Volume 35, Issue 10, October 2009
Index of content:
- LOW-TEMPERATURE MAGNETISM
35(2009); http://dx.doi.org/10.1063/1.3253399View Description Hide Description
Experimental investigations of reversible and irreversible magnetic field induced first-order phase transitions under pressure in the sample of the system have made it possible to construct a magnetic phase diagram in which a wide (of the order of ) metastable region of first-order phase transitions between the ferromagnetic,paramagnetic, and low-temperature phases is present. It is shown that the ferromagnetic phase can be expected to appear spontaneously at pressure of the order of . At atmospheric pressure the low-temperature phase and the irreversibly induced ferromagnetic phase are metastable and vanish at temperatures 49 and , respectively. It is conjectured that the low-temperature region of the diagram and its boundary features are formed under the influence of competition between interacting order parameters, one of which is the ferromagnetic order parameter.
35(2009); http://dx.doi.org/10.1063/1.3253401View Description Hide Description
The results of investigations of the magnetic and magnetocaloric properties of alloys from the system are presented. The magnetization measurements are performed in the temperature interval in magnetic fields up to . The entropy changes with the magnetic field changing from 0 to 2, 4, 5, and are determined from the magnetization isotherms obtained near temperatures of the spontaneous appearance of the ferromagnetic state , and the curves are constructed. It is found that and decrease monotonically with increasing manganese concentration and that the ferromagnetic phase is completely suppressed in . It is found that the concentration dependences of the maximum entropy jump (and the corresponding cold-storage capacity) and the magnitudes of the ferromagnetic moment of the unit cell with maxima for and 0.8 show extremal behavior. The data obtained are compared with the ferromagnetic moments calculated from first principles by the Korringa-Kohn-Rostoker method using the coherent-potential approximation (KKR-CPA)—the discrepancy for is attributed to the appearance of an antiferromagnetic component of the magnetic structure. It is concluded that the alloys have promise for use in magnetic refrigerators operating at room temperature.
35(2009); http://dx.doi.org/10.1063/1.3253402View Description Hide Description
The Monte Carlo method is used to study long-period modulated structures in an anisotropic Ising model with competing interactions (ANNNI model). The character, particularities, and dependence of the modulated structures on the temperature and ratio of the exchange interaction constants between the nearest and next-to-nearest neighbors are determined. The phase diagram is constructed.
35(2009); http://dx.doi.org/10.1063/1.3253403View Description Hide Description
The nonlinear Schrödinger equation is used to study the propagation of small-amplitude nonlinear magnetic pulses (solitons) in an actively dissipative medium (easy-axis ferromagnet) in which an external, circularly polarized, rf magnetic field is applied in spatially localized regions. The interaction of solitons with nonlinearly excited regions of the medium which are coupled with rf pumping centers is studied in the adiabatic approximation. The change of the parameters of solitons during such an interaction is calculated and the possibility of amplification of soliton pulses is examined.