The magnetostructural transformation and magnetocaloric effect in Co-doped MnNiGe_1.05 alloys

Abstract

A series of MnNi1−x Co x Ge1.05 (x = 0, 0.03, 0.05, 0.07, 0.09, and 0.11) alloys were prepared by the arc-melting method. With increasing content of Co, a first-order magnetostructural transformation between the antiferromagnetic TiNiSi-type phase and the ferromagnetic Ni2In-type phase was observed. A magnetic and crystallographic phase diagram for MnNi1−x Co x Ge1.05 alloys was proposed in this paper. Owing to the abrupt and large jump of magnetization around the magnetostructural transformation, MnNi1−x Co x Ge1.05 (x = 0.07, 0.09, 0.11) alloys show large and positive magnetic entropy changes at relatively low field.

First order magneto-structural transition and magnetocaloric effect in MnNiGe0.9Ga0.1

“…and θ p ≃ 235 K for the high temperature Ni 2 In-type hex phase. Since our T t is much smaller than θ p of the Ni 2 In-type hex phase, a strong coupling between magnetic and structural transitions is in accordance with the previous predictions [1,14,19]. It is reported that the magneto-structural transition T t moves towards low temperatures linearly with increasing Ga concentration [16,21].…”

“…It undergoes a structural transition from high temperature Ni 2 In-type hexagonal with space group P 6 3 /mmc (hex) to low temperature TiNiSi-type orthorhombic with space group P nma (orth) phase at T t ∼ 470 K and the low temperature phase shows the onset of a spiral antiferromagnetic (AFM) ordering at T N ≃ 350 K [9][10][11]. The first order structural transition (T t ) can be tuned over a wide temperature range by chemical substitution either at the magnetic Mn/Ni site by Fe/Co/Cr [1,[12][13][14][15] or at the non-magnetic Ge site by Al/Ga/Sn [16][17][18]. It is predicted that when T t is reduced below the Curie temperature θ p of Ni 2 In-type hex phase [below which it is ferromagnetic (FM)], the structural transition gets coupled inductively with the FM state of Ni 2 In-type hex phase resulting in a first order MST at T t [1,14,19].…”

“…The first order structural transition (T t ) can be tuned over a wide temperature range by chemical substitution either at the magnetic Mn/Ni site by Fe/Co/Cr [1,[12][13][14][15] or at the non-magnetic Ge site by Al/Ga/Sn [16][17][18]. It is predicted that when T t is reduced below the Curie temperature θ p of Ni 2 In-type hex phase [below which it is ferromagnetic (FM)], the structural transition gets coupled inductively with the FM state of Ni 2 In-type hex phase resulting in a first order MST at T t [1,14,19]. At the MST, the transition may occurs either from low temperature orth AFM to high temperature hex FM phase [12,14,20,21] or from low temperature orth FM to high temperature hex paramagnetic (PM) phase [1,17].…”

Hydrostatic pressure tuned magneto-structural transition and occurrence of pressure induced exchange bias effect in Mn0.85Fe0.15NiGe alloy

“…and their derivatives have attracted renewed attentions for the observation of fascinating magneto-functional and physical properties such as, large magneticaloric effect (MCE), exchange bias effect (EBE), spin glass (SG) like ground state etc. [1][2][3][4][5][6][7][8][9][10][11][12] Among various members of MEAs, MnNiGe is one of the potential candidates which undergoes a first-order diffusionless structural phase transition, known as martensitic phase transition (MPT), at 470 K during cooling and orders spiral antiferromagnetically below 346 K. 1,3,4,8 Physical and chemical pressures are the two most influencing parameters that can affect the physical properties of these materials simply by modifying structural parameters like lattice volume, bond angle etc. 8,13,14 Among these two, chemical pressure approach (different doping studies) is much popular among the researchers due to easy sample preparation and measurement options.…”

The study of crystal and magnetic properties of MnNi0.85Fe0.15Ge

“…In the case of Fe-doped MnNiGe alloys, the Ni 2 In-type instead of the TiNiSi-type structure is observed at room temperature (RT), suggesting a remarkable reduction of transconformation temperature (T t ). It was reported that the Ni atoms in MnNiGe alloy are non-magnetic, leaving the moments of Mn atoms aligning in the spiral AFM ordering [6].…”