basic condition for the implementation of such a managerial dialogue is the awareness of both components of the managerial pair of the fact that the concept of the subject loses meaning without the existence of the object, and therefore maintaining the process of dialogue-cooperation is possible only under the condition of equality and freedom of the participants and the inter-orientation of each of the partners as the subject, the tool for establishing partnerships is management on the basis of the dialogue communication process with the mutual recognition of each of the participants in their freedom, equality and value - subjectivity. It has been established that the priority factors determining the results of the operation of a typical management pair are not the structure and the relationship between its constituent elements, but the intellectual, moral and psychological characteristics of these elements and the awareness of the latter as partners that jointly solve the problem with the achievement of mutually established and harmonized goals.In order to analyze and justify the choice of the recommended modes of interaction of people in organizational entities, the article covers the main possibilities of increasing the effectiveness of human interaction on the basis of interpreting a typical management pair in the form of two elementary components that can interact in the "subject-object", "subject-subject”, “object-subject” and “object-object” modes, taking into account the fact that each component is characterized by a certain level of subjectivity. At the same time, the authors take into account the fact that during the life of a person and its life cycle in an organizational formation the level of subjectivity of any person varies within the boundary of the linear continuum object - subject, and its subjectity in organizational formation is defined by no means other, as the current state of the ratio of the number of formal and informal influences of the individual as a subject to other members of the organization to the number of the same effects on it as an object from other members of the organization. Due to the fact that the life cycles of the elementary components are characterized by the presence of each of the periods of increase in subjectivity with the achievement of each peak value and the subsequent gradual loss after release or retirement, it is demonstrated that the joint and equally effective activity of the components is possible only provided that they maintain the subject-subject mode of interaction, which corresponds to the dialogue of the two parties, rather than management of or management by one side of the other. Using the superposition of graph- analytic dependencies of Dunig-Kruger and changes in subjectivity throughout life, it is proved that the basic condition for the implementation of such a managerial dialogue is the awareness of both components of the managerial pair of the fact that the concept of the subject loses meaning without the existence of the object, and therefore maintaining the process of dialogue-cooperation is possible only under the condition of equality and freedom of the participants and the inter-orientation of each of the partners as the subject, the tool for establishing partnerships is management on the basis of the dialogue communication process with the mutual recognition of each of the participants in their freedom, equality and value - subjectivity. It has been established that the priority factors determining the results of the operation of a typical management pair are not the structure and the relationship between its constituent elements, but the intellectual, moral and psychological characteristics of these elements and the awareness of the latter as partners that jointly solve the problem with the achievement of mutually established and harmonized goals

Ultrasonic investigations of spin-ices Dy2_2Ti2_2O7_7 and Ho2_2Ti2_2O7_7 in and out of equilibrium

We report ultrasound studies of spin-lattice and single-ion effects in the spin-ice materials Dy$_2$Ti$_2$O$_7$ (DTO) and Ho$_2$Ti$_2$O$_7$ (HTO) across a broad field range up to 60 T, covering phase transformations, interactions with low-energy magnetic excitations, as well as single-ion effects. In particular, a sharp dip observed in the sound attenuation in DTO at the gas-liquid transition of the magnetic monopoles is explained based on an approach involving negative relaxation processes. Furthermore, quasi-periodic peaks in the acoustic properties of DTO due to non-equilibrium processes are found to be strongly affected by {\em macroscopic} thermal-coupling conditions: the thermal runaway observed in previous studies in DTO can be suppressed altogether by immersing the sample in liquid helium. Crystal-electric-field effects having higher energy scale lead to a renormalization of the sound velocity and sound attenuation at very high magnetic fields. We analyze our observations using an approach based on an analysis of exchange-striction couplings and single-ion effects

Thermodynamics of two lattice ice models in three dimensions

In a recent paper we introduced two Potts-like models in three dimensions, which share the following properties: (A) One of the ice rules is always fulfilled (in particular also at infinite temperature). (B) Both ice rules hold for groundstate configurations. This allowed for an efficient calculation of the residual entropy of ice I (ordinary ice) by means of multicanonical simulations. Here we present the thermodynamics of these models. Despite their similarities with Potts models, no sign of a disorder-order phase transition is found.Comment: 5 pages, 7 figure

Magnetisation Studies of Geometrically Frustrated Antiferromagnets SrLn2O4, with Ln = Er, Dy and Ho

We present the results of susceptibility \chi(T) and magnetisation M(H) measurements performed on single crystal samples of the rare-earth oxides SrLn2O4 (Ln = Er, Dy and Ho). The measurements reveal the presence of magnetic ordering transition in SrHo2O4 at 0.62 K and confirm that SrEr2O4 orders magnetically at 0.73 K, while in SrDy2O4 such a transition is absent down to at least 0.5 K. The observed ordering temperatures are significantly lower than the Curie-Weiss temperatures, \theta_{CW}, obtained from the high-temperature linear fits to the 1/\chi(T) curves, which implies that these materials are subject to geometric frustration. Strong anisotropy found in the \chi(T) curves for a field applied along the different crystallographic directions is also evident in the M(H) curves measured both above and below the ordering temperatures. For all three compounds the magnetisation plateaux at approximately one third of the magnetisation saturation values can be seen for certain directions of applied field, which is indicative of field-induced stabilisation of a collinear {\it two-up one-down} structure.Comment: 6 pages, 6 figure

Magnetocaloric effect in pyrochlore antiferromagnet Gd2Ti2O7

An adiabatic demagnetization process is studied in Gd2Ti2O7, a geometrically frustrated antiferromagnet on a pyrochlore lattice. In contrast to conventional paramagnetic salts, this compound can exhibit a temperature decrease by a factor of ten in the temperature range below the Curie-Weiss constant. The most efficient cooling is observed in the field interval between 120 and 60 kOe corresponding to a crossover between saturated and spin-liquid phases. This phenomenon indicates that a considerable part of the magnetic entropy survives in the strongly correlated state. According to the theoretical model, this entropy is associated with a macroscopic number of local modes remaining gapless till the saturation field. Monte Carlo simulations on a classical spin model demonstrate good agreement with the experiment. The cooling power of the process is experimentally estimated with a view to possible technical applications. The results for Gd2Ti2O7 are compared to those for Gd3Ga5O12, a well-known material for low temperature magnetic refrigeration.Comment: 6 pages, 4 figures, accepted versio