Short answer — they use high‑coercivity thin‑film media (i.e., modern HDD platter materials), not the low‑coercivity media you see in old floppy/tape. The three models you named differ in recording method, but all are built from modern, high‑coercivity platter materials designed to resist stray magnetic fields.
Details:
- Seagate ST500LM030 — Seagate Barracuda mobile 2.5" — uses SMR (shingled magnetic recording). SMR is a track‑layout choice, but the underlying platters are still modern thin‑film media with high coercivity.
- WDC WD10JPVX‑08JC3T5 — Western Digital Blue 2.5" — uses CMR (conventional/PMR style), also on modern high‑coercivity platters.
- HGST HTS541010A99E662 (Travelstar) — CMR (PMR family), again modern thin‑film...