Field-induced anisotropic magnetic phase transitions and tricritical phenomena in GdCr_(6)Ge_(6)

The interaction between complex magnetic structures and non-trivial band structures in ternary rare-earth GdCr_(6)Ge_(6) induces exotic and abundant electro-magnetic phenomena.In this work,we perform a systematical investigation on critical behaviors and magnetic properties of the single-crystal GdCr_(6)Ge_(6).The temperature,field,and angle dependence of magnetization unveils strong magnetic anisotropy along the c-axis and isotropic characteristic in the ab-plane.Critical exponentsβ=0.252(1),γ=0.905(9),δ=4.606(3)for H//ab,andβ=0.281(3),γ=0.991(8),δ=4.541(5)for H//c are obtained by the modified Arrott plot method(MAP)and critical isotherm(CI)analysis.The determined exponents for both directions are consistent with the theoretical prediction of a tricritical mean-field model.Based on detailed magnetization measurements and universality scaling,comprehensive magnetic phase diagrams of GdCr6Ge6for H//ab and H//c are constructed,which reveal that the external field induces a ferromagnetic(FM)transition for H//ab while a ferrimagnetic(FIM)one for H//c.Two tricritical points are determined for H//ab(11.2 K,266.3 Oe)and H//c(11.3 K,3.3 kOe)on the phase diagrams,respectively.The field-induced anisotropic magnetic configurations and multiple phases are clarified,where the moments of Gd and Cr form FM coupling for H//ab while FIM one for H//c via the interaction between Gd and Cr sublattices.

Inflection Point as a Manifestation of Tricritical Point on the Dynamic Phase Boundary in Ising Meanfield Dynamics

We studied the dynamical phase transition in kinetic Ising ferromagnetsdriven by oscillating magnetic field in meanfield approximation. The meanfield differentialequation was solved by sixth order Runge-Kutta-Felberg method. We calculatedthe transition temperature as a function of amplitude and frequency of oscillatingfield. This was plotted against field amplitude taking frequency as a parameter.As frequency increases the phase boundary is observed to become inflated. The phaseboundary shows an inflection point which separates the nature of the transition. Onthe dynamic phase boundary a tricritical point (TCP) was found, which separates thenature (continuous/discontinuous) of the dynamic transition across the phase boundary.The inflection point is identified as the TCP and hence a simpler method of determiningthe position of TCP was found. TCP was observed to shift towards high fieldfor higher frequency. As frequency decreases the dynamic phase boundary is observeto shrink. In the zero frequency limit this boundary shows a tendency to merge to thetemperature variation of the coercive field.

Mean-Field Solution of the Mixed Spin-2 and Spin-5/2 Ising Ferrimagnetic System with Different Single-Ion Anisotropies

The mixed spin-2 and spin-5/2 Ising ferrimagnetic system with different anisotropies (DA/z|J|) for the spin-2 and (DB/z|J|) for the spin-5/2 is studied by the use of the mean-field theory based on the Bogoliubov inequality for the free energy. First, the ground state phase diagram of the system at zero temperature is obtained on the (DA/z|J|,DB/z|J|) plane. Topologically, different kinds of phase diagrams are achieved by changing the temperature and the values of the single ion anisotropies DA/z|J| and DB/z|J|. Besides second-order transition lines, first order phase transition lines terminating at tricritical points, are found. The existence and dependence of a compensation temperature on single-ion anisotropies is also investigated.

Mean-Field Solution of a Mixed Spin-3/2 and Spin-2 Ising Ferrimagnetic System with Different Single-Ion Anisotropies

The mixed spin-3/2 and spin-2 Ising ferrimagnetic system with different single-ion anisotropies in the absence of an external magnetic field is studied within the mean-field theory based on Bogoliubov inequality for the Gibbs free energy. Second-order critical lines are obtained in the temperature-anisotropy plane. Tricritical line separating second-order and first-order lines is found. Finally, the existence and dependence of a compensation points on single-ion anisotropies is also investigated for the system. As a result, this mixed-spin model exhibits one, two or three compensation temperature depending on the values of the anisotropies.

Mixed Spin-2 and Spin-3/2 Blume-Emery-Griffiths (BEG) Model on the Bethe Lattice

The mixed spin-2 and spin-3/2 Blume-Emery-Griffiths (BEG) Ising ferrimagnetic system is studied by the Bethe lattice approach. The ground-state phase diagram is constructed. The influence of the crystal-field and the biquadratic interactions among neighboring spins on the thermal behaviors of the system is singled out. The system displays very rich critical behaviors with the existence of tricritical points. Compensation points where the global magnetization of the system vanishes have been detected for appropriate values of the system parameters.

Large,low-field and reversible magnetostrictive effect in MnCoSi-based metamagnet at room temperature

TiNiSi-type MnCoSi-based alloys show large magnetostriction during the magnetic-field-induced metamagnetic transition.However,the high critical field required to drive the transition directly hinders their potential applications.In this work,we systematically investigate the tricritical behavior and magnetostrictive effect in substituted MnCoSi alloys.Replacing Si with Sb or In,Co with Fe or Cu,and Mn with Co,which can simultaneously reduce the critical field and the temperature of tricritical point,are explored.Among the substituted MnCoSi alloys,Mn_(0.983)Co_(1.017)Si displays a temperature of a tricritical point of 250 K and a room-temperature critical field of 0.60 T,which is the lowest up to now.Profited from these optimizations,a large reversible magnetostrictive effect under low field is successfully realized at room temperature.In a field of 1 T,the magnetostriction of Mn_(0.983)Co_(1.017)Si alloy is close to 1000 ppm.Besides,a strong relation between critical field and valence electron concentration is revealed in the transition-metal-substituted MnCoSi alloys.Our work greatly enhances the low-field magnetostrictive performance of MnCoSi-based alloys and make them be of interest in potential applications.