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Tuning structural instability toward enhanced magnetocaloric effect around room temperature in MnCo(1-x)Zn(x)Ge.

Choudhury D, Suzuki T, Tokura Y, Taguchi Y - Sci Rep (2014)

Bottom Line: This effect can be applied to environmentally-benign magnetic refrigeration technology.Fine tuning of x around x = 0.03 leads to the concomitant structural and ferromagnetic transition in a cooling process, giving rise to enhanced magnetocaloric effect as well as magnetic-field-induced structural transition.Analyses of the structural phase diagrams in the T-H plane in terms of Landau free-energy phenomenology accounts for the characteristic x-dependence of the observed magnetocaloric effect, pointing to the importance of the magnetostructural coupling for the design of high-performance magnetocalorics.

View Article: PubMed Central - PubMed

Affiliation: RIKEN Center for Emergent Matter Science (CEMS), Wako 351-0198, Japan.

ABSTRACT
Magnetocaloric effect is the phenomenon that temperature change of a magnetic material is induced by application of a magnetic field. This effect can be applied to environmentally-benign magnetic refrigeration technology. Here we show a key role of magnetic-field-induced structural instability in enhancing the magnetocaloric effect for MnCo(1-x)Zn(x)Ge alloys (x = 0-0.05). The increase in x rapidly reduces the martensitic transition temperature while keeping the ferromagnetic transition around room temperature. Fine tuning of x around x = 0.03 leads to the concomitant structural and ferromagnetic transition in a cooling process, giving rise to enhanced magnetocaloric effect as well as magnetic-field-induced structural transition. Analyses of the structural phase diagrams in the T-H plane in terms of Landau free-energy phenomenology accounts for the characteristic x-dependence of the observed magnetocaloric effect, pointing to the importance of the magnetostructural coupling for the design of high-performance magnetocalorics.

No MeSH data available.


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Magnetization and magnetocaloric effect.Temperature dependence of (a) magnetization at H = 1 T and (b) magnetocaloric effect (-ΔS) for a field change from 0 T to 5 T for selected samples of MnCo1−xZnxGe. Also shown for x = 0.04 in (a) are temperature dependence of normalized intensity IH/(IO + IH) ≡ IH[110]/(IO[211] + IH[110]), where IH[110] and IO[211] are the intensities of [110] and [211] X-ray diffraction peaks of hexagonal and orthorhombic phases, respectively, measured in a heating run (closed triangle) and in a cooling run (open circle) under zero magnetic field. The black, green and brown arrows indicate the magnetic transition (TC) in cooling process, structural transitions in cooling (TSc) and heating (TSh) processes, respectively.
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f2: Magnetization and magnetocaloric effect.Temperature dependence of (a) magnetization at H = 1 T and (b) magnetocaloric effect (-ΔS) for a field change from 0 T to 5 T for selected samples of MnCo1−xZnxGe. Also shown for x = 0.04 in (a) are temperature dependence of normalized intensity IH/(IO + IH) ≡ IH[110]/(IO[211] + IH[110]), where IH[110] and IO[211] are the intensities of [110] and [211] X-ray diffraction peaks of hexagonal and orthorhombic phases, respectively, measured in a heating run (closed triangle) and in a cooling run (open circle) under zero magnetic field. The black, green and brown arrows indicate the magnetic transition (TC) in cooling process, structural transitions in cooling (TSc) and heating (TSh) processes, respectively.

Mentions: In Fig. 2(a), we show the temperature dependence of magnetization of selected samples of MnCo1−xZnxGe below 400 K in H = 1 T. In this temperature range, undoped compound possesses orthorhombic structure, and exhibits the ferromagnetic transition at TC = 327 K with a low-temperature saturation moment of 4.2 µB/f.u. in accord with a previous report23. As the partial substitution of Zn proceeds, the temperature dependence of magnetization exhibits hysteresis behavior for x ≥ 0.03 while ferromagnetic transition temperature TC remains almost unchanged at around 300 K. As shown below, the hysteresis in the magnetization corresponds to the structural transition, thus the structural transition temperature is rapidly reduced as x is increased. For x = 0.03, its structural transition temperature (TSc) in the cooling process coincides with TC, giving rise to a first-order coupled magnetic and structural transition. In the heating process, TC occurs first, followed by the structural transition (TSh). Both the x = 0.04 and 0.05 compounds exhibit ferromagnetic transitions at around 285 K in the hexagonal phase, and structural transitions occur at lower temperatures (TSc and TSh) than TC. This observation is most clearly evidenced for x = 0.04 by the temperature dependence of normalized X-ray diffraction intensity of the hexagonal phase which is also plotted in Fig. 2(a). The structural transition from the high-temperature hexagonal phase to the low-temperature orthorhombic phase is accompanied by an increase in magnetization, as clearly observed for ferromagnetic alloys with x = 0.04 and 0.05. In the case of paramagnetic phase for x = 0, the structural transition manifests itself in the temperature dependence of magnetization as tiny temperature hysteresis between TSh~570 K and TSc~480 K (not shown). The structural transition temperatures TSh and TSc for x = 0.02 lie above TC as well, while the alloy in the orthorhombic phase undergoes the ferromagnetic ordering at TC = 326 K.


Tuning structural instability toward enhanced magnetocaloric effect around room temperature in MnCo(1-x)Zn(x)Ge.

Choudhury D, Suzuki T, Tokura Y, Taguchi Y - Sci Rep (2014)

Magnetization and magnetocaloric effect.Temperature dependence of (a) magnetization at H = 1 T and (b) magnetocaloric effect (-ΔS) for a field change from 0 T to 5 T for selected samples of MnCo1−xZnxGe. Also shown for x = 0.04 in (a) are temperature dependence of normalized intensity IH/(IO + IH) ≡ IH[110]/(IO[211] + IH[110]), where IH[110] and IO[211] are the intensities of [110] and [211] X-ray diffraction peaks of hexagonal and orthorhombic phases, respectively, measured in a heating run (closed triangle) and in a cooling run (open circle) under zero magnetic field. The black, green and brown arrows indicate the magnetic transition (TC) in cooling process, structural transitions in cooling (TSc) and heating (TSh) processes, respectively.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4269893&req=5

f2: Magnetization and magnetocaloric effect.Temperature dependence of (a) magnetization at H = 1 T and (b) magnetocaloric effect (-ΔS) for a field change from 0 T to 5 T for selected samples of MnCo1−xZnxGe. Also shown for x = 0.04 in (a) are temperature dependence of normalized intensity IH/(IO + IH) ≡ IH[110]/(IO[211] + IH[110]), where IH[110] and IO[211] are the intensities of [110] and [211] X-ray diffraction peaks of hexagonal and orthorhombic phases, respectively, measured in a heating run (closed triangle) and in a cooling run (open circle) under zero magnetic field. The black, green and brown arrows indicate the magnetic transition (TC) in cooling process, structural transitions in cooling (TSc) and heating (TSh) processes, respectively.
Mentions: In Fig. 2(a), we show the temperature dependence of magnetization of selected samples of MnCo1−xZnxGe below 400 K in H = 1 T. In this temperature range, undoped compound possesses orthorhombic structure, and exhibits the ferromagnetic transition at TC = 327 K with a low-temperature saturation moment of 4.2 µB/f.u. in accord with a previous report23. As the partial substitution of Zn proceeds, the temperature dependence of magnetization exhibits hysteresis behavior for x ≥ 0.03 while ferromagnetic transition temperature TC remains almost unchanged at around 300 K. As shown below, the hysteresis in the magnetization corresponds to the structural transition, thus the structural transition temperature is rapidly reduced as x is increased. For x = 0.03, its structural transition temperature (TSc) in the cooling process coincides with TC, giving rise to a first-order coupled magnetic and structural transition. In the heating process, TC occurs first, followed by the structural transition (TSh). Both the x = 0.04 and 0.05 compounds exhibit ferromagnetic transitions at around 285 K in the hexagonal phase, and structural transitions occur at lower temperatures (TSc and TSh) than TC. This observation is most clearly evidenced for x = 0.04 by the temperature dependence of normalized X-ray diffraction intensity of the hexagonal phase which is also plotted in Fig. 2(a). The structural transition from the high-temperature hexagonal phase to the low-temperature orthorhombic phase is accompanied by an increase in magnetization, as clearly observed for ferromagnetic alloys with x = 0.04 and 0.05. In the case of paramagnetic phase for x = 0, the structural transition manifests itself in the temperature dependence of magnetization as tiny temperature hysteresis between TSh~570 K and TSc~480 K (not shown). The structural transition temperatures TSh and TSc for x = 0.02 lie above TC as well, while the alloy in the orthorhombic phase undergoes the ferromagnetic ordering at TC = 326 K.

Bottom Line: This effect can be applied to environmentally-benign magnetic refrigeration technology.Fine tuning of x around x = 0.03 leads to the concomitant structural and ferromagnetic transition in a cooling process, giving rise to enhanced magnetocaloric effect as well as magnetic-field-induced structural transition.Analyses of the structural phase diagrams in the T-H plane in terms of Landau free-energy phenomenology accounts for the characteristic x-dependence of the observed magnetocaloric effect, pointing to the importance of the magnetostructural coupling for the design of high-performance magnetocalorics.

View Article: PubMed Central - PubMed

Affiliation: RIKEN Center for Emergent Matter Science (CEMS), Wako 351-0198, Japan.

ABSTRACT
Magnetocaloric effect is the phenomenon that temperature change of a magnetic material is induced by application of a magnetic field. This effect can be applied to environmentally-benign magnetic refrigeration technology. Here we show a key role of magnetic-field-induced structural instability in enhancing the magnetocaloric effect for MnCo(1-x)Zn(x)Ge alloys (x = 0-0.05). The increase in x rapidly reduces the martensitic transition temperature while keeping the ferromagnetic transition around room temperature. Fine tuning of x around x = 0.03 leads to the concomitant structural and ferromagnetic transition in a cooling process, giving rise to enhanced magnetocaloric effect as well as magnetic-field-induced structural transition. Analyses of the structural phase diagrams in the T-H plane in terms of Landau free-energy phenomenology accounts for the characteristic x-dependence of the observed magnetocaloric effect, pointing to the importance of the magnetostructural coupling for the design of high-performance magnetocalorics.

No MeSH data available.


Related in: MedlinePlus