Influence of Cr doping on magnetocaloric effect and physical properties of slowly cooled NiMn^sub 1-x^Cr^sub x^Ge

Slowly cooled NiMn1-xCrxGe (x = 0.04, 0.11, 0.18 and 0.25) has been studied by X-ray (90-480 K) and neutron diffraction (1.6-400 K), differential scanning calorimetry (300-480 K) and magnetic (2.0-400 K, magnetic field up to 90 kOe) measurements. The compounds undergo a martensitic phase transition...

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Bibliographic Details
Published in:Journal of alloys and compounds 2017-12, Vol.726, p.978
Main Authors: Szytula, A, Baran, S, Jaworska-Golab, T, Marzec, M, Deptuch, A, Tyvanchuk, Yu, Penc, B, Hoser, A, Sivachenko, A, Val'kov, V, Dyakonov, V, Szymczak, H
Format: Article
Language:English
Subjects:
Antiferromagnetism
Cooling
Crystal structure
Ferromagnetism
Magnetic properties
Magnetism
Maximum entropy
Neutron diffraction
Phase transitions
Physical properties
Semiconductor doping
Transition temperature
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Summary:Slowly cooled NiMn1-xCrxGe (x = 0.04, 0.11, 0.18 and 0.25) has been studied by X-ray (90-480 K) and neutron diffraction (1.6-400 K), differential scanning calorimetry (300-480 K) and magnetic (2.0-400 K, magnetic field up to 90 kOe) measurements. The compounds undergo a martensitic phase transition changing their crystal structure between the orthorhombic low temperature phase (space group Pnma) and the hexagonal high temperature one (space group P63/mmc). The temperature of the structural phase transition significantly decreases with increasing x (TS = 464 K for x = 0.04 and 373 K for 0.25 on heating and similarly TS = 445 K for x = 0.04 and 355 K for 0.25 on cooling). Antiferromagnetic helicoidal ordering with the propagation vector k = (kx, 0, 0) for x = 0.04 and 0.11 (TN = 357 and 353 K, respectively) and ferromagnetic one for x = 0.25 (TC = 360 K) has been found. The sample with x = 0.18 shows a coexistence of a helicoidal antiferromagnetic structure and the ferromagnetic one below ~170 K while at higher temperatures the ferromagnetic ordering remains stable up to 362 K. For all investigated samples the magnetocaloric effect is observed. Maximum entropy change (-ΔS) increases with increasing Cr concentration from about 8 J/(kg K) at 90 kOe, found for x = 0.04 and 0.11 at the Néel temperature, up to 29 J/(kg K) observed for x = 0.25 in cooling regime at the magnetostructural phase transition temperature.
ISSN:0925-8388
1873-4669