Temperature anomalies observed in liquid 4He columns in magnetic fields with field–field-gradient products >21 T2/cm

Previously reported temperature increases above 4.2 K in an immersion geometry in liquid 4He at fields >19 T have been verified and examined. Magnetic forces (B dB/dx) above a threshold level of ∼21 T2/cm were found to trap 4He bubbles near the center of the field. Significant heat input to the region (from conduction, radiation, etc.) can then raise the temperature by as much as several kelvins. Thus, measurements at very high B dB/dx should not depend on vapor pressure thermometry. To assure temperature accuracy and stability, the temperature should be measured directly at the sample position.