Based on the experimental characteristics of the iso-field heat capacity changing withtemperature for the room-temperature magnetic refrigeration materials Gd, Gdo.74Tb0.26, and(Gd3.5Tb1.5)Si4, the corresponding entropy versus temperature curves are calculated andpresented, the regenerative magnetic Brayton refrigeration cycles, using these magneticmaterials as the working substances, are established.The nonperfect regenerative heatquantity, net cooling quantity, released heat quantity, coefficient of performance (COP) andother performance parameters of these magnetic Brayton refrigeration cycles are analyzedand calculated.Furthermore, the performance characteristics of the Brayton refrigerationcycles employing Gd, Gd0.74Tb0.26, and (Gd3.5Tb1.5)Si4 as the working substance are evaluatedand compared, the influence of nonperfect regenerative heat on the performancecharacteristics of these magnetic Brayton refrigeration cycles is revealed.　　 The cycle model of an irreversible regenerative magnetic Brayton refrigerator usingGd0.74Tb0.26 as the working substance is established.Based on the experimentalcharacteristics of iso-field heat capacities of the material Gd0.74Tb0.26 at 0T and 2T, thecorresponding iso-field entropies are calculated and the thermodynamic performance of anirreversible regenerative magnetic Brayton refrigeration cycle is investigated.The effects ofthe irreversibilities in the two adiabatic processes and non-perfect regenerative process of themagnetic Brayton refrigeration cycle on the cooling quantity, the heat quantity released to thehot reservoir, the net cooling quantity and the coefficient of performance are discussed indetail.Some significant results are obtained.　　 Based on Mean Field Theory (MFT), the entropy of magnetic material Gadolinium(Gd), which is a function of the local magnetic field and temperature, is calculated andanalyzed.This local magnetic field is the sum of the applied field H0 plus the exchange fieldHw =λM and the demagnetizing field Hd =-NM, where the demagnetizing factor N dependson the shape of magnetic materials.Hereby, the impacts of the demagnetizing factor N on themagnetic entropy, magnetic entropy change and main thermodynamics performance of aregenerative magnetic Brayton refrigeration cycle using Gd as the working substance areinvestigated and evaluated in detail.The results obtained underline the importance of theshape of the working substance used in magnetic refrigerators for room-temperatureapplication; elongated materials provide better thermodynamics performance such as higherCOP and net heat absorption.It is pointed out that for low external fields, the magneticrefrigerator ceased to be functional if flat materials were used.　　 Thermodynamic performance analysis for a magnetic composite material in aregeneration Ericsson refrigeration cycle is then presented.The regeneration heats in the tworegenerative processes of the Ericsson refrigeration cycle are usually non-perfect and thisnon-perfect regenerative quantity is calculated and analyzed.Furthermore, from theexperimental data of iso-field heat capacities of Gd, Gd0.74Tb0.26, and (Gd3.sTbl.5)Si4,thermodynamic performance of the corresponding composite material, based on thesematerials, in a regeneration Ericsson refrigeration cycle is evaluated and analyzed.Due to thenon-perfect regeneration, the composite cooling quantity and coefficient of performance ofthe Ericsson refrigeration cycle decrease, but they are still larger than those of each of itscompounds.The calculation method of the magnetic composite presented here can be used asa new basis for creating a new magnetic composite with better regeneration processes in theEricsson refrigeration cycle.　　 A method to obtain the iso-field heat capacity and/or entropy, from experimental isothermal change of entropy and adiabatic temperature change curves, is then obtaiened.Thiscalculation is performed in two steps and then combined to extract the expected data.Thefirst step is the iso-field heat capacities direct calculation while the second step consists in thedirect iso-field entropies calculation.Both of these two steps are then analyzed to avoid theirrespective errors and to keep their respective advantages.The combination shows aremarkable agreement with experimental curves.　　 Based on the experimental isothermal entropy change of the magnetic materialsGdxDy1-x, the thermodynamic performance of a regeneration Ericsson refrigeration cycle isevaluated and analyzed.The effects of non-perfect regeneration on the cyclic performanceare highlighted.For a room temperature hot reservoir, the cooling quantity, non-perfectregeneration heat quantity, and net cooling quantity of the established regeneration Ericssonrefrigeration cycle are calculated as function of the cold reservoir temperature.Furthermore,for several typical compositions x of the GdxDy1-x alloys, the values of the cooling quantity,non-perfect regeneration heat quantity, work input, net cooling quantity, and coefficient ofperformance (COP) are listed for given temperatures of the cold reservoir.The cyclicperformance of the GdxDy1-x alloys with different composition x is compared and somesignificant analyses are provided.　　 The magnetic field effect on the thermodynamics properties of a Magneto CaloricMaterial used as the working substance within regeneration magnetic refrigeration Braytonand Ericsson cycles.Based on the experimental iso-field heat capacities of Gd at variousmagnetic fields, the complete description of the field effect on thermodynamics propertiessuch as the entropy change, cooling heat quantity, regenerative losses and the net coolingquantity is provided.This analysis revealed possibility to reduce the regenerative losses andto improve the net cooling quantity for a given field change by selecting the best initial andfinal field values.The coefficient of performance is then also positively affected.Thesecalculations of thermodynamics properties are then applied to a second Magnetic material,namely Gd0.87Dy0.13.