Effects of pre-deformation on the martensitic transformation and magnetocaloric property in Ni-Mn-Co-Sn ribbons

This paper investigates the martensitic transformation and magnetocaloric effect in pre-deformed Ni-Mn-Co Sn ribbons. The experimental results show that the reverse martensitic transformation temperature TM increases with the increasing pre-pressure, suggesting that pre-deformation is another effective way to adjust TM in ferromagnetic shape memory alloys. Large magnetic entropy changes and refrigerant capacities are obtained in these ribbons as well. It also discusses the origin of the enhanced martensitic transformation temperature and magnetocaloric property in pre-deformed Ni-Mn Co-Sn ribbons.

Effects of the Mn/Co ratio on the magnetic transition and magnetocaloric properties of Mn_(1+x)Co_(1-x)Ge alloys

We have investigated the magnetic transition and magnetocaloric effects of Mn1＋xCo1-xGe alloys by tuning the ratio of Mn/Co. With increasing Mn content, a series of first-order magnetostructural transitions from ferromagnetic to paramagnetic states with large changes of magnetization are observed at room temperature. Further increasing the content of Mn （x = 0.11） gives rise to a single second-order magnetic transition. Interestingly, large low-field magnetic entropy changes with almost zero magnetic hysteresis are observed in these alloys. The effects of Mn/Co ratio on magnetic transition and magnetocaloric effects are discussed in this paper.

The magnetic properties and magnetocaloric effects in binary R-T(R = Pr,Gd,Tb,Dy,Ho,Er,Tm;T = Ga,Ni,Co,Cu)intermetallic compounds

In this paper, we review the magnetic properties and magnetocaloric effects（MCE） of binary R–T（R = Pr, Gd, Tb,Dy, Ho, Er, Tm; T = Ga, Ni, Co, Cu） intermetallic compounds（including RGa series, RNi series, R_（12）Co_7 series, R_3 Co series and RCu_2series）, which have been investigated in detail in the past several years. The R–T compounds are studied by means of magnetic measurements, heat capacity measurements, magnetoresistance measurements and neutron powder diffraction measurements. The R–T compounds show complex magnetic transitions and interesting magnetic properties.The types of magnetic transitions are investigated and confirmed in detail by multiple approaches. Especially, most of the R–T compounds undergo more than one magnetic transition, which has significant impact on the magnetocaloric effect of R–T compounds. The MCE of R–T compounds are calculated by different ways and the special shapes of MCE peaks for different compounds are investigated and discussed in detail. To improve the MCE performance of R–T compounds,atoms with large spin（S） and atoms with large total angular momentum（J） are introduced to substitute the related rare earth atoms. With the atom substitution, the maximum of magnetic entropy change（？SM）, refrigerant temperature width（Twidth）or refrigerant capacity（RC） is enlarged for some R–T compounds. In the low temperature range, binary R–T（R = Pr, Gd,Tb, Dy, Ho, Er, Tm; T = Ga, Ni, Co, Cu） intermetallic compounds（including RGa series, RNi series,R_（12）Co_7 series, R_3 Co series and RCu_2series） show excellent performance of MCE, indicating the potential application for gas liquefaction in the future.

Effects of solidification rate and excessive Fe on phase formation and magnetoclaoric properties of LaFe_(11.6x)Si_(1.4)

The effects of solidification rate and excessive Fe on phase formation and magnetocaloric properties of LaFe11.6xSi1.4(x=1.1,1.2)were investigated by XRD,SEM and VSM measurements.The XRD results show that the amount of LaFeSi phase in the as-cast melt-spun ribbons prepared by a copper wheel at a speed of10m/s is less than that in the as-cast arc melting buttons with the same x values.The annealed melt-spun ribbons contain smaller amount of La(Fe,Si)13(1:13)phase than the corresponding annealed arc melting buttons.Although the melt-spun sample has finer crystalline grains ofα-Fe,as indicated by SEM analysis,its crystalline size has not reached nano-scale.Therefore,the magnetic exchange-coupling between1:13phase andα-Fe phase has not been observed in melt-spun ribbons.Further,the maximum negative magnetic entropy change(?SMax)and relative cooling power(RCP)of annealed melt-spun ribbons under a field change of0?2T are weaker than those of the corresponding annealed arc melting buttons.

Magnetic Properties of Hf0.8Ta0.2（Fe0.97A0.03）2 （A=Al, Co, Mn） Systems

Moessbauer studies on the effect of substitution with 3% Al, Co, Mn atoms in the intermetallic compound of Hf0.8Ta0.2Fe2 are reported. The Al substitution leads to increase of the FM-AFM transition temperature and to decrease of the AFM-PM transition temperature. The Co substitution leads to disappearance of the FM state, only showing some FM impurity component, while Mn substituted compound indicates coexistence of FM and AFM states at low temperature. The phenomena imply complex itinerant electron properties in these magnetic systems.

A Review on the Regulation of Magnetic Transitions and the Related Magnetocaloric Properties in Ni-Mn-Co-Sn Alloys

In Ni-Mn-X（X=In,Sn,Sb） ferromagnetic shape memory alloys,a ferromagnetic transition from paramagnetic to ferromagnetic austenite and a martensitic transformation from ferromagnetic austenite to weak magnetic martensite occur in some particular composition ranges,in which abundant physical properties have been observed by the abrupt change of magnetization and resistivity around their transition temperatures in these alloys.Therefore,tuning the martensitic transformation temperature（TM） and enlarging the workingtemperature interval for Ni-Mn-X（X=In,Sn,Sb） alloys,are of great importance.In the present paper,we will focus on the effect of external factors,including pre-deformation,annealing,and high pressure annealing,on the magnetic transitions and the related magnetocaloric properties in Ni-Mn-Co-Sn ferromagnetic shape memory alloys.Our approaches and the main results in this particular field will be reviewed.