Direct measurements of the magnetocaloric effect in pulsed magnetic fields: The example of the Heusler alloy Ni50_{50}Mn35_{35}In15_{15}

We have studied the magnetocaloric effect (MCE) in the shape-memory Heusler alloy Ni$_{50}$Mn$_{35}$In$_{15}$ by direct measurements in pulsed magnetic fields up to 6 and 20 T. The results in 6 T are compared with data obtained from heat-capacity experiments. We find a saturation of the inverse MCE, related to the first-order martensitic transition, with a maximum adiabatic temperature change of $\Delta T_{ad} = -7$ K at 250 K and a conventional field-dependent MCE near the second-order ferromagnetic transition in the austenitic phase. The pulsed magnetic field data allow for an analysis of the temperature response of the sample to the magnetic field on a time scale of $\sim 10$ to 100 ms which is on the order of typical operation frequencies (10 to 100 Hz) of magnetocaloric cooling devices. Our results disclose that in shape-memory alloys the different contributions to the MCE and hysteresis effects around the martensitic transition have to be carefully considered for future cooling applications.Comment: 5 pages, 4 figure

Magnetocaloric effect of gadolinium in high magnetic fields

International audienceThe magnetocaloric effect of gadolinium has been measured directly in pulsed magnetic fields up to 62 T. The maximum observed adiabatic temperature change is T ad = 60.5 K, the initial temperature T 0 being just above 300 K. The field dependence of T ad is found to follow the usual H 2/3 law, with a small correction in H 4/3. However, as H is increased, a radical change is observed in the dependence of T ad on T 0 , at H = const. The familiar caret-shaped peak situated at T 0 = T C becomes distinctly asymmetric, its high-temperature slope becoming more gentle and evolving into a broad plateau. For yet higher magnetic fields, μ 0 H 140 T, calculations predict a complete disappearance of the maximum near T C and an emergence of a new very broad maximum far above T C

Magnetocaloric effect of gadolinium in high magnetic fields

The magnetocaloric effect of gadolinium has been measured directly in pulsed magnetic fields up to 62 T. The maximum observed adiabatic temperature change is Delta T-ad = 60.5 K, the initial temperature T-0 being just above 300 K. The field dependence of Delta T-ad is found to follow the usual H-2/3 law, with a small correction in H-4/3. However, as H is increased, a radical change is observed in the dependence of Delta T-ad on T-0, at H = const. The familiar caret-shaped peak situated at T-0 = T-C becomes distinctly asymmetric, its high-temperature slope becoming more gentle and evolving into a broad plateau. For yet higher magnetic fields, mu H-0 greater than or similar to 140 T, calculations predict a complete disappearance of the maximum near T-C and an emergence of a new very broad maximum far above T-C

Pressure tuning of the anomalous Hall effect in the chiral antiferromagnet Mn3Ge

We report on the pressure evolution of the giant anomalous Hall effect (AHE) in the chiral antiferromagnet Mn$_3$Ge. The AHE originating from the non-vanishing Berry curvature in Mn$_3$Ge can be continuously tuned by application of hydrostatic pressure. At room temperature, the Hall signal changes sign as a function of pressure and vanishes completely at $p=1.53$ GPa. Even though the Hall conductivity changes sign upon increasing pressure, the room-temperature saturation value of 23 ${\rm \Omega^{-1}cm^{-1}}$ at 2.85 GPa is remarkably high and comparable to the saturation value at ambient pressure of about 40 ${\rm \Omega^{-1}cm^{-1}}$. The change in the Hall conductivity can be directly linked to a gradual change of the size of the in-plane components of the Mn moments in the non-collinear triangular magnetic structure. Our findings, therefore, provide a route for tuning of the AHE in the chiral antiferromagnetic Mn$_3$Ge.Comment: 5 pages, 4 figure

Diabetes mellitus in patients with Herpes Zoster

Background: Herpes Zoster (HZ) is the reactivation of latent varicella-zoster virus due to such risk factors as aging and immunosupression. Diabetes Mellitus (DM) causes immunosupression and can activate HZ. This study focuses on the relationship between Herpes Zoster and Diabetes Mellitus. Materials and Methods: In this cross-sectional study 103 patients referred to the dermatology and infectious disease clinics with HZ (cases) and 142 with other diseases (control) were enrolled to the study. They had no history of DM. Both groups were matched for age, gender and family history of DM. FBS was checked for all participants and FBS ³ 126mg/dl was defined as DM. Results: 35.9 of patients with HZ and 19.7 of control group had DM. There was a significant relationship between HZ and undiagnosed DM (OR=2.28, 95 CI: 1.28-4.06, p=0.0046). On the other hand, DM was 2.28 times more common in HZ patients than in normal population. Conclusion: Undiagnosed DM can cause HZ so the patients suffering from HZ but have no history of DM should be monitored for diabetes

Pulsed high-magnetic-field experiments: New insights into the magnetocaloric effect in Ni-Mn-In Heusler alloys

The present pulsed high-magnetic-field study on Ni 50Mn35In15 gives an extra insight into the thermodynamics of the martensitic transformation in Heusler shape-memory alloys. The transformation-entropy change, ΔS, was estimated from field-dependent magnetization experiments in pulsed high magnetic fields and by heat-capacity measurements in static fields. We found a decrease of ΔS with decreasing temperature. This behavior can be understood by considering the different signs of the lattice and magnetic contributions to the total entropy. Our results further imply that the magnetocaloric effect will decrease with decreasing temperature and, furthermore, the martensitic transition is not induced anymore by changing the temperature in high magnetic fields