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Magnetocaloric effect measurements in ultrahigh magnetic fields up to 120 T

Reon Ogawa, Masaki Gen, Kazuyuki Matsuhira, Yoshimitsu Kohama

TL;DR

Measuring the magnetocaloric effect in ultrahigh magnetic fields (>100 T) is challenging due to microsecond-scale destructive pulses. The authors implement RF impedance thermometry with an Au16Ge84 thin-film thermometer on Ho2Ti2O7 in a single-turn coil setup to capture MCE signals during 120 T field transients. They observe a giant MCE at low fields and a smaller high-field response associated with crystal-field level crossing, estimating an adiabatic temperature rise up to $\Delta T_{\rm ad} \approx 25$ K at 5 K initial. The work validates the approach for ultrafast MCE measurements in destructive fields and identifies key issues (thermometer response time, RF propagation delays, and magnetoresistance) that must be addressed for precise magnetic phase diagram mapping.

Abstract

We report proof-of-concept measurements of the magnetocaloric effect (MCE) in ultrahigh magnetic fields up to 120 T for the classical spin-ice compound Ho$_{2}$Ti$_{2}$O$_{7}$. Radio-frequency resistivity measurements using an Au$_{16}$Ge$_{84}$ thin-film thermometer enable us to detect a rapid change in the sample temperature associated with a crystal-field level crossing in the high-field region in addition to a giant MCE at low fields. We discuss a possible delay in the temperature response and outline prospects for more precise MCE measurements in destructive pulsed fields.

Magnetocaloric effect measurements in ultrahigh magnetic fields up to 120 T

TL;DR

Measuring the magnetocaloric effect in ultrahigh magnetic fields (>100 T) is challenging due to microsecond-scale destructive pulses. The authors implement RF impedance thermometry with an Au16Ge84 thin-film thermometer on Ho2Ti2O7 in a single-turn coil setup to capture MCE signals during 120 T field transients. They observe a giant MCE at low fields and a smaller high-field response associated with crystal-field level crossing, estimating an adiabatic temperature rise up to K at 5 K initial. The work validates the approach for ultrafast MCE measurements in destructive fields and identifies key issues (thermometer response time, RF propagation delays, and magnetoresistance) that must be addressed for precise magnetic phase diagram mapping.

Abstract

We report proof-of-concept measurements of the magnetocaloric effect (MCE) in ultrahigh magnetic fields up to 120 T for the classical spin-ice compound HoTiO. Radio-frequency resistivity measurements using an AuGe thin-film thermometer enable us to detect a rapid change in the sample temperature associated with a crystal-field level crossing in the high-field region in addition to a giant MCE at low fields. We discuss a possible delay in the temperature response and outline prospects for more precise MCE measurements in destructive pulsed fields.

Paper Structure

This paper contains 4 sections, 3 figures.

Table of Contents

  1. Introduction
  2. Experimental methods
  3. Results and discussions
  4. Conclusion and outlook

Figures (3)

  • Figure 1: (a) Block diagram of the MCE measurement setup in the STC system. (b) Schematic illustration of the probe and sample configuration.
  • Figure 2: Time profiles of the MCE measurements for (a) the $B_{\rm max} = 7$ T shot and (b) the $B_{\rm max} = 120$ T shot. Each top panel shows the magnetic-field waveform, and each bottom panel shows the detected amplitude of the RF transmission signal.
  • Figure 3: (a)--(c) Magnetic-field dependence of the amplitude of the RF transmission signal at (a) $T_{\rm ini} = 5$ K, (b) 20 K, and (c) 30 K. The dashed lines are guides to the eye indicating the expected curves during the field-up sweep. (d) Adiabatic MCE data of Ho$_{2}$Ti$_{2}$O$_{7}$ for $B \parallel [111]$ up to 55 T obtained using a nondestructive pulsed magnet 2024_Tan.